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MEDICAL SCHOOL

Dr. ivionroe butter
Memorial.

WORKS BY THE SAME AUTHOR:
Published by D. Appleton & Company.

The Physiology Of Man ; designed to represent the Existing State

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Body. Volume I., Introduction ; Blood ; Circulation ; Kespiration.

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A TEXT-BOOK

OF

HUMAN PHYSIOLOGY;

DESIGNED FOR THE USE OF

PRACTITIONERS AND STUDENTS OF MEDICINE.

BY

AUSTIN FLINT, JE., M. D., LL. D.,

PROFESSOR OP PHYSIOLOGY AND PHYSIOLOGICAL ANATOMY IN THE BELLEVTJE HOSPITAL MEDICAL COLLEGE, WEW

YORK ; FELLOW OF THE NEW YORK STATE MEDICAL ASSOCIATION ; FELLOW OF THK NEW YORK ACADKMY

OF MEDICINE ; CORRESPONDENT OF THE ACADEMY OF NATURAL SCIENCES OF PHILADELPHIA;

MEMBER OF THK AMERICAN PHILOSOPHICAL SOCIETY, KTC., ETC.

ILLUSTRATED BY THREE LITHOGRAPHIC PLATES AND THREE HUNDRED AND
FIFTEEN WOODCUTS.

THIRD EDITION, REVISED AND CORRECTED.

NEW YOKE:
D. APPLETON AND COMPANY,

1, 3, AND 5 BOND STREET.

1886.

Y\

It:

ENTERED, according to Act of Congress, in the year 1875, by

D. APPLETON & COMPANY,
In the Office of the Librarian of Congress, at Washington.

ENTERED, according to Act of Congress, in the year 1879, by

D. APPLETON & COMPANY,
In the Office of the Librarian of Congress, at Washington.

ENTERED, according to Act of Congress, in the year 1881, by

D. APPLETON & COMPANY,
In {herO&ceof tiio LtbrsrianVf C-o'rfgre&s, a£ Washington

PEEFACE TO THE THIRD EDITION.

IN preparing the first edition of this work, published about five years
ago, I hoped that my experience as a practical physiologist and public
teacher and the discipline of eleven years during which I was occupied in
writing my large treatise in five volumes might enable me to make a book
which would meet the wants of practitioners and students of medicine.
My expectations in this regard have been more than fulfilled. My work
has been very favorably received by the profession ; it is extensively used
as a text-book, and two very large impressions of the first edition and a
second edition, published in 1879, have been exhausted. Encouraged by
the favorable reception of the book, I have spared no pains in its revision
for a third edition. I have rewritten certain portions, carefully corrected
all the errors and inaccuracies that I have been able to discover, and have
eliminated here and there statements that did not seem to me to be fully
in accord with the existing state of physiological knowledge. In addition
to minor corrections, I have made the following important alterations : I
have adopted the views of Bowman, lately confirmed by the experiments
of Heidenhain and others, with regard to the functions of the Malpighian
bodies of the kidney. The section upon Animal Heat has been entirely
rewritten ; and I have given an account of my new experiments upon this
subject, published in 18 79, showing the probable generation of heat in
the body by the union of oxygen and hydrogen and the formation of water.
I have introduced a short description of the cerebral convolutions, with
a new diagram, and a brief account of the recent discovery by Boll, of
" retinal red." I have also added a diagram illustrating the mechanism of
micturition, and a figure, kindly prepared for me by Dr. E. G. Loring,
of New York, showing the appearance of the fundus of the eye as seen
with the ophthalmoscope.

Although the work may appear to some readers to be rather formidable
in size, I have endeavored to condense it as much as possible. It undoubt-
edly contains much more than is usually taught in lectures to medical stu-
dents ; but, in a text-book for the use of practitioners as well as students, it
is not desirable, in my opinion, to omit any subject properly belonging to
human physiology. I venture to hope that those who use this work as a
book of reference will find nearly all subjects in which they may be inter-
ested more or less fully discussed, although I have generally omitted foot-
notes referring to other authorities. My main object, however, has been to
meet the requirements of medical students.

NEW YORK, April, 1880.

PEEFAOE TO THE FIKST EDITION.

IN preparing this text-book for the use of students and practitioners of
medicine, I have endeavored to adapt it to the wants of the profession, as they
have appeared to me after a considerable experience as a public teacher of hu-
man physiology. My large treatise in five volumes is here condensed, and I
have omitted bibliographical citations and matters of purely historical interest.
Many subjects, which were considered rather elaborately in my larger work,
are here presented in a much more concise form. I have added, also, numer-
ous illustrations, which I hope may lighten the labors of the student. A few
of these are original, but by far the greater part has been selected from relia-
ble authorities. I have thought it not without historical interest to reproduce
exactly some of the classical engravings from the works of great discoverers,
such as illustrations contained in the original editions of Fabricius, Harvey,
and Asellius. In addition, I have copied a few of the beautiful microscopi-
cal photographs taken at the United States Army Medical Museum by Dr. J. J.
Woodward, who kindly furnished them to me and to whom I here express
my grateful acknowledgments. I have also to thank M. Sappey for his kind-
ness in furnishing electrotypes of many of the superb engravings with which
his great work upon anatomy is illustrated.

My work in five volumes was intended as a book of reference, which I hope
will continue to be useful to those who desire an account of the literature of
physiology as well as a statement of the facts of the science. I have always
endeavored, in public teaching, to avoid giving undue prominence to points in
which I might myself be particularly interested from having made them sub-
jects of special study or of original research. In my text-book, I have carried
out the same idea, striving to teach, systematically and with uniform emphasis,
what students of medicine are expected to learn in physiology, and avoiding
elaborate discussions of subjects not directly connected with practical medi-
cine, surgery, and obstetrics. While I have referred to my original observa-
tions upon the location of the sense of want of air in the general system, the
new excretory function of the liver, the function of glycogenesis, the influ-
ence of muscular exercise upon the elimination of urea, etc., I have not con-
sidered these subjects with great minuteness and have generally referred the
reader to monographs for the details of my experiments.

Finally, in presenting this work to the medical profession, I cannot refrain
from an expression of my acknowledgments to the publishers, who have spared
nothing in carrying out my views and have devoted special pains to the me-
chanical execution of the illustrations.

YORK, November, 1875.

CONTENTS.

CHAPTER I.

THE BLOOD.

General considerations— Transfusion— Quantity of blood— General characters of the blood— Blood-corpuscles-—
Development of the blood-corpuscles— Leucocytes— Development of leucocytes— Composition of the red cor-
puscles— Globuline— Haemaglobine— Analysis of the blood— Composition of the blood- plasma— Inorganic prin-
ciples— Organic saline principles — Organic non-nitrogenized principles — Excrementitious matters — Organic nitro-
genized principles — Plasmine, fibrin, metalbumen, and serine — Peptones — Coloring matter — Coagulation of the
blood— Characters of the clot— Characters of the serum— Circumstances which modify coagulation— Coagulation
of the blood in the organism — Spontaneous arrest of haemorrhage— Cause of the coagulation of the blood — So-
called fibrin-factors — Paraglobuline, or fibrinoplastic matter — Fibrinogen, Page 1

CHAPTER II.

CIRCULATION OF THE BLOOD— ACTION OF THE HEART.

Discovery of the circulation— Physiological anatomy of the heart— Valves of the heart— Movements of the heart-
Impulse of the heart — Succession of movements of the heart — Force of the heart's action — Action of the valves —
Sounds of the heart— Causes of the sounds of the heart— Frequency of the heart's action— Influence of age-
Influence of digestion — Influence of posture and muscular exertion — Influence of exercise — Influence of tem-
perature—Influence of respiration upon the action of the heart— Cause of the rhythmical contractions of the
heart — Influence of the nervous system upon the heart— Division of the pneumogastrics — Galvanization of the
pneumogastrics— Causes of arrest of action of the heart— Blows upon the epigastrium, 31

CHAPTER III.

CIRCULATION OF THE BLOOD IN THE VESSELS.

Physiological anatomy of the arteries— Course of blood in the arteries— Locomotion of the arteries and production
of the pulse— Pressure of blood in the arteries— Pressure in different parts of the arterial system— Depressor-
nerve — Influence of respiration upon the arterial pressure — Eapidity of the current of blood in the arteries — Ra-
pidity in different parts of the arterial system— Circulation of the blood in the capillaries— Physiological anatomy
of the capillaries— Capacity of the capillary system— Course of blood in the capillaries— Relations of the capil-
lary circulation to respiration — Causes of the capillary circulation — Influence of temperature upon the capillary
circulation— Influence of direct irritation upon the capillary circulation— Circulation of the blood in the veins-
Physiological anatomy of the veins— Course of the blood in the veins— Pressure of blood in the veins— Rapidity
of the venous circulation— Causes of the venous circulation— Air in the veins— Function of the valves— Condi-
tions which impede the venous circulation — Rcgurgitant venous pulse— Circulation in the cranial cavity — Cir-
culation in erectile tissues— Derivative circulation— Pulmonary circulation— Rapidity of the circulation— Phe-
nomena in the circulatory system after death, 64

CHAPTER IV.

RESPIRA TION-RESPIRA TOR Y MO VEMENTS.

General considerations— Physiological anatomy of the respiratory organs— Respiratory movements of the larynx-
Epiglottis— Trachea and bronchial tubes— Parenchyma of the lungs— Movements of respiration— Inspiration-
Muscles of inspiration— Expiration— Influence of the elasticity of the pulmonary structure and walls of the chest
upon expiration— Muscles of expiration— Action of the abdominal muscles in expiration— Types of respiration-
Frequency of the respiratory movements— Relations of inspiration and expiration to each other— The respiratory

vi CONTENTS.

sounds— Capacity of the lungs and the quantity of air changed in the respiratory acts— Eesidual air— Eeserve
air — Tidal, or breathing air — Complemental air — Extreme breathing capacity — Kelations in volume of the expired
to the inspired ah- — Diffusion of air in the lungs, Page 114

CHAPTER V.

CHANGES WHICH THE AIR AND THE BLOOD UNDERGO IN RESPIRATION.

Composition of the air — Consumption of oxygen — Exhalation of carbonic acid — Influence of age— Kelations between
the quantity of oxygen consumed and the quantity of carbonic acid exhaled — Exhalation of watery vapor — Ex-
halation of ammonia— Exhalation of organic matter— Exhalation of nitrogen— Changes of the blood in respira-
tion (haematosis) — Difference in color between arterial and venous blood — Comparison of the gases in venous
and arterial blood — Analysis of the blood for gases — Relative quantities of oxygen and carbonic acid in venous
and arterial blood— Nitrogen of the blood — Condition of the gases in the blood— Mechanism of the interchange
of gases between the blood and the air in the lungs— Kelations of respiration to nutrition, etc.— Views of physi-
ologists anterior to the time of Lavoisier — Kelations of the consumption of oxygen to nutrition — Kelations of
the exhalation of carbonic acid to nutrition — Essential processes of respiration — The respiratory sense, or want
on the part of the system which induces the respiratory movements— Respiratory efforts before birth— Cuta-
neous respiration— Asphyxia, .139

CHAPTER VI.

A LIMENTA TION.

Appetite— Circumstances which modify the appetite— Influence of habit— Hunger— Seat of the sense of hunger-
Thirst— Seat of the sense of thirst— Duration of life in inanition— Division of alimentary principles— Nitrogen-
ized alimentary principles — Non-nitrogenized alimentary principles — Inorganic alimentary principles — "Water —
Alcohol — Distilled liquors — Wines, malt liquors, etc. — Coffee — Tea — Chocolate — Condiments and flavoring articles
— Quantity and variety of food necessary to nutrition — Necessity of a varied diet, 171

CHAPTER VII.

DIGESTION, MASTICATION, INSALIVATION, AND DEGLUTITION.

General arrangement of the digestive apparatus — Prehension of solids and liquids — Mastication— Physiological anat-
omy of the teeth — Anatomy of the maxillary bones — Temporo-maxillary articulation — Muscles of mastication —
Muscles which depress the lower jaw— Action of the muscles which elevate the lower jaw and move it laterally
and antero-posteriorly — Action of the tongue, lips, and cheeks in mastication — Summary of the process of masti-
cation— Parotid saliva — Submaxillary saliva — Sublingual saliva — Fluids from the smaller glands of the mouth,
tongue, and fauces— Mixed saliva— Quantity of saliva— General properties and composition of the saliva— Action
of the saliva upon starch— Mechanical functions of the saliva — Deglutition — Physiological anatomy of the parts con-
cerned in deglutition— Muscles of the pharynx— Muscles of the soft palate— Mucous membrane of the pharynx—
(Esophagus— Mechanism of deglutition— First period of deglutition— Second period of deglutition— Protection of
the posterior nares during the second period of deglutition — Protection of the opening of the larynx — Function
of the epiglottis— Study of deglutition by autolaryngoscopy— Third period of deglutition— Intermittent contrac-
tion of the lower third of the oesophagus— Nature of the movements of deglutition— Deglutition of air, . 195

CHAPTER VIII.

STOMA CH-DIGESTION.

Physiological anatomy of the stomach— Peritoneal coat- Muscular coat— Mucous coat— Glandular apparatus in the
stomach— Gastric, or peptic glands— Mucous glands— Closed follicles— Gastric juice— Mode of obtaining the gas-
tric juice— Gastric fistula in the human subject in the case of St. Martin— Secretion of the gastric juice— Com-
position of the gastric juice— Source of the acidity of the gastric juice— Ordinary saline constituents of the gastric
juice— Action of the gastric juice in digestion— Constituents upon which the activity of the gastric juice depends
— Action of the gastric juice upon meats — Action upon albumen, fibrin, caseine, and gelatine — Action upon vege-
table nitrogenized principles— Albuminose, or peptones— Action of the gastric juice upon fats— Action upon sac-
charine and amylaceous principles— Duration of stomach-digestion— Digestibility of different aliments in the stom-
ach—Circumstances which influence stomach-digestion— Character of the contractions of the muscular coat of
the stomach— Movements in the cardiac and in the pyloric portion— Mechanism of the movements of the stomach
— Rumination, and regurgitation from the stomach— Rumination in the human subject— Eructation, . . 226

CONTENTS. vii

CHAPTER IX.

INTESTINAL DIGESTION— DEFECATION.

Physiological anatomy of the small intestine— Glands of Brunner— Intestinal tubules, or follicles of Lieberkuhn—
Solitary glands, or follicles, and the patches of Peyer— Intestinal juice— General properties of the intestinal
juice— Action of the intestinal juice in digestion— Pancreatic juice-Action of the pancreatic juice in digestion-
Destruction of the pancreas— Cases of fatty diarrhoea— Action of the pancreatic juice upon starchy, saccharine,
and nitrogenized principles— Action of the bile in digestion— Biliary fistula— General constitution of the bile-
Variations in the flow of bile— Movements of the small intestine— Peristaltic and antiperistaltic movements-
Function of the gases in the small intestine— Influence of the nervous system upon the peristaltic movements-
Physiological anatomy of the large intestine— Digestion in the large intestine— Contents of the large intestine-
Composition of the faeces— Excretine and excretoleic acid— Stercorine— Movements of the large intestine— Defe-
cation— Gases found in the alimentary canal Page 257

CHAPTER X.

ABSORPTION— LYMPH AND CHYLE.

General considerations of absorption— Absorption by blood-vessels— Absorption by lacteal and lymphatic vessels-
Physiological anatomy of the lacteal and lymphatic system— Absorption by the lacteals— Absorption from parts
not connected with the digestive system— Absorption of fats and insoluble substances— Variations and modifica-
tions of absorption — Imbibition and endosmosis — Imbibition by animal tissues — Mechanism of the passage of
liquids through membranes— Capillary attraction— Endosmosis through porous septa— Endosmosis through ani-
mal membranes— Endosmosis through liquid septa— Diffusion of liquids— Endosmotic equivalents— Modifications
of endosmosis— Application of physical laws to the function of absorption— Transudation— Lymph and chyle-
Mode of obtaining lymph— Quantity of lymph— Properties and composition of lymph— Alterations of the lymph
—Corpuscular elements of the lymph— Leucocytes— Development of leucocytes in the lymph and chyle— Glob-
ulins—Origin and function of the lymph— General properties of the chyle— Composition of the chyle— Compara-
tive analyses of the lymph and the chyle— Microscopical characters of the chyle— Movement of the lymph and
chyle, ... .300

CHAPTER XI.

SECRETION.

General considerations— Differences between the secretions and fluids containing formed anatomical elements— Classi-
fication of the secretions — Mechanism of the production of the true secretions — Mechanism of the production of
the excretions— General structure of secreting organs— Anatomical classification of glandular organs— Classification
of the secreted fluids— Secretions proper (permanent fluids; transitory fluids) — Excretions — Fluids containing
formed anatomical elements— Physiological anatomy of the serous and synovial membranes— Pericardial, peri-
toneal, and pleural secretions — Synovial fluid — Mucus — Mucous membranes — Mechanism of the secretion of mucus
— Composition and varieties of mucus — Microscopical characters of mucus — General function of mucus — Non-
absorption of certain soluble substances, particularly venoms, by mucous membranes — Sebaceous fluids— Physio-
logical anatomy of the sebaceous, ceruminous, and Meibomian glands — Ordinary sebaceous matter — Smegma of
the prepuce and of the labia minora — Vernix caseosa — Cerumen — Meibomian secretion — Function of the Meibo-
mian secretion— Mammary secretion— Physiological anatomy of the mammary glands— Condition of the mam-
mary glands during the intervals of lactation — Structure of the mammary glands during lactation — Mechanism
of the secretion of milk— Conditions which modify the lacteal secretion— Quantity of milk— General characters
of milk — Microscopical characters of milk — Composition of milk — Variations in the composition of milk — Colos-
trum—Lacteal secretion in the newly-born, 841

CHAPTER XII.

EXCRETION BY THE SKIN AND KIDNEYS

Differences between the secretions proper and the excretions— Physiological anatomy of the skin— Physiological
anatomy of the nails and hairs — Sudden blanching of the hair — Uses of the hairs — Perspiration— Sudoriparous
glands— Mechanism of the secretion of sweat— Properties and composition of the sweat— Peculiarities of the
sweat in certain parts— Physiological anatomy of the kidneys— Distribution of blood-vessels in the kidneys
— Lymphatics and nerves of the kidneys — Mechanism of the production and discharge of urine — Formation
of the excrementitious constituents of the urine in the tissues, absorption of these principles by the blood,
and separation of them from the blood by the kidneys— Effects of removal of both kidneys from a living animal
—Effects of tying the ureters in a living animal— Extirpation of one kidney— Influence of blood-pressure, the
nervous system, etc., upon the secretion of urine — Alternation in the action of the kidneys upon the two sides-
Changes in the composition of the blood in passing through the kidneys— Physiological anatomy of the urinary
passages- Mechanism of the discharge of urine— Properties and composition of the urine-General physical prop-

viii CONTENTS.

erties of the urine — Quantity, specific gravity, and reaction of the urine — Composition of the urine — Gases of
the urine — Variations in the composition of the urine— Variations produced by food — Urina potus, urina cibi,
and urina sanguinis — Influence of muscular exercise upon the urine — Influence of mental exertion, . Page 379

CHAPTER XIII.

FUNCTIONS OF THE LIVER.

Physiological anatomy of the liver— Distribution of the portal vein, the hepatic artery, and the hepatic duct-
Origin and course of the hepatic veins— Structure of a lobule of the liver — Arrangement of the bile-ducts in
the lobules — Anatomy of the excretory biliary passages — Nerves and lymphatics of the liver — Mechanism of
the secretion and discharge of bile — Quantity of bile — Variations in the flow of the bile — Discharge of bile from
the gall-bladder— General properties of the bile— Composition of the bile— Origin of the biliary salts— Choles-
terine— Biliverdine — Tests for bile — Excretory function of the liver — Origin of cholesterine — Experiments show-
ing the passage of cholesterine into the blood as it circulates through the brain — Elimination of cholesterine by
the liver— Cholestersemia- Production of sugar in the liver— Evidences of a glycogenic function in the liver-
Does the liver contain sugar during life ? — Mechanism of the production of sugar by the liver — Glycogenic mat-
ter— Variations in the glycogenic function — Production of sugar in foetal life — Influence of digestion and of differ-
ent kinds of food upon glycogenesis— Influence of the nervous system, etc., upon glycogenesis— Artificial dia-
betes— Destination of sugar — Alleged production of fat by the liver — Changes in the albuminoid and the corpus-
cular elements of the blood in their passage through the liver, 431

CHAPTER XIV.

THE DUCTLESS GLANDS.

Probable office of the ductless glands— Anatomy of the spleen— Fibrous structure of the spleen (trabecute)— Malpi-
ghian bodies— Spleen -pulp — Vessels and nerves of the spleen — Some points in the chemical constitution of the
spleen— State of our knowledge concerning the functions of the spleen— Variations in the volume of the spleen
—Extirpation of the spleen— Anatomy of the suprarenal capsules— Cortical substance— Medullary substance
— Vessels and nerves — Chemical reactions of the suprarenal capsules — State of our knowledge concerning
the functions of the suprarenal capsules — Extirpation of the suprarenal capsules — Addison's disease — Anatomy
of the thyroid gland— State of our knowledge concerning the functions of the thyroid gland— Anatomy of the
thymus— Pituitary body and pineal gland, 472

CHAPTER XV.

NUTRITION— ANIMAL HEAT.

Nature of the forces involved in nutrition— Definition of vital properties — Life, as represented in development and
nutrition— Principles which pass through the organism— Principles consumed in the organism— Development of
power and endurance by exercise (training)— Formation and deposition of fat— Conditions under which fat exists
in the organism — Physiological anatomy of adipose tissue — Conditions which influence nutrition — Products of
disassimilation— Animal heat — Limits of variation in the normal temperature in man — Variations with external
temperature— Variations in different parts of the body— Variations at different periods of life— Diurnal variations
— Eelations of animal heat to digestion — Influence of defective nutrition and inanition — Influence of exercise,
mental exertion, and the nervous system, upon the heat of the body-^Sources of animal heat— Connection of the
production of heat with nutrition— Seat of the production of animal heat— Eelations of animal heat to the different
processes of nutrition— Eelations of animal heat to respiration— Exaggeration of the animal temperature in par-
ticular parts after division of the sympathetic nerve and in inflammation — Intimate nature of the calorific pro-
cesses— Equalization of the animal temperature, 436

CHAPTER XVI.

MOVEMENTS— VOICE AND SPEECH.

Amorphous contractile substance — Ciliary movements — Movements due to elasticity — Varieties of elastic tissue —
Muscular movements — Physiological anatomy of the involuntary muscles — Mode of contraction of the invol-
untary muscular tissue — Physiological anatomy of the voluntary muscles — Fibrous and adipose tissue in the
voluntary muscles — Connective tissue — Blood-vessels and lymphatics of the muscular tissue— Connection of
the muscles with the tendons— Chemical composition of the muscles— Physiological properties of the mus-
cles— Muscular contractility, or irritability — Muscular contraction — Changes in the form of the muscular
fibres during contraction— Secousse, Ziickung, or spasm— Mechanism of prolonged muscular contraction —
Tetanus— Electrical phenomena in the muscles — Muscular effort— Passive organs of locomotion — Physiological
anatomy of the bones— Marrow of the bones— Medullocells— Myeloplaxos— Periosteum— Physiological anatomy
of cartilage — Fibro-cartilage — Voice and speech— Sketch of the physiological anatomy of the vocal organs —

CONTENTS. ix

Vocal chords— Muscles of the larynx— Mechanism of the production of the voice —Appearance of the glottis
during ordinary respiration— Movements of the glottis during phonation— Variations in the quality of the voice
depending upon differences in the size and form of the larynx and the vocal chords— Action of the intrinsic
muscles of the larynx in phonation— Action of the accessory vocal organs— Mechanism of the different vocal
registers— Mechanism of speech— The phonograph, Page 522

CHAPTER XVII.

PHYSIOLOGICAL DIVISIONS, STRUCTURE, AND GENERAL PROPERTIES OF THE

NERVOUS SYSTEM.

General considerations— Divisions of the nervous system— Physiological anatomy of the nervous tissue— Anatomical
divisions of the nervous tissue— Medullated nerve-fibres— Simple, or non-medullated nerve-fibres — Gelatinous
nerve-fibres (fibres of Remak)— Accessory anatomical elements of the nerves— Branching and course of the nerves
—Termination of the nerves in the muscular tissue— Termination of the nerves in glands— Terminations of the
sensory nerves— Corpuscles of Pacini, or of Vater— Tactile corpuscles— Terminal bulbs— Structure of the nerve-
centres— Nerve-cells — Connection of the cells with the fibres and with each other — Accessory anatomical elements
of the nerve-centres— Composition of the nervous substance— Eegeneration of the nervous tissue — Reunion of

nerve-fibres — Motor and sensory nerves — Distinct seat of the motor and sensory properties of the spinal nerves

Experiments of Magendie upon the roots of the spinal nerves — Properties of the posterior roots of the spinal nerves
—Properties of the anterior roots of the spinal nerves— Eecurrent sensibility— Mode of action of the motor nerves
— Associated movements — Mode of action of the sensory nerves — Sensation in amputated members — General prop-
erties of the nerves — Nervous irritability— Different means employed for exciting the nerves — Disappearance of
the irritability of the motor and sensory nerves after exsection — Nerve-force— Rapidity of nervous conduction —
—Estimation of the duration of acts involving the nerve-centres— Action of electricity upon the nerves— Induced
muscular contraction — Galvanic current from the exterior to the cut surface of a nerve — Effects of a constant gal-
vanic current upon the nervous irritability— Electrotonus, anelectrotonus, and catelectrotonus— Neutral point-
Negative variation, 563

CHAPTER XVIII.

SPINAL NERVES-MOTOR CRANIAL NERVES.

Special nerves coming from the spinal cord— Cranial nerves— Anatomical classification— Physiological classification—
Motor oculi communis (third nerve)— Physiological anatomy— Properties and functions— Influence upon the
movements of the iris— Patheticus, or trochlearis (fourth nerve)— Physiological anatomy— Properties and func-
tions—Motor oculi externus, or abducens (sixth nerve)— Physiological anatomy— Properties and functions-
Motor nerves of the face— Nerve of mastication (the small, or motor root of the fifth)— Physiological anatomy
— Deep origin — Distribution — Properties and functions of the nerve of mastication — Facial nerve, or nerve of
expression (the portio dura of the seventh) - Physiological anatomy— Intermediary nerve of Wrisberg— Decus-
sation of the fibres of origin of the facial— Alternate paralysis— Course and distribution of the facial— Anasto-
moses with sensitive nerves — Properties and functions of the facial — Functions of the branches of the facial
within the aqueduct of Fallopius— Functions of the chorda tympani— Influence of various branches of the facial
upon the movements of the palate and uvula — Functions of the external branches of the facial — Spinal accessory
nerve (third division of the eighth nerve) — Physiological anatomy — Properties and functions of the spinal ac-
cessory—Functions of the internal branch from the spinal accessory to the pneumogastric— Influence of the
spinal accessory upon the heart — Functions of the external, or muscular branch of the spinal accessory— Sub-
lingual, or hypoglossal nerve (ninth nerve) — Physiological anatomy — Properties and functions of the sublin-
gual— Glosso-labial paralysis, 606

CHAPTER XIX.

SENSORY CRANIAL NERVES.

Trifacial, or trigeminal nerve— Physiological anatomy of the trifacial— Properties and functions of the trifacial— Divi-
sion of the trifacial within the cranal cavity— Immediate effects of division of the trifacial— Remote effects of
division of the trifacial —Division of the trifacial before and behind the ganglion of Gasser— Communication with
the sympathetic at the ganglion of Gasser— Explanation of the phenomena of disordered nutrition after division
of the trifacial— Cases of paralysis of the trifacial in the human subject— Pneumogastric nerve (second division of
the eighth nerve)— Physiological anatomy— Properties and functions of the pneumogastric— General propt-rti<-> «f
the roots — Properties and functions of the auricular nerves — Properties and functions of the pharyngeal nerves —
Properties and functions of the superior laryngeal nerves— Properties and functions of the inferior, or recurrent
laryngeal nerves— Properties and functions of the cardiac nerves, and influence of the pm-umo-rastrics upon the
circulation— Depressor-nerve of the circulation— Properties and functions of the pulmonary branches, and influ-
ence of the pneumogastrics upon respiration — Properties and functions of the resophageal nerves — Properties and
functions of the abdominal branches, 684

x CONTENTS.

CHAPTER XX.

FUNCTIONS OF THE SPINAL CORD.

General arrangement of the cerebro-spinal axis — Membranes of the encephalon and spinal cord — Cephalo-rachidian
fluid— Physiological anatomy of the spinal cord — Direction of the fibres after they have penetrated the cord by the
roots of the spinal nerves — General properties of the spinal cord — Action of the spinal cord as a conductor — Trans-
mission of motor stimulus in the cord — Decussation of the motor conductors of the cord — Transmission of sen-
sory impressions in the cord — The white substance of the posterior columns does not conduct sensory impres-
sions— Action of the gray matter as a conductor — Probable function of the cord in connection with muscular co-
ordination— Decussation of the sensory conductors of the cord— Summary of the action of the cord as a conductor
— Action of the spinal cord as a nerve-centre — Movements in decapitated animals — Definition and applications
of the term " reflex " — Reflex action of the spinal cord — Question of sensation and volition in frogs after decapita-
tion—Character of movements following irritation of the surface in decapitated animals— Dispersion of impres-
sions in the cord— Conditions essential to the manifestation of reflex phenomena — Exaggeration of reflex excita-
bility by decapitation, poisoning with strychnine, etc. — Reflex phenomena observed in the human sub-
jectj Page 666

CHAPTER XXI.

THE ENCEPHALIC GANGLIA.

Physiological divisions of the encephalon— Weight of different parts of the brain and of the entire encephalon— Some
points in the physiological anatomy of the encephalon and its connections — The cerebrum— General properties of
the cerebrum — Functions of the cerebrum — Extirpation of the cerebrum in the lower animals — Pathological facts
bearing upon the functions of the cerebrum — Comparative development of the cerebrum in the lower animals —
Development of the cerebrum in different races of men and in different individuals — Location of the faculty of artic-
ulate language in a restricted portion of the anterior cerebral lobes — The cerebellum — Some points in the physio-
logical anatomy of the cerebellum— Course of the fibres in the cerebellum— General properties of the cerebellum-
Functions of the cerebellum — Extirpation of the cerebellum in animals — Pathological facts bearing upon the func-
tions of the cerebellum— Connection of the cerebellum with the generative function— Development of the cerebel-
lum in the lower animals— Ganglia at the base of the encephalon— Corpora striata— Optic thalami— Tubercula
quadrigemina, or optic lobes — Ganglion of the tuber annulare — Medulla oblongata — Physiological anatomy of the
medulla oblongata — Functions of the medulla oblongata — Connection of the medulla oblongata with respiration-
Vital point — Connection of the medulla oblongata with various reflex acts — Rolling and turning movements fol-
lowing injury of certain parts of the encephalon— General properties of the peduncles, 688

CHAPTER XXII.

SYMPATHETIC NERVOUS SYSTEM-SLEEP.

General arrangement of the sympathetic system— Peculiarities in the intimate structure of the sympathetic ganglia
and nerves— General properties of the sympathetic ganglia and nerves— Functions of the sympathetic system—
Vaso-motor nerves — Reflex phenomena operating through the sympathetic system — Trophic centres and nerves
(so called)— Sleep— General considerations— Condition of the organism during sleep— Dreams— Reflex mental phe-
nomena during sleep— Condition of the brain and nervous system during sleep— Theories of sleep— Anaesthesia
and sleep produced by pressure upon the carotid arteries— Differences between natural sleep and stupor or
coma— Regeneration of the brain-substance during sleep— Theory that sleep is due to a want of oxygen— Condi-
tion of the various functions of the organism during sleep, 729

CHAPTER XXIII.

SPECIAL SENSES— TOUCH, OLFACTION, AND GUSTATION.

General characters of the special senses— Muscular sense (so called)— Appreciation of weight— Sense of touch— Varia-
tions in tactile sensibility in different parts — Table of variations measured by the sesthesiometer — Connection
between the variations in tactile sensibility and the distribution of the tactile corpuscles — Titillation — Apprecia-
tion of temperature — Venereal sense — Olfaction — Nasal fossae — Schneiderian and olfactory membrane — Physio-
logical anatomy of the olfactory nerves— Olfactory bulbs— Olfactory cells and terminations of the olfactory nerve-
fibres — Properties and functions of the olfactory nerves — Mechanism of olfaction— Relations of olfaction to the
sense of taste — Reflex acts through the olfactory nerves— Gustation — Savory substances — Relations between
gustation and olfaction — Taste and flavor — Modifications of the sense of taste — Nerves of taste— Chorda tympani
—Facial paralysis with impairment of taste— Paralysis of general sensibility of the tongue without impairment of
taste— Glosso-pharyngeal nerve (first division of the eighth nerve)— Physiological anatomy— General properties
of the glosso-pharyngeal — Relations of the glosso-pharyngeal nerves to gustation — Mechanism of gustation —
Physiological anatomy of the organ of taste — Papilte of the tongue — Taste-buds, or taste-beakers — Connections
of the nerves with the organs of taste, 749

CONTENTS. xi

CHAPTER XXIV.
VISION:

General considerations— Physiological anatomy and general properties of the optic nerves— Physiological anatomy of

the eyeball — Sclerotic coat— Cornea — Membrane of Descemet, or of Demours — Ligamentum iridis pectinatum

Choroid coat— Ciliary processes— Ciliary muscle— Iris— Pupillary membrane— Ketina— Crystalline lens— Aqueous
humor — Chambers of the eye— Vitreous humor— Summary of the anatomy of the globe — The eye as an optical
instrument— Laws of refraction, dispersion, etc., bearing upon the physiology of vision— Theories of light— Re-
fraction by lenses— Myopia and hypermetropia— Formation of images in the eye— Mechanism of refraction in the
eye — Astigmatism — Movements of the iris — Direct action of light upon the iris — Action of the nervous system upon

the iris — Mechanism of the movements of the iris — Accommodation of the eye to vision at different distances

Changes in the crystalline lens in accommodation— Action of the ciliary muscle— Changes in the iris in accom-
modation— Erect impressions produced by images inverted upon the retina — Single vision with both eyes — Cor-
responding points — The horopter — Appreciation of distance and of the form of objects — Mechanism of the stereo-
scope— Duration of luminous impressions— Irradiation — Movements of the eyeball — Muscles of the eyeball — Parts
for the protection of the eyeball — Eyelids— Muscles which open and close the eyelids — Conjunctival mucous
membrane — Lachrymal apparatus — Composition of the tears, Page 767

CHAPTER XXV.

AUDITION.

Physiological anatomy of the auditory nerves— General properties of the auditory nerves— Topographical anatomy
of the parts essential to the appreciation of sound— The external ear— General arrangement of the parts composing
the middle ear— Anatomy of the tympanum— Arrangement of the ossicles of the ear— Muscles of the middle ear
— Mastoid cells — Eustachian tube — Muscles of the Eustachian tube — Mucous membrane of the middle ear and of
the Eustachian tube— General arrangement of the bony labyrinth — Laws of sonorous vibrations — Noise and musi-
cal sounds— Intensity, pitch, and quality of musical sounds— Musical scale— Harmonics, or overtones— Kesonators
of Helmholtz — Eesultant tones— Summation tones — Harmony — Discord— Tones by influence (consonance) — Uses
of different parts of the auditory apparatus— Uses of the external ear— Structure of the membrana tympani— Uses
of the membrana tympani— Vibrations of the membrane by influence— Appreciation of the pitch of tones— Mech-
anism of the ossicles of the ear — Physiological anatomy of the internal ear — General arrangement of the mem-
branous labyrinth — Vestibule— Semicircular canals — Cochlea — Liquids of the labyrinth— Distribution of nerves in
the cochlea— Organ of Corti— Functions of different parts of the internal ear— Functions of the semicircular canals
— Functions of the parts contained in the cochlea — Summary of the mechanism of audition, .... 815

CHAPTER XXVI.

ORGANS AND ELEMENTS OF GENERATION.

General considerations— Sexual generation— Spontaneous generation (so called)— Female organs of generation— Gen-
eral arrangement of the female organs — External and internal organs — The ovaries — Development of the Graa-
fian follicles — The parovarium — The uterus — The Fallopian tubes — Structure of the ovum— Vitelline membrane —
Vitellus— Germinal vesicle and germinal spot — Discharge of the ovum — Puberty and menstruation — Descrip-
tion of a nrenstrual period— Characters of the menstrual flow— Changes in the uterine mucous membrane during
menstruation — Changes in the Graaflan follicle after its rupture (corpus luteum) — The testicles — Tunica vagi-
nalis — Tunica albuginea— Tunica vasculosa — Seminiferous tubes — Epididymis— Vas deferens — Vesiculae seminales
— Prostate— Glands of the urethra — Semen — Secretions mixed with the products of the testicles— Spermatozoids —
Development of the Spermatozoids— Seminal fluid in advanced age, 852

CHAPTER XXVII.

FECUNDATION AND DEVELOPMENT OF THE OVUM.

Coitus — Action of the male — Action of the female — Entrance of Spermatozoids into the uterus — Course of the sper-
matozoids through the female generative passages— Mechanism of fecundation— Determination of the sex of
offspring — Hereditary transmission — Superfecundation — Influence of the maternal mind upon offspring — Union of
the male with the female element of generation— Passage of the Spermatozoids through the vitellino membrane
—Deformation and gyration of the vitellus— Polar globule— Vitelline nucleus— Segmentation of the vitellus—
Primitive trace of the embryon— Blastodermic layers— Formation of the membranes— Am niotic fluid— Umbili-
cal vesicle— Formation of the allantois and the permanent chorion -Umbilical cord— MembranaB dcddino—
Development and structure of the placenta— General view of the development of the embryon— Development
of the cavities and layers of the trunk in the chick — External blastodennic membrane— Intermediate mem-
brane, in two layers— Internal blastodermic membrane— Neural canal— Chorda dorsalis— Primitive aorta&— Ver-
tebrae—Origin of the Wolffian bodies— PI euro-peritoneal cavity— Development of the skeleton— Development of
the muscles— Development of the skin— Development of the nervous system— Development of the encephalon

xii CONTENTS.

— Development of the organs of special sense — Development of the alimentary system— Formation of the me-
sentery— Formation of the stomach — Development of the large intestine — Formation of the pharynx and cesopha-
gus — Development of the anus — The liver, pancreas, and spleen — Development of the respiratory system— De-
velopment of the face — Development of the teeth — Development of the genito-urinary system— Development
of the Wolffian bodies— Ducts of the Wolfflan bodies and ducts of Miiller— Development of the testicles and
ovaries — Development of the urinary apparatus — External organs of generation — Hermaphroditism— Develop-
ment of the circulatory system— First, or vitelline circulation— Second, or placental circulation— Branchial arches
and development of the arterial and the venous system — Development of the heart — Description of the foetal
circulation — Third, or adult circulation, Page 887

CHAPTER XXVIII.

FCETAL LIFE-DEVELOPMENT AFTER BIRTH-DEATH.

Enlargement of the uterus in pregnancy— Duration of pregnancy— Size, weight, and position of the foetus— The
foetus at different stages of intra-uterine life — Multiple pregnancy— Cause of the first contractions of the uterus
in normal parturition — Involution of the uterus — Meconium — Dextral preeminence — Development after birth —
Ages— Death— Cadaveric rigidity— Putrefaction, 938

LIST OF ILLUSTRATIONS.

PLATE I. (Haeckel.) Fig. A, tortoise (IV weeks). Fig. B, chick (IV days).

" E, tortoise (VI weeks). " F, chick (VIII days).

PLATE II. (Haeckel.) Fig. C, dog (IV weeks). Fig. D, man (IV weeks).

" G, dog (VI weeks). " H, man (VIII weeks).

Plates I. and II., facing page 920.

PLATE III. (Erdl.) Fig. 1, human embryon, at the ninth week.

" 2, human embryon, at the twelfth week.
Plate III., facing page 922.

PIOtTBB PAGE

1. Human red blood-corpuscles. (United States Army Medical Museum.) 7

2. Human red blood-corpuscles arranged in rows, with two white corpuscles, or leucocytes . . 7

3. Blood-corpuscles of the frog. (United States Army Medical Museum.) 8

4. Artificial capillary filled with a sanguineous mixture, seen under a micrometer. (Malassez.) 11

5. Human blood-corpuscles, showing post-mortem alterations 11

6. Human red and white blood-corpuscles 15

7. Crystallized haemaglobine. (Gautier.) 18

8. Fibrinous clot. (Robin.) 30

9. Harvey's observations on the flow of blood in the veins. (Harvey.) 33

10. Diagram of the four cavities of the heart. (Bernard.) 34

11. Heart in situ. (Dalton.) 35

12. Heart, anterior view. (Bonamy and Beau.) 36

13. Left cavities of the heart. (Bonamy and Beau.) 37

14. Right cavities of the heart. (Bonamy and Beau) 38

15. Muscular fibres of the ventricles. (Bonamy and Beau.) 39

16. Anastomosing muscular fibres of the heart. (Morel.) 39

17. Valves of the heart. (Bonamy and Beau.) 40

18. Diagram showing shortening of the ventricles during systole 43

19. Cardiograph. (Chauveau and Marey.) 45

20. Small artery from the mesentery of the frog. (United States Army Medical Museum.) . . 66

21. Apparatus for showing the action of the elasticity of the arteries. (Marey.) 69

22. Sphygmograph of Marey ^2

23. Sphygmograph applied to the arm, with traces of the pulse. (Marey.) *72

24. HaDmadynamometer of Poisseuille ^

25. (A) Cardiometer of Magendie. (B) Compensating instrument of Marey f6

26. Chauveau's instrument for measuring the rapidity of the flow of blood in the arteries. . . 79

27. Capillary blood-vessels. (Eberth.) 81

28. Small artery, and capillaries. (United States Army Medical Museum.) 83

29. Web of the frog's foot. (Wagner.) 85

30. Circulation in the web of the frog's foot. (Wagner.) 85

31. Small artery and capillaries from the lung of the frog. (United States Army Medical

Museum.) 86

xiv LIST OF ILLUSTRATIONS.

FIGURE PACE

32. Portion of the lung of a live triton. (Wagner.) 88

33. Venous radicles uniting to form a small vein. (United States Army Medical Museum.). . 93

34. Valves of the veins. (Fabricius.) 97

35. Trachea and bronchial tubes. (Sappey.) 117

36. Lungs, anterior view. (Sappey.) 118

37. Bronchi and lungs, anterior view. (Sappey.) 119

38. Terminal bronchus and air-cells. (Robin.) 120

39. Section of the parenchyma of the human lung, injected through the pulmonary artery.

(Schultze.) 121

40. Thorax, anterior view. (Sappey.) 122

41. Thorax, posterior view. (Sappey.). , 122

42. Diaphragm. (Sappey.) 124

43. Diagram showing the elevation of the ribs in inspiration. (Beclard.) 126

44. Arrow-root starch-granules. (United States Army Medical Museum.) 181

45. Crystals of margarine and margaric acid. (Funke.) 183

46. Crystals of stearine and stearic acid. (Funke.) 183

47. Stomach, liver, small intestine, etc. (Sappey.) 196

48. Permanent teeth. (Le Bon.) 198

49. Tooth of the cat. (Waldeyer.) : 200

50. Inferior maxilla. (Sappey.) 201

51. Salivary glands. (Le Bon.) 205

52. Cavities of the mouth, pharynx, etc. (Sappey.) 215

53. Muscles of the pharynx, etc. (Sappey.) 216

54. Longitudinal fibres of the stomach. (Sappey.) 227

55. Fibres seen with the stomach everted. (Sappey.) 228

66. Pits in the mucous membrane of the stomach, and orifices of the glands. (Sappey.) 228

57. Peptic and mucous glands. \Sappey.). 230

58. Tube for gastric fistula. (Bernard.) 231

59. Gastric fistula. (Bernard.) 232

60. Dog with a gastric fistula. (Beclard.) 232

61. Gastric fistula in the case of St. Martin. (Beaumont.) 233

62. Matters taken from the pyloric portion of the stomach. (Bernard.) 244

63. Stomach, liver, small intestine, etc. (Sappey.) 258

64. Gland of Brunner. (Frey.) 260

65. Intestinal tubules. (Sappey.) 261

66. Intestinal villus. (Leydig.) 262

67. Capillary net-work of an intestinal villus. (Frey.) 262

68. Epithelium of the small intestine of the rabbit. (Funke.) 262

69. Patch of Peyer. (Sappey.) 264

70. Patch of Peyer seen from its attached surface. (Sappey.) 264

71. Clamp for isolating a portion of the intestine. (Colin.) 265

72. Isolated portion of the intestine. (Colin.) 266

73. Gall-bladder, ductus choledochus and pancreas. (Le Bon.) 268

74. Canula for pancreatic fistula. (Bernard.) 269

75. Canula fixed in the pancreatic duct. (Bernard.) 270

73. Pancreatic fistula. (Bernard.) 271

77. Crystals of glycocholate of soda. (Robin.) 280

78. Dog with a biliary fistula 282

79. Stomach, pancreas, large intestine, etc. (Sappey.) 288

80. Opening of the small intestine into the caecum. (Le Bon.) 289

81. Stercorine from the human faeces 295

82. Stercorine from the human faeces 295

83. Superficial lymphatics of the skin of the palmar surface of the finger. (Sappey.) 304

84. Deep lymphatics of the skin of the finger. (Sappey.) 304

85. Same finger, lateral view. (Sappey.) 304

86. Superficial lymphatics of the arm. (Sappey.) 305

LIST OF ILLUSTRATIONS.

xv

FIGURE PAGB

87. Superficial lymphatics of the leg. (Sappey.)

88. Lacteals. (Asellius.) 307

89. Thoracic duct. (Mascagni.) 308

90. Valves of the lymphatics. (Sappey.) 309

91. Lymphatic plexus, showing the epithelial lining of the vessels. (BelaiefF) 310

92. Lymphatics and lymphatic glands. (Sappey.) 311

93. Different varieties of lymphatic glands. (Sappey.) 313

94. Epithelium of the small intestine of the rabbit. (Funke.) 318

95. Epithelium filled with fat, from the duodenum of the rabbit. (Funke.) 319

96. Villi filled with fat, from the small intestine of an executed criminal. (Funke.) 319

97. Egg prepared so as to illustrate endosmotic action 323

98. Chyle from the lacteals and thoracic duct. (Funke.) 332

99. Sebaceous glands. (Sappey.) 359

100. Ceruminous glands. (Sappey.) 360

101. Meibomian glands. (Sappey.) 361

102. Mammary gland of the human female. (Liegeois.) 367

103. Human milk-globules. (Funke.) 872

104. Colostrum. (Funke.) 377

105. Anatomy of the nails. (Sappey.) 883

106. Section of the nail, etc. (Sappey.) 384

107. Hair and hair-follicle. (Sappey.) 387

108. Root of the hair. (Sappey.) 387

109. Human hair. (United States Army Medical Museum.) 388

110. Transverse section of a human hair. (United States Army Medical Museum.) 388

111. Surface of the palm of the hand. (Sappey.) 391

112. Sudoriparous glands. (Sappey.) 392

113. Vertical section of the kidney. (Sappey.) 396

114. Longitudinal sections of the kidney. (Sappey.) 397

115. Diagrammatic view of the Malpighian bodies and tubes of the kidney. (Sappey.) 398

116. Blood-vessels of the kidney. (Sappey.) ' 401

116.* Diagram showing the mechanism of micturition. (Kiiss.) 409

] 17. Crystals of urea. (Funke.) 414

118. Crystals of uric acid. (Funke.) 417

119. Urateof soda. (Funke.) •. 417

120. Crystals of hippuric acid. (Funke.) 418

121. Crystals of lactate of lime. (Funke.). 418

122. Crystals of creatine. (Funke.) .• 419

123. Crystals of creatinine. (Funke.) 419

124. Crystals of oxalate of lime. (Funke.) 420

125. Crystals of leucine. (Funke.) 420

126. Crystals of tyrosine. (Funke.) 421

127. Crystals of taurine. (Funke.) 421

128. Crystals of chloride of sodium. (Funke.) 422

129. Lobules of the liver, interlobular vessels, and intralobular veins. (Sappey.) 433

130. Transverse section of a single hepatic lobule. (Sappey.) 434

131. Liver-cells from a human fatty liver. (Funke.) 435

132. Portion of a transverse section of an hepatic lobule of the rabbit. (Kolliker.) 436

133. Anastomoses, and racemose glands attached to the biliary ducts. (Sappey.) 437

134. Gall-bladder, hepatic, cystic, and common ducts. (Sappey.) 4

135. Crystals of glycocholate of soda. (Robin.) 44f

136. Cholesterine extracted from the bile 447

137. Catheter for the right side of the heart. (Bernard.) 46'

138. Double sound, used for collecting blood from the hepatic veins. (Bernard.) 4

139. Apparatus for extraction of glycogenic matter. (Bernard.) 4

140. Instrument for puncturing the floor of the fourth ventricle. (Bernard.) 4

141. Operation of puncturing the floor of the fourth ventricle. (Bernard.) 471

xvi LIST OF ILLUSTRATIONS.

FIGURE PAGB

142. Malpighian bodies of the spleen of the pig. (Frey.) 474

143. Thymus from the calf. (Kolliker.) 484

144. Half of the human thymus, laid open. (Kolliker.) 484

145. Adipose vesicles. (Kolliker.) 503

146. Amoeba diffluens. (Longet.) 522

147. Ciliated epithelium. (Le Bon.) 523

148. Small elastic fibres. (Kolliker.) 525

149. Larger elastic fibres. (Robin.) 525

150. Large elastic fibres (fenestrated membrane). (Kolliker.) 526

151. Muscular fibres from the urinary bladder. (Sappey.) 527

152. Muscular fibres from the aorta. (Sappey.) 527

153. Muscular fibres from the uterus. (Sappey.) 527

154. Striated muscular fibres. (United States Army Medical Museum.) 529

155. Striated muscular fibres. (Sappey.) 530

156. Fibres of tendon from the human subject. (Rollett.) 531

157. Net-work of connective tissue. (Rollett.) 532

158. Frog's leg prepared so as to show the effects of woorara. (Bernard.) 536

159. Apparatus to show that muscles do not increase in volume during contraction. (Marey.) 538

160. Diagram of the muscular wave. (Aeby.) .• 540

161. Muscular current in the frog. (Bernard.) 542

162. Longitudinal section of bone. (Sappey.) 544

163. Longitudinal section of bone. (United States Army Medical Museum.) 544

164. Transverse section of bone. (Sappey.) 545

165. Transverse section of bone. (United States Army Medical Museum.) 546

166. Bone-corpuscles. (Rollett.) 546

167. Section of cartilage. (United States Army Medical Museum.) 548

1 68. Section of diarthrodial cartilage. (Sappey ) 548

169. Section of the cartilage of the ear. (Rollett.) 549

170. Longitudinal section of the human larynx. (Sappey.) 550

171. Posterior view of the muscles of the larynx. (Sappey.) 552

172. Lateral view of the muscles of the larynx. (Sappey.) 552

173. Glottis seen with the laryngoscope. (Le Bon.) 554

174. Nerve-fibres from the human subject. (Kolliker.) 568

175. Fibres of Remak. (Kolliker.) 569

176. Mode of termination of the motor nerves. (Rouget.) 671

177. Termination of the nerves in the salivary glands. (Pfliiger.) 572

178. Pacinian corpuscle. (Sappey.) 573

179. Papillae of the skin. (Sappey.) 574

180. Cutaneous papilla and tactile corpuscle. (Kolliker.) 575

181. Corpuscles of Krause. (Ludden.) 575

182. Multipolar nerve-cell. (Kolliker.) 577

183. Gray matter of the spinal cord, treated with nitrate of silver. (Grandry.) 578

184. Multipolar nerve-cell. (Schultze.) 579

185. Multipolar nerve-cell. (Deiters.) 581

186. Connections of nerve-cells and nerve-fibres. (Dean.) 582

187. Corpora amylacea. (Funke.) 585

188. Frog prepared so as to show that woorara destroys the properties of the motor nerves.

(Bernard.) 595

189. Electric forceps. (Liegeois.) 600

190. Frog's leg prepared so as to show the contrasted action of the descending and the ascend-

ing current. (Matteucci.) 601

191. Frog's leg prepared so as to show induced contraction. (Liegeois.) 602

192. Cervical portion of the spinal cord. (Hirschfeld.) 60 J

193. Dorsal portion of the spinal cord. (Hirschfeld.) 6^*

194. Inferior portion of the spinal cord, and cauda equina. (Hirschfeld.) 607

195. Roots of the cranial nerves. (Hirschfeld.) 608

LIST OF ILLUSTRATIONS. xvii

196. Distribution of the motor oculi coramunis. (Ilirschfeld.) .......................... 610

197. Distribution of the patheticus. (Ilirschfeld.) .................................. t 614

198. Distribution of the motor oculi cxternus. (Hirschfeld.) ............................ 614

199. Distribution of the small root of the fifth nerve. (Hirschfeld.) ...................... 616

200. Incisors of the rabbit before and after section of the nerve of mastication. (Bernard.). 617

201. Superficial branches of the facial and the fifth. (Ilirschfeld.) ....................... 619

202. Chorda tympani nerve. (Hirschfeld.) ............................................ 622

203-208. Expressions of the face produced by contractions of the muscles under electrical

excitation. (Le Bon, after Duchenne.) ......................................... 626

209. Spinal accessory nerve. (Ilirschfeld.) ............................................ 628

210. Sublingual nerve. (Sappey.) .................... . .............................. 633

211. Principal branches of the large root of the fifth nerve. (Robin.) .................... 635

212. Ophthalmic division of the fifth. (Hirschfeld.) .................................... 635

21.3. Superior maxillary division of the fifth. (Hirschfeld.) .............................. 636

214. Inferior maxillary division of the fifth. (Hirschfeld.) .............................. 637

215. Cutaneous distribution of sensory nerves to the face, head, and neck. (Beclard.) ....... 638

216. Instrument for dividing the fifth nerve. (Bernard.) .......... .................... 639

217. Operation for division of the fifth nerve. (Bernard.) ............................... 640

218. Anastomoses of the pneumogastric. (Hirschfeld.) .............. . .................. 645

219. Distribution of the pneumogastric. (Hirschfeld.) .................................. 646

220. Branches of the pneumogastric to the heart. (Bernard.) .......................... 654

221. Depressor-nerves. (Cyon and Ludwig.) ............................... ........... 656

222. Transverse section of the spinal cord. (Stilling.) ................................. 670

223. Transverse section of the spinal cord. (Gerlach.) ................................. 671

224. Frog poisoned with strychnine. (Liegcois.) ....................................... 687

225. Vertical section of the encephalon. (Hirschfeld.) ................................. 689

226. Direction of the fibres in the cerebrum. (Le Bon.) ................................ 690

226.* Diagrammatic figure showing the cerebral convolutions. (Dalton.) .................. 692

227. Cerebellum and medulla oblongata. (Hirschfeld.) ........... ...................... 707

228. Corpora striata. (Sappey.) .................................................... 720

229. Anterior view of the medulla oblongata. (Sappey. ) ................................ 725

230. Stylet for breaking up the medulla oblongata. (Bernard.) .......................... 727

231. (A) Cervical and thoracic portion of the sympathetic. (Sappey.) ..................... 732

231. (B) Lumbar and sacral portions of the sympathetic. (Sappey.) ...................... 734

232. Sympathetic ganglion, with multipolar cells. (Leydig.) .............. ............... 735

233. Olfactory ganglion and nerve. (Hirschfeld.) ...................................... 755

234. Terminal filaments of the olfactory nerves. (Kolliker.) ............................ 756

235. Glosso-pharyngeal nerve. (Sappey.) ............................................. 762

236. Papillae of the tongue. (Sappey.) .............................................. 765

237. 238. Varieties of papillie of the tongue. (Sappey.) ................................ 766

239. Taste-buds. (Engelmann.) ..................................................... 766

240. Optic tracts, commissure, and nerves. (Ilirschfeld.) .......................... ..... 768

241. Diagram of the decussation at the optic commissure ................................ 768

242. Choroid coat of the eye. (Sappey.) .............................................. 772

243. Ciliary muscle. (Sappey.) ...................................................... 773

244. Rods of the retina. (Schultze.) ................................................. ?77

245. (A) Vertical section of the retina. (II. Miiller.) ..................... ........... j. ^Q

245. (B) Connection of the rods and cones of the retina with the nervous elements. (Sappey.) )

246. Blood-vessels of the retina. (E. G. Loring.) ....................... . .............. f*79

247. Crystalline lens, anterior view. (Babuchin.) ...................................... ^80

248. Section of the crystalline lens. (Babuchin.) ...................................... ^81

249. Zone of Zinn. (Sappey.) ...................................................... '781

250. Section of the human eye. (Hclmholtz.) ......................................... ^83

251. Refraction by prisms .......................................................... ^

252. Refraction by convex lenses ................................................... 788

253. Section of the lens, etc , showing the mechanise of accommodation. (Fick.) .........

xviii LIST OF ILLUSTKATIONS.

FIGURE PAGE

254. Muscles of the eyeball. (Sappey.) 808

255. Diagram illustrating the action of the muscles of the eyeball. (Fick.) 809

256. Lachrymal and Meibomian glands. (Sappey.) 813

257. Lachrymal canals, lachrymal sac, and nasal canal. (Sappey.) 814

258. General view of the organ of hearing. (Sappey.) 819

259. Ossicles of the tympanum. (Arnold.) 820

260. Ossicles seen from within. (Riidinger.) 820

261. Bony labyrinth. (Riidinger.) 823

262. Resonators of Helmholtz 831

263. Membrani tympani. (Rudinger.) 836

264. Diagram of the labyrinth. — Vestibule and semicircular canals. (Rudinger.) 843

265. Otoliths from various animals. (Rudinger.) 844

266. Section of the first turn of the spiral canal. — Section of the cochlea. (Rudinger.) 845

267. Distribution of the cochlear nerve in the spiral canal. (Sappey.) 847

268. The two pillars of the organ of Corti. (Sappey.) 848

269. Vertical section of the organ of Corti. (Waldeyer.). 848

270. Uterus, Fallopian tubes, and ovaries. (Sappey.) 858

271. Section of the ovary. (Waldeyer.) 861

272. Graafian follicle. (Luschka.) 862

273. Virgin uterus. (Sappey.) 863

274. Muscular fibres of the uterus. (Sappey.) 864

275. Superficial muscular fibres of the uterus. (Liegeois.) 865

276. Inner layer of muscular fibres of the uterus. (Liegeois.) 866

277. Blood-vessels of the uterus and ovaries. (Rouget.) 867

278. Fallopian tube. (Liegeois.) 868

279. External erectile organs of the female. (Liegeois.) 869

280. Ovum of the rabbit. (Waldeyer.) 871

281. Sections of two corpora lutea. (Kolliker.) 877

282. Testicle and epididymis. (Arnold.) 881

283. Vas deferens, vesiculae seminales, and ejaculatory duct. (Liegeois.) 882

284. Human spermatozoids. (Luschka.) 885

285. Development of spermatozoids. (Liegeois.) 886

286. Mulatto woman with twins, one white and the other black ; from a photograph 895

287. Penetration of spermatozoids through the vitelline membrane. (Haeckel.) 896

288. Formation of the polar globule. (Robin.) 897

289. Segmentation of the vitellus. (Liegeois.) 898

290. Primitive trace of the embryon. (Liegeois.) 899

291. Formation of the membranes. (Kolliker.) 902

292. Villi of the chorion. (Haeckel.) 905

293. Placenta and deciduae. (Liegeois.) 910

294-296. Development of the chick. (Briicke.) 913

297. Development of the notocorde. (Robin.) 915

298. Human embryon one month old. (Dalton.) 915

299. Development of the nervous system of the chick. (Wagner.) 917

300. Development of the spinal cord and brain of the human subject. (Tiedemann.) 918

301. Foetal pig, showing umbilical hernia. (Dalton.) 920

302. Development of the bronchial tubes and lungs. (Rathke and Miiller.) 922

303-305. Development of the face. (Coste.) 924, 925

306. Temporary and permanent teeth. (Sappey.) 926

307. Foetal pig, showing the Wolffian bodies. (Dalton.) 927

308. Diagrammatic representation of the genito-urinary system. (Henle.) 929

309. Area vasculosa. (Bischoff.) 932

310. Aortic arches in the mammalia. (Von Baer.) 933

311. Diagram of the fretal circulation .937

312. The Siamese twins 942

313. Cholesterine extracted from meconium. ... ... 944

HUMAN PHYSIOLOGY.

CHAPTER I.

THE BLOOD.

General considerations— Transfusion — Quantity of blood— General characters of the blood — Blood-corpuscles —
Development of the blood -corpuscles — Leucocytes— Development of leucocytes — Composition of the red cor-
puscles— Globuline— Haemaglobine— Analysis of the blood— Composition of the blood- plasma— Inorganic prin-
ciples— Organic saline principles — Organic non-nitrogenized principles — Excrementitious matters — Organic nitro-
genized principles — Plasmine, fibrin, metalbumen, and seriue — Peptones — Coloring matter — Coagulation of the
blood — Characters of the clot — Characters of the serum— Circumstances which modify coagulation — Coagulation
of the blood in the organism — Spontaneous arrest of haemorrhage — Cause of the coagulation of the blood — So-
called fibrin-factors — Paraglobuline, or fibrinoplastic matter — Fibrinogen.

FROM the earliest periods in the history of physiology, the importance of the blood
has been recognized ; and, with the progress of knowledge, this great nutritive fluid has
been shown to be more and more intimately connected with the phenomena of animal
life. It is now known to be the most abundant and highly organized of the fluids of the
body, providing materials for the regeneration of all parts, without exception, receiving
the products of their waste and conveying them to proper organs, by which they are
removed from the system. These processes require, on the one hand, constant regen-
eration of the nutritive constituents of the blood, and, on the other, its constant purifi-
cation by the removal of effete matters.

Those tissues in which the processes of nutrition are active are supplied with blood
by vessels; but some, less highly organized, like the epidermis, hair, cartilage, etc.,
which are called extra-vascular because they are not penetrated by vessels, are none the
less dependent upon the blood, as they imbibe nutritive material from the blood of ad-
jacent parts.

The importance of the blood in the processes of nutrition is evident ; and, in animals
in which nutrition is active, death is the immediate result of its abstraction in large
quantity. Its importance to life can be readily demonstrated by experiments upon the
inferior animals. If we take a small dog, introduce a canula through the right jugular
vein into the right side of the heart, adapt to it a syringe, and suddenly withdraw a great
part of the blood from the circulation, immediate suspension of all the so-called vital
processes is the result. If we then return the blood to the system, the animal is as sud-
denly revived. To perform this experiment satisfactorily, we must accurately adjust the
capacity of the syringe to the size of the animal.

Certain causes, one of which is diminution in the force of the heart's action after
copious haemorrhage, prevent the escape of all the blood from the body, even after
division of the largest arteries; but, after the arrest of the functions which follows
copious discharges of this fluid, life may be restored by injecting into the vessels
the same blood or the fresh blood of another animal. This observation, which was first
1

2 THE BLOOD.

made on the inferior animals, has been applied to the human subject; and it has been
ascertained that, in patients sinking under hemorrhage, the introduction of even a few
ounces of fresh blood may restore the functions for a time, and sometimes permanently.
The operation of transfusion, which consists in the introduction of the blood of one indi-
vidual into the vessels of another, was performed upon animals in the middle of the
seventeenth century, and was soon after attempted in the human subject. So great was
the enthusiasm with which some regarded these experiments, that it was thought pos-
sible even to effect a renewal of youth by the introduction of young blood into the veins
of old persons ; and it was also proposed to cure certain diseases, such as insanity, by
actual renewal of the circulating fluid. These ideas were not without apparent foun-
dation. It was stated, in 1667, that a dog, old and deaf, had his hearing improved and
was apparently rejuvenated by transfusion of blood from a young animal. A year later,
Denys and Emmerets published a case of a maniac who was restored to health by the
transfusion of eight ounces of blood from a calf; and another case was reported of a
man who was cured of leprosy by the same means. But the case of insanity, which was
apparently cured, suffered a relapse, and the patient died during a third attempt at
transfusion. It is almost unnecessary to say that these extravagant expectations were
not realized. In fact, some operations were followed by such disastrous consequences,
that the practice was forbidden by law in Paris in 1668, and soon fell into disuse.

Transfusion, with more reasonable applications, was revived in the early part of this
century (1818) by Blundell, who, with others, demonstrated its occasional efficacy in
desperate hemorrhage and in the last stages of some diseases, especially cholera. There
are now quite a number of cases on record where life has been saved by this means; and
oftentimes, when the result has not been so happy, the fatal event has been consider-
ably delayed.

Numerous experiments on transfusion in animals have been performed, with very
interesting results. Prevost and Dumas have shown that, while an animal may be
restored after hemorrhage by the transfusion of defibrinated blood, no such effect fol-
lows the introduction of the serum ; showing that the vivifying influence in all prob-
ability resides in the corpuscles. Brown-Sdquard has shown that, in parts detached
from the body, after nervous and muscular irritability have disappeared, these properties
may be restored for a time by the injection of fresh blood. He also made a curious ex-
periment in which blood was passed from a living dog into the carotid of a dog just dead
from peritonitis. The animal was so far revived by this operation as to sustain himself
on his feet, wag his tail, etc., and died a second time, twelve and a half hours after. In
this experiment, insufflation was employed in addition to the transfusion.

It may be considered established that, in animals, after hemorrhage, life may be
restored by injecting the blood, defibrinated or not, provided it be introduced slowly,
without admixture with air, and not in too great quantity. In the human subject, es-
pecially after hemorrhage, the vital processes are sometimes restored by careful trans-
fusion of human blood, with the above precautions; remembering that a very small quan-
tity, three or four ounces, will sometimes be sufficient.

of Blood. — The determination of the entire quantity of blood contained in
the body is a question of great interest, and has long engaged the attention of physiolo-
gists, without, however, any absolutely-definite results. Among those who have ex-
perimented on this point, may be mentioned Allen-Moulins, Herbst, Fried. Hoffmann,
"Valentin, Blake, Lehmann and Weber, and Vierordt. The fact that the labors of these
eminent observers have so far been unsuccessful in determining definitely the entire quan-
tity of blood shows the extent of the difficulties to be overcome before the question can
be entirely settled. The chief difficulty lies in the fact that all the blood is not discharged
from the body on division of the largest vessels, as after decapitation ; and no perfectly-
accurate means have been devised for estimating the quantity which remains in the

QUANTITY OF BLOOD. 3

vessels. The estimates of experimenters present the following wide differences : Allen-
Monlins, who was one of the first to study this question, estimated the quantity of blood
at one-twentieth the weight of the entire body. The estimate of Herbst was a little
higher. Hoffmann estimated the quantity at one-fifth the weight of the body. These
observers estimated the quantity remaining in the system after opening the vessels, bv
mere conjecture. Valentin was the first who attempted to overcome this difficulty by
experiment. For this purpose he employed the following process : He took first a small
quantity of blood from an animal for purposes of comparison ; then he injected into the
vessels a known quantity of a saline solution, and, taking another specimen of blood some
time after, he ascertained by evaporation the proportion of water which it contained,
and compared with the proportion in the first specimen. He reasoned that the excess of
water in the second specimen over the first would give the proportion of the water intro-
duced to the whole mass of blood ; and, as the entire quantity of water introduced was
known, the entire quantity of blood could be deduced therefrom. Suppose, for example,
that the excess of water in the second specimen should be one part to ten of the blood,
it would show that one part of water had been mixed with ten of the blood ; and, if
we had injected in all five ounces of water, we should have the whole quantity of blood
ten times that, or fifty ounces. This method, however, is open to the objection that it is
impossible to take note of the processes of imbibition and exhalation which are con-
stantly in operation.

The following process, which is, perhaps, the one least open to sources of error, was
employed by Lehmann and Weber, and applied directly to the human subject, in the
case of two decapitated criminals : These observers estimated the blood remaining in
the body after decapitation, by injecting the vessels with water until it came through
nearly colorless. The liquid was carefully collected, evaporated to dryness, and the dry
residue was assumed to represent a certain quantity of blood, the proportion of dry
residue to a definite quantity of blood having been previously ascertained. If we could
be certain that only the solid matter of the blood was thus removed, such an estimate
would be tolerably accurate. As it is, we may consider it as approximating very nearly
to the truth. We quote the following account of these observations :

" My friend, Ed. Weber, determined, with my cooperation, the weights of two crimi-
nals both before and after their decapitation. The quantity of blood which escaped
from the body was determined in the following manner : Water was injected into the
vessels of the trunk and head, until the fluid escaping from the veins had only a pale-red
or yellow color ; the quantity of the blood remaining in the body was then calculated,
by instituting a comparison between the solid residue of this pale-red aqueous fluid, and
that of the blood which first escaped. By way of illustration, I subjoin the results
yielded by one of the experiments. The living body of one of the criminals weighed
60,140 grammes (132-7 pounds), and the same body after decapitation, 54,600 grammes;
consequently, 5,540 grammes of blood had escaped 28-560 grammes of this blood
yielded 5'36 grammes of solid residue; 60'5 grammes of sanguineous water collected
after the injection, contained 3'724 grammes of solid substances; 6,050 grammes of the
sanguineous water that returned from the veins were collected, and these contained
37-24 grammes of solid residue, which corresponds to 1,980 grammes of blood ; conse-
quently, the body contained 7,520 grammes (16-59 pounds), 5,540 escaping in the ai-t of
decapitation, and 1,980 remaining in the body; hence, the weight of the whole Mood
was to that of the body nearly in the ratio of 1 : 8. The other experiment yielded a
precisely similar result.

" It cannot be assumed that such experiments as these possess extreme accuracy, but
they appear to have the advantage of giving in this manner the minimum of the blood
contained in the body of an adult man ; for although some solid substances, not belong-
ing to the blood, may be taken up by the water from the parenchyma of the orirans per-
meated with capillary vessels, the excess thus obtained is so completely counteracted by

4 THE BLOOD.

the deficiency caused by the retention of some blood in the capillaries, and in part by
transudation, that our estimate of the quantity of blood contained in the human body
may be considered as slightly below the actual quantity."

The process just described gives the most accurate idea of the probable quantity of
blood in the human body ; and, although more recent investigations have been made
upon the lower animals, by different methods, they are all more or less open to objec-
tion. We may assume, then, that, in a person of ordinary muscular and adipose devel-
opment, the proportion of blood to the weight of the body is about one to eight, the
entire quantity of blood in the body being from sixteen to eighteen pounds. The relative
quantity of blood is said to be less in the infant than in the adult, and to be diminished
in old age. It has been found, also, in observations on the inferior animals, to be greater
in the male than in the female.

Prolonged abstinence from food, except when large quantities of liquid are ingested,
has a notable effect in diminishing the mass of blood, as indicated by the small quantity
which can be removed from the body, under these circumstances, with impunity ; and it
has been experimentally demonstrated that the entire quantity of blood is considerably
increased during digestion. Bernard drew from a rabbit weighing about two and a half
pounds, during digestion, over ten and a half ounces of blood without producing death;
while he found that the removal of half that quantity from an animal of the same size,
fasting, was followed by death. Wrisberg has reported a case of a female criminal, very
plethoric, from whom twenty-one pounds, seven and three-quarters ounces of blood
flowed after decapitation. As the relations of the quantity of blood to the digestive
function are so important, it is unfortunate that the conditions of the system in this
respect were not noted in the observations of Lehmann and Weber. It is evident, there-
fore, that the quantity of blood in the body is considerably increased during digestion ;
but as regards the extent of this increase, we cannot form any very definite idea. It is
only shown that there is a marked difference in the effects of hemorrhage in animals,
during digestion and fasting.

General Characters of the Blood.

Opacity. — The opacity of the blood depends upon the fact that it is not a homogene-
ous fluid, but is composed of two distinct elements, a clear plasma and corpuscles, which
are both nearly transparent, but whiclj have a different refractive power. If both of these
elements had the same refractive power, the mixture would present no obstacle to the
passage of light; but, as it is, the rays, which are refracted in passing from the air
to the plasma, are again refracted when they enter the corpuscles, and again, when
they pass from the corpuscles to the plasma, so that they are lost, even in a thin layer
of the fluid. This loss of light in a mechanical mixture of two transparent liquids of
unequal refractive power can be demonstrated by the following simple experiment : If
to a little chloroform colored red, clear water be added in a test-tube, these liquids re-
main distinct from each other, and both are transparent ; but if we agitate them vio-
lently, the chloroform is temporarily subdivided into globules and mixed with the water;
and, as they refract light differently, the mixture is opaque.

Odor, Taste, Reaction, and Specific Gravity. — The blood has a faint but characteristic
odor. This may be developed so as to be very distinct by the addition of a few drops
of sulphuric acid, when an odor peculiar to the animal from which the blood has been
taken becomes very marked.

The taste of the blood is faintly saline, on account of the presence of a considerable
proportion, three or four parts per thousand, of chloride of sodium in the plasma.

The reaction of the blood is always distinctly alkaline. According to Zuntz, the
alkalinity diminishes rapidly after the blood is drawn from the vessels. The alkaline
reaction is due to the presence of basic carbonate and phosphate of soda in the plasma.

The specific gravity of defibrinated blood is from 1052 to 1057" (Robin), being some-

COLOR OF THE BLOOD. 5

what less in the female than in the male. Its density varies greatly under different con-
ditions of digestion.

Temperature. — The temperature of the blood is generally given as from 98° to 100°
Fahr. ; but recent experiments have shown that it varies considerably in different parts
of the circulatory systsm, independently of exposure to the refrigerating influence of the
atmosphere. By the use of very delicate registering thermometers, Bernard has suc-
ceeded in establishing the following facts with regard to the temperature in various
parts of the circulatory system in dogs and sheep :

1. The blood is warmer in the right than in the left cavities of the heart.

2. It is warmer in the arteries than in the veins, with a few exceptions.

8. It is generally warmer in the portal vein than in the abdominal aorta, indepen-
dently of the digestive act.

4. It is constantly warmer in the hepatic than in the portal veins.

He found the highest temperature in the blood of the hepatic vein, where it ranged
from 101P to 107°. In the aorta, it ranged from 99° to 105°.

We may assume, then, in general terms, that the temperature of the blood in the
deeper vessels is from 100° to 107° Fahrenheit.

Color of the Blood. — The color of the blood is due to the corpuscles. In the arterial
system it is uniformly red. In the veins it is generally dark blue and sometimes almost
black. This difference in color between the blood in the arterial and in the venous sys-
tem was a matter of controversy at the time of Harvey. By the discoverer of the cir-
culation, the difference, which is now universally known and admitted as regards most
of the veins, was supposed to be merely accidental and dependent on external causes.
Fifty years later, Lower demonstrated the change of color in the blood as it passes
through the lungs, and associated it with the true cause ; viz., the absorption of oxygen.
The color in the veins, however, is not constant. Many years ago, John Hunter ob-
served, in a case of syncope, that the blood drawn by venesection was bright red ; and
more recently, Bernard has demonstrated that, in some veins, the blood is nearly if not
quite as red as in the arterial system. The color of the venous blood depends upon the
condition of the organ or part from which it is returned. The red color was first no-
ticed by Bernard in the renal veins, where it contrasts very strongly with the black
blood in the vena cava. He afterward observed that the redness only existed during the
functional activity of the kidneys ; and when, from any cause, the secretion of urine
was arrested, the blood became dark. He was led, from this observation, to examine
the venous blood from other glands ; and, directing his attention to those which he was
able to examine during their functional activity, particularly the salivary glands, he found
the blood red in the veins during secretion, but becoming dark as soon as secretion wae
arrested. These observations may be easily verified by opening the abdomen of a living
animal, exposing the renal veins, and introducing a canula into the ureter, so as to
be able to note the flow or arrest of the urine. So long as the urine continues to flow,
the blood in these vessels is bright red ; but when secretion becomes arrested, as it soon
does after exposure of the organs, it presents no difference from the blood in the
vena cava. In the submaxillary gland, by the galvanization of a certain nerve which he
calls the motor nerve of the gland, Bernard has been able to produce secretion, and, by
the galvanization of another nerve, to arrest it; in this way changing at will the color
of the blood in the vein. It has been found by the same observer that division of the
sympathetic in the neck, which dilates the vessels and increases the supply of blood to
one side of the head, produces a red color of the blood in the jugular. He has also
found that paralysis of a member by division of the nerve has the same effect on the
blood returning by the veins.

The explanation of these facts is evident when we reflect upon the reasons why the
blood is red in the arteries and dark in the veins. Its color depends upon the corpus-
cles ; and as the blood passes through the lungs it loses carbonic acid and gains oxygen,

6 THE BLOOD.

changing from black to red. In its passage through the capillaries of the system, in the
ordinary processes of nutrition, it loses oxygen and gains carbonic acid, changing from
red to black. During the intervals of secretion, the glands receive just enough blood
for their nutrition, and the ordinary interchange of gases takes place, with the con-
sequent change of color ; but, during their functional activity, the blood is supplied
in greatly-increased quantity, in order to furnish the watery elements of the secretions.
Under these circumstances, it does not lose oxygen and gain carbonic acid in any great
quantity, as has been demonstrated by actual analysis, and consequently there is no
marked change in color. When filaments of the sympathetic are divided, the vessels
going to the part are dilated, and the supply of blood is increased to such an extent,
that a certain proportion passes through without parting with its oxygen (a fact which
has also been demonstrated by analysis), and consequently it retains its red color. The
explanation in cases of syncope is probably the same, although this is merely a suppo-
sition. Even during secretion, a certain quantity of carbonic acid is formed in the
gland, which, according to Bernard, is carried off in solution in the secreted fluid.

It may be stated, then, in general terms, that the color of the blood in the arteries is
bright red ; and, in the ordinary veins, like the cutaneous or muscular, it is dark blue,
almost black. It is red in the veins coming from glands during secretion, and dark during
the intervals of secretion.

Anatomical Elements of the Blood.

In 1661, the celebrated anatomist, Malpighi, in examining the blood of the hedgehog,
with the imperfect lenses at his command, discovered little floating particles which he
mistook for granules of fat, but which were the blood-corpuscles. He did not extend his
observations in this direction; but, a few years later (1673), Leeuwenhoek, by the aid
of simple lenses of his own construction, ranging in magnifying power from forty to one
hundred and sixty diameters, first saw the corpuscles of human blood, which he minutely
described in a paper published in the Philosophical Transactions, in 1674. To Leeuwen-
hoek is generally ascribed the honor of the discovery of the blood-corpuscles.1 About a
century later, William Hewson described another kind of corpuscles in the blood, which
are much less abundant than the red, and which are now known under the name of white
globules, or, as they have been called by Eobin, leucocytes.

Without following the progress of microscopical investigations into the constitution
of the blood, it may be stated that it is now known to be composed of a clear fluid, the
plasma, or liquor sanguinis, holding certain corpuscles in suspension. These corpusclef
are as follows:

1. Eed corpuscles; by far the most abundant, constituting a little less than one-half
of the mass of blood.

2. Leucocytes, or white corpuscles ; much less abundant, existing only in the pro-
portion of one to several hundred red corpuscles.

3. Granules ; exceedingly minute, called, by Milne-Edwards, globulins, and, by Kolli-
ker, elementary granules. These are few in number, and are probably fatty particles
from the chyle. They are to be regarded as accidental constituents of the blood.

Eed Corpuscles.— -These little bodies give to the blood its red color and its opacity.
They are true, organized structures, containing organic nitrogenized and inorganic ele-
ments molecularly united, and, as an exception to the general rule, a little fatty matter
in union with the organic principles. They constitute a little less than one-half the mass

1 Some writers give the credit of the discovery of the blood-corpuscles to Swammerdam. In 1658, Swammerdam
studied the blood-corpuscles of the frog and described them very accurately; but his researches were not published
until 1738, a number of years after his death. In questions of priority, it is usual to date discoveries from the time
of their first publication.

BLOOD-CORPUSCLES.

FIG. 1.— Human Uood -corpuscles ; magnified 870 diam-
eters. (From a photograph taken at the United States
Army Medical Museum.)

of blood, and, according to the observations of all who have investigated this subject, are
more abundant in the male than in the female.

The form of the blood-corpuscles is peculiar. They are flattened, biconcave, circular
disks, with a thickness of from one-fourth to one-third of their diameter. Their edges
are rounded, and the thin, central portion
occupies about one-half of their diameter.
Their consistence is not much greater than
that of the plasma. They are very elastic,
and, if deformed by pressure, immediately
resume their original shape when the press-
ure is removed. Their specific gravity is
from 1088 to 1105, considerably greater
than the specific gravity of the plasma,
which is about 1028. (Robin.)

When the blood has been drawn from
the vessels and coagulates slowly, the great-
er density of the red corpuscles causes them
to gravitate to the lower portions of the
clot, leaving the white corpuscles and fibrin
at the surface. This is the cause of the
" buffy-coat " mentioned by some writers.
If coagulation be prevented by the addition
of a small quantity of sulphate of soda,
there is quite a marked gravitation of red corpuscles after standing for some hours.

The peculiar form of the blood-corpuscles gives them a very characteristic appearance
under the microscope. Examined with a magnifying power of from three hundred to five
hundred diameters, those which present their flat surfaces have a shaded centre when the
edges are exactly in focus. This appearance was formerly supposed to indicate the ex-
istence of a nucleus having a constitution different from that of the rest of the corpuscle.
It is now understood to be an optical effect, the result of the form of the corpuscles ; their
biconcavity rendering it impossible for the centre and edges to be exactly in focus at the
same instant, so that, when the edges are in focus, the centre is dark, and, when the cen-
tre is bright, the edges are shaded.

As the blood-corpuscles are examined
by the microscope by transmitted light,
they are nearly transparent and of a pale-
amber color. It is only when they are col-
lected in masses that they present the red
tint characteristic of blood as it appears
to the naked eye. This yellow or amber
tint is quite characteristic. A pretty good
idea of the color may be obtained by large-
ly diluting blood in a test-tube and holding
it between the eye and the light.

In examining blood under the micro-
scope, the corpuscles are seen in many
different positions ; some flat, some on
their edges, etc. This assists us in recog-
nizing their peculiar form.

It has long been observed that the blood- FIG. 2.-//M»m-n red Mo<>fi-c<»'/»wt<'* ;//™«f/, <i in rmcs,

u-ith two ichite corpuscles, or leucocytes.

corpuscles have a remarkable tendency to

arrange themselves in rows like rouleaux of coin. This appearance has attracted univer-
sal attention, and for a long time it was not satisfactorily explained. Robin, however, has

8

THE BLOOD.

given what seems to be the true explanation. He has shown that, shortly after removal
from the vessels, there exudes from the corpuscles an adhesive substance which smears
their surface and causes them to stick together. Of course the tendency is to adhere by
their flat surfaces. In examining a specimen of blood under the microscope, the presence
of this adhesive exudation may be demonstrated by employing firm and gradual pressure
on the glass cover, when the adherent corpuscles may be separated, in some instances,
and, with oblique light, we can see a little transparent filament between them, which
draws them together, as it were, when the pressure is removed. This phenomenon is due
to a post-mortem change ; but it occurs so soon, that it presents itself in nearly every
specimen of fresh blood, and is therefore mentioned in connection with the normal char-
acters of the blood-corpuscles.

Dimensions. — The diameter of the blood-corpuscles has a more than ordinary anatom-
ical interest ; for, varying perhaps less in size than other anatomical elements, they are
often taken as the standard by which we form an idea of the size of other microscopic
objects. The diameter usually given is -^^ of an inch. The exact measurement given
by Robin is .0073 of a millimetre, or ^^ of an inch. It is stated by some authors that
the size of the corpuscles is very variable, even in a single specimen of blood. We have
repeatedly measured them and found a diameter of g^inr °f an inch. Very few are to
be found which vary from this measurement. Kolliker, who gives their average diame-
ter as s~frW °f an mcn? states that "at least ninety -five out of every hundred corpuscles
are of the same size."

We cannot leave the subject of the size of the blood-corpuscles without a notice of the
measurements in the blood of different animals. This point is interesting, from the fact
that it is often an important question to determine whether a given specimen of blood be
from the human subject or from one of the inferior animals. Comparative measurements
also have an interest on account of a relation which seems to exist in the animal scale
between the size of the blood-corpuscles and muscular activity. In all the mammalia,
with the exception of the camel and llama, in which the corpuscles are oval, the blood
has nearly the same anatomical characters as in the human subject. In only two animals,
the elephant and sloth, are the red corpuscles larger than in man ; in all others, they are
smaller, or of nearly the same diameter. By reference to the table, it will be seen that,

in some animals, the corpuscles are very much
smaller than in man; and, by accurate meas-
urements, we are enabled to distinguish their
blood from the blood of the human subject.
But, in forming an opinion on this subject,
it must be remembered that there is some
variation in the size of tlie corpuscles of the
same animal. We can easily distinguish the
blood of the human subject, or of the mam-
mals generally, from that of birds, fishes, or
reptiles; for, in these classes of animals, the
corpuscles are oval and contain a granular
nucleus.

Milne-Edwards has attempted to show,
by a comparison of the diameter of the
blood-corpuscles in different species, that
their size bears an inverse ratio to the mus-
cular activity of the animal. Reference to the
table will show that this relation holds good
to some extent, while there certainly exists none between the size of the corpuscles and
the size of the animal. In deer, animals remarkable for muscular activity, the corpuscles

FIG. 8. — Blood-corpuscles of the frog ; magnified 370
diameters. (From a photograph taken at the
United States Army Medical Museum.)

MAMMALS.

9

are very small, ^Vir °f an iQc^ I while in the sloth they are 7^-7, and in the ape, which
is comparatively inactive, ^sW But, on the other hand, in the dog, which is quite
active, we have a corpuscle of ^Vfr of an inch, and in the ox, which is certainly not so
active, the diameter of the corpuscle is ¥2^7 of an inch. Although this relation between
the size of the blood-corpuscles and muscular activity is not invariable, it is certain that,
the higher we go in the great classes of animals, the smaller are the blood- corpuscles;
the largest being found in the lowest orders of reptiles, and the smallest, in the mam-
malia. The blood of the invertebrates, with a few exceptions, contains no colored cor-
puscles.

Table of Measurements of Red Corpuscles.

This table is taken from the table of Mr. Gulliver, published in the Sydenham edition of Hewson's
Works, page 237. Nearly five hundred measurements were made by Mr. Gulliver; and of these,
one hundred of the most important have been selected. It will be observed that the diameter of
the human blood-corpuscle is greater than that generally given. It must be borne in mind that all
these measurements are mere approximations ; but they are useful, as showing the relations of the
corpuscles in different animals, and enabling us to distinguish the blood of the human subject from
that of some of the inferior animals. The measurements are all given in fractions of an English
inch ; and, in making the selections, the common names of the animals have been substituted for
the technical names given in the original.

Mammals.

Corpuscles Circular,

Diameter.

Man,

Chimpanzee, .
Ourang-outang, .
Black monkey,
Red monkey,
Cape baboon, .
Brown baboon, .
Dog-faced baboon, .
Lazy monkey,
Bat, ....
Long-eared bat, .

Mole,

Hedgehog, ....

Badger,

Polar bear, ....
Brown bear of Europe, .
Black bear of North America.
Raccoon,. .

Dog,

Fox,

Jackal, ....

Wolf,

Striped hyena,

Spotted hyena,

Cat, . .

Lion, ....

Tiger,

Leopard,

Panther, ....
Ferret, ....

TiVs

WKF

aoW

Tooo

Diameter.
Weasel, . . . » .

Polecat,

Otter,

Seal,

Porpoise,

Whale,

Hog,

Indian elephant, ....
Indian rhinoceros, ....

Horse,

Ass,

Stag, ......

Fallow deer,

Virginia deer, . ...

Giraffe, nhr

Antelope, triW

Gazelle, . •

Goat,

Sheep,

Ox,

Buffalo,

Musk deer of Java, .... TiraTir
Flying squirrel, ....
Red squirrel, ....
Black squirrel,

Gray squirrel, T'OOTT

Marmot, w*

Brown rat, WIT

Black rat, ^r*

Mouse, Wr*

10 THE BLOOD.

Diameter. Diameter.

Water rat, ^^ Opossum, ^5r

Porcupine, W3^ Kangaroo, T^

Beaver, ^-3-

Guinea-pig, ^-g L. diam. S. diam.

Rabbit, WOT Dromedary (oval), .

Two-toed sloth, W&y Camel (oval),

Birds.

Long
Diameter.
Eagle (ring-tailed), . . . T^
Owl, TfVa
Jay, -ro^T
Raven, YaVr
Starling, ^-3-
Wren, FaVa
Sparrow, -%-fa „
Woodpecker, .... YiW
Swallow, .... g-iVr
Stork, . WKT

Corpuscles Oval.

Short
Diameter. D

Long
iameter.

TgVaf
YoGV
T&aTT

ITl if 2"

Short
Diameter.

¥6 4~3

*sW

•a^9¥
•^A'T

•xdrs Turtle-dove,
4-jVr Peacock, ....
40*00 Cock,
TsV? Turkev,

^WT Guinea-fowl,
asVu Quail,

•s-fov Goose, . . .

7-JS

•7-A-o Duck,

-Z?ej9^765.

Corpuscles Oval.

Long Short Long Short

Diameter. Diameter. Diameter. Diameter.

Green turtle, .... -^-T T-8Vj Lizard, -nfey y^

Land tortoise, .... T^ ^^ Viper, .... 1^7-4 rfoy

Amphibia.

Corpuscles Oval.

Long Short Long Short

Diameter. Diameter. Diameter. Diameter.

Frog, iiVs TSVr Toad,

-?7sAe5.

Corpuscles Oval.

Long Short Long Short

Diameter. Diameter. Diameter. Diameter.

Perch, ..... TTihrs irsV? Pike, ..... j(nnr "jseT
Carp, -2-j^y 7^- Eel, T^-J y-g^J

Enumeration of the Blood- Corpuscles. — In most of the quantitative analyses of the
blood, the proportion of moist corpuscles to the entire mass of blood is stated to be a
little less than one-half. This estimate is necessarily rather rough ; and it would be in-
teresting to ascertain, if possible, the normal variations in the proportion of corpuscles,
under different conditions of the system, particularly as these bodies play so important a
part in many of the functions of the organism. Actual enumerations of the blood-cor-
puscles have been made by Vierordt, Weckler, and others, and quite recently by Malas-
sez (1874). It is stated by Malassez that the error, in his calculations, does not amount to
more than two or three per cent. The process employed by Malassez is the following:

ENUMERATION OF THE BLOOD-CORPUSCLES.

11

The blood to be examined is diluted with ninety-nine parts of a liquid composed of
one volume of a solution of gum-arabic of a specific gravity of 1020 with three volumes
of a solution of equal parts of sulphate of soda and chloride of sodium, also of a spe-
cific gravity of 1020. The mixture, containing one part of blood in one hundred, is in-
troduced into a small thermometer-tube with
an elliptical bore, the sides of the tube being
ground 11 at for convenience of microscopical
examination. The capacity of the tube is to
be calculated, by estimating the weight of a
volume of mercury contained in a given
length. The tube is then filled with the di-
luted blood, and the number of corpuscles in
a given length of the tube is counted by
means of a microscope fitted with an eye-
piece micrometer. In this way, the number
of corpuscles in a given volume of blood can
be readily estimated. In man, the number
in a cubic millimeter of blood (a millimeter =
about YJ of an inch) is estimated at about
four million.

According to the observations of Malas-
sez, the proportion of corpuscles is about the
same in all parts of the arterial system. In
the veins, the corpuscles are more abundant than in the arteries. In the venous system,
the blood of the splenic veins presents the largest proportion of corpuscles, and the pro-
portion is smallest in the blood of the hepatic veins. These results favor the idea
that the red corpuscles are formed, to a certain extent, in the spleen, and that some
are destroyed in the liver ; but farther observations are necessary to render this view
certain.

FIG. 4.— Artificial
eous mixture,
crometer. (Malassez.)

I capillary, jelled with a sanguin-
, seen under a quadrilateral mi-

Post-mortem Changes in the ^Blood-
Corpuscles. — In examining the fresh blood
under the microscope, after the specimen
has been under observation a short time,
the corpuscles assume a peculiar appear-
ance, from the development, on their sur-
face, of very minute, rounded projections,
like the granules of a raspberry. A little
later, when they have become partly de-
siccated, they present a shrunken appear-
ance, and their edges are more or less ser-
rated. Under these conditions, their orig-
inal form may be restored by adding to
the specimen a liquid of about the den-
sity of the serum. When they have been
completely dried, as in blood spilled upon
clothing or on a floor, months or even
years after, they can be made to assume
their characteristic form by carefully moist-
ening them with an appropriate liquid. This property is taken advantage of in exam-
inations of old spots supposed to be blood ; and, if the manipulations be carefully con-
ducted, the corpuscles may be recognized without difficulty by the microscope.

If pure water be added to a specimen of blood under the microscope, the corpuscles

FIG. 5.— Human blocd-corpitfdfs, showing post-mortem
alteration*.

12 THE BLOOD.

swell up, become spherical, and are finally lost to view by solution. The same effect
follows almost instantaneously on the addition of acetic acid.

Structure. — The structure of the blood-corpuscles is very simple. They are perfectly
homogeneous, presenting, in their normal condition, no nuclei or granules, and are not
provided with an investing membrane. A great deal has been said by anatomists con-
cerning this latter point ; and some are of the opinion that the corpuscles are cellular in their
structure, being composed of a membrane, with viscid, semifluid contents. Without going
fully into the discussion of this question, it may be stated that few have assumed to have
actually demonstrated this membrane ; but certain observers have inferred its existence
from the fact of the corpuscles swelling, and, as they term it, bursting on the addition
of water. The appearances presented upon the addition of iodine to blood previously
treated with water, which have been supposed to indicate the presence of shreds of
ruptured vesicles, are not sufficiently distinct to demonstrate the existence of a membrane.
The great elasticity of the corpuscles, the persistence with which they preserve their
biconcave form, and their general appearance, rather favor the idea that they are homo-
geneous bodies of a definite shape, than that they have a cell- wall with semifluid con-
tents; especially as the existence of a membrane has been only inferred and not posi-
tively demonstrated. Their mode of nutrition is like that of other anatomical elements.
They are bathed in a nutritive fluid, the plasma, and, as fast as their substance becomes
worn out and eifete, new material is supplied. In this way, they undergo the same
molecular changes as other anatomical structures. When destroyed or removed from the
body in haemorrhages, new corpuscles are gradually developed, until their quantity
reaches the normal standard.

Development of the Blood- Corpuscles. — Very early in the development of the ovum,
the blood-vessels appear, constituting what is called the area vasculosa. At about the
same time, the blood-corpuscles are developed, it may be before, or it may be just after the
appearance of the vessels, for this point is undetermined. The blood becomes red when
the erabryon is about one-tenth of an inch in length. From this time until the end of
the sixth or eighth week, they are from thirty to one hundred per cent, larger than in
the adult. Most of them are circular, but some are ovoid, and a few are globular. At
this period, nearly all of them are provided with a nucleus; but, from the first, there are
some in which this is wanting. The nucleus is from -ly-oVjr to -g-^Vo °f an inch in diameter,
globular, granular, and insoluble in water and acetic acid. As development advances,
these nucleated corpuscles are gradually lost; but, even at the fourth month, we may
still see a few remaining. After this time, they present no anatomical differences from
the blood-corpuscles in the adult.

In many works on physiology and general anatomy, we find accounts of the develop-
ment of the red corpuscles from the colorless corpuscles, or leucocytes, which are sup-
posed to become disintegrated, their particles becoming developed into red corpuscles ;
but there seems to be no positive evidence that such a process takes place. The red cor-
puscles appear before the leucocytes are formed ; and it is only the fact that the two
varieties coexist in the blood-vessels which has given rise to such a theory. It is most
reasonable to consider that the red corpuscles are formed by a true genesis in the san-
guineous blastema. There is, farthermore, no sufficient evidence that any particular
organ or organs have the function of producing the blood-corpuscles. It is regarded by
some as a necessity that there should be an organ for the destruction of the corpuscles,
and one for their formation. Eegarding them, as we certainly must, as organized bodies
which are essential anatomical elements of the blood, it is difficult to imagine what
reasons, based on their function, should lead physiologists to seek so persistently after an
organ for their destruction. The hypothesis that they are used in the formation of pig-
mentary matter seems hardly sufficient to account for this. The observations of Malassez.

FUNCTION OF THE BLOOD-CORPUSCLES. 13

which show an increase in the number of corpuscles in the blood coming from the spleen
and a diminution in the blood of the hepatic veins, are not sufficiently definite to serve
as a demonstration that the spleen is a blood-forming organ; and the same remark
may be applied to observations upon the formation of blood-corpuscles by the marrow
of the bones.

In the present state of our knowledge, the following seem to be the most rational
views with regard to the development and nutrition of the blood-corpuscles:

1. At the time of their first appearance in the ovum, they are formed by no special
organs, for no special organs then exist ; but they appear by genesis in the sanguineous
blastema.

2. When fully formed, they are regularly-organized anatomical elements, subject to
the same laws of gradual molecular waste and repair as any of the anatomical elements
of the tissues.

3. They are generated de novo in the adult, when diminished in quantity by haemor-
rhage or otherwise ; and, under these circumstances, they are probably formed in the
liquor sanguinis, by the same process by which they take their origin in the ovum.

Function of the Blood-Corpuscles. — Although the albuminoid constituents of the plasma
of the blood are essential to nutrition, the red corpuscles are the parts most immediately
necessary to life. We have already seen, in treating of transfusion, that life may be re-
stored to an animal in which the functions have been suspended from haemorrhage, by the
introduction of fresh blood ; and, while it is not necessary that this blood should contain
the elements of fibrin, it has been shown by the experiments of Prevost and Dumas and
others, that the introduction of serum, without the corpuscles, has no restorative effect.
When all the arteries leading to a part are tied, the tissues lose their properties of con-
tractility, sensibility, etc., which may be restored, however, by supplying it again with
the vivifying fluid. We shall see, when we come to treat of the function of respiration,
that one great distinction between the corpuscular and fluid elements of the blood is the
great capacity which the former have for absorbing gases. Direct observations have
shown that blood will absorb from ten to thirteen times as much oxygen as an equal bulk
of water; and this is dependent almost entirely on the presence of the red corpuscles. A»
all the tissues are constantly absorbing oxygen and giving off carbonic acid, a very im-
portant function of the corpuscles is to carry oxygen to all parts of the body. In the
present state of our knowledge, this is the only well-defined function which can be
attributed to the red corpuscles, and it undoubtedly is the principal one. They have an
affinity, though not so great, for carbonic acid, which, after the blood has circulated in
the capillaries of the system, takes the place ot the oxygen. In some experiments per-
formed a few years ago on the effects of haemorrhage and the seat of the " lesoin de re-
spirer," we demonstrated that one of the results of removal of blood from the system
was a condition of asphyxia, dependent upon the absence of these respiratory elements.

Leucocytes, or White Corpuscles of the Blood. — In addition to the red corpuscles of
the blood, this fluid always contains a number of colorless bodies, globular in form, in the
substance of which are embedded a greater or less number of minute granules. These
have been called b£ Robin, leucocytes. This name seems more appropriate than that of
white or colorless blood-corpuscles, inasmuch as they are not peculiar to the blood, but
are found in the lymph, chyle, pus, and various other fluids, in which they were formerly
known by different names. All who have been in the habit of examining the animal
fluids microscopically have noticed the great similarity between the corpuscular elements
found in the above-mentioned situations ; and, as microscopes have been improved and
investigations have become more exact, the varieties of corpuscles have been narrowed
down. It is now pretty generally acknowledged that the corpuscles found in mucus and
pus are identical ; also, that there is no difference between the white corpuscles found in

14 THE BLOOD.

the lymph, chyle, and blood ; and, finally, it has been shown that all of these bodies,
which were formerly supposed to present marked distinctive characters, belong to the
same class, presenting but slight differences in different situations. The description which
will be given of the white corpuscles of the blood, and the effects of reagents, will an-
swer, in the main, for all the corpuscular bodies that are grouped under the name of
leucocytes.

Leucocytes are normally found in the blood, lymph, chyle, semen, colostrum, and
vitreous humor. Pathologically, they are found in the secretion of mucous mem-
branes, following irritation, and in inflammatory products, when they are called pus-
corpuscles.

In examining a specimen of blood with the microscope, we immediately notice the
marked difference between the leucocytes and red corpuscles. The former are globular,
with a smooth surface, somewhat opaque from the presence of more or less granular
matter, white, and larger than the red corpuscles.

In examining the circulation under the microscope, we are struck with the adhesive
character of the leucocytes as compared with the red corpuscles. The latter circulate
with great rapidity in the centre of the vessels, while the leucocytes have a tendency to
adhere to the sides, moving along slowly, and occasionally remaining for a time entirely
stationary, until they are swept along by a change in the direction or force of the
current.

The size of the leucocytes varies somewhat, even in any one fluid, such as the blood.
Their average diameter may be stated as -g^sif °f an mch. It is in pus, where they exist in
greatest abundance, that their microscopical characters may be studied with greatest ad-
vantage. In this fluid, after it is discharged, the corpuscles sometimes present remarkable
deformities. They become polygonal in shape, and sometimes ovoid, occasionally presenting
projections from their surface, which give them a stellate appearance. These alterations,
however, are only temporary; and, after from twelve to twenty-four hours, they resume
their globular shape. On the addition of acetic acid, they swell up, become transparent,
with a delicate outline, and present in their interior one, two, three, or even four rounded,
nuclear bodies, generally collected in a mass. This is rather to be considered as a coagu-
lation of a portion of the corpuscle, than a. nucleus brought out by the action of the acid
which renders the corpuscle transparent ; although in some corpuscles it is seen without
the addition of any reagent. This appearance is produced, though more slowly, by the
addition of water.

Leucocytes vary considerably in their external characters in different situations.
Sometimes they are very pale and almost without granulations, while at others they are
filled with fatty granules and are not rendered clear by acetic acid. As a rule, they
increase in size and become granular when confined in the tissues. In colostrum, where
they are called colostrum-corpuscles, they generally undergo this change. As the result
of inflammatory action, when they are sometimes called inflammatory or exudation-cor-
puscles, leucocytes frequently become much hypertrophied and are filled with fatty
granules.

The deformation of the leucocytes, to which allusion has already been made, is some-
times so rapid and changeable as to produce creeping movements, due to the projection
and retraction of portions of their substance. These movements are of the kind called
amo3boid, and are supposed to be important in the process of migration of the corpus-
cles, which has lately been described.

The quantity of leucocytes compared to the red corpuscles can only be given approxi-
matively. It has been estimated by counting under the microscope the red corpuscles and
leucocytes contained in a certain space. Moleschott gives the proportion as 1:335;
others, at from 1 : 300 to 1 : 500. It has been found by Dr. E. Hirt, of Zittau, whose
observations have been confirmed by others, that the relative quantity of leucocytes
is much increased during digestion. He found, in one individual, a proportion of 1 : 1800

DEVELOPMENT OF LEUCOCYTES.

15

before breakfast ; an hour after breakfast, which was taken at 8 o'clock, 1 : TOO ; be-
tween 11 and 1 o'clock, 1:1500; after dining, at 1 o'clock, 1:400; two hours after
1 : 1475 ; after supper, at 8 p. M., 1 : 550 ; at 11£ P. M., 1 : 1200. The leucocytes are
much lighter than the red corpuscles, and, when the blood coagulates slowly, are fre-
quently found with a certain amount of Colorless fibrin forming a layer on the surface of
the clot, which is called the " buffy-coat."
Their specific gravity is about 1070.

Many observers, among whom may be
mentioned Donne, Kolliker, Gray, Hirt,
and Malassez, have noticed a great in-
crease in the number of leucocytes in the
blood coming from the spleen, and have
supposed that they are formed chiefly in
this organ. It is inconsistent with the
mode of development of these corpuscles
to suppose that any special organ is exclu-
sively engaged in their production ; and
their persistence in animals after extirpa-
tion of the spleen shows that they are de-
veloped in other situations.

The function of the leucocytes is not
understood. The supposition that they

FIG. 6. — Human red and white, blood-corpuscles.

break down and become nuclei for the de-
velopment of red corpuscles, which at one
time obtained, is a pure hypothesis, which has no positive basis in fact.

Development of Leucocytes. — These corpuscles appear in the blood-vessels very early
in fetal life, before the lymphatics can be demonstrated. They arise in the same way as
the red corpuscles, by genesis from materials existing in the vessels. They appear in
lymphatics, before these vessels pass through the lymphatic glands, in the foetus anterior
to the development of the spleen, and also on the surface of mucous membranes ; so
they cannot be considered as produced exclusively by the lymphatic glands, as has been
supposed. There is no organ nor class of organs in the body specially charged with their
formation; and, although they frequently appear as a result of inflammation, this process
is by no means necessary for their production. Eobin. has carefully noted the phenom-
ena of their development in recent wounds. The first exudation consists of clear fluid,
with a few red corpuscles ; then, a finely granular blastema. In from a quarter of an
hour to an hour, pale, transparent globules, from -5-^ to -^5*5-5- of an inch in diameter,
make their appearance, which soon become finely granular and present the ordinary
appearance of leucocytes. They are thus developed, like other anatomical elements, by
organization of the necessary elements furnished by a blastema, and not by the action
of any special organ or organs.

This view of the mode of development of leucocytes seems to be established by the
following very elegant experiments of Onimus, showing that corpuscles may bo devel-
oped, under favorable conditions, in a perfectly clear, homogeneous blastema:

Onimus used the clear fluid taken without delay from rapidly-developed blisters,
which he found ordinarily contained no leucocytes, but which he carefully filtered in
order to remove all sources of error. The filtered liquid contained no morphological
elements; but, on the other hand, he found that, if the liquid were allowed to remain
for an hour or more in contact with the derma, it always contained leucocytes and epi-
thelial cells. Under these circumstances, even after filtration, the liquid contained a low
leucocytes ; but, after six or seven hours of repose in a conical vessel, the corpuscular
elements gravitated to the bottom, leaving the upper portion of the liquid perfectly clear.

16 THE BLOOD.

This liquid, entirely free from anatomical elements, was enclosed in little sacs formed
of an animal membrane (gold-beater's skin) and introduced under the skin of a living
rabbit. At the end of twelve hours, a few small leucocytes and granulations had made
their appearance ; at the end of twenty -four hours, the fluid had become somewhat
opaque, and contained a large number of leucocytes and granulations ; and, at the end
of thirty-six hours, the fluid was white, milky, and composed almost entirely of leucocytes
and granulations. The leucocytes, which were examined also by Prof. Robin, presented
all the characters by which these corpuscles are ordinarily recognized. These experi-
ments were repeated with more than forty different specimens of fluid from blisters.

The experiments were thea varied in order to show the influence of the membrane
and the composition of the blastema upon the development of leucocytes. By modify-
ing the membrane in which the blastema was enclosed, it was found that the corpuscles
were rapidly developed in proportion to the activity of the osmotic action. When thick
animal membranes were used, their development was slow, and, in some instances, did
not take place at all. There was no development of leucocytes in a clear blastema en-
closed in a sac of caoutchouc or in glass tubes hermetically sealed ; and from this it was
concluded that osmotic action is a necessary condition, and that the mere heat of the
body is not sufficient to develop these corpuscles, even in an appropriate blastema. The
influence of this constant molecular movement is in striking contrast to the conditions
of absolute repose which are so essential to the formation of crystals from ordinary
saline solutions.

One of the most interesting points in these experiments is connected with the influ-
ence of the composition of the blastema upon the development of leucocytes. It was
found that these bodies were never developed in a blastema in which the fibrin had been
coagulated. Experimenting with two liquids, the only difference in their constitution
being that in one the fibrin had been coagulated by repeatedly plunging the glass tube in
which it was contained into cool water, while the other was kept at the ordinary tem-
perature, a little bicarbonate of soda being added to prevent coagulation, it was found
that leucocytes were developed as usual in the fluid which contained the fibrinous elements,
and that none appeared in the other. On placing the liquid with its coagulum enclosed
in a sac under the skin, it was found that, after a time, the fibrin was redissolved, but
no leucocytes made their appearance.

The theory which has for its motto, omnis cellula e cellula, receives no support from
these experiments. Onimus added to fluids which had been deprived of fibrinous matters,
epithelial cells and pus-corpuscles, but, even after thirty-six hours, he never found any
additional development of corpuscular elements. Leucocytes added to fluids in which
the fibrinous elements were unchanged did not seem to exert any influence upon the de-
velopment of new corpuscles.

Elementary Corpuscles. — Little granules are found in the blood, especially during
digestion, which, as they were supposed to take part in the formation of the white cor-
puscles, have been called elementary granules or corpuscles. They probably are little
fatty particles of the chyle which come from the thoracic duct, and are not positively
known to have any connection with the formation of the other corpuscular elements of
the blood.

Composition of the Red Corpuscles.

The red corpuscles of the blood contain an organic nitrogenized principle, called
globuline, combined with inorganic principles and a coloring matter. The composition
of the leucocytes has not been accurately determined. The inorganic matters contained
in the red corpuscles are in a condition of intimate union with the other constituents,
and can only be separated by incineration. It may be stated, in general terms, that
most, if not all of the various inorganic constituents of the plasma exist also in the cor-

H^EMAGLOBINE. 17

puscles, which latter are particularly rich in the salts of potassa. Iron exists in the col-
oring matter of the corpuscles. In addition, the corpuscles contain cholesterine, lece-
thine, a certain amount of fatty matter, and probably some of the organic saline princi-
ples of the blood.

Globuline. — Eollett, by alternately freezing and thawing blood several times in succes-
sion in a platinum vessel, has succeeded in separating the coloring matter from the red cor-
puscles. When the blood is afterward warmed and liquefied, the fluid is no longer opaque,
but is dark and transparent. Microscopical examination then reveals the corpuscles, entire-
ly decolorized and floating in a red, semitransparent serum. Denis extracted the organic
principle of the corpuscles by adding to defibrinated blood about one-half its volume of
a solution of chloride of sodium containing one part in ten of water. Allowing this to
stand for from ten to fifteen hours, there appears a viscid mass, which is very carefully
washed with water until all the coloring matter and the salt added has been removed.
The whitish, translucid mass which remains is called globuline. Denis has also ex-
tracted a small quantity of fibrin from the corpuscles. Globuline is readily extracted
from the blood of birds, but is obtained with difficulty from the blood of the human
subject.

Hmmagloline. — This is the coloring matter of the red corpuscles. It has been called
by different writers, hsemaglobuline or hasmatocrystalline ; but the crystals called haema-
tine and haematosine are derivatives of hasmaglobine and are not true proximate princi-
ples. Efemaglobine may be extracted from the red corpuscles by adding to them, when
congealed, ether, drop by drop. A jelly-like mass is then formed, which is passed rap-
idly through a cloth, crystals soon appearing in the liquid, which may be separated by
filtration. (Gautier.)

The crystals of ha3maglobine extracted from human blood are in the form of four-
sided prisms, elongated rhomboids, or rectangular tablets, of a purplish-red color. They
are composed of carbon, hydrogen, oxygen, nitrogen, sulphur, and a small quantity of
iron. They are soluble in water and in very dilute alkaline solutions, and the hasmaglo-
bine is precipitated from these solutions by ferrocyanide of potassium, nitrate of mer-
cury, chlorine, or acetic acid. The proportion of this coloring matter to the entire mass
of blood is about one hundred and twenty-seven parts per thousand. It constitutes
from \% to T97 of the dried corpuscles. A solution of heBmaglobine in one thousand
parts, examined with the spectroscope, gives two dark bands between the letters D and
E in Frauenhofer's scale.

Treated with oxygen or prepared in fluids in contact with the air, there occurs a
union of oxygen with the coloring matter, forming what has been called oxyhsemaglobine.
There can be no doubt that the oxygen enters into an intimate, though rather unstable
combination with ha3maglobine, and this is an important point to be considered in con-
nection with the absorption of oxygen by the blood in respiration. A solution of oxy-
hsemaglobine presents a different spectrum from a solution of pure haemaglobine. If
we examine a solution of oxyhaBmaglobine with the spectroscope and then discharge
the oxygen by prolonged ebullition in a vacuum, the characteristic bands of pure hsema-
globine make their appearance. The union of oxygen with hasmaglobine is unstable and
the oxgen can be removed by a current of hydrogen, nitrous oxide, or carbonic acid. A
current of carbonic oxide displaces the oxygen, and the carbonic oxide forms a very sta^
ble combination with the coloring matter. It is well known that carbonic oxide is h
very poisonous gas, which becomes fixed in the corpuscles so that they become inca-
pable of absorbing oxygen.

According to recent observations, oxygen combined with hfemaglobine exists in the
condition of ozone. A solution of oxyhremaglobine is readily decomposed by a current
of sulphuretted hydrogen, forming, like ozone, water and a precipitate of sulphur.
2

18

THE BLOOD.

HaBmatine may be produced by decomposition of hsemaglobine, by a process which
it is not necessary to describe, as the hsematine is not a proximate principle. Hsematoi-
dine is also a product of decomposition of hgemaglobine, but it does not contain iron.
Hsematoidine is more interesting, however, from the fact that it is frequently found in
old clots that have been long extravasated in the tissues. Eobin found a notable quan-
tity of crystals of ha3matoidine in a cyst of the liver.

Assuming, as we certainly may, that the
blood furnishes material for the nourishment
of all the tissues and organs, we should ex-
pect to find entering into its composition all

/ rH" >T /9 the proximate principles existing in the body

NiSN>,, ^ L...J'<-J //^ which undergo no change in nutrition, like

the inorganic principles, and organic matters
capable of being converted into the organic
elements of every tissue. Farthermore, as
the products of waste are all taken up by the

blood before their final elimination, these also

x\ n ^'^ should enter into its composition. With these

v\ Itf-'f * ^ facts in our minds, we can readily appreciate

the importance of accurate proximate ana-
lyses of the circulating fluid.

Notwithstanding the immense amount of
labor bestowed by the most eminent chemists
of the day upon the quantitative analysis of
the blood, and the great physiological interest
attaching to every advance in our knowledge
in this direction, the chemical difficulties in-
volved are so great, that even now there are
no analyses which give the exact quantities
of each of its inorganic constituents. This is
owing to the great difficulty in the analysis of
any fluid in which inorganic and organic prin-
ciples are so closely united ; for there is no
more delicate problem in analytical chemistry
than the determination of the presence and the
proportions of inorganic substances united with

organic matter. Of the animal fluids which are easily obtained, the blood, from the large
proportion of different organic principles which enter into its composition, presents the
greatest difficulties to the analytical chemist. Another difficulty is the necessity of a
proximate, and not an ultimate analysis. It is not sufficient to give the amount of cer-
tain chemical elements which the blood contains; we must ascertain the amount of
these elements in the state of union with each other to form proximate principles.

Most of the constituents of the blood are found both in the corpuscles and plasma.
It is difficult to determine all of the different constituents of these two parts of the blood.
It has been shown, however, by Schmidt, of Dorpat, that the phosphorized fats are more
abundant in the globules, while the fatty acids are more abundant in the plasma. The
salts with a potash-base have been found by the same observer to exist almost entirely
in the corpuscles, and the soda-salts are four times more abundant in the plasma than in
the corpuscles. In addition to the nutritive principles, \ve have, entering into the com-
position of the blood, urea, cholesterine, urate of soda, creatine, creatinine, and other
substances the characters of which are not yet fully determined, belonging to the class
of excrementitious principles. Their consideration comes more appropriately under the
head of excretion, and they will be fully taken up in the chapters devoted to that subject.

FIG 1.— Crystallised hcemaglobine. (Gautier.)
a, ft, crystals from the venous blood of man ; c, blood
of the cat ; d, blood of the Guinea pig ; «, blood
of the marmot ; /, blood of the squirrel. (Gau-
tier.)

COMPOSITION OF THE BLOOD-PLASMA. 19

Analysis of the Blood.

In the analyses given in the older works on physiology, the blood, having been divided
into plasma and corpuscles, was supposed to contain, in the plasma, two organic princi-
ples, called albumen and fibrin. Kecent investigations, however, have shown that the
organic constituents of the plasma are more complex; and the more modern an.-ilvsi-s of
the blood give other organic principles, which have been separated by new methods.
As these have been very generally accepted by modern writers, it becomes necessary to
describe them in detail, and we shall adopt the new nomenclature, as far as the different
organic principles have been established by definite observations. An argument in favor
of this subdivision of the matters formerly recognized as fibrin and albumen is the fact,
which has long been apparent, that the organic constituents of the blood, particularly
albumen, are known to possess certain peculiar properties which distinguish them from
these principles as they are found elsewhere. The following table, which we have care-
fully compiled from recent authorities, particularly Robin, gives approximatively the quan-
tities of the different constituents of the blood-plasma. These may be divided into the
following classes: 1. Inorganic principles; 2. Organic saline principles; 3. Organic non-
nitrogenized principles ; 4. Excrementitious matters ; 5. Organic nitrogenized principles.

Composition of the Blood-Plasma.
Specific gravity, 1028.

Water, 779 parts per 1,000 in the male ; 791 parts per 1,000 in the female.
Chloride of sodium, 3 to 4 parts per 1,000.
" " potassium, 0'359 parts per 1,000.

" ammonium, proportion not determined.
Sulphate of potassa, 0'288 parts per 1,000.

" " soda, proportion not determined.
Carbonate of potassa, " " "

" soda (with bicarbonate of soda), 1-200 parts per 1,000.
" lime, proportion not determined.
" magnesia, " "

Phosphate of lime of the bones, and neutral phosphate,
" magnesia,

" potassa, J. 1-500 parts per 1,000.

" iron (probable),

Basic phosphates and neutral phosphate of soda,
Silica, copper, lead, and magnesia, traces occasionally.
Lactate of soda, proportion not determined.

" " lime (probable), proportion not determined.
Pneumate of soda, " " "

".f

Oleate of soda, ")

1 -2

Margarate of soda,

&S,

Stearate " "

0

Y i , u tt

Butyrate " "

>- 1-475 parts per 1,000.

Oleine,

«- ~
•Z "H*

Margarine,

si

Stearine,

O .2

Lecethine, containing nitrogen and called phosphorized

fatty matter, 0'400 parts per 1,000.

1^

(Jlucose, 0-002 parts per 1,000.

11

(Jlyco^cmc matter, proportion not determined.

0 &

Inosite (muscles), " " "

w

Plasmine, 25 parts (dried) per 1,000.

20 THE BLOOD.

Carbonic acid in solution.

Urea, 0177 parts per 1,000, in arterial blood; 0*088, in the blood of the renal vein.

Urate of soda, proportion not determined.

" " potassa (probable), proportion not determined.
" " lime, " " " "

" " magnesia, "
" " ammonia, "

Sudorates of soda, etc., " " "

Inosates, " " "

Oxalates, " "

Creatinine, " " "

Leucine, " " "

Hypoxanthine, " " "

Cholesterine, 0'455 to 0*751 parts per 1,000, in the entire blood.

Fibrin, 3 parts per 1,000.
Metalbumen, 22 parts per 1,000.
Serine, 53 parts (dried) per 1,000.

(Moist fibrin, 8*820 parts per 1,000, in the entire blood.

Metalbumen and serine constitute the albumen of the older analyses. Albumen,
about 75 parts [dried] and 330 parts [moist] per 1,000, in the entire blood.)
Peptones, 4 parts (dried) and 28 parts (moist) per 1,000.
(_ Coloring matters of the plasma, proportion and characters not determined.

We shall take the above table as a guide for our study of the individual constituents
of the blood-plasma. As regards gases, in addition to carbonic acid, which we have
classed with the excrementitious matters, the blood contains oxygen, nitrogen, and
hydrogen. The nitrogen and hydrogen are not important, and the relations of oxygen
will be fully considered under the head of respiration. Most of the coloring matter of
the blood exists in the red corpuscles, which contain a peculiar principle which we
have already considered in connection with the chemical constitution of these bodies.

In studying the composition of the blood, as well as the composition of food, the
tissues, secreted fluids, etc., it is convenient to divide its constituents into classes, and this
we have done in the simplest manner possible.

It is evident, the blood receiving all the products of disassimilation as well as the
nutritive principles resulting from digestion, that there should be a division of its con-
stituents into nutritive and excrementitious. We have classed certain principles together
as excrementitious. These are the various products of disassimilation of the organism,
which are taken up by the blood or conveyed to the blood-vessels by the lymphatics,
exist in the blood in small quantity, and are constantly being separated from the blood
by the different excreting organs. Their constant removal from the blood is the expla-
nation of the excessively minute proportion in which they exist in this fluid. Their
relations to the organism will he fully considered under the head of excretion.

Excluding, then, for the present, all consideration of the products of disassimilation,
we have to study the various constituents of the blood that are more or less directly
concerned in nutrition.

Physiological chemists recognize certain constituents of the organism, called proxi-
mate principles, which may be elementary substances, but which are more frequently
compounds. We speak of chloride of sodium as a proximate principle existing in the
blood, because, as chloride of sodium, it gives to the blood certain properties. We do not
regard the chemical elements, chlorine and sodium, as proximate principles, because they
do not exist in the blood uncombined. Still, a proximate principle may be a chemical
element, as in the case of oxygen, which, as oxygen, performs, in the blood, certain
important functions.

Adopting, in the main, the definition given by Robin, we may regard as a proximate

COMPOSITION OF THE BLOOD-PLASMA. 21

principle, a substance extracted from the body, which cannot be subdivided without
chemical decomposition and loss of certain characteristic properties. This definition
will apply to all classes of proximate principles, organic as well as inorganic.

Taking as a basis, the classification proposed by Robin, we may divide the proximate
principles of the blood, and, indeed, of the entire organism, as follows :

1. Inorganic Principles. — This class is of inorganic origin, definite chemical compo-
sition, and crystallizable. The substances forming it are all introduced from without,
and are all discharged from the body in the same form in which they entered. They
never exist alone, but are always combined with the organic principles, to form the
organized fluids or solids. This union is " atom to atom," and so intimate that they are
taken up with the organic elements, as the latter are worn out and become effete, and
are discharged from the body, although themselves unchanged. To supply the place of
the principles thus thrown off, a fresh quantity is deposited in the process of nutrition.
They give to the various organs important properties ; and, although identical with sub-
stances in the inorganic world, in the interior of the body, they behave as organic sub-
stances. They require no special preparation for absorption, but are soluble and taken
in unchanged. They are received into the body in about the same proportion at all
periods of life, but their discharge is notably diminished in old age, giving rise to cal-
careous incrustations and deposits and a considerable increase in the calcareous matter
entering into the composition of the tissues. As examples of this class we may cite
writer, chloride of sodium, the carbonates, sulphates, phosphates, and other inorganic
salts.

The functions of water in the blood are sufficiently evident. It acts as a solvent for
the inorganic salts, the organic salts, and the excrementitious matters. In conjunction
with the nitrogenized principles, it constitutes a medium in which the corpuscles are sus-
pended withouf solution.

The various salts enumerated in the table exist in solution in water and are more or
less intimately combined with the coagulable organic principles. Of these, the chloride
of sodium is the most abundant. It undoubtedly has an important function in giving
density to the plasma and in regulating the processes of endosmosis and exosmosis. In
connection with the organic salts and crystallizable excrementitious matters, it may be
stated, in general terms, that the blood contains from 14 to 10 parts per 1,000 of matters
in actual solution, of which from 6 to 8 parts consist of inorganic salts. The presence of
these principles in solution, with the organic coagulable principles, prevents the solution
of the corpuscular elements of the blood. The presence of the chlorides and the alka-
line sulphates assists in dissolving the sulphates, carbonates, and the calcareous phos-
phates. A portion of the carbonates and phosphates are decomposed in the system and
furnish bases for certain of the organic salts, such as the lactates, urates, etc.

2. Organic Saline Principles. — These principles are for the most part formed in the
organism, and they exist in the blood in very small quantity. The lactates are probably
produced by decomposition of a portion of the bicarbonates and the union of the bases
with lactic acid, the lactic acid resulting from a change of a portion of the saccharine
matter in the blood. The pneumate of soda is the result of the union of pneumic acid,
an acid principle found in the lungs, with the base. The physiological relations of these
principles are little understood. The salts formed by the union of fatty acids with bases
are probably produced by decomposition of the fatty principles, a great part of which is
derived from the food.

3. Organic Non-nitrogenized Principles. — These usually exist in the blood in sm.-ill
quantity and are derived mainly from the food. Leccthinc, although it contains nitro^vn.
is introduced into this class because it presents many of the properties of the fats. It
exists in the blood, bile, nervous substance, and the yolk of egg. This principle is sup-
posed by Robin to be almost identical with protagon. Its chemical properties and
physiological relations are not well understood. The saccharine principles and glyco-

22 THE BLOOD.

genie matter are derived in part from the food and in part from the liver, where sugar
and glycogenic matter are manufactured. They are of organic origin, definite chemical
composition, and crystallizable. The fats and sugars are distinguished from other or-
ganic principles by the fact that they are composed of carbon, hydrogen, and oxygen.
In the sugars, the hydrogen and oxygen exist in the proportion to form water, which
fact has given them the name of hydrocarbons or hydrates of carbon. The principles
of this class play an important part in development and nutrition. . One of them, sugar,
appears very early in foetal life, formed first by the placenta, and afterward by the liver,
its formation by tm3 latter organ continuing during life. Fat is a necessary element of
food, and is also formed in the interior of the body. The exact influence which these
substances have on development and nutrition is not known; but experiments and obser-
vation have shown that this influence is important. They will be considered more fully
under the head of nutrition.

4. Excrementitious Matters. — A full consideration of these principles, which are all
formed by the process of disassimilation of the tissues and are taken up by the blood to
be eliminated by the proper organs, belongs to excretion. The relations of carbonic
acid to the system will be fully considered in connection with respiration.

5. Organic Nitrogenized Principles. — This class of proximate principles is of organic
origin, indefinite chemical composition, and non-crystallizable. Substances forming this
class are apparently the only principles which are endowed with so-called vital properties,
taking materials for their regeneration from the nutritive fluids and appropriating them to
form part of their own substance. Considered from this point of view, they are differ-
ent from any thing which is met with out of the living body. They are all, in the body,
in a state of continual change, wearing out and becoming effete, when they are trans-
formed into excrementitious substances. The process of repair in this instance is not
the same as in inorganic substances, which enter and are discharged from the body with-
out undergoing any change. The analogous substances which exist in food undergo a
very elaborate preparation by digestion, before they can even be absorbed by the blood-
vessels ; and still another change takes place when they are appropriated by the various
tissues. They exist in all the solids, semisolids, and fluids of the body, never alone, but
always combined with inorganic substances. As a peculiarity of chemical constitution,
they all contain nitrogen, which has given them the name of nitrogenized or azotized
principles. In studying their properties more fully, we shall see that they are by far the
most important elements in the organism. The elaborate preparation which they require
for absorption involves the most important part of the function of digestion. Their ab-
solute integrity is necessary to the operation of the essential functions of many tissues,
as muscular contraction or conduction of nervous force. An exact knowledge of all
the transformations which take place in their regeneration and the process by which
they are converted into effete or excrementitious matters would enable us to comprehend
nutrition, which is the most important part of physiology ; but as yet we know little of
these changes, and may consider ourselves fortunate in understanding a few of the laws
in accordance with which they are regulated.

Of the different classes of proximate principles existing in the blood, it is at once
apparent that the organic nitrogenized principles are more complex in their constitution,
properties, and functions than the other classes. These principles, as they exist in the
blood, possess peculiar and characteristic properties, which it will be necessary to study
in detail.

Plasmine, Fibrin, Hetalbumen, Serine. — The name plasmine was given by Denis to a
peculiar principle which he extracted from the blood by the following process : The
blood drawn directly from an artery or vein is received into a vessel containing one-sev-
enth part of its volume of a concentrated solution of sulphate of soda, which prevents
coagulation ; in a short time the corpuscles gravitate to the bottom of the vessel, and

PLASMINE, FIBRIN, METALBUMEN, SERINE, PEPTONES, ETC. 23

the plasma may be separated by decantation ; to the plasma is added an excess of pul-
verized chloride of sodium, when a soft, pulpy substance is precipitated, which is plas-
mine. This substance, after desiccation, bears a proportion of about twenty-five pau-
per thousand of blood. It is soluble in from ten to twenty parts of water, when a por-
tion of it coagulates and may be removed by stirring with twigs or a bundle of broom-
corn, in the way in which fibrin is separated from the blood. The fibrin thus separated
is called by Denis concrete fibrin, and the substance which remains in solution, dissolved
fibrin. By most writers of the present day, the dissolved fibrin of Denis is called metal-
bumen, a name which we shall adopt.

According to Denis, plasmine is a proximate principle of the blood, and, after extrac-
tion by the process just described, is decomposed into concrete fibrin and dissolved
fibrin, or metalbumen. Having removed the concrete fibrin from the solution of plas-
mine, the metalbumen is coagulated by the addition of sulphate of magnesia, which doec
not coagulate ordinary albumen. The proportion of dried metalbumen in the blood is
about twenty-two parts per thousand. The proportion of dried fibrin is about three
parts per thousand.

After the extraction of plasmine from the blood, another coagulable substance re-
mains, which is called serine. This is coagulated by heat, the strong mineral acids, and
absolute alcohol, but is not coagulated by ether, which coagulates albumen of the white
of egg. Serine bears a close resemblance to ordinary albumen, but is stated to be much
more osmotic. Its proportion, desiccated, in the blood is about fifty-three parts per
thousand.

We cannot admit the existence of new coagulable principles in the blood unless it be
shown that the processes by which they are extracted do not involve decomposition of
established proximate constituents. The processes just described do not seem to involve
artificial decomposition. It is perfectly proper, in analyzing the blood, to prevent spon-
taneous coagulation by the addition of the sulphate of soda, as this salt simply keeps
the blood lluid without apparently changing its organic constituents, and the plasmine is
simply precipitated by the chloride of sodium. It is evident, also, that the substance
called metalbumen, being coagulated by sulphate of magnesia, is not albumen, and
serine also presents some important points of difference from albumen. Admitting the
existence, then, of plasmine and serine, it is important to understand clearly the charac-
ters of these principles as compared with what were formerly called fibrin and albumen.

Instead of fibrin and albumen in the blood, we now recognize two new principles, in
the natural condition of the circulating fluid, which are called plasmine and serine. The
substance known as fibrin is one of the products of decomposition of plasmine. Metal-
bumen and serine constitute what was formerly called albumen. Fibrin is not a proxi-
mate principle, but is formed in the spontaneous decomposition of plasmine. Metalbu-
men is the other product of decomposition of plasmine. The fibrin of arterial blood
has long been known to differ somewhat from the fibrin of venous blood, when the blood
has been allowed to coagulate spontaneously. Arterial fibrin is insoluble in a solution
of chloride of sodium which will dissolve the fibrin of venous blood.

Peptones, etc. — A certain quantity of nitrogenized matter, distinct from the principle*
just described, has been extracted from the blood, which is analogous to peptone or
albuminose. This is separated by coagulating the serum of the blood with hot acetic
acid and filtering, when the peptones pass through in the filtrate. These principles ;uv
probably derived from the food. Their proportion in the plasma is about four parts,
dried, per thousand, or twenty-eight parts before desiccation.

A small quantity of coloring matter exists in the plasma. If we separate the corpus-
cles as completely as possible, the clear liquid still has a reddish-amber color. This col-
oring matter has never been isolated and studied. It is analogous to the coloring mat-
ters of the red corpuscles, the bile, and the urine.

24 THE BLOOD.

In addition to the organic nitrogenized principles which we have described, some
authors recognize a substance called paraglobuline, or fibrinoplastic matter, and fibrino-
genic matter. These are supposed to be factors of fibrin, which come together in the
coagulation of the blood. They will be considered in connection with the theories of
coagulation. The so-called albuminates of soda and potassa have not been positively
established as proximate principles.

Coagulation of the Blood.

The remarkable property in the blood of spontaneous coagulation has been recog-
nized almost as far back as we can look into the history of physiology ; and, since the
discovery of the circulation, there have been few subjects connected with the physiology
of the blood which have excited more universal interest ; but the ideas with regard to
the cause of this phenomenon were for a long time entirely speculative. The first defi-
nite experiments upon this subject were performed by Malpighi. He was followed by
Borelli, Euysch, and a host of others, who hold conspicuous places in the history of our
science, among whom may be mentioned Hunter, Hewson, Mtiller, Thackrah, J. Davy,
Magendie, JSTasse, and Dumas. Although much labor has been expended OD this subject,
the final cause of coagulation is by no means definitely settled.

The blood retains its fluidity while it remains in the vessels and circulation is not
interfered with. It is then composed, as we have seen, of a clear plasma, holding cor-
puscles in suspension. Shortly after the circulation is interrupted, or after blood is
drawn from the vessels, it coagulates or " sets " into a jelly-like mass. In a few hours,
we find that contraction has taken place, and a clear, straw-colored fluid has been ex-
pressed, the blood thus separating into a solid portion, the crassamentum, or clot, and a
liquid, which is called serum. The ssrnm contains all the elements of the blood except
the corpuscles and fibrin, which together form the clot. Fibrin is one of the products
of decomposition of plasmine. Coagulation takes place in the blood of all animals, com-
mencing a variable time after its removal from the vessels. In the human subject, ac-
cording to Nasse, when the blood is received into a moderately-deep, smooth vessel, the
phenomena of coagulation present themselves in the following order :

First, a gelatinous pellicle forms on the surface, which occurs in from one minute and
forty -five seconds to six minutes ; in from two to seven minutes, a gelatinous layer has
formed on the sides of the vessel ; and the whole mass becomes of a jelly-like consistence, in
from seven to sixteen minutes. Contraction then begins, and, if we watch the surface
of the clot, we see little drops of clear serum making their appearance. This fluid in-
creases in quantity, and, in from ten to twelve hours, separation is complete. The clot,
which is heavier, sinks to the bottom of the vessel, unless it contain bubbles of gas or
the surface be very concave. In most of the warm-blooded animals, the blood coagulates
more rapidly than in man. It is particularly rapid in the class of birds, in some of which
it takes place almost instantaneously. Observations have shown that coagulation is more
rapid in arterial than in venous blood. In the former, the proportion of fibrin formed is
notably greater, and, as we have seen, the characters of the fibrin are somewhat differ-
ent. A solution of chloride of sodium dissolves the fibrin of venous blood, but does not
dissolve the fibrin of an arterial clot.

The relative proportions of the serum and clot are very variable, unless we include in
our estimate of the serum that portion which is retained between the meshes of the coag-
ulated mass. As the clot is composed of corpuscles and fibrin, and as these in their
moist state represent in general terms about one-half of the blood, it may be stated
that, after coagulation, the actual proportions of the clot and serum are about equal.
If we take simply the serum which separates spontaneously, we have a large quantity
when the clot is densely contracted, and a very small quantity when it is loose and
soft. Usually, the clot retains about one-fifth of the serum.

COAGULATING PRINCIPLE OF THE BLOOD. 35

Characters of the Clot. — On removing the clot, after the separation of the serum is
complete, it presents a gelatinous consistence, and is more or less firm, according to the
degree of contraction which has taken place. As a general rule, when coagulation has
heen rapid, the clot is soft and but slightly contracted. When, on the other hand, coagu-
lation has been slow, it contracts for a long time and is much denser. When coagulation
is slow, the clot frequently presents what is known as the cupped appearance, having a
concave surface, a phenomenon which depends merely on the extent of its contraction.
It also presents a marked difference in color at its upper portion. The blood having
remained fluid for some time, the red corpuscles settle, by virtue of their greater weight,
leaving a colorless layer on the top. This is the buffy-coat spoken of by some authors.
Although this frequently presents itself in the blood drawn in inflammations, it is by no
means pathognomonic of this condition, and is liable to occur whenever coagulation is
slow or has been retarded by artificial means. It is always present in the blood of the
horse. Examined microscopically, the buffy-coat presents fibrils of coagulated fibrin
with some of the white corpuscles of the blood. On removing a clot of venous blood
from the serum, the upper surface is florid from contact with the air, while the rest of it
is dark ; and, on making a section, if the coagulation have not been too rapid, the gravi-
tation of the red corpuscles is apparent. The section, which is at first almost black, soon
becomes red from contact with the atmosphere. If the clot be cut into small pieces, it
will undergo farther contraction, and express a part of the contained serum. If the clot
be washed under a stream of water, at the same time kneading it with the fingers, we
may remove almost all the red corpuscles, leaving the meshes of fibrin, which, on micro-
scopical examination, presents the fibrillated appearance to which we have already referred.

Characters of the Serum. — After coagulation, if the serum be carefully removed, it
is found to be a fluid of a color varying from a light amber to quite a deep, but clear red.
This depends upon a peculiar coloring matter which has never been isolated. The specific
gravity of the serum is about 1028, somewhat less than that of the entire mass of blood.
It contains all the principles found in the plasma, or liquor sanguinis, with the exception
of the elements of fibrin. It can hardly be called a physiological fluid, as it is formed
only after coagulation of the blood and never exists isolated in the body. The effusions
which are commonly called serum, although they resemble this fluid in some particulars,
are not identical with it, being formed by a process of transudation rather than separa-
tion from the blood, as in coagulation. The serum must not be confounded with the
plasma or liquor sanguinis, which is the natural clear portion of the blood.

Coagulating Principle of the Blood. — Acquainted, as we are, with the properties of
fibrin, it is evident that this substance is the agent which produces coagulation of the
blood. In fact, whatever coagulates spontaneously is called fibrin, and whatever requires
some agent to produce this change of consistence is called by another name. But, before
the properties of fibrin were fully understood, the question of the coagulating principle
was a matter of much discussion. Malpighi was probably the first to isolate fibrin, which
he did by washing the clot in a stream of water, which removed the corpuscles and left a
whitish, fibrous net-work. His experiments are set forth in an article in which he at-
tempted to show that the so-called polypi of the heart were formed of fibrin, although it
was not then called by that name. These observations were soon confirmed by others;
and it then became a question whether this substance existed as a fluid in the liquor san-
guinis, or was furnished by the corpuscles after the removal of blood from the vessels.
This was decided by Ilewson, whose simple and conclusive experiments leave no doubt
that coagulation of the blood is due to fibrin, and that this substance is entirely distinct
from, and independent of the corpuscles. This observer, taking advantage of the prop-
erty possessed by certain saline substances of preventing the coagulation of the blood,
was the first to separate the liquor sanguinis from the corpuscles. He mixed fresh blood

26 THE BLOOD.

with a little sulphate of soda, which prevented coagulation, and, after the mixture had
been allowed to stand for a time, the corpuscles gravitated to the bottom of the vessel.
The clear fluid was then decanted and diluted with twice its quantity of water, when
fibrin became coagulated.

The facts thus demonstrated by Hewson were confirmed by Mtiller, in 1882. He suc-
ceeded in separating the plasma from the corpuscles in the blood of the frog by simple
filtration, first diluting it with a saccharine solution. The great size of the corpuscles in
this animal prevents their passage through a filter, and the clear fluid which is thus sepa-
rated soon forms a colorless coagulum.

From these observations, it is evident that the coagulation of the blood is due to the
formation of fibrin. Coagulation of this substance first causes the whole mass of blood
to assume a gelatinous consistence ; and, by virtue of its contractile properties, it soon
expresses the serum, while the red corpuscles are retained. One of the causes which
operate to retain the corpuscles in the clot is the adhesive matter which covers their
surface after they escape from the vessels, which produces the arrangement in rows like
piles of coin, which we have already noted under the head of microscopical appearances.
This undoubtedly prevents those which are near the surface from escaping from the clot
during its contraction.

Circumstances which modify Coagulation out of the Body. — The conditions which
modify coagulation of the blood have been closely studied by Hewson, Davy, Thackrah,
Kobin and Verdeil, and others. They are, in brief, the following:

Blood flowing slowly from a small orifice is more rapidly coagulated than when it
is discharged in a full stream from a large orifice. If it be received into a shallow
vessel, it coagulates much more rapidly than when received into a deep vessel. If the
vessel be rough, coagulation is more rapid than if it be smooth and polished. If the
blood, as it flows, be received on a cloth or a bundle of twigs, it coagulates almost in-
stantaneously. In short, it appears that all circumstances which favor exposure of the
blood to the air hasten its coagulation. The blood will coagulate more rapidly in a va-
cuum than in the air.

Coagulation of the blood is prevented by rapid freezing, but it takes place afterward
when the fluid is carefully thawed. Between 32° and 140° Fahr., elevation of tempera-
ture increases the rapidity of coagulation. According to Richardson, agitation of the
blood in closed vessels retards, and in open vessels hastens coagulation.

Various chemical substances retard or prevent coagulation. Among them we may
mention the following: solutions of potash and of soda; carbonate of soda; carbonate
of ammonia; carbonate of potash; ammonia; sulphate of soda. In the menstrual flow,
the blood is kept fluid by mixture with the abundant secretions of the vaginal mucous
membrane.

Coagulation of the Blood in the Organism. — The blood coagulates in the vessels after
death, though less rapidly than when removed from the body. As a general proposition,
it may be stated that this takes place in from twelve to twenty-four hours after circula-
tion has ceased. Under these circumstances, the blood is found chiefly in the venous
system, as the arteries are generally emptied by post-mortem contraction of their mus-
cular coat ; but, in the veins, coagulation is slow and imperfect. Coagula are found,
however, in the left side of the heart and in the aorta, but they are much smaller than
those in the right side of the heart and in the large veins. These coagula present the
general characters we have already described. They are frequently covered by a soft,
whitish film, analogous to the buffy-coat, and are dark in their interior.

It was supposed by John Hunter that coagulation of the blood did not take place in
animals killed by lightning, or by prolonged muscular exertion, as when hunted to death ;
but it appears from the observations of others that this view is not correct. J. Davy

COAGULATION OF THE BLOOD IN THE ORGANISM. 27

reported a case of death by lightning where a loose coagulum was found in the heart
twenty-four hours after. In this case, decomposition was very far advanced, and it is
probable that the coagulura had become less firm from that cause. His observations also
show that coagulation occurs after poisoning by hydrocyanic acid, and in animals hunted
to death.

Coagulation in different parts of the vascular system is by no means unusual during
life. In the heart, we sometimes find coagula which bear evidence of having existed for
some time before death. These were called polypi by some of the older writers, and are
often formed of fibrin almost free from red corpuscles. They generally occur when death
is very gradual and when the circulation continues for some time with greatly-diminished
activity. It is probable that a small coagulum is first formed, from which the corpuscles
are washed away by the current of blood ; that this becomes larger by farther depositions,
until we have large, vermicular masses of fibrin, attached, in some instances, to the
chordee tendineee. Clots produced in this way may be distinguished from those formed
after death by their whitish color, dense consistence, and the closeness with which they
adhere to the walls of the heart.

Bodies projecting into the caliber of a blood-vessel soon become coated with a layer
of fibrin. Eough concretions about the orifices of the heart frequently induce the deposi-
tion of little masses of fibrin, which sometimes become detached and are carried to vari-
ous parts of the circulatory system, as the lungs or brain, plugging up one or more of the
smaller vessels. The experiment has been made of passing a thread through a small
artery, allowing it to remain for a few hours, when it is found coated with a layer of
coagulated fibrin.

Blood generally coagulates when effused into the areolar tissue or into any of the
cavities of the body ; although, effused into the serous cavities, the tunica vaginalis for
example, it has been known to remain fluid for days and even weeks, and coagulate when
let out by an incision. In the Graafian follicles, after the discharge of the ovum, we
sometimes have the cavity filled with blood, which forms a clot and is slowly removed
by absorption.

Coagulation thus takes place in the vessels as the result of stasis or of very great retarda-
tion of the circulation, and in the tissues or cavities of the body, whenever it is accident-
ally effused. In the latter case, it is generally removed in the course of time by absorp-
tion. This takes place in the following way : First, we have disappearance of the red
corpuscles, or decoloration of the clot, and the fibrin is then the only substance which
remains. This becomes reduced from afibrillated to a granular condition, softens, finally
becomes amorphous, and is absorbed ; although, when the size of the clot is considerable,
this may occupy weeks, and even months, and may never be completely effected. Effused
in this manner, the constituents of the blood act as foreign bodies ; the corpuscles cease
to be organized anatomical elements capable of self-regeneration, break down, and are
absorbed. The fibrin which remains undergoes the same process, the stages through
which it passes being always those of decay, and not of development. In other words,
the clot is incapable of organization.

Office of the Coagulation of the Blood in arresting Hcemorrhage. — The property of the
blood under consideration has a most important office in the arrest of haemorrhage. The
effect of an absence or great diminution of the coagulability of the circulating fluid is
exemplified in instances of what is called the haamorrhagic diathesis; a condition in which
slight wounds are apt to be followed by alarming, and it may be fatal hemorrhage. This
condition of the blood is not characterized by any peculiar symptoms except the obsti-
nate flow of blood from slight wounds; and this may continue for years. In a case
which came under our observation a few years since, excision of the tonsils was 1<>1-
lowed by bleeding, which continued for several days, and was arrested with great dif-
ficulty. On inquiry it was ascertained that the patient, a young man about twenty

28 THE BLOOD.

years of age, in other respects perfectly healthy, had been subject from early life to per-
sistent haemorrhage from slight wounds.

Circumstances which accelerate coagulation have a tendency to arrest haemorrhage.
It is well known that exposure of a bleeding surface to the air has this effect. The way
in which the vessel is divided has an important infiuence. A clean cut will bleed more
freely than a ragged laceration. In division of large vessels, this difference is sometimes
very marked. Cases are on record in which the arm has been torn off at the shoulder-
joint, and yet the haemorrhage was, for a time, spontaneously arrested ; while we know
that division of an artery of comparatively small size, if it be cut across, would be fatal
if left to itself. Under these circumstances, the internal coat is torn in shreds, which
retract, their curled ends projecting into the caliber of the vessel and having the same
effect on the coagulation of blood as a bundle of twigs. In laceration of such a large
vessel as the axillary artery, the arrest cannot be permanent, for, as soon as the system
recovers from the shock, the contractions of the heart will force out the coagulated blood
which has closed the opening.

From the foregoing considerations, it is evident that the remarkable phenomenon of
coagulation of the blood, which has so much engaged the attention of physiologists, has
rather a mechanical than a vital function ; for its chief office is in the arrest of haemor-
rhage. Coagulation never takes place in the organism, unless the blood be in an abnormal
condition with respect to circulation. Here its operations are mainly conservative ; but,
as almost all conservative processes are sometimes perverted, clots in the body may be
productive of injury, as in the instances of cerebral apoplexy, clots in the heart occurring
before death, the detachment of emboli, etc.

Cause of the Coagulation of the Blood. — If we adopt the views regarding the compo-
sition of the blood which involve the production of fibrin as a result of the decomposition
of plasmine, we must change in toto our ideas of the cause of the coagulation of the blood.
According to our present ideas, fibrin does not exist as a proximate principle, and plas-
mine is never decomposed in the body, under perfectly normal conditions; but, if the
blood be drawn from the body, effused from the vessels, or if the circulation be arrested
for a certain time, plasmine is decomposed, fibrin is formed, and the blood coagulates.

In another work, written in 1864, we discussed the question of the cause of the co-
agulation of the blood quite fully ; but fibrin was then generally regarded as a proxi-
mate principle itself, and not as a product of decomposition. The theory that we then
adopted was the one proposed by Richardson, in 1856 ; viz., that the blood normally
contains a small quantity of ammonia, the presence of which keeps the fibrin in a liquid
state ; that ammonia is constantly being taken up by the blood from the tissues and ex-
haled by the lungs, and that, when the circulation of the blood is arrested, or when the
blood is effused or drawn from the vessels, ammonia is exhaled and coagulation takes
place. This theory has been formally abandoned by Richardson, who adheres, however,
to the accuracy of his experiments. If these experiments be entirely reliable, they seem
to prove the theory ; but it is stated by Robin, that, using chemical processes which will
detect T.-fftfl.Tnnr °f ammonia, not a trace of this substance is to be found in the blood ;
that a small quantity of ammonia added to the blood does not prevent coagulation ; and
that the blood secured against evaporation will nevertheless coagulate. The chemical
experiments of Richardson were not very delicate, and the objections to them, made by
Robin, are probably well-founded. We are justified, therefore, in abandoning the the-
ory that coagulation of the blood is due to the evolution of ammonia.

We may take the same position with regard to the older theories of coagulation,
which were nearly all vague and unsatisfactory. The idea that exposure to the air is the
cause of coagulation, which was held by Hew son, is disproved by the simple fact that
coagulation takes place in a vacuum. The vital theory of Hunter, which was adopted
by most physiologists of his time, is too indefinite for discussion at the present day, and

CAUSE OF THE COAGULATION OF THE BLOOD. 39

really expresses utter want of knowledge on the subject. The theory that motion is the
cause of the fluidity of fibrin in the body, is disproved by the fact that violent agitation
of the blood out of the body docs not prevent coagulation ; and thus it is with nearly
all the theories that have been advanced.

The idea which we have to present does not explain why the blood coagulates, but
it gives a certain notion of the probable conditions under which plusmine exists in the
circulating fluid :

Plasmine, circulating in the blood-vessels, under normal conditions, is a liquid, and
its decomposition into metalbumen and fibrin is abnormal. Plasmine is undoubtedly an
important nutritive principle, and is constantly undergoing change as it is used in the
nutrition of the nitrogenized constituents of the various tissues and organs, the material
thus expended being supplied by the nitrogenized constituents of the food. It is, there-
fore, like other nitrogenized constituents of the organism, in a condition of constant
metamorphosis ; and all that we can say is that, while in this condition, getting material
from some parts and giving off matters in others, it does not undergo those decomposing
changes which are observed when it is effused, drawn from the body, or the circulation
is arrested, which involve coagulation of the blood.

The above expresses nearly all that we positively know of the cause of the coagula-
tion of the blood ; but the question in fact reduces itself to the rather unsatisfactory
proposition that the blood coagulates because, when its nitrogenized principles are re-
moved from those constant molecular changes which are characteristic of the class of
nitrogenized principles as they exist in the living organism, decomposition takes place,
which results in the production of a coagulating matter. It is hardly to be expected
that physiologists would be satisfied with this, which is indeed little more than a confes-
sion of ignorance ; but it must be remembered that we are very little acquainted with
the molecular changes taking place constantly in the living body. When we understand
these more thoroughly, we may obtain a better knowledge of the causes of coagulation
of the blood, cadaveric rigidity of muscles, and other changes which take place when
the processes of nutrition cease.

Within the last few years, A. Schmidt (1861) has proposed a theory of coagulation
which involves the coming together of certain principles called fibrin-factors. This the-
ory, which had been indicated by Buchanan, in 1845, has been adopted and more or
less modified by Kuhne, Virchow, and others. If blood-plasma, rendered neutral with
acetic acid, be diluted with ten times its volume of water at 32° Fahr. and then be treated
with a current of carbonic-acid gas, a flocculent precipitate is formed, which has been
called paraglobuliue, or fibrinoplastic matter. This substance may be dissolved in water
containing air or oxygen in solution. After this precipitate has been separated, if the
clear liquid be diluted with about twice its volume of ice-cold water and be again treated
for a long time with a current of carbonic acid, a viscid scum is produced, which has been
called fibrinogen. A small quantity of paraglobuline added to a solution of fibrinogen pro-
duces coagulation of a substance like fibrin. More recently, a third principle, a ferment,
has been described by Schmidt, which he considers necessary to this formation of fibrin.

It is very questionable whether the substances called paraglobuline and fibrinogen ex-
ist in the blood as peculiar principles. Eobin considers paraglobuline as identical with
metalbumen, which is itself one of the products of the decomposition of plasmine. It
is true that the so-called paraglobuline added to the liquid of hydrocele or other serosities
not spontaneously coagulable produces coagulation, but this occurs, though more slowly,
when the serum separated from the coagulated blood is added to these liquids.

It is more in accordance with our positive knowledge to state that we understand
nothing with regard to the cause of coagulation of the blood beyond the tact that plas-
mine, when removed from its normal condition in the circulation, decomposes into coat:-
ulating fibrin and metalbumen, than to admit the existence of fibrinogen, a ferment, and
paraglobuline, all of which may be products of decomposition.

30 THE BLOOD.

It is a curious fact that leech-drawn blood remains fluid in the body of the ani-
mal. Richardson has observed, also, that the blood flowing from a leech-bite presents
the same persistent fluidity, which explains the well-known fact that the insignificant
wound gives rise to considerable haemorrhage. On this point he has made the following
curious experiment :

" After the leech was removed from the arm, the wound it had produced continued
to give out blood very freely. I caught the blood thus flowing at different intervals,
allowing it to trickle into teaspoons of the same size and shape. The results were curi-
ous. The blood which was received into the first spoon, and which was collected imme-
diately after the removal of the leech, was dark, and showed the same feebleness of
coagulation as the blood taken from the leech itself. Another portion of blood, received
into a second spoon five minutes later, coagulated in twenty-five minutes with moderate
firmness. A third portion of blood, caught ten minutes later still, coagulated in eight
minutes ; while at the end of half an hour the blood which still flowed from the wound
coagulated firmly, and in fine red clots, in two minutes. Ultimately the blood coagu-
lated as it slowly oozed from the wound, so that the wound itself was sealed up."

The existence of projections into the caliber of vessels, or the passage of a fine thread
through an artery or vein, will determine the formation of a small coagulum upon the
foreign substance, while the circulation is neither interrupted nor retarded. These facts
demand explanation ; but all we can say with regard to them is, that, in the present
state of our knowledge, explanation is difficult, if not impossible. The process, under
these circumstances, cannot be subjected to direct experiment, as in the case of blood
coagulating out of the body ; but a reasonable inference is that the foreign substance
arrests the circulation of a certain portion of plasmine, which then undergoes decompo-
sition.

During coagulation, fibrin assumes a filamentous form, presenting, tinder the micro-
scope, the appearance of rectilinear fibrillse. These fibrilloa gradually increase in num-
ber and, as contraction of the clot occurs, becomes irregularly crossed. They are always

FIG. 8.— Coagulated fibrin. (Kobin.)

Fibrinous clot, without red corpuscles, and containing leucocytes, thrown off in the form of a whitish pseudo-mem-
brane in a case of ulceration of the neck of the uterus with haemorrhage.

straight, however, and never assume the undulating appearance characteristic of the
white fibrous tissue. The appearance just described does not indicate a process of or-
ganization. When fibrin is effused into any of the tissues or organs from rupture of
vessels, it acts as a foreign substance, and, in time, becomes entirely or in part absorbed,
The gradual production of membranes of new formation, as one of the results of inflam-
mation, these becoming organized, is entirely different from sudden haemorrhagic
effusions.

The blood of the renal and hepatic veins, capillary blood, and the blood which passes

DISCOVERY OF THE CIRCULATION. 31

from the capillary system into the veins after death, does not generally coagulate or
coagulates very imperfectly ; in other words, these varieties of blood do not readily form
fibrin. The reason of this peculiarity is not known ; but the fact affords a partial ex-
planation of the normal fluidity of the blood ; for this fluid, passing over the- entire
course of the circulation in about thirty seconds, seems to be constantly IUMM^ its coagu-
lability in its passage through the liver, kidneys, and the general capillary system, as fast
as its coagulability is increased in the other parts. Taking into consideration the rapidity
of the circulation, it is evident that the blood cannot coagulate while the normal cir-
culation is maintained, and while it is undergoing the constant changes incident to gen-
eral nutrition.

CHAPTER II.

CIRCULATION OF THE BLOOD— ACTION OF THE HEART.

Discovery of the circulation — Physiological anatomy of the heart — Valves of the heart — Movements of the heart —
Impulse of the heart— Succession of movements of the heart— Force of the heart's action— Action of the valves-
Sounds of the heart — Causes of the sounds of the heart— Frequency of the heart's action — Influence of age—
Influence of digestion— Influence of posture and muscular exertion — Influence of exercise — Influence of tem-
perature— Influence of respiration on the action of the heart — Cause of the rhythmical contractions of the heart
— Influence of the nervous system on the heart— Division of the pneumogastrics — Galvanization of the pneu-
mogastrics — Causes of arrest of action of the heart — Blows upon the epigastrium.

HARVEY discovered the circulation of the blood in 1616, taught it in his public lect-
ures in 1619, and, in 1628, published the " Exercitatio Anatomica de Motu Cordis et
Sanguinis in Animalibus."1 This momentous discovery, from the isolated facts bearing
upon it which were observed by anatomists, to its grand culmination with Harvey, so
fully illustrates the gradual development of most great physiological truths, that it does
not seem out of place to begin our study of the circulation with a rapid sketch of its
history.

The facts bearing upon the circulation, which were developed before the time of Har-
vey, were chiefly anatomical. The writings of Hippocrates are very indefinite upon all
points connected with the circulatory system ; and no clear and positive statements are
to be found in ancient works before the time of Aristotle. The work of Aristotle most
frequently quoted by physiologists is his " History of Animals ; " and in this occurs a
passage which seems to indicate that he thought that air passed from the lungs to the
heart; but in his work, De Partibus Animalium, it is stated that there are two great
blood-vessels, the vena cava and aorta, arising from the heart, and that the aorta and
its branches carry blood. Galen, however, demonstrated experimentally the presence of
blood in the arteries, by including a portion of one of these vessels between two liga-
tures, in a living animal ; but his ideas of the communication between the arteries and
veins were erroneous, for he believed in the existence of small orifices in the septum be-
tween the ventricles of the heart, a mistake that was corrected by Vesalius, at about the
middle of the sixteenth century.

In 1553, Michael Servetus, who is generally regarded as the discoverer of the pas-
sage of the blood through the lungs, or the pulmonary circulation, described in a work
on theology the course of the blood through the lungs, from the right to the left side of
the heart. This description, complete as it is, was merely incidental to the development
of a theory with regard to the formation of the soul, and the development of what were
called animal and vital spirits (spiritus). The same year, at the instigation of Calvin,
Servetus was burned alive at Geneva, and a copy of his book was also committed to the
flames. A few months b.'fora. a number of these books was burned at \'ienn:i, and

32 CIRCULATION OF THE BLOOD.

but two perfect copies are now known to be in existence ; one is in the National Library
in Paris and the other is in the Public Library in Vienna.

A few years later, Colombo,1 professor of anatomy at Padua, and Cesalpinus, of Pisa,
described the passage of the blood through the lungs, though probably without any
knowledge of what had been written by Servetus. To Cesalpinus is attributed the first
use of the expression circulation of the blood. He also remarked that, after ligature or
compression of veins, the swelling is always below the point of obstruction.

The history of the discovery of the valves in the veins is quite obscure, although pri-
ority of observation is almost universally conceded to Fabricius. As regards this point,
we can depend only upon the dates of published memoirs, notwithstanding the assertion
of Fabricius, that he had seen the valves in 1574. In 1545, Etienne described, in branches
of the portal vein, " valves, which he called apophyses, and which he compared to the
valves of the heart." In 1551, Amatus Lusitanus published a letter from Cannanus, in
which it is stated that he had found valves in certain of the veins. In 1563, Eustachius
published an account of the valves of the coronary vein. In 1586, a clear account, by
Piccolhominus, of the valves of the veins was published. Fabricius gave the most accu-
rate descriptions and delineations of the valves, and his first publication is said to have
appeared in 1603. He demonstrated them to Harvey, at Padua ; and it is probable that
this was the origin of the first speculations by Harvey on the mechanism of the circula-
tion. Shortly after the return of Harvey from Padua in 1602, he advanced beyond the
study of inanimate parts by dissections, and investigated animated nature by means of
vivisections. As is evident, when we consider the state of science at that time, anato-
mists had long been preparing the way for the discovery of the circulation, although
they knew little of the functions of the parts they described. The conformation of the
heart and vessels, and even the arrangement of the valves of the veins, did not lead them
to suspect the course of the blood ; but a few well-conceived experiments on living ani-
mals have made it appear so simple, that we now wonder it remained unknown so long.
Farthermore, these experiments made it evident that there was a communication at the
periphery between the arteries and the veins.

In the work of Harvey are described, first the movements of the heart, which he
exposed and studied in living animals. He described minutely all the phenomena which
accompany its action ; its diastole, when it is filled with blood, and its systole, when the
fibres of which the ventricles are composed contract simultaneously, and " by an admi-
rable adjustment all the internal surfaces are drawn together, as if with cords, and so is
the charge of blood expelled with force." From the description of the action of the
ventricles, he passes to the auricles, and shows how these, by their contraction, fill the
ventricles with blood. By experiments upon serpents and fishes, he proved that the
blood fills the heart from the veins, and is sent out into the arteries. Exposing the heart
and great vessels in these animals, he applied a ligature to the veins, which had the
effect of cutting off the supply from the heart so that it became pale and flaccid ; and
by removing the ligature the blood could be seen flowing into the organ. When, on the
contrary, a ligature was applied to the artery, the heart became unusually distended,
which continued so long as the obstruction remained. When the ligature was removed,
the heart soon returned to its normal condition.

Harvey completed his description of the circulation, by experiments showing the
course of the blood in the arteries and veins and the uses of the valves of the veins.

1 In a recent memoir by M. Chereau, entitled Riatoire cFun livre (Bulletin de Facademie de medecine, Paris
1879, 2me serie, tome viii., p. 75S, et seq ), the credit of the discovery of the pulmonary circulation is given to Colom-
bo. M. Chereau argues that Servetus mast have learned of the pulmonary circulation from Colombo, who was pro-
fessor of anatomy at Padua, or from his pupils. Colombo certainly gave a very clear description of the lesser circula-
tion, but his work, De re anatomicti, bears the date of 1559, while the Chriatianistmi Retfitutio was published in
1553. The claim made by Chereau in behalf of Colombo rests upon citations from authors, showing that although Co-
lombo published his work in 1559, it must have been written and the doctrines therein contained taught long before
the publication of the Chrisiianismi Restitutio.

DISCOVERY OF THE CIRCULATION".

33

These experiments are models of simplicity and pertinence. First, he showed that a
ligature tightly applied to a limb prevented the blood from entering the artery and
arrested pulsation. The ligature then relaxed and applied with moderate tightness so
as to compress only the superficial veins allowed the blood to pass into the part by the
arteries, but prevented its return by the veins, which consequently became excessively
congested. The ligature being removed, the veins soon emptied themselves and the
member regained its ordinary appearance. He observed the " knots " in the veins of the
arm when a ligature was applied, as for phlebotomy, and showed that the space be-
tween these knots, which are formed by the valves, could be emptied of blood by press-
ing toward the heart, and would not fill itself while the finger was kept at the lower
extremity. It was impossible, by pressure with the fingers, to force the blood back
through one of the valves.

FIG. 9.—ffarvey'8 observations on the flow of blood in tlu veim. (Harvey.)

By such simple, yet irresistibly conclusive experiments was completed the chain of
evidence establishing the fact of the circulation of the blood. Truly it is said that here
commenced an epoch in the study of physiology; for then the scientific world began to
3

34

CIRCULATION OF THE BLOOD.

emancipate itself from the ideas of the ancients, which had held despotic sway for two
centuries, and to study Nature for themselves by means of experiments.

Although Harvey described so perfectly the course of the blood and left not a shadow
of doubt as to the communication between the arteries and veins, it was left to others to
actually see the blood in movement and follow it from one system of vessels to the other.
In 1661, Malpighi saw the blood circulating in the vessels of the lung of a living frog,
examining it with magnifying glasses; and, a little later, Leeuwenhoek saw the circula-
tion in the wing of a bat. The great discovery was then completed.

Enough has been said in the preceding historical sketch to give a general idea of the
course of the great nutritive fluid and the natural anatomical and physiological divisions
of the circulatory system. There is a constant flow from the central organ to all the
tissues and organs of the body, and a constant return of the blood after it has passed
through these parts. But before the blood, which has thus been brought back, is fit to
return again to the system, it must pass through the lungs and undergo the changes
incident to respiration. In some animals, like fishes, the same force sends the blood
through the gills, and from them through the system. In others, like the reptiles, a
mixture of aerated and non-aerated blood takes place in the heart, and the general
system never receives blood that has been fully arterialized. But in man and all
warm-blooded animals, the organism demands blood that has been fully purified and
oxygenated by its passage through the lungs, and here we find the first great and com-
plete divisions of the circulation into the pulmonary and systemic, or, as they have been
called, the lesser and greater circulation. The heart in this instance is double; hav-
ing a right and left side which are entirely distinct from each other. The right heart

receives the blood as it is brought
from the system by the veins and
sends it to the lungs; the left heart
receives the blood from the lungs
and sends it to the system. It must
be borne in mind, however, that al-
though the two sides of the heart
are distinct from each other, their
action is simultaneous ; and, in
studying the motions of this or-
gan, we shall find that the blood
is sent simultaneously from the
right side to the lungs, and from
the left side to the system. It will
not be necessary, therefore, to sep-
arate the two circulations in our
study of their mechanism ; for the
simultaneous action of both sides
of the heart enables us to study
its functions as a single organ, and
the constitution and operations of
the two kinds of vessels do not
present any material differences.
For convenience of study, the circulatory system may be divided into heart and
vessels, the latter being of three kinds: the arteries, which carry blood from the
heart to the system ; the capillaries, which distribute the blood more or less abun-
dantly in different parts of the system ; and the veins, winch return the blood from
the system to the heart. The functions of each of these divisions may be considered
separately.

FIG. 10. — Lftagram of the four cavities of the heart. (Bern*
od, right auricle ; vd, right ventricle ; og, left auricle , vg,
ventricle. The arrows indicate the course of the blood.

(Bernard.)
left

ANATOMY OF THE HEART.

35

Physiological Anatomy of the Heart.

The heart of the human subject is a pear-shaped, muscular organ, situated in the
thoracic cavity, with its base in the median line and its apex at the fifth intercostal
space, three inches to the left of the median line or one inch within the line of
the left nipple. Its weight is
from eight to ten ounces in
the female, and from ten to
twelve ounces in the male. It
has four distinct cavities; a
right and a left auricle, and a
right and a left ventricle. Of
these, the ventricles are the
more capacious. The heart is
held in place, or may be said
to be attached by the great
vessels to the posterior wall
of the thorax, while the apex
is free and capable of a cer-
tain degree of motion. The
whole organ is enveloped in a
fibrous sac called the pericar-
dium. This sac is lined by a
serous membrane, which is at-
tached to the great vessels at
the base and reflected over its
surface. The membrane is lu-
bricated by a drachm or two FIG. 11.— Heart in situ. (Dalton, in Flint, "on the Heart.")

Of fluid, SO that the movements a' &' c;^tc" [ibs5 a< 2- 3, etc intercostal spaces; vertical line, median line;

triangle, superficial cardiac region ; x on the fourth nb, nipple.

of the heart are normally ac-
complished without any friction. The serous pericardium does not present any dif-
ferences from serous membranes in other situations. The cavities of the heart are lined
by a smooth membrane, called the endocardium, which is continuous with the lining
membrane of the blood-vessels.

The right auricle receives the blood from the venae cava3 and empties it into the right
ventricle. The auricle presents a principal cavity, or sinus, as it is called, with a little
appendix, called from its resemblance to the ear of a dog, the auricular appendix. It has
two large openings for the vena cava ascendens and the vena cava descendens, with a
small opening for the coronary vein which brings the blood from the substance of the
heart itself. It has, also, another large opening, called the auriculo-ventricular opening,
by which the blood flows into the ventricle. The walls of this cavity are quite thin as
compared with the ventricles, measuring about one line. They are composed of mus-
cular fibres arranged in two layers, one of which, the external, is common to both auri-
cles, and the other, the internal, is proper to each. These muscular fibres, although
involuntary in their action, belong to the striated, or what is termed voluntary variety,
and are similar in structure to the fibres of the ventricles. The fibres of the auricles are
much fewer than those of the ventricles. Some of them are looped, arising from a
cartilaginous ring which separates the auricles and ventricles, and passing over the
auricles ; and others are circular, surrounding the auricular appendages and the open-
ings of the veins, extending, also, a short distance along the course of these vessels.
One or two valvular folds are found at the orifice of the coronary vein, preventing a
reflux of blood, but there are no valves at the orifices of the venae cavro.

The left auricle receives the blood which comes from the lungs by the pulmonary

36

CIRCULATION OF THE BLOOD.

veins. It does not differ materially in its anatomy' from the right. It is a little smaller,
and its walls are thicker, measuring about a line and a half. It has four openings hy which

it receives the blood from the
four pulmonary veins. These
openings are not provided with
valves. Like the right auricle,
it has a large opening by which
blood flows into the left ven-
tricle. The arrangement of the
muscular fibres is essentially the
same as in the right auricle. In
adult life, the cavities of the au-
ricles are entirely distinct from
each other. Before birth, they
communicate by a large open-
ing, the foramen ovale, and the
orifice of the inferior vena cava
is provided with a membranous
fold, the Eustachian valve,
which serves to direct the
blood from the lower part of
the body through the opening
into the left auricle. After
birth, the foramen ovale is
closed and the Eustachian valve
gradually disappears.

The ventricles, in the human
subject and in warm-blooded
animals, constitute the bulk of
the heart. They have a ca-
pacity somewhat greater than
that of the auricles and are
provided with thick muscular
walls. It is by the powerful

„ artery ; 11, branch of the coronary vein ; 12, 12, 12, lym- „ „.*.; „„ ,
phatic vessel

rior coronary artery; 11, branch of the coronary vein ; 12, 12, 12, lym-
els.

FIG. 12. — Heart, anterior mew. (Bonamy and Beau.)
1, right ventricle ; 2, left ventricle ; 3, 4, right auricle ; 5, 6, left auri-
cle; 7, pulmonary artery; 8, aorta; 9, superior vena cava; 10, ante-

action of this portion of tlie
heart that the blood is forced,
on the one hand, to the lungs and back to the left side, and on the other, through the
entire system of the greater circulation to the right side. It has been asserted that the
capacity of the right ventricle is considerably greater than that of the left. The most
recent and conclusive observations on this subject are those of Hiffelsheim and Robin.
In these experiments, the cavities were filled with an injection of wax, and the estimates
were made by calculating the am&unt of liquid displaced by the moulds of the different
cavities. Care was taken to make the injection in animals before cadaveric rigidity had
set in, or after it had passed away, in the human subject. The comparative results ob-
tained by these observers are the most interesting, for the cavities were undoubtedly dis-
tended by the injection to their extreme capacity, and contained more than they ever
do during life. They found the capacity of the right auricle from one-tenth to one-
eighth greater than that of the left. The capacity of the right ventricle was from
one-tenth to one-eighth greater than that of the left, but more frequently there was less
disparity between the two ventricles than between the auricles. The capacity of each
ventricle exceeded that of the corresponding auricle by from one-fourth to one-third.
Nine times out of ten, this predominance of the ventricle was more marked on the
left side. The absolute capacity of the left ventricle, according to these observations,

ANATOMY OF THE HEART.

37

16 ±

is from 143 to 212 cubic centimeters, or from about 4'8 to 7 ounces. This is much
greater than most estimates, which place the capacity of the various cavities, moderately
distended, at about 2 ounces.

Notwithstanding the disparity in the
extreme capacity of the various cavities,
the quantity of blood which enters these
cavities is necessarily equal to that which
is expelled. This has been stated to be
a littje more than two ounces. There
are no means of estimating with exact-
ness the quantity of blood discharged 15
with each ventricular contraction ; and
we find the question rather avoided in
works on physiology. All we can say
is that, from observations on the heart
during its action, it never seems to con-
tain much more than half the quantity in
all its cavities that it does when fully
distended by injection ; but it is the right
cavities which are most dilatable, and
probably the ordinary quantity of blood
in the left ventricle is from four-fifths to
five-sixths of its extreme capacity.

The cavities of the ventricles are
triangular or conoidal, the right being
broader and shorter than the left, which
extends to the apex. The inner surface
of both cavities is marked by peculiar
ridges and papilla, which are called
columns carnese. Some of these are
mere fleshy ridges projecting into the
cavity; others are columns attached by
each extremity and free at the central
portion; and others are papillae giving
origin to the chords tendinea3, which are
attached to the free edges of the auriculo-
ventricular valves. These fleshy columns
interlace in every direction and give the inner surface of the cavities a reticulated ap-
pearance. This arrangement evidently facilitates the complete emptying of the ventri-
cles during their contraction.

The walls of the left ventricle are uniformly much thicker than on the right side.
Bouillaud found the average thickness of the right ventricle at the base to be two and
a half lines, and the thickness of the left ventricle at the corresponding part, seven lines.

The arrangement of the muscular fibres constituting the walls of the ventricles is
more regular than in the auricles, and their course enables us to explain some of the phe-
nomena which accompany the heart's action. The direction of the fibres cannot be
well made out unless the heart have been boiled for a number of hours, when part
of the intermuscular tissue is dissolved out, and the fibres can be easily separated and
followed. Without going into a minute description of their direction, it is sufficient to
state, in this connection, that they present two principal layers; a superficial layer com-
mon to both ventricles, and a deep layer proper to each. The superficial fibres pass
obliquely from right to left from the base to the apex; here they take a spiral course,
become deep, and pass into the interior of the organ to form the column® carnese.

FIG. 13.— Left cavitie? of the heart. (Bonamy and Beau.)
1, left ventricular cavity ; 2, mitral valve ; 8, 4, column*
carnece ; 5, aortic opening; 6, aorta; 7, 8, 9, aortic
valves; 10, right ventricular cavity; 11, interventricular
septum; 12. pulmonary artery; 13, 14, pulinonic valves;
15, left auricular cavity; 16, 16, right pulmonary veins,
with 17, 17, openings of the veins; IS, section of the cor-
onary vein.

CIRCULATION OF THE BLOOD.

These fibres envelop both ventricles. They may be said to arise from cartilaginous rings
which surround the auriculo-ventricular orifices. The external surface of the heart is
marked by a little groove which indicates the division between the two ventricles. The

deep fibres are circular, or transverse,
and surround each ventricle separately.
The muscular tissue of the heart
is of a deep-red color and resembles, in
its gross characters, the tissue of ordi-
nary voluntary muscles ; but, as already
intimated, it presents certain peculiar-
ities in its minute anatomy. The fibres
are considerably smaller and more gran-
ular than those of ordinary muscles. They
are, moreover, connected with each other
by short inosculating branches, while in
the voluntary muscles each fibre runs
from its origin to its insertion enveloped
in its proper sheath, or sarcolemma. The
muscular fibres of the heart have no sar-
colemma. These peculiarities, particular-
ly the inosculation of the fibres, favor the
contraction of the ventricular walls in
every direction and the complete expul-
sion of the contents of the cavities with
each systole.

The distribution of the nerves to the
heart and the arrangement of the ganglia
and nerve-terminations in its substance
will be taken up in connection with the
influence of the nervous system upon he
action of the heart.

Each ventricle has two orifices; one
by which it receives the blood from the
auricle, and the other by which the blood
passes from the right side to the lungs
and from the left side to the system.
All of these openings are provided with
valves, which are so arranged as to allow the blood to pass in but one direction.

Tricuspid Valve. — This valve is situated at the right auriculo-ventricular opening. It
has three curtains, formed of a thin but resisting membrane, which are attached around
the opening. The free borders are attached to the chordss tendineae, some of which arise
from the papillae on the inner surface of the ventricle, and others, directly from the walls
of the ventricle. When the organ is empty, these curtains are applied to the walls of
the ventricle, leaving the auriculo-ventricular opening free ; but when the ventricle is
completely filled and the fibres contract, they are forced up, their free edges become
applied to each other, and the opening is closed.

Pulmonic Valves. — These valves, also called the semilunar or sigmoid valves of the
right side, are situated at the orifice of the pulmonary artery. They are strong mem-
branous pouches, with their convexities, when closed, looking toward the ventricle.
They are attached around the orifice of the pulmonary artery and are applied very
nearly to the walls of the vessel when the blood passes in from the ventricle ; but at
other times their free edges meet in the centre, opposing the regnrgitation of blood. At
the centre of the free edge of each valve is a little corpuscle called the corpuscle of

FIG. 14.— Right cavities of the heart. (Bonamy and Beau.)
1, right ventricular cavity; 2, posterior curtain of the
tricuspid valve ; 8, right auricular cavity ; 4, cofa/m-
nce carnece of the right auricle ; 5, section of the coro-
; 6,

nary vein ; 6, Eustachian valve ; 7, ring of Vieussens ;
8, fossa ovalis; 9, superior vena cava; 10, inferior -vena
cava; 11, aorta; 12, 12, right pulmonary veins.

ANATOMY OF THE HEART.

39

Arantius; and, just above the margins of attachment of the valves, the artery presents
three little dilatations, or sinuses, called the sinuses of Valsalva. The corpuscles of
Arantius probably aid in the adapta-
tion of the valves to each other and
in the effectual closure of the orifice.

Mitral Valve. — This valve, some-
times called the bicuspid, is situated
at the left auriculo-ventricular orifice.
It is called mitral from its resem-
blance, when open, to a bishop's mi-
tre. It is attached to the edges of the
opening, and its free borders are held
in place, when closed, by the chordae
tendinese of the left side. It presents
no material difference from the tri-
cuspid valve, with the exception that
it is divided into two curtains instead
of three.

Aortic Valves. — These valves, also
called the semilunar or sigrnoid valves
of the left side, present no difference
from the valves at the orifice of the
pulmonary artery. They are situated
at the aortic orifice.

The physiological anatomy of the
tricuspid and mitral valves may be
studied by cutting away the auricles
so as to expose the auriculo-ventric-
ular openings, introducing a pipe into
the pulmonary artery and aorta, after
destroying the semilunar valves, and
then forcing w.ater into the ventricles

by a syringe or from a hydrant. In this way the play of the valves may be strikingly
exhibited.

We can study the action of the semilunar valves by cutting away enough of the ven-
tricles to expose them and forcing water into the vessels. These experiments give an

FIG. 15. — Muscular fibre* qfthe rentrides. (Bonamy and Beau.)
1, superficial fibres, common to both ventricles ; 2, fibres of the
left ventricle ; 3, deep fibres, passing upward toward the
base of the heart ; 4, fibres penetrating the left ventric.e.

FIG. 1G.— Anastomosing muscular fibres of the heart. (Morel.)

idea of the immense strength of the valves ; for they can hardly be ruptured by a force
which is not sufficient to rupture the vessels themselves.

40 CIRCULATION OF THE BLOOD.

FIG. 17.— Valves of the heart. (Bonamy and Beau.)

1, Eight auriculo-ventricular orifice, closed by the tricuspid valve; 2, fibrinous ring; 8, left auriculo-ventricular
orifice, closed by the mitral valve; 4, fibrinous ring; 5, aortic orifice and valves; 6, pulmonic orifice and valves ;
7, 8, 9, muscular fibres.

Movements of the Heart.

In studying the phenomena which accompany the action of the heart, we shall fol-
low the course of the blood, beginning with it as it flows from the vessels into the auri-
cles. The dilatation of the cavities of the heart is called the diastole, and the contrac-
tion of the heart, the systole. When these terms are used without any qualification,
they are understood as referring to the ventricles ; but they are also applied to the action
of the auricles, as the auricular diastole or systole, which, as we shall see, is distinct
from the action of the ventricles.

A complete revolution of the h'eart consists in the filling and emptying of all its cavi-
ties, during which they experience an alternation of repose and activity. As these phe-
nomena occupy, in many warm-blooded animals, a period of time less than one second,
it will be appreciated that the most careful study is necessary in order to ascertain their
exact relations to each other. When the heart is exposed in a living animal, the most
prominent phenomenon is the alternate contraction and relaxation of the ventricles ;
but this is only one of the operations of the organ. In all the mammalia, the anatomy
and action of the vascular system are to all intents and purposes the same as in the hu-
man subject ; and, although the exposure of the heart by opening the chest modifies some-
what the force and frequency of its pulsations, the various phenomena follow each other
in their natural order and present essentially their normal characters. The operation of
exposure of the heart may be performed on a living animal without any great difficulty ;
and. if we simply take care to keep up artificial respiration, the action of the heart will
continue for a considerable time. We may keep the animal quiet by the administration
of ether or by poisoning with woorara, the latter agent acting upon the motor nerves
but having no effect upon the heart. Having opened the chest, we see the heart, envel-
oped in its pericardium, contracting regularly ; and, on slitting up and removing this
covering, the various parts are completely exposed. The right ventricle and auricle and
a portion of the left ventricle can be seen without disturbing the position of the parts ;
but the greater part of the left auricle is concealed. As both auricles and ventricles act
together, the parts of the heart which are exposed are sufficient for purposes of study.

Action of the Auricles. — Except the short time occupied in the contraction of the
auricles, these cavities are continually receiving blood on the right side from the system,
by the venae cavae, and on the left side from the lungs, by the pulmonary veins. This

MOVEMENTS OF THE HEART. 41

continues until the cavities of the auricles are completety filled, the blood coming in by
a steady current; and, during the repose of the heart, the blood is also flowing through
the auriculo-ventricular orifices into the ventricles. When the auricles have become
fully distended, they contract quickly and with considerable power (the auricular sys-
tole), and force the blood into the ventricles, producing complete diastole of these cavi-
ties. Daring this contraction, the blood not only ceases to flow in from the veins, but
some of it is regurgitated, as the orifices by which the vessels open into the auricles are
not provided with valves. The size of the auriculo-ventricular orifices is one reason
why the greater portion of the blood is made to pass into the ventricles ; and, farther-
more, during the auricular systole, the muscular fibres which are arranged around the
orifices of the veins constrict them to a certain extent, which tends to diminish the reflux
of blood. There can be no doubt that some regurgitation takes place from the auricles
into the veins, but this prevents the possibility of over-distention of the ventricles.

It has been shown by experiments that the systole of the auricles is not immediately
necessary to the performance of the circulation ; and the contractility of the auricles
may be temporarily exhausted by prolonged irritation, the ventricles continuing to act,
keeping up the circulation of blood.

Action of the Ventricles. — Immediately following the contraction of the auricles, by
which the ventricles are completely distended, we have contraction of the ventricles.
This is the chief active operation performed by the heart and is generally spoken of as
the systole. As we should expect from the great thickness of the muscular walls, the
contraction of the ventricles is very much more powerful than that of the auricles. By
their action, the blood is forced from the right side to the lungs by the pulmonary artery,
and from the left side to the system by the aorta. Regurgitation into the auricles is pre-
vented by the closure of the tricuspid and mitral valves. This act accomplished, the
heart has a period of repose, the blood flowing into the auricles, and from them into the
ventricles, until the auricles are filled and another contraction takes place.

Locomotion of the Heart. — The position of the heart after death or during the re-
pose of the organ is with its base directed slightly to the right and its apex to the left
side of the body. With each ventricular systole, it raises itself up, the apex is sent for-
ward, and is moved slightly from left to right. The movement from left to right is a
necessary consequence of the course of the superficial fibres. The fibres on the anterior
surface of the organ are longer than those on the posterior surface, and pass from the
base, which is comparatively fixed, to the apex, which is immovable. As a consequence
of this anatomical arrangement, the heart is moved upward and forward during its sys-
tole. The course of the fibres from the base to the apex is from right to left ; and, as
they shorten, the apex is of necessity slightly moved from left to right.

The locomotion of the entire heart forward was observed by Harvey, in the case of
the son of the Viscount Montgomery. The young man, aged about nineteen years, suf-
fered a severe injury to the chest, resulting in an abscess, which on cicatrization left
an opening into which Harvey could introduce three fingers and the thumb. This
opening was directly over the apex of the heart. The action of the portion of the heart
thus exposed is described by Harvey in the following words :

" We also particularly observed the movements of the heart, viz. : that in the dias-
tole it was retracted and withdrawn ; whilst in the systole it emerged and protruded ;
and the systole of the heart took place at the moment the diastole or pulse in the wrist
was perceived. To conclude, the heart struck the walls of the chest, and became promi-
nent at the time it bounded upward and underwent contraction on itself."

The locomotion of the heart takes place in the direction of its axis and is due to the
sudden distention of the great vessels at its base. These vessels are eminently elastic,
and, as they receive the charge of blood from the ventricles, become enlarged in every

42 CIRCULATION OF THE BLOOD.

direction and consequently project the entire organ against the walls of the chest. This
movement is aided by the recoil of the ventricles as they discharge their contents. The
displacement of the heart during its systole has long been observed in vivisections and
may be demonstrated in any of the mammals. The most interesting observations on
this point are those of Chauveau and Faivre, which were made upon a monkey. In this
animal, in which the position of the heart is very much the same as in the human sub-
ject, the locomotion of the organ was fully established.

Twisting of the Heart. — The spiral course of the superficial fibres would lead us to
look for another phenomenon accompanying its contraction ; namely, twisting. If we
attentively watch the apex of the heart, especially when its action has become a little
retarded, there is a palpable twisting of the point upon itself from left to right with the
systole, and an untwisting with the diastole.

Hardening of the Heart.— If the heart of a living animal be grasped by the hand, it
will be observed that at each systole it becomes hardened. The fact that it is composed
almost exclusively of fibres, resembling very closely those of the voluntary muscles,
explains this phenomenon. Like any other muscle, it is sensibly hardened during con-
traction.

Shortening and Elongation of the Heart. — The phenomena which we have just de-
scribed are admitted by all writers on physiology and can easily be observed ; but the
change in length of the heart during its systole has been a matter of discussion. All who
have studied the heart in action have observed changes in length during contraction and
relaxation ; but the contemporaries of Harvey were divided as to the periods in the heart's
action which are attended with elongation and shortening. Harvey himself is not abso-
lutely definite on this point. In one passage he says, in describing the systole, " that it is
everywhere contracted, but especially towards the sides, so that it looks narrower, a lit-
tle longer, more drawn together." In his description of the case of the son of the Vis-
count Montgomery, who suffered from ectopia cordis, he states that during the systole
the heart " emerged and protruded." Vesalius, Fontana, and some others, contended for
elongation during the systole ; but Haller, Steno, Lancisi, and Bassuel stated that it be-
comes shortened. The view generally entertained at the present day is that the heart is
shortened during its systole. There is no doubt that the point of the heart is protruded
during the ventricular systole, but this protrusion is not due to elongation of the ventricles.
By suddenly cutting the heart out of a warm-blooded animal and watching the phenom-
ena which accompany the few regular contractions which follow, it is seen that the ven-
tricles invariably shorten during the systole. This can easily be appreciated by the
eye, but more readily if the point of the organ be brought just in contact with a plane
surface at right angles, when, at each contraction, it is unmistakably observed to recede.
The following experiments we have frequently repeated before the class of the Bellevue
Hospital Medical College, and have satisfied ourselves of their accuracy. A large New-
foundland pup, about nine months old, was poisoned with woorara, artificial respiration
was kept up, and the heart exposed. After showing the protrusion of the point and
the apparent elongation of the heart while in the chest, the organ was rapidly removed,
placed upon the table, and confined by two long needles passed through the base, pinning
it to the wood. It contracted for one or two minutes, and at each systole the ventricles
were manifestly shortened. The point was then placed against an upright, and it re-
ceded with each systole about an eighth of an inch. This phenomenon was apparent to
all present. In another experiment, performed a few weeks later, the heart, which had
been exposed in the same way, was examined in situ, by pinning it with two needles to
a thin board passed under the organ. The presence of the needles did not seem to in-
terfere with the heart's action, and, at each ventricular systole, the point evidently
approached the base. To render this absolutely certain, a knife was fixed in the wood

SUCCESSION OF THE MOVEMENTS OF THE HEART. 43

at right angles to and touching the point during the diastole, and a small silver tube was

introduced through the walls into the left ventricle. At each contraction a jet of

blood spurted out through the tube, and the point of the heart receded from the knife

about an eighth of an inch. The animal experimented upon was a dog, a little above

the medium size. These simple experiments demonstrate that, in the dog at least, the

ventricles shorten during their systole. The ar-

rangement of the muscular fibres is too nearly iden-

tical in the heart of the warm-blooded animals to

leave room for doubt that it also shortens in the

human subject. The error which has arisen in this

respect, and which obtained in our first experiments

made in 1861, is due to the locomotion and pro-

trusion of the entire organ, so as to make the point

strike against the chest. A little reflection indicates

the mechanism of this phenomenon. During the

intervals of contraction, the great vessels, particu-

larly the aorta and pulmonary artery, which attach

the base of the heart to the posterior wall of the

FIG. 18.— Diagram of the shortening of
thorax, are filled but not distended with blood ; at the ventricles during systole.

each systole, however, these vessels are distended The drtt" °f the

to their utmost capacity ; their elastic coats permit
of considerable enlargement, as can be seen in the living animal, and this enlarge-
ment, taking place in every direction, pushes the whole organ forward. We have
also considerable locomotion of the heart from recoil. It is for this reason that,
observing the heart in situ, the ventricles seem to elongate. It is only when we
examine the heart firmly fixed, or contracting after it is removed from the body,
that we can appreciate the actual changes which occur in the length of the ventricles.
During the systole the ventricles are shortened and are narrowed in their transverse
diameter, but their antero-posterior diameter is slightly increased.

In addition to the marked changes in form, position, etc., which the heart undergoes
during its action, we observe, on careful examination, that the surface of the ventricles
becomes marked with slight longitudinal ridges during the systole. This was not noted
by Harvey, but is mentioned by Haller.

Impulse of the Heart. — Each movement of the heart produces an impulse, which can
be readily felt and sometimes seen, in the fifth intercostal space, a little to the left of the
median line. Vivisections have demonstrated that the impulse is synchronous with the
contraction of the ventricles. If the hand be introduced into the chest of a living animal,
and the finger be placed between the point of the heart and the walls of the thorax,
every time that we have a hardening of the point, the finger will be pressed against the
side. If the impulse of the heart be felt while the finger is on the pulse, it is evident
that the heart strikes against the thorax at the time of the distention of the arterial
system. The impulse is due to the locomotion of the ventricles. In the words of Harvey,
" the heart is erected, and rises upwards to a point, so that at this time it strikes against
the breast and the pulse is felt externally." In the case of the son of the Viscount Mont-
gomery, already referred to, Harvey gives a most graphic description of the manner in
which the heart is u retracted and withdrawn " during the diastole, and " emerged and
protruded " during the systole.

Succession of the Movements of the Heart.— We have already followed, in a general
way, the course of the blood through the heart and the successive action of the various
parts ; but we have yet to consider these points more in detail, and to ascertain, if
possible, the relative periods of activity and repose in each portion of the organ.

44 CIRCULATION OF THE BLOOD.

The great points in the succession of movements are readily observed in the hearts
of cold-blooded animals, in which the pulsations are very slow. In examining the heart
of the frog, turtle, or alligator, the alternations of repose and activity are very strongly
marked. During the intervals of contraction, the whole heart is flaccid, and the ventricle
is comparatively pale ; we then see the auricles slowly filling with blood ; when they
have become fully distended, they contract and fill the ventricle, which, in these animals,
is single; the ventricle immediately contracts, its action following upon the contraction
of the auricles as if it were propagated from them. When the heart is filled with blood,
it has a dark-red color, which contrasts strongly with its appearance after the systole.
This operation may occupy from ten to twenty seconds, giving an abundance of time for
observation. The case is different, however, with the warm-blooded animals, in which
the anatomy of the heart is nearly the same as in man. Here a normal revolution may
occupy less than a second; and it is evident that the varied phenomena we have just
mentioned are followed with the utmost difficulty. In spite of this rapidity of action, it
can be seen that a rapid contraction of the auricles precedes the ventricular systole, and
that the latter is synchronous with the impulse.

Various estimates have been made of the relative time occupied by the auricular and
ventricular contractions; and the question has been at last definitely settled by the
observations of Marey, who has constructed very ingenious and delicate instruments for
registering the form and frequency of the pulse. He devised a series of most interesting
experiments, in which he was enabled to register simultaneously the pulsations of the
different divisions of the heart, and has succeeded in establishing a definite relation be-
tween the contractions of the auricles and ventricles. The method of Marey enables
us to determine, to a small fraction of a second, the duration of the contraction of each
of the divisions of the heart.

The method of transmitting the movement from the heart to a registering apparatus
is very simple. The apparatus consists of two little elastic bags connected together by
an elastic tube, the whole closed and filled with air. A pressure, like the pressure of
the fingers, upon one of these bags produces, of course, an instantaneous and correspond-
ing dilatation of the other. If we suppose one of these bags to be introduced into one
of the cavities of the heart, and the other placed under a small lever arranged on a pivot
so as to be sensible to the slightest impression, it is evident that any compression of the
bag in the heart would produce a corresponding change in volume in the other bag,
which would be indicated by a movement of the lever. Marey arranged the lever with
its short arm on the elastic bag, and the long arm, provided with a pen, moving against
a roll of paper, which passes along at a uniform rate. "When the lever is at rest with the
paper set in motion, the pen will make a horizontal mark ; but when the lever ascends
and descends, a corresponding trace will be made, and the duration of any movement
can readily be estimated by calculating the rapidity of the motion of the paper. The bag
which receives the impression is called by Marey the initial bag, and the other, which is
connected with the lever, is called the terminal bag. The former may be modified in
form with reference to the situation in which it is to be placed.

The experiments of M. Marey, with reference to the relations between the systole of
the auricles, the systole of the ventricles, and the impulse of the heart, were performed
upon horses, in the following way :

A sound is introduced into the right side of the heart through the jugular vein, an
operation which may be performed with certainty and ease. This sound is provided with
two initial bags, one of which is lodged in the right auricle, while the other passes into
the ventricle. The bags are connected with distinct tubes which pass one within the
other, and are connected by elastic tubing with the registering apparatus. At each sys-
tole of the heart, the bags in its cavities are compressed and produce corresponding
movements of the levers, which may be registered simultaneously.

To register the impulse of the heart, an incision is made through the skin and the ex-

SUCCESSION OF THE MOVEMENTS OF THE HEART.

45

ternal intercostal muscle over the point where the apex-beat is felt. A little bag, stretched
over two metallic buttons separated by a central rod, is then carefully secured in the
cavity thus formed, and connected by an elastic tube with the registering apparatus.
All the tubes are provided with stop-cocks, so that each initial bag may be made to com-
municate with its lever at will. When the operation is concluded and the sound firmly
secured in place by a ligature around the vein, the animal experiences no inconvenience,
is able to walk about, eat, etc., and there is every evidence that the circulation is not in-
terfered with. The cylinders which carry the paper destined to receive the traces are
arranged to move by clock-work at a given rate. The paper may also be ruled in lines,
the distances between which represent certain fractions of a second. Fig. 19 represents
the apparatus reduced to one-sixth of its actual size. Two of the levers are connected

FIG. 19.— Cardiograph. (Chauveau and Marey.)

"The instrument is composed of two principal elements: A E, the registering apparatus, and A S, the sphypmo-
graphie apparatus, that is to say, which receives, transmits, and amplifies the movements which are to be
studied." The compression exerted upon the bag c, which is placed over the apex of the heart between the in-
tercostal muscles, is conducted by the tube tc, which is filled with air, to the first lever. The compression ex-
erted upon the bags o and «, in the double sound, is conducted by the tubes t o and tv to the two remaining levers.
The movements of the levers are registered simultaneously by the cylinders A E.

with the double sound for the right auricle and ventricle, and one is connected with the
bag destined to receive the impulse of the heart. In an experiment upon a horse, every
thing being carefully arranged in the way indicated, the clock-work was set in motion,
and the movements of the three levers produced traces upon the paper which were
interpreted as follows :

1. The paper was ruled so that each division represented one-tenth of a second. The
traces formed by the three levers indicated four revolutions of the heart. The first revo-
lution occupied 1TV sec., the second, 1T2^ sec., the third, 1^ sec., and the fourth, 1 sec.

2. The auricular systole, as marked by the first lever, immediately preceded the ven-
tricular systole, and occupied about two-tenths of a second. The elevation of the lever
indicated that it was much more feeble than the ventricular systole, and sudden in its
character ; the contraction, when it had arrived at the maximum, being immediately fol-
lowed by relaxation.

3. The ventricular systole, as marked by the second lever, immediately followed the
auricular systole, and occupied about four-tenths of a second. The almost vertical direc-
tion of the trace and the degree of elevation showed that it was sudden and powerful in

46 CIRCULATION OF THE BLOOD.

its character. The abrupt descent of the lever showed that the relaxation was almost
instantaneous.

4. The impulse of the heart, as marked by the third lever, was shown to be absolute-
ly synchronous with the ventricular systole.

Condensing the general results obtained by Marey, which are of course subject to a
certain amount of variation, we have, dividing the action of the heart into ten equal
parts, three distinct periods, which occur in the following order :

Auricular Systole. — This occupies two-tenths of the heart's action. It is feeble as
compared with the ventricular systole, and relaxation immediately follows the contraction.

Ventricular Systole. — This occupies four-tenths of the heart's action. The contrac-
tion is powerful and the relaxation, sudden. It is absolutely synchronous with the im-
pulse of the heart.

Auricular Diastole. — This occupies four-tenths of the heart's action.

Force of the Heart. — There are few points in physiology concerning which opinions
have been more widely divergent than the question of the force employed by the heart at
each contraction. Borelli, who was the first to give a definite estimate of this force, put
it at 180,000 pounds, while the calculations of Keill give only 5 ounces. These estimates,
however, were made on purely theoretical grounds. Borelli estimated the force em-
ployed by the deltoid in sustaining a given weight held at arm's length, and formed his
estimate of the power of the heart by comparing the weight of the organ with that of
the deltoid. Keill made his estimate from a calculation of the rapidity of the current
of blood in the arteries. Hales was the first to investigate the question experimentally,
by the application of the cardiometer. He showed that the pressure of blood in the
aorta could be measured by the height to which the fluid would rise in a tube connected
with that vessel, and estimated the force of the left ventricle by multiplying the press-
ure in the aorta by the area of the internal surface of the ventricle. The cardiometer
has undergone various improvements and modifications, but the above is the principle
which is so extensively made use of at the present day in estimating the pressure of the
blood in different parts of the circulatory system. First we have the improvement of
Poiseuille, who substituted a U-tube partly filled with mercury for the long straight tube
of Hales ; and then, the various forms of cardiometers constructed by Magendie, Ber-
nard, Marey, and others, which will be more fully discussed in connection with the arte-
rial circulation. These instruments have been made use of by Marey, with very good
results, in investigating the relative force exerted by the different divisions of the heart.

Hales estimated, from experiments upon living animals, the height to which the blood
would rise in a tube connected with the aorta of the human subject, at 7 feet 6 inches,
and gives the area of the left ventricle as 15 square inches. From this he calculates the
force of the left ventricle as equal to 61 '5 pounds. Although this estimate is only an ap-
proximation, it seems to be based on more reasonable data than any other.

The apparatus of Marey for registering the contractions of the different cavities of
the heart enabled him to ascertain the comparative force of the two ventricles and the
right auricle ; the situation of the left auricle precluding the possibility of introducing a
sound into its cavity. By first subjecting the bags to known degrees of pressure, the de-
gree of elevation of a lever may be graduated so as to represent the degrees of the car-
diometer. In analyzing traces made by the left ventricle, the right ventricle, and right
auricle, in the horse, Marey found that, as a general rule, the comparative force of the
right and left ventricles is as one to three. The force of the right auricle is comparatively
insignificant, being in one case, as compared with the right ventricl^ only as one to ten.

Action of the Valves. — We have already indicated the course of the blood through
the cavities of the heart, and it has been apparent that the necessities of the circulation
demand some arrangement by which the current shall always be in one direction. The

AURICULO-VENTRICULAR VALVES. 47

anatomy of the valves which guard the orifices of the ventricles gives an idea of their
function ; but we have yet to consider the precise mechanism by which they are opened
and closed and the way in which regurgitation is prevented.

In man and the warm-blooded animals, there are no valves at the orifices by which
the veins open into the auricles. As lias already been seen, compared with the ventri-
cles, the force of the auricles is insignificant ; and it has farthermore been shown by ex-
periment that the ventricles may be filled with blood and the circulation continue, when
the auricles are entirely passive. Although the orifices are not provided with valves,
the circular arrangement of the fibres about the veins is such, that during the contrac-
tion of the auricles the openings are considerably narrowed, and regurgitation cannot
take place to any great extent. The force of the blood flowing into the auricles like-
wise offers an obstacle to its return. There is really no valvular apparatus which oper-
ates to prevent regurgitation from the heart into the veins ; for the valvular folds,
which are so numerous in the general venous system, and particularly in the veins of
the extremities, do not exist in the venae cavre. The continuous flow of blood from the
veins into the auricles, the feeble character of the auricular contractions, the arrange-
ment of the fibres around the orifices of the vessels, and the great size of the auriculo-
ventricular openings, are conditions which provide sufficiently for the flow of blood into
the ventricles.

Action of the Auriculo- Ventricular Valves. — After the ventricles have become com-
pletely distended by the auricular systole, they take on their contraction, which, it will
be remembered, is very many times more powerful than the contraction of the auricles.
They have to force open the valves which close the orifices of the pulmonary artery and
aorta and empty their contents into these vessels. To accomplish this, at the moment of
the ventricular systole, there is an instantaneous and complete closure of the auriculo-
ventricular valves, leaving but one opening through which the blood can pass. That
these valves close at the moment of contraction of the ventricles is demonstrated by the
experiments of Chauveau and Faivre, who introduced the finger through an opening into
the auricle and actually felt the valves close at the instant of the ventricular systole.
This tactile demonstration, and the fact that the first sound of the heart, which is pro-
duced in great part by the closure of the auriculo-ventricnlar valves, is synchronous
with the ventricular systole, leave no doubt as to the mechanism of the closure of these
valves. It is probable that, as the blood flows into the ventricles, the valves are slight-
ly floated out, but they are not closed until the ventricles, contract.

If a bullock's heart be prepared by cutting away the auricles so as to expose the
mitral and tricuspid valves, securing the nozzles of a double syringe in the pulmonary
artery and aorta, after having destroyed the semilunar valves, and if fluid be injected
simultaneously into both ventricles, the play of the valves will be exhibited. The mitral
valve effectually prevents the passage of fluid, its edges being so accurately approxi-
mated that not a drop passes between them ; but, when the pressure is considerable, a
certain quantity of fluid passes the tricuspid valve. There is, indeed, a certain amount
of insufficiency of the tricuspid valve, which does not exist on the opposite side ; but it
is very questionable whether there can be a sufficient amount of force exerted by the right
ventricle to produce any regurgitation of blood at the right auriculo-ventricular orifice.

The fact just noted was first pointed out by Mr. T. W. King, and is called by him the
" safety-valve function of the right ventricle." Mr. King reasoned, in support of his view of
the " safety-valve " function, as follows : The right ventricle sends its blood to the lungs,
where the walls of the capillaries are very thin. The lungs themselves are exceedingly
delicate, and an effusion of blood or considerable congestion would be liable to be followed
by serious consequences. To prevent this, the right ventricle is not permitted to exert
all its force, under all circumstances, upon the blood going into the pulmonary artery,
but the lungs may be relieved by a slight regurgitation, which takes place through

48 CIRCULATION" OF THE BLOOD.

the tricuspid valve. The lungs are still farther protected by the sufficiency of the mitral
valve, which prevents regurgitation from the left ventricle. In the systemic circulation,
extravasation of blood would not be followed by any serious results, and the circulating
fluid is made to pass through a considerable extent of elastic vessels, before it is distrib-
uted in the tissues. The value of this reasoning of course depends upon the simple ques-
tion whether or not there be any conditions of the circulation under which regurgitation
at the right auriculo-ventricular orifice can occur, the tricuspid valve being normal.
Judging from the amount of pressure required to produce regurgitation at this orifice in
our experiments upon bullocks' hearts, it does not .seem probable that a " safety-valve
function" actually exists; for the force required is much greater than could be exerted
by the right ventricle under any circumstances.

Action of the Aortic and Pulmonic Valves. — The action of the semilunar valves is
nearly the same upon both sides. In the intervals of the ventricular contractions, they
are closed and prevent regurgitation of blood into the ventricles. The systole, however,
overcomes the resistance of these valves and forces the contents of the ventricles into the
arteries. During thit, time, the valves are applied, or nearly applied, to the walls of the
vessel ; but so soon as the ventricles cease their contraction, the constant pressure of the
blood, which, as we shall see hereafter, is very great, instantaneously closes the openings.

The action of the semilunar valves can be exhibited by cutting away a portion of the
ventricles in the heart of a large animal, securing the nozzles of a double syringe in the
aorta and pulmonary artery, and forcing water into the vessels. In performing this ex-
periment in 1864, we noticed that, while the aortic semilunar valves oppose the passage of
the liquid so effectually that the aorta maybe ruptured before the valves will give way, a
certain degree of insufficiency exists, under a high pressure, at the orifice of the pulmo-
nary artery. It is not probable, however, that the pressure of blood in the pulmonary
artery is ever sufficient to produce regurgitation when the valves are normal.

It is probable that the corpuscles of Arantius, which are situated in the middle of each
valvular curtain, assist in the accurate closure of the orifice. The sinuses of Valsalva,
situated in the artery behind the valves, are regarded as facilitating the closure of the
valves by allowing the blood to pass easily behind them.

Sounds of the Heart. — If the ear be applied to the praecordial region, it will be found
that the action of the heart is accompanied by certain sounds. A careful study of these
sounds and of their modifications in disease has enabled the practical physician to distin-
guish, to a certain extent, the conditions of the heart by auscultation. This increases
the interest which attaches to the audible manifestations of the action of the great central
organ of the circulation.

The appreciable phenomena which attend the heart's action are connected with the
systole of the ventricles. It is this which produces the impulse against the walls of the
thorax, and, as we shall see farther on, the dilatation of the arterial system, called the
pulse. It is natural, therefore, in studying these phenomena, to take the systole as a
point of departure, instead of the action of the auricles, which we cannot appreciate
without vivisections; and the sounds, which are two in number, have been called first
and second, with reference to the systole.

The first sound is absolutely synchronous with the apex-beat. The second sound
follows the first with scarcely an appreciable interval. Between the second and the
first sound, there is an interval of silence.

Some writers have attempted to represent the sounds of the heart and their relations
to each other, by certain syllables, as, " lubb-dup or lull tub ; " but it seems unnecessary
to attempt to make such a comparison, which can only be appreciated by one who is
practically acquainted with the heart-sounds, when the sounds themselves can be so
easily studied.

CAUSES OF THE SOUNDS OF THE HEART. 49

Both sounds are generally heard with distinctness over any part of the prcecordia.
The first sound is heard with its maximum of intensity over the hody of the heart, a little
below and within the nipple, between the fourth and fifth ribs, and is propagated with
greatest facility downward, toward the apex. The second sound is heard with its maxi-
mum of intensity at the base of the heart, between the nipple and the sternum, at about the
locality of the third rib, and is propagated upward, along the course of the great vessels.

The rhythm of the sounds bears a certain relation to the rhythm of the heart's action,
which we have already discussed ; the difference being, that we here regard the heart's
action as commencing with the systole of the ventricles, while, in following the action of
different parts of the organ, we followed the course of the blood and commenced with
the systole of the auricles. Laennec was the first to direct special attention to the rhythm
of these sounds, although they had been recognized by Harvey, who compared them to the
sounds made by the passage of fluids along the oesophagus of a horse when drinking. He
divided a single revolution of the heart into four parts : the first two parts are occupied
by the first sound ; the third part, by the second sound ; and in the fourth part there is
no sound. He regarded the second sound as following immediately after the first. Some
authors have described a " short silence " as occurring after the first sound, and a " long
silence," after the second sound. The short silence, if appreciable at all, is so indistinct
that it may practically be disregarded.

Most physiologists regard the duration of the first sound as a little less than two-fourths
of the heart's action, and the second sound as a little more than one-fourth. When we
come to consider the mechanism of the production of the two sounds, we shall see that,
if our views on that point be correct, the first sound should occupy the period of the ven-.
tricular systole, or four-tenths of the heart's action, the second sound about three-tenths,
and the repose three-tenths.

The first sound is relatively dull, low in pitch, and is made up of two elements ; one,
a valvular element, in which it resembles in character the second sound, and the other, an
element which is due to the action of the heart as a muscle. It has been ascertained that
all muscular contraction is attended with a certain sound. To this is added an impulsion
element, which is produced by the striking of the heart against the walls of the thorax.

The second sound is relatively sharp, high in pitch, and has but one clear element,
which we have already alluded to as valvular.

Causes of the Sounds of the Heart. — There is now scarcely any difference of opinion
with regard to the cause of the second sound of the heart. The experiments of Rouanet,
published in 1832, settled beyond a doubt that it is due to a closure of the aortic and
pulmonary semilunar valves. In his essay upon this subject, Rouanet acknowledges his
indebtedness for the first suggestion of this explanation to Mr. Carswell, who was at
that time prosecuting his studies in Paris. The experiments by which this is demon-
strated are as simple as they are conclusive. First we have the experiments of Rouanet,
who imitated the second sound by producing sudden closure of the aortic valves by a
column of water. We then have the experiments, even more conclusive, of the British
Commission, in which the semilunar valves were caught up by curved hooks introduced
through the vessels of a living animal, the ass, with the result of abolishing the second
sound and substituting for it a hissing murmur. When the instruments were with-
drawn and the valves permitted to resume their action, the normal sound returned.

It is unnecessary to discuss the various theories which have been advanced to explain
the second sound, as it is now generally acknowledged to be due to the sudden closure
of the semilunar valves at the orifices of the aorta and pulmonary artery. We remark,
however, that the sound is heard with its maximum of intensity over the site of these
valves, and is propagated along the great vessels, to which they are attached. It also
occurs precisely at the time of their closure ; viz., immediately following the ventricular
systole.

4

50 CIRCULATION OF THE BLOOD.

The cause of the first sound of the heart has not, until within a few years, been so
well understood. It was maintained by Rouanet that this sound was produced by the
sudden closure of the auriculo-ventricular valves; but the situation of these valves ren-
dered it difficult to .demonstrate this by actual experiment. We have already seen, that,
while the second sound is purely valvular in its character, the first sound is composed of
a certain number of different elements ; but auscultatory experiments have been made by
which all but the valvular element are eliminated and the character of the first sound
made to resemble that of the second. Conclusive observations on this point were made
a few years ago by Dr. Austin Flint, constituting part of an essay which received the
prize of the American Medical Association in 1858. In this essay, the following points
were established :

1. If a folded handkerchief be placed between the stethoscope and integument, the
first sound is divested of some of its most distinctive features. It loses the quality of im-
pulsion and presents a well-marked valvular quality.

2. In many instances, when the stethoscope is applied to the proacordia while the
subject is in a recumbent posture and the heart is removed by force of gravity from the
anterior wall of the thorax, the first sound becomes purely valvular in character and as
short as the second.

3. When the stethoscope is applied to the chest a little distance from the point where
the first sound is heard with its maximum of intensity, it presents only its valvular ele-
ment.

These observations, taken in connection with the fact that the first sound occurs when
the ventricles contract and necessarily accompanies the closure of the auriculo-ventricular
valves, show pretty conclusively that these valves produce at least one element of the
sound. In farther support of this opinion, we have the fact that the first sound is heard
with its maximum of intensity over the site of the valves and is propagated downward
along the ventricles, to which the valves are attached. Actual experiments are not want-
ing to confirm this view. Chauveau and Faivre have succeeded in abolishing the first
sound by the introduction of a wire ring into the auriculo-ventricular orifice through a
little opening in the auricle, so as to prevent the closure of the valves. When this is
done, the first sound is lost; but on taking it out of the opening the sound returns.
These observers also abolished the first sound by introducing a small curved tenotomy-
knife through the auriculo-ventricular orifice and dividing the chordae tendineae. In
this experiment a loud rushing murmur took the place of the sound. These observations
and experiments settle beyond question the fact that the closure of the auriculo-ven-
tricular valves produces one element of the first sound.

The other elements which enter into the composition of the first sound are not so
prominent as the one we have just considered, although they serve to give it its pro-
longed and u booming " character. These elements are, a sound like that produced by
any large muscle during its contraction, called by some the muscular murmur, and the
sound produced by the impulse of the heart against the walls of the chest.

There can be no doubt but that the muscular murmur is one of the elements of the
first sound ; and it is this which gives its prolonged character when the stethoscope is
applied over the body of the organ, as the sound produced in muscles continues during
the whole period of their contraction. Admitting this to be an element of the first sound,
we can understand how its duration must necessarily coincide with that of the ventricular
systole. We can appreciate, also, how all but the valvular element is eliminated when
the stethoscope is moved from the body of the heart, the muscular sound not being prop-
agated as completely as the sound made by the closure of the valves.

The impulse of the heart against the walls of the thorax also contributes to produce
the first sound. This is demonstrated by noting the difference in the sound when the
subject is lying upon the back, and when he is upright, by interposing any soft sub-
stance between the stethoscope and the chest, or by auscultating the heart after the

FREQUENCY OF THE HEART'S ACTION. 51

sternum has been removed. Under these conditions, the first sound loses its booming
c.haracter, retaining, however, the muscular element, when the instrument is applied to
the exposed organ.

The first sound of the heart is complex. It is produced by the sudden closure of the
auriculo-ventricular valves at the beginning of the ventricular systole, to which are super-
tulded, the muscular sound, due to the contraction of the muscular fibres of the heart, and
the impulsion-sound, due to the shock of the organ against the walls of the thorax.

The second sound is simple. It is produced by the sudden closure of the aortic and
ptilmonic semilunar valves, immediately following the ventricular systole.

It is of the greatest importance, with reference to pathology, to have a clear idea of
the currents of blood through the heart, with their exact relation to the sounds and
intervals. At the commencement of the first sound, the blood is forcibly thrown from
the ventricles into the pulmonary artery on the right side and the aorta on the left,
and the auriculo-ventricular valves are suddenly closed. During the entire period oc-
cupied by this sound, the blood is flowing rapidly through the arterial orifices, and the
auricles are receiving blood slowly from the vena? cava3 and the pulmonary veins. When
the second sound occurs, the ventricles having become suddenly relaxed, the recoil of
the arterial walls, acting upon the column of blood, immediately closes the semilunar
valves upon the two sides. The auricles continue to dilate, and the ventricles are slowly
receiving blood. Immediately following the second sound, during the first part of the
interval, the auricles become fully dilated ; and, in the last part of the interval, imme-
diately preceding the first sound, the auricles contract and the ventricles are fully
dilated. This completes a single revolution of the heart.

Frequency of the Heart*1 z Action. — Physicians have always attached the greatest im-
portance to the frequency of the action of the heart, as one of the important indications
of the general condition of the system. The variations which are met with in health, de-
pending upon age, sex, muscular activity, the condition of the digestive system, etc., point
to the fact that the action of the heart is closely allied to the various functions of the
economy and readily sympathizes with their derangements. As each ventricular systole
is followed by an expansion of the arteries, which is readily appreciated by the touch, it
is more convenient to study the succession of these movements by exploring the vessels
than by examination of the heart itself. Leaving out certain of the qualities of the pulse,
this becomes an exact criterion of the acts of the heart.

The number of pulsations of the heart is not far from seventy per minute in an adult
male and is from six to ten more in a female. There are individual cases, however, in
which the pulse is normally much slower or more frequent than this, a fact which must be
remembered when examining the pulse in disease. It is said that the pulse of Napoleon I.
was only forty per minute. Dr. Dunglison mentions a case which came under his own
observation, in which the pulse presented an average of thirty-six per minute. The same
author states that the pulse of Sir William Congreve was never below one hundred and
twenty-eight per minute, in health. It is by no means unfrequent to find a healthy pulse
of a hundred or more a minute ; but, in the cases reported in which the pulse has been
found to be forty or less, it is possible that every alternate beat of the heart was so feeble
as to produce no perceptible arterial pulsation. In this case, the fact may be ascertained
by listening to the heart while the finger is placed upon the artery. Such an instance has
lately come under our observation, in which the pulse was apparently but thirty-five p*.-r
minute.

Influence of Age and Sex .—In both the male and female, observers have constantly
found a great difference in the rapidity of the heart's action at different periods of life.
The observations of Dr. Guy upon this point are very many and were made with the
utmost care with regard to the conditions of the system at the time the pulse was taken

52 CIRCULATION" OF THE BLOOD.

in each case. All were taken at the same hour and with the subject in a sitting posture.
Dr. Guy found the pulsations of the heart in the foetus to be pretty uniformly 140 per
minute. At birth, the pulse is 130. It gradually diminishes during the first year to
about 128. The second year, the diminution is quite rapid, the tables of Dr. Guy giving
107 as the mean frequency at two years of age. After the second year, the frequency
progressively diminishes until adult life, when it is at its minimum, which is about 70 per
minute. It is a common but erroneous impression that the pulse diminishes in frequency
in old age. On the contrary, numerous observations show that at the later periods of
life the movements of the heart become slightly accelerated, ranging from 75 to 80.

During early life there is no marked and constant difference in the rapidity of the
pulse in the sexes ; but, toward the age of puberty, the development of the sexual pecu-
liarities is accompanied with an acceleration of the heart's action in the female, which
continues even into old age. The differences at different ages are shown in the following
table, compiled from the observations of Dr. Guy :

AGES. MALES. FEMALES.

Average pulsations. Average pulsations.

From 2 to 7 years .... 97 98

« 8 " 14 " . . . .84 .94

" 14 " 21 " . . . . 76 82

« 21 " 28 " . . • .73 80

" 28 " 35 " . . . . 70 78

" 35 " 42 " . . . .68 78

" 42 " 49 " . . . . 70 77

" 49 " 66 " . . . . 67 76

" 56 " 63 " . . . . 68 77

" 63 " 70 " . . . .70 78

" 70 " 77 " . . . . 67 81

" 77 " 84 " . . . .71 82

Influence of Digestion. — The condition of the digestive system has a marked influence
on the rapidity of the pulse, and there is generally an increase in the pulse of from five
to ten beats per minute after each meal. Prolonged fasting diminishes its frequency by
from twelve to fourteen beats. Alcohol first diminishes and afterward accelerates the
pulse. Coffee is said to accelerate the pulse in a marked degree. It has been ascertained
that the pulse is accelerated to a greater degree by animal than by vegetable food. These
variations have long been recognized by physiologists.

Influence of Posture and Muscular Exertion. — It has been observed that the position
of the body has a very marked influence upon the rapidity of the pulse. Experiments
of a very interesting character have been made by Dr. Guy and others, with a view to
determine the difference in the pulse in different postures. In the male, there is a differ-
ence of about ten beats between standing and sitting, and fifteen beats between standing
and the recumbent posture. In the female, the variations with position are not so great.
The average given by Dr. Guy is, for the male standing, 81 ; sitting, 71 ; lying, 66 ; —
for the female : standing, 91 ; sitting, 84 ; lying, 80. This is given as the average of a
large number of observations. There were a few instances, however, in which there was
scarcely any variation with posture, and some in which the variation was much greater
than the average. In the inverted posture, the pulse was found to be reduced about
fifteen beats.

The question at once suggests itself whether the acceleration of the pulse in sitting
and standing may not be due, in some measure, to the muscular effort required in mak-
ing the change of posture. This is answered by the farther experiments of Dr. Guy, in
which the subjects were placed on a revolving board, and the posture changed without

INFLUENCE OF EXERCISE AND TEMPERATURE. 53

any muscular effort. The same results as those cited above were obtained in these ex-
periments, showing that the difference is due to the position of the body alone. In a
single observation, Dr. Guy found the pulse, standing, to be 89 ; lying, 77 ; difference,
12. With the posture changed without any muscular effort, the results were as follows:
standing, 87; lying, 74; difference, 13. Various theoretical explanations of these vari-
ations have been offered by physiologists; but Dr. Guy seems to have settled experi-
mentally the fact that the acceleration is due in part to the muscular effort required to
maintain the body in the sitting and standing positions. The following are the results
of experiments which bear conclusively on this point, in which it is shown that when
the body is carefully supported in the erect or sitting posture, so as to be maintained
without muscular effort, the pulse is less frequent than when the subject is standing;
and, farthermore, that the pulse is accelerated, in the recumbent posture, when the body
is only partially supported:

" 1. Difference between the pulse in the erect posture, without support, and leaning
in the same posture, in an average of twelve experiments on the writer, 12 beats ; and
on an average of eight experiments on other healthy males, 8 beats.

" 2. Difference in the frequency of the pulse in the recumbent posture, the body fully
supported, and partially supported, 14 beats, on an average of five experiments.

"3. Sitting posture (mean of ten experiments on the writer), back supported, 80;
unsupported, 87 ; difference, 7 beats.

" 4. Sitting posture with the legs raised at right angles with the body (average of
twenty experiments on the writer), back unsupported, 86 ; supported, 68 ; difference, 18
beats. An average of fifteen experiments of the same kind on other healthy males gave
the following numbers: back unsupported, 80; supported, 68; a difference of 12 beats."

Influence of Exercise, etc.—li is a fact generally admitted that muscular exertion in-
creases the frequency of the pulsations of the heart ; and the experiments just cited show
that the difference in rapidity, which is by some attributed to change in posture (some
positions, it is fancied, offering fewer obstacles to the current of blood than others), is
mainly due to muscular exertion. Every one knows, indeed, that the action of the heart
is much more rapid after violent exertion, such as running, lifting, etc. Experiments on
this point date from quite a remote period. Bryan Robinson, who published a treatise
on the "Animal Economy" in 1734, states, as the result of observation, that a man in
the recumbent position has 64 pulsations per minute ; sitting, 68 ; after a slow walk, 78 ;
after walking four miles in an hour, 100 ; and 140 to 150 after running as fast as he
could. This general statement, which has been repeatedly verified, shows the powerful
influence of the muscular system on the heart. The fact is so familiar that it need not
be farther dwelt upon.

The influence of sleep upon the action of the heart reduces itself almost entirely to
the proposition that, during this condition, we have an entire absence of muscular effort,
and consequently the number of beats is less than when the individual is aroused. It
has been found that there is no difference in the pulse between sleep and perfect quiet in
the recumbent posture. This fact obtains in the adult male; but it is said by Quetelet
that there is a marked difference in females and young children, the pulse being always
slower during sleep.

Influence of Temperature. — The influence of extremes of temperature upon the heart
is very decided. The pulse may be doubled by remaining a very few minutes exposed
to extreme heat. Bence Jones and Dickinson have ascertained that the pulse may be
very much reduced in frequency, for a short time, by the cold douche. It has also been
remarked that the pulse is habitually more rapid in warm than in cold climates.

Although many circumstances materially affect the rapidity of the heart's action, they
do not complicate, to any great extent, our examinations of the pulse in disease. In

54 CIECULATION OF THE BLOOD.

cases which present considerable febrile movement, the patient is generally in the recum-
bent posture. The variations induced by violent exercise are easily recognized, while
those dependent upon temperature, the condition of the digestive system, etc., are so
slight that they may practically be disregarded. It is necessary to bear in mind, how-
ever, the variations which exist in the sexes and at different periods of life, as well as
the possibility of individual peculiarities, when the action of the heart may be extraor-
dinarily rapid or slow.

Influence of Respiration upon the Action of the Heart. — The relations between the
functions of circulation and respiration are very intimate, and one function cannot go on
without the other. If circulation be arrested, the muscles, being no longer supplied with
fresh blood, soon lose their contractile power, and respiration ceases. We shall also find
that circulation is impossible if respiration be permanently arrested. When respiration
is imperfectly performed, the action of the heart is slow and labored. All physicians
are familiar with the slow, full pulse, indicating labored action of the heart, which
occurs in profound coma. The effects of arrest of respiration are marked in all parts
of the circulatory system, arteries, capillaries, and veins; but the disturbances thus pro-
duced all react upon the heart, and the modifications which take place in the action of
this organ are of the greatest interest and importance.

If the heart be exposed in a living animal and artificial respiration be kept up,
although the pulsations are increased in frequency and diminished in force, after a time
they become perfectly regular and continue thus so long as air is adequately supplied to
the lungs. Under these circumstances, we have the respiration entirely at our com-
mand and can study the effects of its arrest upon the heart with the greatest facility.
If we arrest respiration, we observe the following changes in the action of the heart :
For a few seconds pulsations go on as usual, but in about a minute they begin to
diminish in frequency. At the same time, the heart becomes engorged with blood, and
the distention of its cavities rapidly increases. For a time its contractions are com-
petent to discharge the entire contents of the left ventricle into the arterial system, and
a cardiometer applied to an artery will indicate a great increase in the pressure of blood.
A corresponding increase in the movements of the mercury will be noted at each
action of the heart, indicating that the organ is acting with abnormal vigor. If respira-
tion be still discontinued, the engorgement becomes intense, the heart at each diastole
being distended to its utmost capacity. It now becomes incapable of emptying itself,
the contractions become very unfrequent, perhaps three or four in a minute, and are
progressively enfeebled. The organ is dark, almost black, owing to the circulation of
venous blood in its substance. If respiration be not resumed, this distention continues,
the contractions become less frequent and more feeble, and in a few minutes they en-
tirely cease.

The arrest of the action of the heart, under these circumstances, is chiefly mechani-
cal. The unaerated blood passes with difficulty through the capillaries of the system,
and, as the heart is constantly at work, the arteries become immensely distended. This
is proven by the great increase in the arterial pressure while these vessels are full of
black blood. If we now closely examine the heart and great vessels, we are able to
note distinctly the order in which they become distended. These phenomena were par-
ticularly noticed and described by Prof. Dalton, and they demonstrate conclusively that,
in asphyxia, the obstruction to the circulation commences, not in the lungs, as is com-
monly supposed, but in the capillaries of the system, and is propagated backward to
the heart through the arteries. The distention of the heart in asphyxia is therefore due
to the fact that unaerated blood cannot circulate in the systemic capillaries. When thus
distended, the muscular fibres of the heart become paralyzed, like any muscle after a
severe strain.

If respiration be resumed at any time before the heart's action has entirely ceased, the

RHYTHMICAL CONTRACTIONS OF THE HEART. 55

organ in a few moments resumes its normal function. We first notice a change from the
dusky hue it has assumed to a vivid red, which is owing to the circulation of arterial
blood in its capillaries. The distention then becomes gradually relieved, and, for a few
moments, the pulsations are abnormally frequent. If we now open an artery, it will be
found to contain red blood. An instrument applied to an artery will show a diminution
in arterial pressure and in the force of the heart's action, if the arrest of respiration have
been carried only far enough to moderately distend the heart ; or there is an increase
in the pressure and force of the heart, if its action have been nearly arrested. A few
moments of regular insufflation will cause the pulsations to resume their normal char-
acter and frequency.

In the human subject, the effects of temporary or permanent arrest of respiration on
the heart are undoubtedly the same as those observed in experiments upon the warm-
blooded animals. In the same way, also, it is possible to restore the normal action of the
organ, if respiration be not too long suspended, by the regular introduction of fresh air
into the lungs. The numerous examples of animation restored by artificial respiration, in
drowning, etc., are evidence of this fact. In cases of asphyxia, those measures by which
artificial respiration is most effectually maintained have been found most efficient.

Certain individuals have been said to have the power of temporarily arresting the
action of the heart by a voluntary suspension of respiration. The most remarkable case
of this kind on record is that of Colonel Townshend, which is quoted in many works on
physiology. Colonel Townshend was said to be able to arrest respiration and the action
of the heart so completely as to simulate death. When in this condition, the pulse was
not perceptible at the wrist or over the prascordia, a mirror held before the mouth was
not tarnished, and he was to all appearances dead. On one occasion, in the presence of
several medical gentlemen, he remained in this condition for half an hour ; afterward
the functions of respiration and circulation becoming gradually reestablished. This, to
say the least, is a very remarkable case, but it is credited by many physiologists.

Cause of the Rhythmical Contractions of the Heart.

The phenomena attending the action of the heart present few difficulties in their
investigation, compared with the study of the cause of the regular contractions and
relaxations, which commence early in foetal development to terminate only with life.
This interesting question has long engaged the attention of physiologists and has been
the subject of numerous experiments and speculations. It would be idle to follow the
various theories which have been proposed to account for this constant action, except as
a subject of purely historical interest ; for many of them are based upon a very imperfect
knowledge of the phenomena of the circulation. At the present day, although we are
perhaps as far as ever from a knowledge of the actual cause of the regular movements,
we are pretty well acquainted with the various conditions by which they are regulated
and modified. We know, for example, how to induce contraction in a living muscle or
one which is just separated from the organism and has not yet lost what we call its vital
properties, but we must confess our utter ignorance when we ask ourselves why it acts
in response to a stimulus. The advances that have been made in chemistry and micro-
scopical anatomy do not -disclose the so-called vital principle; and when we come to
examine the various conditions under which the heart will continue its contractions, we
are arrested by the impossibility of fathoming the mystery of the cause of contract ion.
The heart is, anatomically, very much like the voluntary muscles ; but it has a constant
function to perform and seems to act without any palpable excitation, while the latter,
which have an occasional function, act only under the influence of a natural stimulus, like
the nervous force, or under artificial irritation. The movements of the heart are not the
only examples of what seems to be spontaneous action. The ciliated epithelium is in mo-
tion from the beginning to the end of life, and will continue for a certain time, even after
the cells are detached from the organism. This motion cannot be explained, unless we

56 CIRCULATION OF THE BLOOD.

call it an explanation to say that it is dependent on vital properties. But if we are yet
ignorant of the actual cause of the rhythmical contraction of the heart, we are pretty
well acquainted with the influences which render its action regular, powerful, and
sufficient for the purposes of the economy. It will facilitate our comprehension of this,
to compare the action of the heart with that of the ordinary voluntary muscles.

In the first place, every one knows that the action of the heart is involuntary. We
can neither arrest, retard, nor accelerate its pulsations by a direct effort of the will. In
this statement, we of course except those examples of arrest by the stoppage of respira-
tion or acceleration by violent exercise, etc. In this respect the heart differs from cer-
tain muscles, like the muscles of respiration, which act involuntarily, it is true, but the
action of which may be temporarily arrested or accelerated by a direct voluntary effort.
The last-mentioned fact gives us the difference between the heart and all other striated
muscles. All of them, in order to contract, must receive a stimulus, either natural or
artificial. The natural stimulus comes from the nervous centres and is conducted by the
nerves. If the nerves going to any of the respiratory muscles, for example, be divided,
the muscle is paralyzed and will not contract without some kind of irritation. Connec-
tion with the nervous system does not seem necessary to the action of the heart, for
it will contract, especially in the cold-blooded animals, some time after its removal from
the bod}7". 4

When a muscle has been removed from the body and is subjected to a stimulus, such
as galvanism or mechanical or chemical irritation, it is thrown into contraction ; but, if
carefully protected from irritation, it will remain quiescent. Contraction in this instance
is evidently produced by the application of the stimulus; but the question arises, Why
does the muscle thus respond to stimulation? This is a question which it is impossible to
answer satisfactorily, but one concerning which our ideas, since the time of Haller, have
assumed a definite form. This great physiologist called the property which causes the
muscle thus to contract, irritability; which is nothing more nor less than an unexplained
property inherent in the muscle and continuing so long as it retains its absolute physical
and chemical integrity. More than a hundred years ago, Haller described certain tissues
of the body as possessing this " irritability," such as the muscles, stomach, bladder, etc.,
and the different degrees of irritability with which each one was endowed. He ap-
plied this theory to the action of the heart, which he considered as the part endowed
with irritability to the highest degree. His theory of the action of the heart was that its
rhythmical contraction depended upon the irritability inherent in its muscular fibres. He
was far from denying the various influences which modified this action, but regarded its
actual power of contraction as independent.

Experiments have shown that the heart will pulsate for a time when removed from
all connection with other parts of the organism.1 In the cold-blooded animals, in which
the irritability of the tissues remains for some time after death, this is particularly marked.
It is not the blood in the cavities of the heart which causes it to contract, for it will
pulsate when its cavities have been emptied. It is not the contact of the air, for the
heart will pulsate in a vacuum. The heart does not receive its irritability from the
nervous system, for, when removed from the body, it has no connection with the nervous
system; and it is not probable that it receives any influence from sympathetic ganglia
which have lately been discovered in its substance, for detached portions of the heart
will pulsate, and the contractions of the organ will continue in animals poisoned with
woorara, which is known to paralyze the motor system of nerves.2

1 A number of instances of contractions of the heart in cold-blooded animals, continuing for a long time after
excision are on record. Dr. Dunglison, in his work on Physiology, mentions several instances in which the heart pul-
sated for from ten to twenty-four hours after removal from the body. The most remarkable examples of this pro-
longed action were in the heart of the sturgeon. In one instance, in an experiment on a large alligator, we found the
heart pulsating, in situ, twenty-eight hours after the animal had been killed by the injection of a solution of woorara.
The heart was then excised and continued to beat during a long series of experiments, until it was arrested by
powerful compression with the hand after it had been filled with water and the vessels tied.

a It is stated by Friedliinder that no portion of the heart, however small, will contract rhythmically unless it con-

RHYTHMICAL CONTRACTIONS OF THE HEART. 57

It, is unnecessary to refer to the various experiments which have demonstrated the
in lepen deuce of the contractions of the heart. They are of such a simple nature that
they may be verified hy any one who will take the trouble to excise the heart of a frog
or turtle, place it under a small bell-glass so that it will not be subject to possible irrita-
tion from currents of air, and watch its pulsations. In such an observation as this, it is
evident that, for a certain time, contractions, more or less regular, will take place; and
the experiments referred to above show that they occur without any external influ-
ence. In short, it is evident that the muscular fibres of the heart possess an irritability,
by virtue of which they will contract intermittently for a time, although no stimulus be
applied ; as the ordinary striated muscular fibres have an irritability, by virtue of which
they will respond, for a time, to the application of a stimulus.

It is manifestly necessary that the action of the heart should be constant, regular, and
powerful ; and when we say that the irritability inherent in its muscular tissue is such
that it will contract for a time without any external stimulus, we by no means assume
that this is the cause of its physiological action. It is only an important and incontestable
property of the muscular fibres of the heart, and its regular action is dependent upon
other conditions.

In the first place, we have to inquire what makes the action of the heart regular.
The answer to this is, that the changes of nutrition, by which, through the blood circu-
lating in its substance, the waste of its tissue is constantly supplied, preserve the integrity
of the fibres, and keep them, consequently, in a condition to contract. This is true,
likewise, of the ordinary striated muscular fibres. If the supply of blood be cut off from
the substance of the heart, especially in the warm-blooded animals, the organ soon loses
its irritability. This was admirably shown by the experiments of Erichsen. This
observer, after exposing the heart in a warm-blooded animal and keeping up artificial
respiration, ligated the coronary arteries, thus cutting off the greatest part of the supply
of blood to the muscular fibres. He found, as the mean of six experiments, that the heart
ceased pulsating, although artificial respiration was continued, in 23£ minutes. After the
pulsations had ceased, they could be restored by removing the ligatures and allowing the
blood to circulate again in the substance of the heart.

In the second place, the regular and powerful contractions of the heart are provided
for by the circulation of the blood through its cavities. Although the heart, removed
from the body, will contract for a time without a stimulus, it can be made to contract
during the intervals of repose by an irritant, such as the point of a needle or a feeble
current of galvanism. For a certain time after the heart has ceased to contract sponta-
neously, contractions may be induced in this way. This can easily be demonstrated in
the heart of any animal, warm-blooded or cold-blooded. This irritability, which is
manifested, under these circumstances, in precisely the same way as in ordinary muscles,
is different in degree in different parts of the organ. Haller and others have shown that
it is greater in the cavities than on the surface ; for, long after irritation applied to the
exterior fails to excite contraction, the organ will respond to a stimulus applied to its
interior. The experiments of Haller also show that fluids in the cavities of the heart
have a remarkable influence in exciting and keeping up its contractions. This observa-
tion is of much interest, as showing conclusively that the presence of blood is necessary
to the natural and regular action of the heart. We quote one of the experiments on this
point performed upon a cat :

" . . . . The superior vena cava having been divided, and the inferior limited,
and the pulmonary artery opened, and the right ventricle emptied by a sufficient com-
pression, and the aorta ligated, all with promptitude, I saw the right auricle repose
first, the right ventricle continued to beat for some time in unison with the left ventri-

tain franslla ; but this point cannot be regarded as definitively settled and is e\-oe<'.lin.<;Iy dilnYnlt to dftmnino. The
fact that nervous and muscular irritability are entirely distinct from each other is a strong argument in favor of tho
Independent irritability of tho inuscubr tissue of the heart.

58 CIRCULATION OF THE BLOOD.

cle, and its walls descended toward the middle line of the heart : but this ventricle did
not delay to lose its movement the first. As for the other ventricle, which could no
longer empty itself into the aorta, it was filled with blood and its movement continued
for four hours. ..."

This experiment was confirmed by numerous others. It will be observed that one
side of the heart was made to cease its pulsations, while the other side continued to con-
tract, by simply removing the blood from its interior ; which conclusively proves that,
although the heart may act for a time independently, the presence of blood in its cavities
is a stimulus capable of prolonging its regular pulsations. Schiff has gone still farther,
and has succeeded in restoring the pulsations in the heart of a frog, which had ceased
after it had been emptied, by introducing a few drops of blood into the auricle. Our
own experiments upon the hearts of alligators and turtles show that, when removed
from the body and emptied of blood, the pulsations are feeble, rapid, and irregular ; but
that when filled with blood, the valves being destroyed so as to allow free passage in
both directions between the auricles and ventricle, the contractions become powerful and
regular. In these experiments, when water was introduced instead of blood, the pulsa-
tions became more regular, but were more frequent and not so powerful as when blood
was used. These experiments show also that the action of the heart may be affected by
the character, particularly the density, of the fluid which passes through it, which may
explain its rapid and feeble action in anaemia.

It seems well established that the heart, although capable of independent action, is ex-
cited to contraction by the blood as it passes through its cavities. A glance at the suc-
cession of its movements, particularly in cold-blooded animals, in which they are so slow
that the phenomena can be easily observed, will show how these contractions are in-
duced. If we look at the organ as it is in action, we see first a distention of the auri-
cle, and this is immediately followed by a contraction filling the ventricle, which in its
turn contracts. Undoubtedly, the tension of the fibres, as well as the contact of blood
in its interior, acts as a stimulus ; and, as all the fibres of each cavity are put on the
stretch at the same instant, they contract simultaneously. The necessary, regular
distention of each cavity thus produces rhythmical and forcible contractions ; and the
mere fact that the action of the heart alternately empties and dilates its cavities in-
sures regular pulsations, so long as blood is supplied and no disturbing influences are in
operation.

The muscular fibres of the heart seem to be endowed with an inherent property,
called irritability, by virtue of which they will contract for a certain time without the
application of a stimulus. Irritability, manifested in this way, continues so long as, by
the processes of nutrition, the fibres are maintained in their integrity. The muscular
tissue, however, may be thrown into contraction, during the intervals of repose, by the
application of a stimulus, a property which is observed in all muscular fibres. The irri-
tability manifested in this way is much more marked in the interior than on the exterior
of the organ. Blood in contact with the lining membrane of the heart acts as a stimu-
lus in a remarkable degree and is even capable of restoring irritability after it has be-
come extinct. The passage of blood through the heart is the natural stimulus of the
organ and may be said to be the cause of its regular pulsations, although it by no means
endows the fibres with their contractile properties.

Influence of the Nervous System on the Heart.

The movements of the heart, as we have seen, are not directly under the control of
the will ; and observations on the human subject, as well as on living animals, have
shown that the organ is devoid of general sensibility. The latter fact was demonstrated
in the most satisfactorv manner by Harvey, in the case of the Viscount Montgomery.
In this case, the heart was exposed, and Harvey found that it could be touched and
handled without even the knowledge of the subject. This has been verified in other in-

INFLUENCE OF THE NEKVOUS SYSTEM ON THE HEART. 59

stances in the human subject. Its physiological movements are capable of being influ-
enced in a remarkable degree through the nervous system, notwithstanding this insensi-
bility and in spite of the fact that the muscular fibres composing it are capable of con-
traction when removed from all connection with the body and that the regular pulsa-
tions can be kept up for a long time by the mere passage of blood through its cavities.
The influence thus exerted is so great, that some eminent authorities have held the opin-
ion that the cause of the irritability of the organ was derived from the nerves. One of the
most distinguished advocates of this opinion was Legallois. This observer arrested the
action of the heart of the rabbit by suddenly destroying the spinal cord, from which he
drew the conclusion that the heart derived its contractile power from the cerebro-spinal
system. The experiments which we have already cited, showing the continuance of the
heart's action after excision, disprove this so completely, that it was not thought worth
while to discuss this view while treating of the cause of its rhythmical contractions.
The same may be said with regard to the experiments of Brachet, in which he endeav-
ored to prove that the contractility of the heart is derived from the cardiac plexus of the
sympathetic system of nerves. The fact that the heart does not depend for its contrac-
tility upon external nervous influence may be regarded as long since definitely settled ;
but within a few years the discovery in its substance of ganglia belonging to the sympa-
thetic system has revived, to some extent, the view that its irritability is derived from
nerves. It is not necessary to follow out all the experiments which combine to demonstrate
the incorrectness of this view. Bernard, by a series of admirably-conceived experi-
ments upon the effects of the woorara poison, has succeeded in demonstrating the dis-
tinction between muscular and nervous irritability. In an animal killed with this re-
markable poison, the functions of the motor nerves are entirely abolished, so that gal-
vanization or other irritation does not produce the slightest effect ; yet the muscles re-
tain their irritability, and, if artificial respiration be kept up, the circulation will con-
tinue for a long time. The heart, by this means, seems to be isolated from the nervous
system as completely as if it were excised ; and galvanization of the pneumogastric
nerves in the neck, which, in a living animal, will immediately arrest its action, has no
effect. On the other hand, poisoning by the sulphocyanide of potassium destroys the
muscular irritability and leaves the nerves intact. By these experiments, which we
have frequently repeated, we can completely separate the nervous from the muscular
irritability and show their entire independence of each other ; and there is every rea-
son to suppose that the heart, like the other muscles, does not derive its contractility
from any other system. It is evident, however, that the heart is often powerfully influ-
enced through the nerves. Sudden and violent emotions will occasionally arrest its ac-
tion and have been known to produce death. Palpitations are to be accounted for in
the same way. Some of the modifications which we have already considered, depending
on exercise, digestion, etc., are effected through the nerves; and it is through this system
that the heart and all the important organs of the body are made to a certain extent
mutually dependent. It becomes interesting and highly important, then, to study their
influences and follow out, as clearly as possible, the action of the nerves which are dis-
tributed to the heart.

The anatomical connections of the heart with the nervous centres are mainly through
the sympathetic and the pneumogastric nerves. We can study the influence of these
nerves to most advantage in two ways; first, by dividing them and watching the effect
of depriving the heart of their influence, and second, by exciting them by means of a
feeble current of galvanism. It is well known that in an animal just killed the " nervous
force" may be closely imitated by galvanism, which is better than any other means of
stimulation, as it does not affect the integrity of the nerves and the amount of the irrita-
tion may be easily regulated.1

1 We shall not discuss the effects upon the heart of sudden destruction of the preat nervous centres. It has been
Bhown that the heart becomes arrested when the brain is crushed, as by a blow with a hammer, when the medulla

60 CIRCULATION OF THE BLOOD.

Experiments on the influence of the sympathetic nerves upon the heart are not quite
so satisfactory as we might desire. It has been asserted that the action of the heart is
immediately arrested by destroying the cardiac plexus. With regard to this, we must
take into account the difficulty of making the operation and the disturbance of the heart
consequent upon the necessary manipulations. It has been shown pretty conclusively,
however, that stimulation of the sympathetic in the neck has the effect of accelerating the
pulsations of the heart. The extreme difficulty of dividing all the branches of the sympa-
thetic going to the organ leaves a doubt as to whether such an operation would definitely
abridge its action.

We have next to consider the influence of the pneumogastrics upon the heart. Ex-
periments on these nerves are made with greater facility than on the nerves of the sym-
pathetic system, and the results are much more satisfactory. Like all the cerebro-spinal
nerves, the influence generated in the nervous centre from which they take their origin is
conducted along the nerve and manifested at its distribution. When they are divided,
we may be sure that, as far as they are concerned, all the organs which they supply are
cut off from nervous influence ; and, when galvanized in their course, we imitate or ex-
aggerate the influence sent from the nervous centre.

The invariable effect on the heart of division of the pneumogastric nerves in the neck
is an increase in the frequency and a diminution in the force of its pulsations. One or two
writers have denied this fact, but it is confirmed by the testimony of nearly all experi-
menters. To anticipate a little in the history of the pneumogastric nerves, it may he
stated that, while they are exclusively sensitive at their origin, they receive, after having
emerged from the cranial cavity, a number of filaments from various motor nerves.
That they influence certain muscles, is shown by the paralysis of these muscles after divi-
sion of the nerves in the neck, as, for example, the arrest of the movements of the glottis.
Having this double property of motion and sensation, and being distributed in part to
an organ composed almost exclusively of muscular fibres, which, as we have seen, is not
endowed with general sensibility, we should expect that their section would arrest, or at
least diminish, the frequency of the heart's action. What explanation, then, can we offer
for the fact that this seems actually to excite the movements of the heart? We shall be
better prepared to answer this question after we have studied the effects of galvanization
of the nerves in a living animal or in one in which the action of the heart is kept up by
artificial respiration.

Numerous experiments have been made with reference to the effects on the heart of
galvanic currents, both feeble and powerful, passed through the pneumogastrics before
division, of currents passed through the upper and lower extremities after division, etc.,
a full detail of which belongs properly to the physiological history of the nervous system.
In this connection, a few of these facts only need be stated.

It has been shown by repeated experiments, which we have frequently confirmed, that
a moderately-powerful interrupted galvanic current passed through both pneumogastrics
will arrest the action of the heart, and that the organ remains quiescent so long as the
current is continued. This experiment has been performed upon living animals, both
with and without exposure of the heart. The arrest is not due to violent and continued
contraction of the muscular fibres ; on the contrary, the heart is relaxed, its ventricles
are flaccid, and its fibres are for the time paralyzed. The question then arises whether
this action be exerted directly on the heart through the nerves, or whether an influence
be conveyed to the nervous centre and transmitted to the heart in another way. This
is settled by the experiment of dividing the nerves and galvanizing alternately the ex-
tremities connected with the heart and those connected with the nervous centres. It has

oblongata or the spinal cord is suddenly destroyed, and even the crushing of a foot, in the frog, has been known to
product this effect. In fine, this may be done by any extensive injury to the nervous system; but this fact does net
teach us much with regard to the physiological influences of the nerves. For example, while crushing of the brain
nrrests the heart, the brain may be removed from a living animal and the heart will beat for days. Experiments
upon the influence of the medulla oblongata and spinal cord are by no means satisfactory.

INFLUENCE OF THE NERVOUS SYSTEM ON THE HEART. 61

been ascertained that galvanization of the extremities connected with the heart arrests
its action, while galvanization of the central extremities has no such effect. Another
interesting fact also shows that the influence exerted upon the heart is through the motor
filaments of the pneumogastrics. It has been demonstrated by Bernard, in a very curious
series of experiments which we shall not fully discuss in this connection, that the woorara
poison paralyzes only the motor nerves, leaving the sensory nerves intact. If we expose
the heart and the pneumogastric nerves in a warm-blooded animal poisoned with this agent,
and continue the pulsations by keeping up artificial respiration, we find that the most
powerful current of galvanism passed through the pneumogastrics has no efi'ect upon the
heart.

When we corne to the study of the nervous system, we shall see that the inhibitory
action of the pneumogastrics upon the heart is derived from the spinal accessory nerves,
a fact which has been proven beyond question by a very ingenious series of experiments,
which will be fully described hereafter.

Although galvanization of the pneumogastrics arrests the action of the heart in nearly
all animals, there are some in which this does not take place, as in birds ; a fact which is
stated by Bernard, but for which he offers no explanation. In some experiments insti-
tuted on this subject a few years ago on alligators, we noticed a singular peculiarity which
throws some light on the question we are now considering. Desiring to demonstrate to
the class at the New Orleans School of Medicine the action of the heart in this animal,
an alligator six feet in length was poisoned with woorara and the heart exposed. The
animal came under the influence of the poison in about thirty minutes, when the dissec-
tion was commenced, and was quite dead when the heart was exposed. The pneumogas-
trics were then exposed and galvanized, with the effect of promptly arresting the action
of the heart. This observation was verified in another experiment. We were at first at a
loss to account for the absence of effect of the woorara on the motor filaments of the
pneumogastric nerves ; but on reflection we thought it might be due to slow absorption of
the poison in so large a cold-blooded animal. With a view of ascertaining whether there
be any difference in the promptness with which different nerves in the body are affected
by this agent, we made the following experiment upon a dog : The animal was brought
under the influence of ether, and the heart, the pneumogastrics, and the sciatic nerve
were exposed. Galvanization of the sciatic produced muscular contraction, and stimula-
tion of the pneumogastrics arrested the heart promptly. A grain of woorara, dissolved in
water, was then injected under the skin of the thigh. One hour after the injection of
the woorara, the sciatic was found insensible to galvanism, but the heart could be ar-
rested by galvanization of the pneumogastrics, although it required a powerful current.
A weaker current diminished the frequency and increased the force of its pulsations.
In this experiment, the operation of opening the chest undoubtedly diminished the ac-
tivity of absorption of the poison and consequently retarded its effects upon the nervous
system. Taken in connection with the observations on alligators, it shows that the motor
nerves are not all affected at the same time, and that the pneumogastrics resist the action
of this peculiar poison after the motor nerves generally are paralyzed.

Our knowledge of the inherent properties of the muscular fibres of the heart and of
the effects of the passage of blood through its cavities, which together are competent to
keep up for a time regular pulsations without the intervention of the nervous system,
taken in connection with the facts just stated concerning the influence of section or gal-
vanization of the pneumogastric nerves, enables us to comprehend pretty well the influ-
ence of these nevves on the heart. They undoubtedly perform the important function
of regulating the force and frequency of its pulsations. Hardly any reflection is necessary
to convince us of the importance of such a function, and how it must of necessity be
accomplished through the pneumogastrics. It is important, of course, that the heart
should act at all times with nearly the same force and frequency. Wo h.-ive seen that
the inherent properties of its fibres are competent to make it contract, and the necessary

62 CIRCULATION OF THE BLOOD.

intermittent dilatation of its cavities makes these contractions assume a certain regular-
ity ; but the quantity and density of the blood are subject to very considerable variations
within the limits of health, which, without some regulating influence, would undoubtedly
cause variations in the heart's action, so considerable as to be injurious. This is shown
by the comparatively-inefficient and palpitating action of the heart when the pneumogas-
trics are divided. These nerves convey to the heart a constant influence, which we may
compare to the insensible tonicity imparted to voluntary muscles by the general motor
system. For we know that when a set of muscles on one side is paralyzed, as in facial
palsy, their tonicity is lost, they become flaccid, and the muscles on the other side, with-
out any effort of the will, distort the features. We can imitate an exaggeration of this
force by a feeble current of galvanism, which renders the pulsations of the heart less
frequent and more powerful, or exaggerate it still more by a more powerful current,
which arrests the action of the heart altogether. Phenomena are not wanting in the
human subject to verify these views. Causes which operate through the nervous sys-
tem frequently produce palpitation and irregular action of the heart. Cases are not
uncommon in which palpitation habitually occurs after a full meal. There are instances
on record of immediate death from arrest of the heart's action as a consequence of
fright, anger, grief, or other severe mental emotions. Syncope from these causes is by
no means uncommon. In the latter instance, when the heart resumes its functions,
the nervous shock carried along the pneumogastrics is only sufficient to arrest its action
temporarily. When death takes place, the shock is so great that the heart never
recovers from its effects.

/Summary of certain Causes of Arrest of the Action of the Heart.

In warm-blooded animals, the heart's action speedily ceases after it is deprived of
its natural stimulus, the blood. It is not from experiments on the inferior animals
alone that we derive proof of this fact. It is well known that, in profuse haemorrhage
in the human subject, the contractions of the heart are progressively enfeebled, and,
when the loss of blood has proceeded to a certain extent, are permanently arrested.
Cases of transfusion after haemorrhage show that when blood is introduced the heart
may be made to resume its pulsations. The same result takes place in death by asthe-
nia ; and cases are on record in which life has been prolonged, as in haemorrhage, by trans-
fusion of even a small quantity of healthy blood. These facts have been demonstrated
on the inferior animals by experiments already cited. The experiment of Haller, in
which the action of the right side of the heart of a cat was arrested by emptying it of
blood, while the left side, which was filled with blood, continued to pulsate, showed
that the absence of blood in its cavities is competent of itself to arrest the heart. The
experiments of Erichsen, who paralyzed the heart by ligating the coronary arteries, and
of Schiff, who produced a local paralysis by ligating the vessel going to the right
ventricle, show that the heart may also be arrested by cutting off the circulation of
blood in its substance. Both of these causes must operate in arrest of the heart's
action in htemorrhage.

The mechanical causes of arrest of the heart's action are of considerable pathologi-
cal importance. The heart, in common with other muscles, may be paralyzed by me-
chanical injury. A violent blow upon the deltoid paralyzes the arm ; a severe strain
will paralyze the muscles of an extremity ; and, in the same way, excessive distention
of the cavities of the heart will arrest its pulsations. This is shown by arrest of the
circulation in asphyxia. We have already seen that, under these circumstances, the heart
is incapable of forcing the unaerated blood through the systemic capillaries. The heart
finally becomes enormously strained and distended and is consequently paralyzed. The
same result follows the application of a ligature to the aorta. This effect may be pro-
duced, also, in the cold-blooded animals, in which, if the heart be left undisturbed, the

CAUSES OF ARREST OF THE ACTION OF THE HEART. 63

pulsations will continue for a long time. The following experiment illustrating this
point was performed upon the heart of an alligator six feet in length:

The animal was poisoned with woorara, and twenty-eight hours after death tin-
heart, which had been exposed and left in situ, was pulsating regularly. It was then
removed from the body, and, after some experiments on the comparative force, etc., of
the pulsations when empty and when filled with blood, was filled with water, tne
valves having been destroyed so as to allow free passage of the fluid through the cavi-
ties, and the vessels ligated. The ventricles, still filled with water confined in their
cavity, were then firmly compressed with the hand, so as to subject the muscular fibres
to powerful compression. From that time, the heart entirely ceased its contractions
and became hard like a muscle in a state of cadaveric rigidity. This experiment shows
how completely and promptly the heart, even of a cold-blooded animal, may be ar-
rested in its action by mechanical injury.

Cases of death from distention of the heart are not infrequent in practice. It is well
established that the form of organic disease which most frequently leads to sudden
death is that in which the heart is liable to great distention. We refer to disease at the
aortic orifice. In other lesions there is not this tendency ; but, when the aortic orifice
is contracted or the valves are insufficient, any great disturbance of the circulation will
cause the heart to become engorged, which is liable to produce a fatal result;

Most persons are practically familiar with the distressing sense of suffocation which
frequently follows a blow upon the epigastrium ; and a few cases are on record of in-
stantaneous death following a comparatively slight concussion in this region. We had an
opportunity, in the winter of 1854-'5, of witnessing an autopsy in a case of this kind. A
young mulatto man, employed as a waiter at the Louisville Hotel, received a blow in the
epigastrium while frolicking, which produced instantaneous death. On post-mortem ex-
amination, no lesion was discovered. Although these cases are rare, they are well recog-
nized, and the eifects are generally attributed to injury of the solar plexus. The dis-
tress is precisely what would occur from sudden arrest of the heart's action ; for it is
the blood charged with oxygen and sent by the heart to the system, which supplies the
wants of the tissues, and not the simple entrance of air into the lungs ; and arrest of
the circulation of arterial blood, from any cause, produces suffocation as completely
as though the trachea were ligated. This fact we have clearly proven by experiments.
It is a question whether the arrest of the heart, if this be the pathological condition, be
due to concussion of the nervous centre or to the direct effects of the blow upon the
organ itself. Our present data do not enable us to answer this question definitely, but
they rather incline us to the opinion that in such accidents the symptoms are due to
direct injury of the heart. An additional argument in favor of this view is founded on
our knowledge of the mode of operation of the sympathetic system. The effects of
stimulation or irritation of this system are not instantaneously manifested, as is the case
in the cerebro-spinal system, but are developed slowly and gradually.

As far as we have been able to learn by experiment, the nervous influences which
arrest the action of the heart operate through the pneumogastrics and are derived from
the spinal accessory nerves. As we have just seen, we can closely imitate this action by
galvanism. The causes of arrest in this way are numerous. Among them may be men-
tioned, sudden and severe bodily pain and severe mental emotions. With the exception
of arrest of the heart from loss of blood and from distention, from whatever cause it
may occur, stoppage of the heart takes place from influences operating through the
nervous system. It may be temporary, as in syncope, or it may be permanent ; and ex-
amples of the latter, though rare, are sufficiently well authenticated.

64 CIRCULATION OF THE BLOOD.

CHAPTER III.

CIRCULATION OF THE BLOOD IN THE VESSELS.

Physiological anatomy of the arteries— Course of blood in the arteries— Locomotion of the arteries and production
of the pulse — Pressure of blood in the arteries— Pressure in different parts of the arterial system- Depressor
Derve — influence of respiration on the arterial pressure — Rapidity of the current of blood in the arteries — Rapid-
ity in different parts of the arterial system— Circulation of the blood in the capillaries— Physiological anatomy
of the capillaries — Capacity of the capillary system — Course of blood in the capillaries — Relations of the capil-
lary circulation to respiration — Causes of the capillary circulation — Influence of temperature on the capillary cir-
culation— Influence of direct irritation on the capillary circulation — Circulation of the blood in the veins— Physio-
logical anatomy of the veins— Course of the blood in the veins— Pressure of blood in the veins— Rapidity of the
venous circulation— Causes of the venous circulation — Air in the veins— Function of the valves — Conditions
which impede the venous circulation — Regurgitant venous pulse— Circulation in the cranial cavity — Circulation
in erectile tissues— Derivative circulation— Pulmonary circulation— Rapidity of the circulation— Phenomena in
the circulatory system after death.

IN man and in all animals possessed of a double heart, each contraction of this organ
forces a charge of blood from the right ventricle into the pulmonary artery, and from
the left ventricle into the aorta. We have seen how the valves which guard the orifices
of these vessels effectually prevent regurgitation during the intervals of contraction.
There is, therefore, but one direction in which the blood can flow in obedience to this
intermittent force ; and the fact that, even in the smallest arteries, there is an accelera-
tion in the current coincident with each contraction of the heart, which disappears when
the action of the heart is arrested, shows that the ventricular systole is the prime cause
of the arterial circulation. But this part of the physiology of the circulation is not so
simple as we might at first be led to suppose. The arteries have the important function
of supplying nutritive matter to all the tissues, of furnishing to the glands materials out
of which the secretions are formed, and, in short, are the vessels of supply to every part
of the organism. The supply of blood regulates, to a considerable extent, the processes of
nutrition and has an important bearing on the general and special functions ; and the
various physiological processes necessarily demand considerable modifications in the
quantity of arterial blood which is furnished to parts at different times. For example,
during secretion, the glands require several times as much blood as in the intervals of
their action. The force of the heart, we have seen, varies but little within the limits of
health ; and the conditions necessary to the proper distribution of blood in the economy
are regulated almost exclusively by the arterial system. These vessels are not inert
tubes, but are endowed with elasticity, by which the circulation is considerably facili-
tated, and with contractility, by which the supply to any part may be. modified, inde-
pendently of the action of the heart. Sudden flushes or pallor of the countenance are
examples of the facility with which this may be effected. It is evident, therefore, that
the properties of the coats of the arteries are of great physiological importance. We
shall then commence the study of this division of the circulatory system with a consid-
eration of its physiological anatomy.

Physiological Anatomy of the Arteries.

The vessels which carry the venous blood to the lungs are branches of a great trunk
which takes its origin from the right ventricle. They do not differ in structure from the
vessels which carry the blood to the general system, except in the fact that their coats
are somewhat thinner and more distensible. The aorta, branches and ramifications of
which supply all parts of the body, is given off from the left ventricle. Just at its ori-
gin, behind the semilunar valves, the aorta has three sacculated pouches, called the si-
nuses of Valsalva. Beyond this point the vessels are cylindrical. As we recede from
the heart, the arteries branch, divide, and subdivide, until they are reduced to micro-

PHYSIOLOGICAL ANATOMY OF THE ARTERIES. 65

scopic size. The branches, with the exception of the intercostal arteries, which make
nearly a right angle with the thoracic aorta, are given off at an acute angle. As a rule,
the arteries are nearly straight, taking the shortest course to the parts which they sup-
ply with hlood; and, while the branches progressively diminish in size, but few are
given off between the great trunk and the small vessels which empty into the capil-
lary system. Haller counted but twenty branches of the mesenteric artery between tho
aorta and the capillaries of the intestines. So long as a vessel gives off no branches, its
caliber does not progressively diminish ; as the common carotids, which are as large at
their bifurcation as they are at their origin. There are one or two instances in which
vessels, although giving off numerous branches in their course, do not diminish in size for
some distance ; as the aorta, which is as large at the point of division into the iliacs as
it is in the chest, and the vertebral arteries, which do not diminish in caliber until they
enter the foramen magnum. With these exceptions, as we recede from the heart, the
caliber of the vessels progressively diminishes. It has long been remarked that the
combined caliber of the branches of an arterial trunk is much greater than that of the
main vessel ; so that the arterial system, as it branches, increases in capacity.

The arrangement of the arteries is such that the requisite supply of blood is sent to
all parts of the economy by the shortest course and with the least expenditure of force
from the heart. Generally, the vessels are so situated as not to be exposed to pressure
and consequent interruption of the current of blood ; but, in certain situations, as about
some of the joints, there is necessarily some liability to occasional compression. In
certain situations, also, as in the vessels going to the brain, particularly in some of the in-
ferior animals, it is necessary to moderate the force of the blood-current, on account of
the delicate structure of the organs in which they are distributed. Here Nature makes
a provision in the shape of anastomoses, by which, on the one hand, compression of a
vessel simply diverts, and does not arrest the current of blood, and, on the other hand,
the current is rendered more equable and the force of the heart is moderated.

The arteries are provided with membranous sheaths, of greater or less strength, as
the vessels are situated in parts more or less exposed to disturbing influences or acci-
dents.

Researches into the minute anatomy of the arteries have shown that they are pos-
sessed of three pretty well marked coats. As these vary very considerably in arteries of
different sizes, it will be convenient, in their description, to divide the vessels into three
classes :

1. The largest arteries ; in which are included all that are larger than the carotids
and common iliacs.

2. The arteries of medium size ; that is, between the carotids and iliacs and the
smallest.

3. The smallest arteries ; or those less than TV or T^ of an inch in diameter.

The largest arteries are endowed with great strength and elasticity. Their external
coat is composed of white, or inelastic fibrous tissue, with a few longitudinal and oblique
fasciculi of involuntary muscular fibres. This coat is no thicker in the largest vessels
than in some of the vessels of medium size; and in some medium-sized vessels it is
actually thicker than in the aorta. This is the only coat which is vascular.

The middle coat, on which the thickness of the walls of the vessel depends, is com-
posed chiefly of the yellow elastic tissue. This tissue is disposed in numerous layers.
First we have a thin layer of ramifying elastic fibres, and then a number of layers of
elastic membrane, with numerous oval longitudinal openings, which has given it the
name of the " fenestrated membrane." Between the different layers of this membrane
are found a few unstriped or involuntary muscular fibres. These muscular fibres, how-
ever, are not numerous and have but little physiological importance. A small portion
of the aorta and pulmonary artery next the heart is entirely free from muscular fibres.
In the largest arteries, the fibres are arranged in fasciculi, with amorphous and fibrous
5

66

CIRCULATION" OF THE BLOOD.

connective tissue running in a circular, longitudinal, and oblique direction. The longi-
tudinal and oblique fibres exist chiefly in the outer coat. The middle coat of the largest
arteries gives them their yellowish hue and the elasticity for which they are so remark-
able.

The internal coat of the largest arteries does not differ materially from the lining
membrane of the rest of the arterial system. It is identical in structure with the endo-
cardium, the membrane lining the cavities of the heart, and is continued through the
entire vascular system. It is a thin, homogeneous, elastic membrane, covered with a
layer of elongated epithelial scales, with oval nuclei, their long diameter following the
direction of the vessel.

The arteries of medium size possess considerable strength, some elasticity, and very
great contractility. In the outer and inner coats we do not distinguish any great differ-
ence between these and the largest arteries, even in thickness. The essential difference

FIG. 20. — Small artery from the mesentery of the frog, showing epithelium and circular muscular fibres :
magnified 500 diameters. (From a photograph taken at the United States Army Medical Museum.)

in the anatomy of these vessels is found in the middle coat. Here we have a continua
tion of the elastic elements found in the largest vessels, but relatively diminished in
thickness and mingled with the fusiform, involuntary muscular fibres arranged, for the
most part, at right angles to the course of the vessel. These fibres are found chiefly in
the inner layers of the middle coat, and only in arteries smaller than the carotids and
primitive iliacs. In arteries of medium size, like the femoral, profunda femoris, radial,
or ulnar, they exist in several layers. There is no distinct division, as regards the middle
coat, between the largest arteries and those of medium size. As we recede from the
heart, muscular fibres gradually make their appearance between the elastic layers, pro-
gressively increasing in quantity, while the elastic elements are diminished.

ELASTICITY OF THE ARTERIES. 67

In the smallest arteries, the external coat is thin and disappears just before the ves-
sels empty into the capillary system ; so that the very smallest arterioles have only the
inner coat and a layer of muscular fibres. Although the greatest part of the muscular
fibres in the middle coat of the arteries are arranged at right angles to the course of the
vessels, nearly all of the arteries, in the human subject, are provided with longitudinal
and oblique muscular fasciculi, which are sometimes external, sometimes internal, and
sometimes on both sides of the circular layers.

The middle coat is composed of circular muscular fibres, without any admixture of
elastic elements. In vessels T|-^ of an inch in diameter, we have two or three layers of
fibres ; but, as we near the capillaries and as the vessels lose the external fibrous coat,
these fibres exist in a single layer.

The internal coat presents no essential difference from the coat in other vessels, with
the exception that the epithelium is less distinctly marked.

A tolerably-rich plexus of vessels is found in the external coats of the arteries.
These are called the vasa vasorum and come from the adjacent arterioles, having no di-
rect connection with the vessel on which they are distributed. A few vessels penetrate
the external layers of the middle coat, but none are ever found in the internal coat.

Nervous filaments, principally from the sympathetic system, accompany the arteries,
in all probability to their remotest ramifications. These are not distributed in the walls
of the large vessels, but rather follow them in their course, their filaments of distribu-
tion being found in those vessels in which the muscular element of the middle coat pre-
dominates. When we come to treat of the physiology of the organic system of nerves,
we shall see that the " vaso-motor " nerves play an important part in regulating the
function of nutrition. Lymphatics have not been found in the coats of any of the blood-
vessels.

Course of the Blood in the Arteries. — At every pulsation of the heart, all the blood
contained in the ventricles, excepting, perhaps, a few drops, is forced into the great vessels.
We have already studied the valvular arrangement by which the blood, once forced into
these vessels, is prevented from returning into the ventricles during the diastole. The
sketch we have given of the anatomy of the arteries has prepared us for a complexity
of phenomena in the circulation in these vessels, which would not obtain if they were
simple, inelastic tubes. In this case, the intermittent force of the heart would be felt
equally in all the vessels, and the arterial circulation would be subject to no modifications
which did not come from the action of the central organ. As it is, the blood is received
from the heart into vessels endowed, not only with great elasticity, but with contractility.
The elasticity, which is the prominent property of the largest arteries, moderates the
intermittency of the heart's action, providing a continuous supply to the parts; while
the contractility of the smallest arteries is capable of increasing or diminishing the supply
in any part, as may be required in the various functions.

Elasticity of the Arteries. — This property, which is particularly marked in large
vessels, has long been recognized. If, for example, we forcibly distend the aorta with
water, it may be dilated to more than double its ordinary capacity and will resunu its
original size and form as soon as the pressure is removed. This simple experiment teaches
us that, if the force of the heart be sufficient to distend the great vessels, their elasticity
during the intervals of its action must be continually forcing the blood toward the
periphery. The fact that the arteries are distended at each systole is abundantly proven
by actual experiment ; although the immense capacity of the arterial system, as compared
with the small charge of blood which enters at each pulsation, renders the actual dis-
tention of the vessels less than we should be led to expect from the force of the heart's
contraction. The most satisfactory experiments on this subject are those of Poiseuille.
This observer illustrated the dilatation of the arteries in the following way: Having

68 CIRCULATION OF THE BLOOD.

exposed a considerable extent of the primitive carotid in a horse, he enclosed a portion
in a tin tube filled with water and connected with a small upright graduated tube of glass.
The openings around the artery, as it passed in and out of the apparatus, being carefully
sealed with tallow, it is evident that any dilatation of the vessel would be indicated by
an elevation of the water in the graduated tube. This experiment invariably showed a
marked dilatation of the artery with each contraction of the heart.

It being fully established that the arteries are dilated with each ventricular systole, it
becomes important to study the influence of their elasticity upon the current of blood.
Division of an artery in a living animal exhibits one of the important phenomena due to
the elastic and yielding character of its walls. We observe, even in vessels of consider-
able size, as the carotid or femoral, that the flow of blood is not intermittent but remit-
tent. With each ventricular systole, there is a sudden and marked impulse ; but, during
the intervals of contraction, the blood continues to flow with considerable force. As we
recede from the heart, the impulse becomes less and less marked ; but it is not entirely
lost, even in the smallest vessels, the flow becoming constant only in the capillary system.
That the force of the heart is absolutely intermittent, is shown by the following experi-
ment : If the heart be exposed in a living animal, and a canula be introduced through the
walls into one of the ventricles, we have a powerful jet at each systole, but no blood is
discharged during the diastole. The same absolute intermittency of the current will be
seen if the aorta be divided. It is evident that we must look to the arteries themselves
for the force which produces a flow of blood during the intervals of the heart's action.
The conversion of the intermittent current in the largest vessels into a nearly-constant
flow in the smallest arterioles is effected by the physical property of elasticity. This may
be illustrated in any elastic tube of sufficient length. If we connect with a syringe a series
of rubber tubes progressively diminishing in caliber and discharging by a very small orifice,
and inject water in an intermittent current, if the apparatus be properly adjusted, the
fluid will be discharged at the end of the tube in a continuous stream. Nearer the
syringe, the stream will be remittent; and, directly at the point of connection of the
syringe with the tube, the stream will be intermittent. The intermittent impulse may be
said, in this case, to be progressively absorbed by the elastic walls of the tube. Each
impulse first distends that portion of the tube nearest to it, and farther on the distention
is diminished until it becomes inappreciable. If the syringe be connected with two
tubes, one elastic and the other inelastic, the current will be either remittent or contin-
uous in the one, and intermittent in the other. This modification of the impulse of the
heart has great physiological importance ; for it is evidently essential that the current of
blood, as it flows into the delicate capillary vessels, should not be alternately intermitted
and impelled with the full power of the ventricle. After all, it is in the capillaries that
the blood performs its functions ; and here we should have a constant supply of the fluid
in proper quantity and in proper condition to meet the nutritive and other requirements
of the parts.

The elasticity of the arteries favors the flow of blood toward the capillaries by a
mechanism which is easily understood. The blood discharged from the heart distends the
elastic vessel, which reacts, after the distending force ceases to operate, and compresses
its fluid contents. This reaction would have a tendency to force the blood in two direc-
tions, were it not for an instantaneous closure of the valves, which renders regurgitation
with the heart impossible. The influence, then, can only be exerted in the direction of the
periphery ; and, if we can imagine as divided an action which is propagated with such
rapidity, the reaction of that portion of the vessel immediately distended by the heart
distends a portion farther on, which, in its turn, distends another portion, and so the wave
passes along until the blood is discharged into the capillaries. In this way we can see
that, in vessels removed a sufficient distance form the heart, the force exerted on the
blood by the reaction of the elastic walls is competent to produce a very considerable
current during the intervals of the heart's action. This theoretical view is fully carried

CONTRACTILITY OF THE ARTERIES. 69

out by the following simple and conclusive experiment of Marey : He connected two
tubes of equal size, one of rubber and the other of glass, with the stop-cock of a large
vase filled with water. The elastic tube was provided with a valve near the stop-cock,
which prevented the reflux of fluid, and both were fitted with tips of equal caliber.
When, by alternately opening and closing the stop-cock, water was allowed to flow
into these tubes in an intermittent stream, it was found that a greater quantity was

FIG. 21. — Apparatus for showing the action of the elasticity of the arteries. (Marey.)
V, vessel of water; R, stop-cock ; T, double tube ; S, valve ; a, a, glass tube ; 6, 6, rubber tube.

discharged by the elastic tube; but an equal quantity was discharged by both tubes
when the stop-cock was left open and the fluid allowed to pass in a continuous stream.
This simple experiment shows that not only does the elasticity of the arteries convert the
intermittent current in the largest vessels into a current more and more nearly continuous
as we approach the periphery, but that when reflux is prevented, as it is by the semilunar
valves, the resiliency of the arteries assists the circulation.

Contractility of the Arteries. — It is a well-established anatomical fact that the
medium-sized and smallest arteries contain contractile elements; and it is also a fact,
proven by actual experiment, that, as a consequence of the condition of these fibres,
the vessels undergo considerable variation in their caliber. The opinions of the older
physiologists on this question have only an historical interest and will not, therefore,
be discussed. Among the more recent investigations on this subject, we have the experi-
ments of Cl. Bernard and of Schiff, which have been repeatedly confirmed, showing that,
through the nervous system, the muscular coats of arteries may be readily made to con-
tract or become relaxed. If the sympathetic be divided in the neck of a rabbit, in a very
few minutes the arteries of the ear on that side are notably dilated. If the divided ex-
tremity of the nerve be galvanized, the vessels soon take on contraction and may become
smaller than on the opposite side. These experiments demonstrate, in the most conclu-
sive manner, the contractile properties of the small arteries and give us an idea how the
supply of blood to any particular part may be regulated. The vessels may be most ef-
fectually excited through the nervous system ; and it is on account of the difficulty in
producing marked results by direct irritation, that the older physiologists were divided
on the subject of their " irritability."

The contractility of the "arteries has great physiological importance. As their func-
tion is simply to supply blood to the various tissues and organs, it is evident that, when
the vessels going to any particular part are dilated, the supply of blood is necessarily in-
creased. This is particularly well marked in the glands, which, during the intervals of
secretion, receive a comparatively small quantity of blood. Bernard has shown that gal-
vanization of what he calls the motor nerve of a gland dilates the vessels, largely increases

70 CIRCULATION OF THE BLOOD.

the supply of blood, and induces secretion ; while galvanization of the sympathetic fila-
ments contracts the vessels, diminishes the supply of blood, and arrests secretion. The
pallor of parts exposed to cold, and the flush produced by heat, are due, on the one hand,
to contraction, and on the other, to dilatation of the small arteries. Pallor and blushing
from mental emotions are examples of the same kind of action.

The ulterior effects on nutrition, which result from dilatation of the vessels of a part,
are of great interest. When the supply of blood is much increased, as in section of the
sympathetic in the neck, nutrition is exaggerated, and the temperature of the part is
raised beyond that of the rest of the body.

The idea, which at one time obtained, that the arteries were the seat of rhythmical
contractions which had a favorable influence on the current of blood is entirely erro-
neous.1 It is hardly necessary to repeat that the prime cause of the arterial circulation
is the force of the left ventricle. We have seen that the elasticity of the arteries pro-
duces a flow during the intervals of the heart's action, and the question now arises
whether the force thus exerted be simply a return of the force required to expand the
vessels, which has been borrowed, as it were, from the heart, or something superadded
to the force of the heart. The experiment of Marey, already alluded to, settles this ques-
tion. When water was forced in an intermittent current into two tubes, one elastic and
the other inelastic but discharging by openings of equal size, by far the greater quantity
was discharged by the elastic tube. A little reflection will show how the action of the
elastic arteries must actually assist the circulation. The resiliency of the vessel is con-
tinually pressing their contents toward the periphery, as regurgitation is rendered impos-
sible by the closure of the semilunar valves. The dilatation of the vessels with each sys-
tole of course admits an increased quantity of blood ; and it has been experimentally
demonstrated that the same intermittent force exerted on an inelastic tube will discharge
a less quantity of liquid from an opening of equal caliber.

Superadded, then, to the direct action of the heart, we must recognize, as a cause in-
fluencing the flow of blood in the arteries, the resiliency of the vessels, especially of these
of large size, this force being derived originally from the heart. Thus it will be seen th;.t
the arteries are constantly kept distended with blood by the heart ; and, by virtue of
their elasticity and the progressive increase in the capacity of this system as they
branch, the powerful contractions of the central organ only serve to keep up an
equable current in the capillaries. The small vessels, by virtue of their contractile
walls, regulate the distribution of the blood, acting as the guards or sentinels of
the process of nutrition, and, in fact, of all the numerous functions in which the blood
is concerned.

Locomotion of the Arteries and Production of the Pulse.— At each contraction of the
heart, the arteries are increased in length and many of them undergo a considerable loco-
motion. This may be readily observed in vessels which are tortuous in their course and
is frequently very marked in the temporal artery in old persons. The elongation may
also be seen if we watch attentively the point where an artery bifurcates, as at the divis-
ion of the common carotid. It is simply the mechanical eifect of sudden distention,
which, while it increases the caliber of the vessel, causes an elongation even more
marked.

The finger placed over an exposed artery or one which lies near the surface expe-
riences a sensation at every beat of the heart as though the vessel were striking against
it. This has long been observed and is called the pulse. Ordinarily it is appreciated
when the current of blood is subjected to a certain amount of obstruction, as in the radial,

1 Schiff has noticed rhythmical contractions in the superficial arteries of the ear in the rabbit and in some other ani-
mals; but this phenomenon is exceptional, and the movements do not appear to favor the current of blood. The
recent experiments of Dr. J. J. Mason, of New York, show conclusively, to our mind at least, that there is not a peri-
staltic action of the muscular coats of the small arteries, capable of assisting the circulation. This view, however, is
opposed to the ideas ol'Legros and Onimus and of some other physiologists.

FORM OF THE PULSE. 71

which can readily be compressed against the bone. In an artery imbedded in soft parts
which yield to pressure, the actual dilatation of the vessel being very slight, pulsation is
felt with difficulty, if at all. When obstruction of an artery is complete, as in ligation of
a vessel, the pulsation above the point of ligature is very marked and can be readily ap-
preciated by the eye. The explanation of this exaggeration of the movement is the fol-
lowing: Normally, the blood passes freely through the arteries and produces, in the
smaller vessels, very little movement or dilatation ; when, however, the current is ob-
structed, as by ligation or even compression with the finger, the force of the heart is not sent
through the vessel to the periphery but is arrested and therefore becomes more marked
and easily appreciated. In vessels which have become undilatable and incompressible
from calcareous deposits, the pulse cannot be felt. The character of the pulse indicates,
to a certain extent, the condition of the heart and vessels. We have spoken, when treat-
ing of the heart, of the varying rapidity of the pulse, as it is a record of the rapidity of
the action of this organ ; but it remains for us to consider the mechanism of its produc-
tion and its various characters.

Under ordinary circumstances, the pulse may be felt in all arteries which are ex-
posed to investigation ; and, as it is due to the movement of the blood in the vessels, the
prime cause of its production is the contraction of the left ventricle. The experiments
of Marey have shown that the impulse given to the blood by the heart is not felt in all
the vessels at the same instant. By ingenious contrivances, which will be described
farther on, this observer has succeeded in registering simultaneously the impulse of the
heart, the pulse of the aorta, and the pulse of the femoral artery. He has thus ascer-
tained that the contraction of the ventricle is anterior, in point of time, to the pulsation
of the aorta, and that the pulsation of the aorta precedes the pulse in the femoral. This
only confirms the views of other physiologists, particularly Wreber, who described this
progressive retardation of the pulse as we recede from the heart, estimating the difference
between the ventricular systole and the pulsation of the artery in the foot at one-seventh
of a second.

It is evident from what we know of the variations which occur in the force of the
heart's action, the quantity of blood in the vessels, and from the changes which may
take place in the caliber of the arteries, that the characters of the pulse must be subject
to numerous variations. Many of these may be appreciated simply by the sense of touch.
We find writers treating of the soft and compressible pulse, the hard pulse, the wiry
pulse, the thready pulse, etc., as indicating various conditions of the circulatory system.
The character of the pulse, aside from its frequency, has always been regarded as of great
importance in disease ; and the variations which occur in health form a most interesting
subject for physiological inquiry.

Form of the Pulse.— It is evident that few of the characters of a pulsation, occupying
as it does but one-seventieth part of a minute, can be ascertained by the sense of touch
alone. This fact has been appreciated by physiologists; and, within the last few years,
in order to accurately study this important subject, instruments for registering the pulse
have been constructed, to enable us to analyze the dilatation and movements of the
vessels. The idea of such an instrument was probably suggested by the following
simple observation : When the legs are crossed, with one knee over the other, the beating
of the popliteal artery will produce a marked movement in the foot. If we could apply
to an artery a lever provided with a marking point in contact with a slip of paper moving
at a definite rate, this point would register the movements of the vessel and its clumin-s
in caliber. The first physiologist who put this in practice was Vierordt, who constructed
quite a complex instrument, so arranged that the impulse from an accessible artery, like
the radial, was conveyed to a lever, which marked the movement upon a revolving
cylinder of paper. This instrument was called a " sphygmograph." The traces made by
it were perfectly regular and simply marked the extremes of dilatation, exaggerated, of

72 CIRCULATION OF THE BLOOD.

course, by the length of the lever, and the number of pulsations in a given time. The
latter can be easily estimated by more simple means; and, as the former did not convey
any very definite physiological idea, the apparatus was regarded rather as a curiosity
than an instrument for accurate research.

Fro. 22. — SphygmograpJi of Marey.

The apparatus is securely fixed on the forearm, so that the spring under the screw V is directly over the radial artery.
The movements of the pulse are transmitted to the long and light wooden lever L and registered upon the sur-
face P, which is moved at a known rate by the clock-work H. The apparatus is so adjusted that the movements
of the vessel are accurately amplified and registered by the extreme point of the lever.

FIG. 23 (&).—Sphygmograph of Marey applied to the arm.

FIG. 23 (B).— Trace of Vierordt.

FIG. 28 (C).— Trace of Marey.
Portions of four traces taken in different conditions of the pulse.

The principle on which the instrument of Vierordt was constructed was correct; and
it only remained to construct one which would be easy of application and produce a trace
representing the shades of dilatation and contraction of the vessels, in order to lead to
important practical results. These indispensable conditions are fully realized in the

FORM OF THE PULSE. 73

sphygmograph of Marey, to whose researches on the circulation we have repeatedly
referred. The instrument simply amplifies the changes in the caliber of the vessel ; and,
although its application is, perhaps, not so easy as to make it generally useful in practice,
in the hands of Marey it has given us a definite knowledge of the physiological character
of the pulse and its modifications in certain diseases, information which is exceedingly
desirable and which could not be arrived at by other means of investigation. In short,
its mechanism is so accurate that, when skilfully used, it gives on paper the actual
" form of the pulse." This instrument, applied to the radial artery, gives a trace very
different from that obtained by Vierordt, which was simply a series of regular eleva-
tions and depressions. A comparison of the traces obtained by these two observers
gives an idea of the defects which have been remedied by Marey ; for it is evident that
the dilatation and contraction of the arteries cannot be so regular and simple as would
be inferred merely from the trace made by the instrument of Vierordt.

Analyzing the traces of Marey, we see that there is a dilatation following the systole
of the heart, marked by an elevation of the lever, more or less sudden, as indicated by
the angle of the trace, and of greater or less amplitude. The dilatation, having arrived
at its maximum, is followed by reaction, which may be slow and regular, or may be, and
generally is, interrupted by a second and slighter upward movement of the lever. This
second impulse varies very much in amplitude. In some rare instances, it is nearly as
marked as the first and may be appreciated by the finger, giving the sensation of a double
pulse following each contraction of the heart. This is called the dicrotic pulse. As a
rule, the first dilatation of the vessel is sudden and is indicated by an almost vertical
line ; this is followed by a slow reaction, indicated by a gradual descent of the trace,
which is not, however, absolutely regular, but is marked by a slight elevation indicating
a second impulse. The amplitude of the trace, or the distance between the highest and
the lowest points marked by the lever, depends upon the amount of constant tension of
the vessels. Marey has found that the amplitude is in an inverse ratio to the tension ;
which is very easily understood, for, when the arteries are but little distended, the force
of the heart must be more marked in its effects than when the pressure of blood is very
great. Any circumstance which facilitates the flow of blood from the arteries into the
capillaries will, of course, relieve the tension of the arterial system, lessen the obstacle
to the force of the heart, and increase the amplitude of the pulsation, and vice versa.
In support of this view, Marey has found that cold applied to the surface of the body
contracting, as it does, the smallest arteries, increases the arterial tension and dimin-
ishes the amplitude of the pulsation, while a moderate elevation of temperature pro-
duces an opposite effect.

In nearly all the traces given by Marey, the descent of the lever indicates more or less
oscillation of the mass of blood. The physical properties of the larger arteries render
this inevitable. As they yield to the distending influence of the heart, reaction occurs
after this force is taken off and, if the distention be very great, gives a second impulse to
the blood. This is quite marked, unless the tension of the arterial system be so great as
to offer too much resistance. One of the most favorable conditions for the manifestation
of dicrotism is diminished tension, which is always found coexisting with a very marked
exhibition of this phenomenon.

The delicate instrument employed by Marey enabled him to accurately determine and
register these various phenomena, by observations on the arteries of the human subject
and the lower animals ; and, by means of an ingeniously constructed " schema," repre-
senting the arterial system by elastic tubes and the left ventricle by an elastic bag pro-
vided with valves and acting as a syringe, he satisfactorily established the conditions of
tension, etc., necessary to their production. In this schema, the registering apparatus,
simpler in construction than the sphygmograph, could be applied to the tubes with more
accuracy and ease. He demonstrated, by experiments with this system of tubes, that
the amplitude of the pulsations, the force of the central organ being the same, is greatest

74 CIRCULATION OF THE BLOOD.

when the tuhes are moderately distended, or when the tension of fluid is low, and vice versa.
He demonstrated, also, that a low tension favors dicrotism. In this latter observation,
he diminished the tension by enlarging the orifices by which the fluid was discharged
from the tubes, imitating the dilatation of the small vessels, by which the tension is di-
minished in the arterial system. He also demonstrated that an important and essential
element in the production of dicrotism is the tendency to oscillation of the fluid in the
vessels during the intervals between the contractions of the heart. This can only occur
in a fluid which has a certain weight and acquires a velocity from the impulse ; for,
when air was introduced into the apparatus, dicrotism could not be produced under any
circumstances, as the fluid did not possess weight enough to oscillate between the im-
pulses. Water produced a well-marked dicrotic impulse under favorable conditions;
and with mercury, the oscillations made two, three, or more distinct impulses. By
these experiments he proved that the blood oscillates in the vessels, if this movement
be not suppressed by too great pressure or tension. This oscillation gives the successive
rebounds that are marked in the descending line of the pulse, and is capable, in some
rare instances when the arterial tension is very slight, of producing a second rebound
of sufficient force to be appreciated by the finger.

Without treating of the variations in the character of the pulse in disease, due to the
action of the muscular coat, we shall consider some of the external modifying influences
which come within the range of physiology. The smallest vessels and those of medium
size possess to an eminent degree what is called tonicity, or the property of maintaining
a certain continued amount of contraction. This contraction is antagonistic to the dis-
tending force of the blood, as is shown by opening a portion of an artery included be-
tween two ligatures in a living animal, when the contents will be forcibly discharged and
the caliber of that portion of the vessel is very much diminished. Too great distention
of the vessels by the pressure of blood seems to be prevented by this constant action of
the muscular coat; and thus the conditions are maintained which give the pulse the
characters we have just described.

By excessive and continued heat, the muscular tissue of the arteries may be dilated
so as to offer less resistance to the distending force of the heart. Under these circum-
stances, the pulse, as felt by the finger, will be found to be larger and softer than normal.
Cold, either general or local, has an opposite effect ; the arteries become contracted, and
the pulse assumes a harder and more wiry character. Usually, prolonged contraction of
the arteries is followed by relaxation, as is seen in the full pulse and glow of the surface
which accompany reaction after exposure to cold.

It has been found, also, that there is a considerable difference in the caliber of the
arteries at different periods of the day. The diameter of the radial has been found very
much greater in the evening than in the morning, producing, naturally, a variation in the
character of the pulse. We learn from these physiological variations, how, in disease,
when they become more considerable, they may give important information with regard
to the condition of the system.

Pressure of Blood in the Arteries.

The reaction of the elastic walls of the arteries during the intervals of the heart's
action gives rise to a certain amount of constant pressure, by which the blood is con-
tinually forced toward the capillaries. The discharge of blood into the capillaries has a
constant tendency to diminish this pressure ; but the contractions of the left ventricle,
by forcing repeated charges of blood into the arteries, have a compensating action. By
the equilibrium between these two agencies, a certain degree of tension is maintained in
the arteries, which is called the arterial pressure.

The first experiments with regard to the extent of the arterial pressure were made
by Hales, an English physiologist, more than a hundred years ago. This observer,
adapting a long glass tube to the artery of a living animal, ascertained the height of the

PRESSURE OF BLOOD IN THE ARTERIES.

75

column of blood which could be sustained by the arterial pressure. In some experiments
on the carotid of the horse, the blood mounted to the height of from eight to ten feet.

All experiments on the arterial pressure are made
on' the principle of the experiment of Hales, which,
with reference simply to the constant pressure in the
arteries, is as useful as those of later date and much
more striking. The only inconvenience is in the ma-
nipulation of the long tube ; but this may be avoided
by setting it in a strip of wood, when it can be easily
handled. If a large artery, as the carotid, be exposed
in a living animal, and a metallic point, connected
with a vertical tube of small caliber and from seven
to eight feet long by a bit of elastic tubing, be secured
in the vessel, the blood will rise to the height of about
six feet and remain at this point almost stationary,
indicating, by a slight pulsatile movement, the action
of the heart. On carefully watching the level in the
tube, in addition to the rapid oscillation coincident
with the pulse, another oscillation will be observed,
which is less frequent and which corresponds with
the movements of respiration. The pressure, as indi-
cated by an elevation of the fluid, is slightly increased
during expiration and diminished during inspiration.1

The experiment with the long tube gives us the
best general idea of the arterial pressure, which will
be found to vary between five and a half and six feet
of blood, or a few inches more of water. The oscil-
lations produced by the contractions of the heart are
not very marked, on account of the great friction in
so long a tube ; but this is favorable to the study of
the constant pressure. It has been found that the
estimates above given do not vary very much in ani-
mals of different sizes. Bernard found the pressure in the carotid of a horse but little
more than in the dog or rabbit. In the larger animals, it is the force of the heart which
is increased, and not, to any considerable extent, the constant pressure in the vessels.

The experiments of Hales were made with a view of calculating the force of the
heart and were not directed particularly to the conditions and variations of the arterial
pressure. It is only since the experiments performed by Poiseuille with the hfflinadyna-
mometer, in 1828, that we have any reliable data on this latter point. Poiseuille's
instrument for measuring the force of the blood is a simple graduated U-tube, half filled
with mercury, with one arm bent at a right angle, so that it can easily be connected with
the artery. The pressure of the blood is indicated by a depression in the level of the
mercury on one side and a corresponding elevation on the other. This instrument 19
generally considered as possessing great advantages over the long glass tube; but, for
estimating simply the arterial pressure, it is much less useful, as it is more sensitive to
the impulse of the heart. For the study of the cardiac pressure, it has the disadvantage,
in the first place, of considerable friction, and, again, the weight of the column of
mercury produces an extent of oscillation By its mere impetus, greater than that which
would actually represent the force of the heart.

An important improvement in the hcemadynamometer was made by Magendie. This
apparatus, the cardiometer, in which Bernard has made some important modifications, is

i In all these experiments on the arterial or cardiac pressure, it is necessary to fill part of the tube, or whatever
apparatus we may use, with a solution of carbonate of soda, in order to prevent coagulation of the blood as it passes
out of the vessels.

FIG. <i±.—na>madynamometer qfPoiseuille,
modified by Ludwig, Spengler, and
Valentin.

The instrument is connected with the ves-
sel V V, in such a manner that the
circulation is not interrupted. The ele-
vation of the mercury in the branch B C
indicates the amount of pressure.

76

CIRCULATION' OF THE BLOOD.

the one now generally used. It consists of a small but thick glass bottle, with a fine,
graduated glass tube about twelve inches in length, communicating with it, either through
the stopper or by an orifice in the side. The stopper is pierced by a bent tube which is
to be connected with the blood-vessel. The bottle is filled with mercury so that it will
rise in the tube to a point which is marked zero. It is evident that the amount of press-
ure on the mercury in the bottle will be indicated by an elevation in the graduated tube ;
and, moreover, from the fineness of the column in the tube, we avoid some of the in-
conveniences which are due to the weight of mercury in the hsemadynamometer, and we
also have less friction. This instrument is appropriately called the cardiometer, as it in-
dicates most accurately, by the extreme elevation of the mercury, the force of the heart;

FIG. 25 (A).— Section of the cardiometer of MagendU,
as modified by Bernard.

A strong glass- bottle is perforated at each side and fitted
with an iron tube, with an opening, T, by which the
mercury enters. One end of the iron tube is closed,
and the other is bent upward and connected with
the graduated glass tube T'. which has a caliber of
from TJ5 to f of an inch. The bottle is filled with
mercury until it rises to n' in the tube which is
marked zero. The cork is perforated by the tube <,
which is connected by a rubber tube with the point
C, which is introduced into the vessel.

FIG. 25 (B).— Compensating instrument of Marey.

but it is not as perfect in its indications of the mean arterial pressure, for, in the abrupt
descent of the mercury during the diastole of the heart, the impetus causes the level to
fall considerably below the real standard of the constant pressure. Marey has succeeded
in correcting this difficulty in what he calls the "compensating" instrument, which is
constructed on \ he following principle : Instead of a simple glass tube which communi-
cates with the mercury in the bottle, as in Magendie's cardiometer, he has two tubes,
one of which is like the one already described and represents oscillations produced by
the heart, while the other is larger, and has, at the lower part, a constriction of the

INFLUENCE OF RESPIRATION. 77

caliber, which is here reduced to capillary fineness. The latter tube is designed to give the
mean arterial pressure ; the constricted portion offering such an obstacle to the rise of
the mercury that the intermittent action of the heart is not felt, the mercury rising slowly
to a certain level, which is constant and varies only with the constant pressure in the
vessels.

We have only an approximative idea of the average pressure in the arterial system in
the human subject, deduced from experiments on animals. It has already been stated to
be equal to about six feet of water or six inches of mercury.

The most interesting questions connected with the subject of the arterial press-
ure are the comparative pressure in different parts of the arterial system, the conditions
which modify the arterial pressure, and its influence on the pulse. These points have all
been pretty fully investigated by experiments on animals and observations on systems of
elastic tubes arranged to represent the blood-vessels.

Pressure in Different Parts of the Arterial System.— The experiments of Hales, Poi-
seuille, Bernard, and others, seem to show that the constant arterial pressure does not
vary in arteries of different sizes. These physiologists have experimented particularly
on the carotid and crural, and have found the pressure in these two vessels about the
same. From their experiments they conclude that the force is equal in all parts of the
arterial system. Th« experiments of Volkmann, however, have shown that this conclu-
sion has been too hasty. With the registering apparatus of Ludwig, he has taken the
pressure in the carotid and the metatarsal arteries and has always found a considerable
difference in favor of the former. In an experiment on a dog, he found the pressure equal
to one hundred and seventy-two millimeters in the carotid, and one hundred and sixty-
five in the metatarsal. In an experiment on a calf, the pressure was one hundred and
sixteen mm. in the carotid, and eighty-nine mm. in the metatarsal; and in a rabbit,
ninety-one mm. in the carotid, and eighty-six mm. in the crural. These experiments show
that the pressure is not absolutely the same in all parts of the arterial system, that it is
greatest in the arteries nearest the heart, and that it gradually diminishes as we near the
capillaries. The difference is very slight, almost inappreciable, until we come to vessels of
very small size ; but here the pressure is directly influenced by the discharge of blood into
the capillaries. The cause of this diminution of pressure in the smallest vessels is the prox-
imity of the great outlet of the arteries, the capillary system ; for, as we shall see farther
on, the flow into the capillaries has a constant tendency to diminish the pressure in the
arteries. It is obvious that this influence can only be felt in a very marked degree in the
vessels of smallest size.

Influence of Respiration. — It is easy to see, in studying the arterial pressure with any
of the instruments we have described, that there is a marked increase with expiration
and a diminution with inspiration. The fact that expiration will increase the force of the
jet of blood from a divided artery has long been observed and accords perfectly with the
above statement. In tranquil respiration, the influence upon the flow of blood is due
simply to the mechanical action of the thorax. With every inspiration, the air-cells are
enlarged, as well as the blood-vessels of the lungs, the air rushes in through the trachea,
and the movement of the blood in the veins near the chest is accelerated. At the same
time, the blood in the arteries is somewhat retarded in its flow from the thorax, or at least
does not feel the expulsive influence which follows with the act of expiration. The arterial
pressure at that time is at its minimum. With the expiratory act, the air is expelled by
compression of the lungs, the flow of blood into the thorax by the veins is retarded to a
certain extent, while the flow of blood into the arteries is favored. This is strikingly
exhibited in the augmented force, with expiration, in the jet from a divided artery.
Under these circumstances the arterial pressure is at its maximum. In perfectly tranquil
respiration, the changes due to inspiration and expiration are slight, presenting a differ-

78 CIRCULATION OF THE BLOOk.

ence of not more than half an inch to an inch in the cardiometer. When the respiratory
movements are exaggerated, the oscillations are very much more marked.

Interruption of respiration is followed by a very great increase in the arterial press-
ure. This is due, not to causes within the chest, but to obstruction to the circulation in
the capillaries. We are already aware of the influence which the flow of blood into the
capillaries is constantly exerting upon the arterial pressure. This tendency to diminish
the quantity of blood in the arteries, and consequently the pressure, is constantly coun-
teracted by the blood sent into the arteries by the contractions of the heart. With an in-
terruption of the respiratory function, the non-aerated blood passes into the arteries but
cannot flow readily through the capillaries ; and, as a consequence, the arteries are abnor-
mally distended and the pressure is greatly increased. If respiration be permanently
arrested, the arterial pressure becomes, after a time, diminished below the normal
standard, and is finally abolished, on account of the stoppage of the action of the heart.
If respiration be resumed before the heart has become arrested, the pressure soon returns
to its normal condition.

Muscular effort considerably increases the arterial pressure. This is due to two causes.
In the first place, the chest is generally compressed, favoring the flow of blood into the
great vessels. In the second place, muscular exertion produces a certain amount of ob-
struction to the discharge of blood from the arteries into the capillaries. Numerous
experiments upon animals have shown a great increase in pressure in the struggles which
occur during severe operations. It has been shown that galvanization of the sympa-
thetic in the neck and irritation of certain of the cerebro-spinal nerves increase the arterial
pressure, probably from an influence on the muscular coats of some of the arteries, caus-
ing them to contract and thereby diminishing the total capacity of the arterial system.

Effects of ffcemorrhage. — Diminution in the quantity of blood has a remarkable ef-
fect upon the arterial pressure. If, in connecting the instrument with the arteries, we
allow even one or two jets of blood to escape, the pressure will be found diminished per-
haps one-half, or even more. It is hardly necessary to discuss the mechanism of the effect
of the loss of blood on the tension of the vessels, but it is wonderful how soon the press-
ure in the arteries regains its normal standard after it has been lowered by haemorrhage.
As the pressure depends largely upon the quantity of blood, as soon as the vessels absorb
the serosities in sufficient quantity to repair the loss, the pressure is increased. This
takes place in a very short time, if the loss of blood be not too great.

Experiments on the arterial pressure with the cardiometer have verified the fact
stated in treating of the form of the pulse ; namely, that the pressure in the vessels bears
an inverse ratio to the distention produced by the contractions of the heart. In the car-
diometer, the mean height of the mercury indicates the constant, or arterial pressure ;
and the oscillations, the distention produced by the heart. It is found that when the
pressure is great, the extent of oscillation is small, and vice versa. It will be remembered
that the researches of Marey demonstrated that an increase of the arterial pressure
diminishes the amplitude of the pulsations, as indicated by the sphygmograph, and that
the amplitude is very great when the pressure is slight. It is also true, as a general rule,
that the force of the heart, as indicated by the cardiometer, bears an inverse ratio to the
frequency of its pulsations.

Depressor Nerve of the Circulation— Within the last few years, an important discovery
has been made by Cyon and Ludwig, of a nerve arising in the rabbit by two roots, one
from the main trunk of the pneumogastric and the other from the superior laryngeal
nerve, which joins the sympathetic filaments in the chest and passes to the heart. This
nerve has a reflex action, as was shown by the experiments of Cyon, its galvanization
reducing the arterial pressure by one-third or one-half. This action is known to be
reflex, for, when the nerve is divided, galvanization of the central end affects the arterial

RAPIDITY OF THE CURRENT OF BLOOD IN THE ARTERIES. 79

pressure, while no such result follows stimulation of the peripheral extremity ; and the
effect is manifested when the pneumogastrics have been divided and no direct nervous
influence is exerted over the heart. It is thought that the reduction in the arterial press-
ure following galvanization of the so-called depressor nerves is mainly due to the action
of the splanchnic nerves, by which the abdominal vessels become largely dilated. If the
abdomen be opened and one or more of the splanchnic nerves be divided, the arterial
pressure is immediately diminished, and the pressure is restored if the divided ends of
the nerves be galvanized. If, after division of the splanchnic nerves and the conse-
quent diminution of the arterial pressure, the depressor nerves be galvanized, the press-
ure still undergoes some additional diminution, but this is much less than the diminution
which follows galvanization of the depressor nerves without section of the splanchnic.
The action of these nerves will be more fully considered in connection witli the physiology
of the nervous system.

Rapidity of the Current of Blood in the Arteries. — The question of the rapidity of
the arterial circulation has long engaged the attention of physiologists; but the experi-
ments of Volkrnann, with his hasmadrometer, and of Yierordt, with a peculiar instru-
ment which he devised for the purpose, did not lead to results that were entirely
satisfactory.

The best instrument for measuring the rapidity of the circulation in the arteries was
devised by Chauveau, of the Veterinary School at Lyons. This will give, by calculation,
the actual rapidity of the circulation ; and, what is more interesting, it marks accurately
the rapid variations in velocity which occur at different periods of the heart's action.

The instrument to be applied to the carotid of the horse consists of a thin brass tube,
about an inch and a half in length and of the diameter of the artery (about three-eighths
of an inch), which is provided with an
oblong, longitudinal opening, or window,
near the middle, about two lines long and
one line wide. A piece of thin vulcan-
ized rubber is wound around the tube
and firmly tied so as to cover this open-
ing. Through a transverse slit in the
rubber, is introduced a very light metallic
needle, an inch and a half in length and
flattened at its lower part. This is made
to project about half-way into the caliber
of the tube. A flat, semicircular piece
of metal, divided into an arbitrary scale,
is attached to the tube, to indicate the
deviations of the point of the needle.

The apparatus is introduced carefully
into the carotid of a horse, by making a
slit in the vessel, introducing first one
end of the tube directed toward the

FIG. 26.— Chauveau" s instrument for measuring the ra-
pidity of thefloiv of blood in the artertes.
The instrument viewed in face— a, the tube to be fixed
in the vessel; 6, the dial which marks the extent ol
movement of the needle d ; e, a lateral tube for the at-
tachment of a cardiometer, if desired.

heart, then allowing a little blood to
enter the instrument, so as to expel the
air, and, when full, introducing the other
end, securing the whole by ligatures above
and below.

When the circulation is arrested, the needle should be vertical, or mark zero on the
scale. When the flow is established, a deviation of the needle occurs, which varies in
extent with the rapidity of the current. Having removed all pressure from the vessel f
as to allow the current to resume its normal character, the deviations of the needle are
carefully noted, as they occur with the systole of the heart, with the diastole, etc. After

80 CIRCULATION OF THE BLOOD.

withdrawing the instrument, it is applied to a tube of the size of the artery, in which a
current of water is made to pass with a rapidity which will produce the same devia-
tions as occurred when the instrument was connected with the blood-vessel. The ra-
pidity of the current in this tube may be easily calculated by receiving the fluid in a
graduated vessel and noting the time occupied in discharging a given quantity. By this
means we ascertain the rapidity of the current of blood. This instrument is on the same
principle as the one constructed by Vierordt, but in sensitiveness and accuracy it is much
superior. In the hands of Chauveau, the results, particularly those with regard to varia-
tions in the rapidity of the current, are very interesting.

Rapidity of the Current in the Carotid. — It has been found that three currents, with
different degrees of rapidity, may be distinguished in the carotid :

1. At each ventricular systole, we have, as the average of the experiments of Chau-
veau, the blood moving in the carotids at the rate of 20T% inches per second. After this,
the rapidity quickly diminishes, the needle returning quite or nearly to zero, which would
indicate complete arrest.

2. Immediately succeeding the ventricular systole, we have a second impulse given to
the blood, which is synchronous with the closure of the semilunar valves, the blood mov-
ing at the rate of 8T6¥ inches per second. Chauveau calls this the dicrotic impulse.

3. After the dicrotic impulse, the rapidity of the current gradually diminishes, until
just before the systole of the heart, when the needle is nearly at zero. The average rate,
after the dicrotic impulse, is 5^ inches per second.

The above experiments give us, for the first time, correct notions of the rapidity and
variations in the flow of blood in the larger vessels ; and it is seen that they correspond
in a remarkable degree with the experiments of Marey on the form of the pulse. Marey
showed that there is a marked oscillation of the blood in the vessels, due to a reaction
of their elastic walls, following the first violent distention by the heart ; that, at the time
of closure of the semilunar valves, the arteries experience a second, or dicrotic distention,
much less than the first ; and, following this, there is a gradual decline in the distention
until the minimum is reached. Chauveau shows by experiments with his instrument
that, corresponding to the first dilatation of the vessels, the blood moves with great
rapidity ; following this, the current suddenly becomes nearly arrested ; this is followed by a
second acceleration in the current, less than the first ; and, following this, we have a
gradual decline in the rapidity up to the time of the next pulsation.

Rapidity in Different Parts of the Arterial System. — From the fact that the arterial
system increases in capacity as we recede from the heart, we should expect to find a cor-
responding diminution in the rapidity of the flow of blood. There are, however, many
circumstances, aside from simple increase in the capacity of the vessels, which modify
the blood-current and render inexact any calculations made upon purely physical principles.
Such are the tension of the blood, the conditions of contraction or relaxation of the
smallest arteries, etc. It is necessary, therefore, to have recourse to actual experiments
to arrive at any definite results on this point. The experiments of Volkmann showed a
great difference in the rapidity of the current in the carotid and metatarsal arteries, the
averages being 10 inches per second in the carotid and 2*2 inches in the metatarsal. The
same difference, although not quite so marked, was found by Chauveau between the carot-
id and the facial. The last-named observer also noted an important modification in the
character of the current in the smaller vessels. As we recede from the heart, the sys-
tolic impulse becomes rapidly diminished, being reduced in one experiment about two-
thirds ; the dicrotic impulse becomes feeble or may even be abolished ; but the constant
flow is very much increased in rapidity. This fact coincides with the ideas already
advanced with regard to the gradual conversion, by virtue of the elasticity of the vessels,
of the impulse of the heart into, first, a remittent, and, in the very smallest arteries, a
nearly constant current.

The rapidity of the flow in any artery must be subject to constant modifications due

CIRCULATION OF THE BLOOD IN THE CAPILLARIES. 81

to the condition of the arterioles which are supplied by it. When these little vessels are
dilated, the artery of course empties itself with greater facility, and the rapidity is in-
creased. Thus the rapidity bears a relation to the arterial pressure ; as, independently of
a diminution in the entire quantity of the circulating fluid, variations in the pressure
depend chiefly on causes which facilitate or retard the flow of blood into the capillaries.
A good example of enlargement of the capillaries of a particular part is in mastication,
when the salivary glands are brought into activity and the quantity of blood which they
receive is greatly increased. Chauveau found an immense increase in the rapidity of the
flow in the carotid of a horse during mastication. The enlargement of the vessels
of the glands during their function has been conclusively proven by the experiments of
Bernard. It must be remembered that, in all parts of the arterial system, the rapidity
of the current of blood is constantly liable to increase from dilatation of the small ves-
sels and to diminution from their contraction.

Circulation of the Blood in the Capillaries.

Before entering upon the study of the capillary circulation, we should define what we
mean by the capillary vessels as distinguished from the smallest arteries and veins. From
a strictly physiological point of view, the capillaries are to be regarded as commencing

FIG. 27.— Capillary blood-vessels from the pecten of the eye of the bird. (Eberth.)

a, small capillaries, with fusiform cells; &, capillaries with polygonal cells; ft', hyaloid membrane investing the capil-
laries; c, capillaries from the intestine of the snail.

6

82 CIRCULATION OF THE BLOOD.

at the point where the blood is brought near enough to the tissues to enable them to sep-
arate the elements necessary for their regeneration and to give up the products of their
physiological decay. With our present knowledge, it is impossible to assign any limit
where the vessels cease to be simple carriers of blood ; and it does not seem probable that
it will ever be known to what part of the vascular system the processes of nutrition are
exclusively confined. The divisions of the blood-vessels must be, to a certain extent,
arbitrarily defined; and we should feel at liberty to adopt the views of any reliable ob-
server with regard to the kind of vessels which are to be considered as capillaries. The
most simple, and what seems to be the most physiological view, is to regard as capillaries
those vessels which have but a single tunic; for, in these, the blood is brought in closest
proximity to the tissues. Vessels which are provided, in addition, with a muscular or
with muscular and fibrous coats are to be regarded either as small arteries or as venous
radicles. This view is favored by the character of the currents of blood as seen in
microscopical observation of the circulation in transparent parts. Here an impulse is
observed with each contraction of the heart, until we come to vessels which have but
one coat and are so narrow as to allow the passage of but a single line of blood-
corpuscles.

Physiological Anatomy of the Capillaries. — If the arteries be followed out to their
minutest ramifications, they will be found progressively diminishing in size as they branch,
and their coats, especially the muscular, becoming thinner and thinner, until at last they
present an internal structureless coat, lined by epithelium with oval, longitudinal nuclei,
a middle coat, formed of but a single layer of circular muscular fibres, and an external
coat, composed of a very thin layer of longitudinal fibres of the white inelastic tissue.
These vessels are from ^i^ to -^ of an inch in diameter. They become smaller as they
branch, and undoubtedly possess the property of contractility, which is particularly
marked in the arterial system. Following the course of the vessels, when they are re-
duced in size to about -g-i^ of an inch, the external fibrous coat is lost, and the vessel then
presents only the internal coat and a single layer of muscular fibres. These become smaller
as they branch, finally lose the muscular coat, and have then but a single tunic. These
last we shall consider as the true capillary vessels.

The minute structure of the capillary vessels is of considerable importance and
interest and has been very closely investigated within the last few years. It was for-
merly thought that the smallest vessels, which we describe as the true capillaries, were
composed of a single, homogeneous membrane, from -^^-^ to ^-jVfr of an inch thick, with
nuclei embedded in its substance, but not provided with an epithelial lining. Recent
observations, however, have shown that the membrane is homogeneous, elastic, perhaps
contractile, and, in some parts at least, is provided with fusiform or polygonal epithelium
of excessive tenuity. The borders of the epithelial cells may be seen by staining the ves-
sels with nitrate of silver. In the smallest capillaries, the cells are narrow and elongated
or fusiform ; and in the larger vessels, they are more polygonal, with very irregular borders.
The nuclei which have been observed in the walls of the vessels belong to this layer of
epithelium. By the same process of staining with nitrate of silver, we frequently observe
irregular, non-nucleated areas ; and it has been supposed by some that these indicate the
presence of stomata, or orifices in the walls of the vessels. This latter point, however,
has not been definitely determined. It cannot at present be stated positively whether or
not orifices normally exist in the walls of the blood-vessels. Most of the anatomical
points we have just mentioned have been developed by observations upon the vessels of
the frog.

The diameter of the capillaries is generally as small as, or it may be smaller than
that of the blood-corpuscles ; so that these bodies always move in a single line and
must become deformed in passing through the smallest vessels, recovering their natural
shape, however, when they pass into vessels of larger size. The capillaries are smallest

PHYSIOLOGICAL ANATOMY OF THE CAPILLARIES.

83

in the nervous and muscular tissue, retina, and patches of Peyer, where they have a di-
ameter of from ^Vo to Woo- of an incii- In the mucous layer of the skin and in the
mucous membranes, they are from 3-^- to ^y1^ of an inch in diameter. They are
largest in the glands and bones, where they are from ^W to ^Vfr of an inch in diam-
eter. These measurements indicate the size of the vessels and not their caliber. Tak-
ing out the thickness of their walls, it is only the very largest of them that will admit of
the passage of a blood-disk without a change in its form.

FIG. 28. — Small artery and capillaries from the muscular coals of the urinary "bladder of the frog; magnified

400 diameters. (From a photograph taken at the United States Army Medical Museum.)

This preparation shows the epithelium of the vessels. It is injected with nitrate of silver, stained with carmine, and

mounted in Canada balsam.

Unlike the arteries, which grow smaller as they branch, and the veins, which be-
come larger, as we follow the course of the blood, by union with each other, the capil-
laries form a true plexus of vessels of nearly uniform diameter, branching and inosculat-
ing in every direction and distributing blood to the parts as their physiological necessi-
ties demand. This mode of inosculation is peculiar to these vessels, and the plexus is rich
in the tissues, as a general rule, in proportion to the activity of their nutrition. Al-
though their arrangement presents certain differences in different organs, the capillary
vessels have everywhere the same general characteristics, the most prominent of which
are uniform diameter and absence of any positive direction. The net-work thus formed is
very rich in the substance of the glands and in the organs of absorption ; but the vessels
are only distended with blood during the physiological activity of these parts. In the
lungs, the meshes are particularly close. In other parts, the vessels are not so abundant,
presenting great variations in different tissues. In the muscles and nerves, in which nu-
trition 13 very active, the supply is much more abundant than in other parts, like fibro-

84 CIRCULATION OF THE BLOOD.

serous membranes, tendons, etc. In none of the tissues do we find capillaries penetrat-
ing the anatomical elements, as the ultimate muscular or nervous fibres. Some tissues
receive no blood, at least they contain no vessels which are capable of carrying red
blood, and are nourished by imbibition of the nutrient plasma of the circulating fluid.
Examples of these, which are called extra-vascular tissues, are cartilage, nails, and
hair.

The foregoing anatomical sketch gives an idea of how near the blood is brought to
the tissues in the capillary system, and how, once conveyed there by the arteries, and the
supply regulated by the action of the muscular coat of the smaller vessels, the blood is
distributed for the purposes of nutrition, secretion, absorption, exhalation, or whatever
function the part has to perform. This will be still more apparent when we come to
consider the course of the blood in the capillaries and the immense capacity of this sys-
tem, as compared with the arteries or veins.

The capacity of the capillary system is immense. It is only necessary to consider
the great vascularity of the skin, mucous membranes, or muscles, to realize this fact.
In injections of these parts, it seems, on microscopical examination, as though they con-
tained nothing but capillaries. In preparations of this kind, the elastic and yielding
coats of the capillaries are distended to their utmost limit. Under some circumstances,
in health, they are largely distended with blood, as the mucous lining of the alimentary
canal during digestion, the whole surface presenting a vivid-red color, indicating the
great richness of the capillary plexus. Various estimates of the capacity of the capil-
lary, as compared with the arterial system, have been made, but they are simply approxi-
mative, and there seems to be no means by which an estimate, with any pretensions to
accuracy, can be formed. The various estimates which are given are founded upon cal-
culations from microscopical examinations of the rapidity of the capillary circulation as
compared with the circulation in the arteries. In this way, it has been estimated that
the entire capacity of the capillary system is from five hundred to eight hundred times
that of the arterial system. It must be evident to any one who has witnessed the capil-
lary circulation under the microscope, that the conditions under which the animal under
examination is placed are liable to interfere with the current of blood ; and the periodi-
cal congestion of certain parts, the fugitive flushes of the skin, the condition of the
smallest arteries induced by changes of temperature, exercise, etc., make it evident that
the current of blood is liable to great variations. It is impossible to strictly apply to
the capillary circulation in the various parts of the human subject observations on the
wing of a bat or the mesentery of a cat. We must consider, then, these estimates as
mere suppositions, and they are given for what they are worth.

Phenomena of the Capillary Circulation. — The most convenient situation for the
practical study of the capillary circulation is the tongue or the web of the frog. Here
may be studied, not only the movement of the blood in the true capillaries, but the cir-
culation in the smallest arteries and veins, the variations in caliber of these vessels,
especially the arterioles, by the action of their muscular tunic, and, indeed, the action
of vessels of considerable size. This has been a most valuable means of studying the
circulation in the capillaries as contrasted with the flow in the small arteries and veins, and
the only one, indeed, which could give us any definite idea of the action of these vessels.

The magnificent spectacle of the capillary circulation was first observed by Malpighi,
in the lungs, and afterward by Leeuwenhoek, Spallanzani, Ilaller, Cowper, and others,
in other parts. We see the great arterial rivers, in which the blood flows with wonder-
ful rapidity, branching and subdividing, until the circulating fluid is brought to the net-
work of fine capillaries, where the corpuscles dart along one by one. The blood is then
collected by the veins and carried in great currents to the heart. This exhibition, to
the student of Nature, is of inexpressible grandeur ; and our admiration is not dimin-
ished when we come to study the phenomena in detail. We find here a subject as inter-

PHENOMENA OF THE CAPILLARY CIRCULATION.

85

esting as was the action of the heart when first seen by Harvey, involving some of the
most important phenomena of the circulation. It can be seen how the arterioles regu-
late the supply of blood to the tissues ; how the blood distributes itself by the capilla-
ries; and, finally, having performed its office, how it is collected and carried off by the

veins.1

FIG. 29.— Web of the frog's hind foot; magnified. ("Wagner.)
«, a, veins ; &, 6, &, arteries.

In studying the circulation under the microscope, the anatomical division of the
blood into corpuscles and a clear plasma is observed. This is peculiarly evident in cold-
blooded animals, the corpuscles being comparatively large and floating in a plasma
which forms a distinct layer next the walls of the vessel. The leucocytes, which are
much fewer than the red corpuscles, are generally found in the layer of plasma.

FIG. 30.— Circulation in the u-eb of the frog's foot. (Wagner.)

The black spots, some of them star-shaped, are pigmentary matter, a, a venous trunk, composed of three principal
branches (6, 6, 6), and covered with a plexus of smaller vessels (c, c).

1 Various methods of preparing the animal for examination have been employed. The one we have found most
convenient, in examining the circulation in the frog, is to break up the medulla with a needle, an operation which

86

CIRCULATION OF THE BLOOD.

In vessels of considerable size, as well as in some capillaries, the corpuscles, occupy-
ing the central portion, move with much greater rapidity than the rest of the blood,
leaving a layer of clear plasma at the sides, which is nearly motionless. This curious
phenomenon is in obedience to a physical law regulating the passage of liquids through
capillary tubes for which they have an attraction, such as exists, for example, between
the blood and the vessels. In tubes reduced to a diameter approximating that of the
capillaries, the attractive force exerted by their walls upon a liquid, causing it to enter
the tube to a certain distance, called capillary attraction, becomes an obstacle to the pas-
sage of fluid in obedience to pressure. Of course, as the diameter of the tube is re-

FIG. 31. — Small artery and capillaries from tJie lung of a frog ; magnified 500 diameters. (From a photograph
taken at' the United States Army Medical Museum.)

duced, this force becomes relatively increased, for a larger proportion of the liquid con-
tents is brought in contact with it. When we come to the smallest arteries and veins,
and still more the capillaries, the capillary attraction is sufficient to produce the mo-
tionless layer, called the " still layer " by many physiologists, and the liquid moves only
in the central portion. The plasma occupies the position next the walls of the vessels,
for it is this portion of the blood which is capable of " wetting " the tubes. The trans-
does not interfere with the circulation, and to attach the animal by pins to a thin piece of cork, stretching the web over
an orifice in the cork, to allow the passage of light, and securing it with pins through the toes. The membrane is
then moistened with water and covered with thin glass, and, if the general surface be kept moist, the circulation may
be studied for hours. By gently inflating the lungs with a small blow-pipe, securing the air by a ligature passed
around the larynx beneath the mucous membrane, and opening the chest, the pulmonary circulation may be studied.
The circulation may be examined in the tongue (which presents a magnificent view of the circulation as well as of the
nerves and muscular fibres) by drawing it out of the mouth and spreading it into a thin sheet, securing it with pins.
The circulation may also be observed in the mesentery of a small, warm-blooded animal, like the mouse, by fixing it
upon the frog- plate, opening the abdomen, and drawing out the membrane ; but it is not seen so well or so convenient-
ly as in the tongue or web of the frog.

PHENOMENA OF THE CAPILLAPwY CIRCULATION. 87

parent layer was observed by Malpighi, Ilaller, and all who have described the capillary
circulation. Poiseuille recognized its true relation to the blood-current and explained
the phenomenon of the still layer by physical laws, which had been previously estab-
lished with regard to the flow of liquids in tubes of the diameter of from one-twenty-
fifth to one- eighth of an inch, but which he had succeeded in applying to tubes of the
size of the capillaries.

A red corpuscle occasionally becomes involved in the still layer, when it moves
slowly, turning over and over, or even remains stationary for a time, until it is taken up
again and carried along with the central current. A few white corpuscles are con-
stantly seen in this layer. They move along slowly and apparently have a tendency to
adhere to the walls of the vessel. This is due to the adhesive character of the surface of
the white corpuscles as compared with the red, which can easily be observed in examin-
ing a drop of blood between glass surfaces, the red corpuscles moving about with great
facility, while the white have a tendency to adhere.

Great differences exist in the character of the flow of blood in the three varieties of
vessels which are under observation. In the arterioles, which may be distinguished from
the capillaries by their size and the presence of the muscular and fibrous coats, the move-
ment is distinctly remittent, even in their most minute ramifications. The blood moves
in them with much greater rapidity than in either the capillaries or veins. They become
smaller as they branch, and carry the blood always in the direction of the capillaries.
The veins, which are relatively larger than the arteries, carry the blood more slowly
and in a continuous stream from the capillaries toward the heart. In both the arteries
and veins, the current is frequently so rapid that the form of the corpuscles cannot be
distinguished. Only a portion of the white corpuscles occupy the still layer, the rest
being carried on in the central current.

The circulation in the true capillaries is sui generis. Here the blood is distributed in
every direction, in vessels of nearly uniform diameter. The vessels are generally so small
as to admit but a single row of corpuscles, which move almost like beings endowed with
volition. In a single vessel, a line of corpuscles may be seen moving in one direction at
one moment, a few moments after, taking a directly opposite course. Spallanzani,
in one of his observations, describes the following phenomenon : Two single rows of
corpuscles, passing in two capillary vessels of equal size, were directed toward a third
capillary vessel, formed by the union of the two others, which would itself admit but a
single corpuscle. The corpuscles in one of these vessels seemed to hold back until those
from the other had passed in, when they followed in their turn. When the circulation is
normal, the movement in the capillaries is always quite slow as compared with the move-
ment in the arterioles, and is continuous. Here, at last, the intermittent impulse of the
heart is lost. The corpuscles do not necessarily circulate in all the capillaries which are
in the field of view. Certain vessels may not receive a corpuscle for some time, but, after
a while, one or two corpuscles become engaged in them and a current is finally established.

Many interesting little points may be noticed in examining the circulation for a suffi-
cient length of time. A corpuscle is frequently seen caught at the angle where a vessel
divides into two, remaining fixed for a time, distorted and bent by the force of the cur-
rent. It soon becomes released, and, as it enters the vessel, it regains its original form.
In some of the vessels of smallest size, the corpuscles are slightly deformed as they pass
through. The scene is changed with every different part which is examined. In the
tongue, in addition to the arterioles and venules with the rich net-work of capillaries,
dark-bordered nerve-fibres, striated muscular fibres, and pavement-epithelium can be
distinguished. In the lungs, the view is very beautiful. Large, polygonal air-cells are
observed, bounded by capillary vessels, in which the corpuscles move with extreme
rapidity. It has been observed that the larger vessels are crowded to their utmost capa-
city with corpuscles, leaving no still layer next the walls, such as is seen in the circula-
tion in other situations.

88

CIRCULATION OF THE BLOOD.

When the circulation has been for a long time under observation, as the animal
becomes enfeebled, very interesting changes in the character of the flow of blood take
place. The continuous stream in the smallest vessels diminishes in rapidity, and, after a
time, when the contractions of the heart have become infrequent and feeble, the blood
is nearly arrested, even in the smallest capillaries, during the intervals of the heart's
action, and the current becomes remittent. As the central organ becomes more and
more enfeebled, the circulation becomes intermittent, and the blood receives an impulse
from each contraction, remaining stationary during the intervals. At this time, the cor-
puscles cease to occupy exclusively the central portion of the vessels, and the clear layer

FIG. 32.— Portion of the lung of a

triton, drawn under tfte microscope and magnified 150 diameters.
(Wagner.)

of plasma next their walls, which was observed in the normal circulation, is no longer
apparent. Following this, there is an actual oscillation in the capillaries. At each con-
traction of the heart, the blood is forced onward a little distance, but it almost immediately
returns to about its former position. This phenomenon has long been observed and is
explained in the following way : As the heart has become enfeebled, the contractions
are so infrequent and ineffectual, that, during their intervals, the constant flow in the
capillaries is entirely arrested ; for the arterial pressure, which is its immediate cause
and which is maintained by the successive charges of blood sent into the arteries at each
ventricular systole, is lost. But, as the blood is contained in a connected system of closed
tubes, the feeble impulse of the heart is propagated through the vessels and produces a
slight impulse, even in the smallest capillaries, which dilates them and forces the fluid a
little distance. As soon, however, as the heart ceases to contract, the current is arrested,
and the blood, meeting with a certain amount of obstruction from the fluid in the small
veins, which are still farther removed from the heart, is made to return to its former
position. This phenomenon continues for a short time only, for the heart soon loses its
contractility, and the circulation in all the vessels is permanently arrested.

Rapidity of the Capillary Circulation.— -The circulation in the capillaries of a part

KAPIDITY OF THE CAPILLARY CIRCULATION. 89

is subject to such great variations, and the differences in different situations are so con-
siderable, that it is impossible to give any definite rate which will represent the general
rapidity of the capillary circulation. It is for this reason that it has been found imprac-
ticable to estimate the capacity of the capillary as compared with the arterial system.
The rapidity of the flow of blood is by no means so great as it appears in microscopical
examinations, being, of course, exaggerated in proportion to the magnifying power
employed. It is, nevertheless, to microscopical investigations that we are indebted for
the scanty information we possess on this subject. The estimates which have been made
by various observers refer generally to cold-blooded animals and have been arrived at by
simply calculating the time occupied by a blood-corpuscle in passing over a certain dis-
tance. Hales, who was the first to investigate this question, estimated that, in the frog,
a corpuscle moved at the rate of an inch in ninety seconds. The estimates of Weber and
Valentin are considerably higher, being about one-fiftieth of an inch per second. Volk-
mann calculated the rapidity in the mesentery of the dog, which would approximate
more nearly to the human subject, and found it to be about one-thirtieth of an inch
per second. Vierordt made a number of curious observations upon himself, by which
he professed to be able to estimate the rapidity of the circulation in the little vessels of
the eye. He states that when the eye is fatigued, and sometimes when the nervous
system is disordered, compression of the globe in a certain way will enable one to see
a current like that in a capillary plexus. This he believed to be the capillary circula-
tion, and, by certain calculations, he formed an estimate of its rapidity, putting it at from
one-fortieth to one-twenty-eighth of an inch per second. The latter figure accords pretty
nearly with the observations of Volkmann upon the dog. How far these observations
are to be relied upon, it is impossible to say. Certainly no great importance would be
attached to them if they did not, in their results, approximate to the estimates of Volk-
mann, which probably represent, more nearly than any, the rapidity of the current in
the capillaries of the human subject. After what has been said of the variations in the
capillary circulation, it is evident that the foregoing estimates are by no means to be
considered exact.

Relations of the Capillary Circulation to Respiration. — In treating of the influence
of respiration upon the action of the heart, the arterial pressure, pulse, etc., it has already
been stated that non-aerated blood cannot circulate freely in the capillaries. Various
ideas with regard to the effects of asphyxia upon the circulation have been advanced,
which will be again discussed in connection with respiration. The fact is evident that
arrest of respiration produces arrest of circulation. This is ordinarily attributed to an
impediment to the passage of blood through the lungs when they no longer contain the
proper quantity of oxygen. This view is entirely theoretical and has been disproved by
experiments dating more than half a century ago. In 1789, Goodwyn advanced the
theory that, in asphyxia, the blood passes through the lungs but is incapable of exciting
contractions in the left ventricle. Bichat, in his celebrated essay " Sur la me et la mort,"
1805, proved by experiment that black blood passes through the lungs in asphyxia and is
found in the arteries. His theory was that non-aerated blood, circulating in the capilla-
ries of the nervous centres, arrests their function, thus acting indirectly upon the circu-
lation ; and that finally the heart itself is paralyzed by the circulation of black blood in
its substance.

The immediate effects of asphyxia upon the circulation are referable to the general
capillary system. This fact we demonstrated conclusively by experiments upon the frog,
published in 1857. In these experiments, the medulla oblongata was broken up, and the
web of the foot was submitted to microscopical examination. This operation does not in-
terfere with the circulation, which may be observed for hours without difficulty. The cu-
taneous surface was then coated with collodion, care only being taken to avoid the web
under observation. The effect on the circulation was immediate. It instantly became less

90 CIRCULATION OF THE BLOOD.

rapid, until, at the expiration of twenty minutes, it had entirely ceased. The entire
coating of collodion was then instantly peeled off. Quite a rapid circulation immediately
commenced, but it soon began to decline and in twenty minutes had almost ceased. In
another observation, the coating of collodion was applied without destroying the medulla.
The circulation was affected in the same manner as before and ceased in twenty-five
minutes. These experiments, taken in connection with observations on the influence of
asphyxia upon the arterial pressure, conclusively show that non-aerated blood cannot
circulate freely in the systemic capillaries. Venous blood, however, can be forced
through them with a syringe, and, even in asphyxia, it slowly filters through. If air be
admitted to the lungs before the heart has lost its contractility, the circulation is restored.
No differences in the capillary circulation Have been noticed accompanying the ordinary
acts of inspiration and expiration.

Causes of the Capillary Circulation. — The contractions of the left ventricle are evi-
dently capable of giving an impulse to the blood in the smallest arterioles ; for a marked
acceleration of the current accompanying each systole can be distinguished in all but the
true capillaries. It has also been shown by experiments after death, that blood can be
forced through the capillary system and returned by the veins by a force less than that
exerted by the left ventricle. This, however, cannot rigidly be applied to the natural
circulation, as the smallest arteries are endowed during life with contractility, which is
capable of modifying the blood-current. Dr. Sharpey adapted a syringe, with a hgema-
dynamometer attached, to the aorta of a dog just killed, and found that fresh defibrinated
blood could be made to pass through the double capillary systems of the intestines and
liver, by a pressure of three and a half inches of mercury. It spurted out at the vein in
a full jet under a pressure of five inches. In this observation, the aorta was tied just
above the renal arteries. The same pressure, the ligature being removed, forced the
blood through the capillaries of the inferior extremities. This is much less than the arte-
rial pressure, which is equal to from five and a half to six inches of mercury.

It is thus seen that the pressure in the arteries which forces the blood toward the
capillaries is competent, unless opposed by excessive contraction of the arterioles, not only
to cause the blood to circulate in these vessels, but to return it to the heart by the veins.
This fact is so evident, that it is unnecessary to discuss the views of Bichat and some
others, who supposed that the action of the heart had no effect upon the capillary circu-
lation. It must be admitted that this is its prime cause ; and the only questions to be
considered are, first, whether there be any reason why the force of the heart should not
operate on the blood in the capillaries, and second, whether there be any force in these
vessels which is superadded to the action of the heart. The first of these questions is
answered by microscopical observations on the circulation. A distinct impulse, follow-
ing each ventricular systole, is observed in the smallest arteries ; the blood flows from
them directly and freely into the capillaries ; and there is not the slightest ground for
the supposition that the force is not propagated to this system of vessels.

Various writers have supposed the existence of a " capillary power," which they have
regarded as of greater or less importance in producing the capillary circulation. The
ideas of some are purely theoretical, but others base their opinion on microscopical
observations. These views do not demand extended discussion. There is a force in
operation, the action of the heart, which is capable of producing the capillary circula-
tion; and there is nothing in the phenomena of the circulation in these vessels, which is
inconsistent with its full operation. Under these circumstances, it is unphilosophical to
invoke the aid of the currents produced in capillary tubes in which liquids of different
characters are brought in contact, or a " capillary power " dependent upon a so-called
vital nutritive attraction between the tissues and the blood, unless we do it on the basis
of phenomena observed in the capillaries when the action of the heart is suppressed.
When the heart ceases its action, movements in the capillaries are sometimes due to the

CAUSES OF THE CAPILLARY CIRCULATION. 91

contractions of the arteries, a property which has already been fully considered. Move-
ments which have been observed in membranes detached from the body are due to the
mere emptying of the divided vessels or to simple gravitation. It must be remembered
that, in microscopical examinations, the movements observed are immensely exaggerated
by the magnifying power, and we receive, at first sight, an erroneous impression of their
rapidity. The movements of the blood in detached membranes, due merely to gravitation,
have been so satisfactorily explained by the experiments of Poiseuille, that it is deemed
unnecessary to refer to the observations of those who have attributed this phenomenon
to other causes.

Physiologists who, like Bichat, have been unable to explain the local variations in the
capillary circulation without the intervention of a force resident in these vessels or in the
surrounding tissues, have not appreciated the action of the arterioles. These little vessels
are endowed to an eminent degree with contractility and, by the contractions and relaxa-
tions of their muscular walls, they regulate the supply of blood to the capillaries of in-
dividual parts. Their action is competent to produce all the variations which are ob-
served in the capillary circulation.

It is evident, then, that the arterial pressure, which is itself derived from the action
of the heart, is competent to produce the circulation of the blood, as we observe it, with
all its variations, in the capillary vessels ; that there is no evidence of the intervention of
any other force ; but, on the contrary, microscopical observations and experiments on the
arteries and veins, thus far, show that there is no other force in operation.

It has been asserted that there is a circulation of the blood in the area vasculosa, the
first blood-vessels that are developed, before the heart is formed ; but there are no definite
and reliable observations which show that there is any regular movement of the blood,
which can be likened to the circulation as it is observed after the development of the
heart, anterior to the appearance of a contractile central organ. Another example of
what is supposed to be circulation without the intervention of the heart is in cases of
acardiac foetuses. Monsters without a heart, which have undergone considerable develop-
ment and which present systems of arteries, capillaries, and veins, have been described.
All of these, however, are accompanied by a twin, in which the development of the cir-
culatory system is quite or nearly perfect.

Influence of Temperature on the Capillary Circulation. — "Within moderate limits, a
low temperature, induced by local applications, has been found to diminish the quantity
of blood sent to the capillaries and retard the circulation, while a high temperature
increases the supply of blood and accelerates its current. The mechanism of this is
beautifully shown by the experiments of Poiseuille. This observer found that when a
piece of ice was applied to the web of a frog's foot, the mesentery of a small warm-blooded
animal, or to any part in which the capillary circulation can be observed, the number of
corpuscles circulating in the arterioles became very much diminished, " those which car-
ried two or three rows of corpuscles giving passage to but a single row." The circulation
in the capillaries first became slower and then entirely ceased in parts. On removing
the ice, in a very few minutes the circulation regained its former characters. If, on the
other hand, the part be covered with water at 104° Fahr., the rapidity of the current in
the capillaries is so much increased that we can hardly distinguish the form of the cor-
puscles.

Influence of Direct Irritation upon the Capillary Circulation. — Experimental re-
searches on the effects of direct irritation of the capillaries, in parts where the circulation
can be observed microscopically, have been quite numerous since Thompson studied the
effects of saline solutions on the web of the frog's foot, in 1813. The most noticeable
papers on this subject are those of Dr. Wilson Philip and Mr. Wharton Jones. The latter
paper, which received the Astley Cooper prize for 1850, is based on very extended and

92 CIRCULATION OF THE BLOOD.

carefully-conducted observations, in which the author, by means of various irritants,
succeeded in producing very curious and interesting phenomena, which he regarded as
inflammatory. It is not our object to discuss the nature of inflammation or to treat of the
changes in the character of the capillary circulation which are supposed to attend this
condition, as this subject is entirely pathological ; but it must be remembered, in con-
sidering the effects of direct irritation on the capillary circulation, that the phenomena
thus observed in cold-blooded animals cannot be taken as absolutely representing the
characters of inflammation in the human subject. When an irritation is applied to a
transparent part, the phenomena observed may be due to many causes, as the direct
effects upon the contractile elements of the blood-vessels, reflex action through the
nervous system, and the direct influence of the application upon the constitution of the
blood. Saline or other fluids are competent to modify, to a very considerable extent, the
composition of the blood, when separated from it only by the thin, permeable walls of the
vessels; and the phenomena which follow their application are necessarily very complex.
The process of inflammation is by no means completely understood ; but it is pretty gen-
erally acknowledged to be a modification of nutrition. We are hardly prepared to admit
that this modification, whatever it may be, can be induced under our very eyes, simply
by the application of irritants. With these views, microscopical researches on the " state
of the blood and blood-vessels in inflammation" do not assume the importance which is
attributed to them by many authors. Keeping this in mind, we may state the following
as a summary of the phenomena which have been observed in the capillary circulation,
as the result of irritation applied to transparent parts :

The application of the irritant is immediately followed by constriction of the arterioles
and diminution in the rapidity of the current in them as well as in the capillaries.

This constriction of the vessels is but momentary, if a powerful irritant, like a very
strong solution of a salt, be used. It is followed by a dilatation of the vessels and an
increase in the rapidity of the circulation.

Soon after the vessels have become dilated, the rapidity of the circulation becomes
progressively diminished, until oscillation of the blood in the vessels takes place, which
occurs when the circulation is about to cease. This oscillation finally gives place to com-
plete stagnation ; and the vessels become crowded with blood, so that the transparent
layer next their walls is no longer observed. In this condition, it has often been noticed
that the proportion of colorless corpuscles is increased.

Following the contraction and subsequent dilatation of the vessels, there are stasis and
engorgement of the parts which have been exposed to irritation. If the irritation bo
discontinued, this condition is gradually relieved, and the blood resumes its normal
current.

In inflammation, as it is observed in the conjunctiva and in other vascular parts, there
unquestionably is congestion of the vessels ; but there is no positive evidence of stagnation
of blood in the parts as a constant occurrence. The circulation seems, indeed, to be more
active than in health. With regard to the microscopical phenomena just mentioned, the
contraction of the arterioles is simply the effect of a stimulus upon their muscular coats;
and dilatation takes place probably in consequence of the excessive contraction, for it has
been shown that this condition of the muscular fibres is pretty constantly followed by
unusual relaxation. It has never yet been determined how far the stasis of the blood is
due to an osmotic action of solutions employed in the experiments.

Circulation of the Blood in the Veins. — The blood, distributed to the capillaries of all
the tissues and organs by the arteries, is collected from these parts in the veins and
carried back to the heart. In studying the anatomy of the capillary system or in ob-
serving the passage of the blood from the capillaries to larger vessels in parts of the
living organism which can be submitted to microscopical examination, it is seen that the
capillaries, vessels of nearly uniform diameter and anastomosing in every direction, give

CIRCULATION OF THE BLOOD IN THE VEINS. 93

origin, so to speak, to a system of vessels, which, by union with others as we follow their
course, become larger and larger, and carry the blood away in a uniform current. These
are called the venules, or venous radicles. They are the peripheral radicles of the
numerous vessels which transport the blood, after it has served the purposes of nutrition
or secretion, to the central organ.

The venous system may be considered, in general terms, as divided into two sets of
vessels; one, which is deep-seated and situated in proximity to the arteries, and the

FIG. 88.— Venous radicles, uniting to form a small vein, from ihe, muscular font of the urinary bladder of the

frog ; magnified 400 diameters. (From a photograph taken at the United States Army Medical Museum.)
This preparation shows the epithelium of the vessels. It is injected with nitrate of silver, stained with carmine,

and mounted in Canada balsam.

other, which is superficial and receives for the most part the blood from the cutaneous
surface. The entire capacity of these vessels, as compared with that of the arteries, is
very great. As a general rule, each vein, when fully distended, is larger than its adjacent
artery. Many arteries are accompanied by two veins, as the arteries of the extremities ;
while certain of them, like the brachial or spermatic, have more than two. Added to
these is the superficial system of veins which have no corresponding arteries. It is true
that some arteries have no corresponding veins, but examples of this kind are not suffi-
ciently numerous to diminish, in any marked degree, the great preponderance of the veins,
both in number and volume. It is impossible to give an accurate estimate of the extreme
capacity of the veins as compared with the arteries ; but, from the best information we
have, it is several times greater. Borelli estimated that the capacity of the veins was to
the capacity of the arteries, as 4 to 1 ; and Haller, as 2J to 1. The proportion is very
variable in different parts of the body. In some situations the capacity of the veins and
arteries is about equal ; while in others, as in the pia mater, the veins will contain, when
fully distended, six times as much as the arteries.

94 CIRCULATION OF THE BLOOD.

In attempting to compare the quantity of blood normally circulating in the veins with
that contained in the arteries, we find such variations in the venous system at different
times and in different parts, both in the quantity of blood, rapidity of circulation, pressure,
etc., that a definite estimate is impossible. It would be unphilosophical to attempt even
an approximate comparison, as the variations in the venous circulation constitute one of
its greatest and most important physiological peculiarities, which must be fully appreciated
in order to form a just idea of the function of the veins. The arteries are always full,
and their tension is subject to comparatively slight variations. Following the blood into
the capillaries, we observe the immense modifications in the circulation with varying physi-
ological conditions of the parts, to which we have already referred. As would naturally be
expected, the condition of the veins varies with the changes in the capillaries, from which
the blood is taken. In addition to this, there are independent variations, as in the erectile
tissues, in the veins of the alimentary canal during absorption, in veins subject to press-
ure, etc.

Following the veins in their course, it is observed that anastomoses with each other
form the rule, and not the exception as in the arteries. There are always a number of
channels by which the blood may be returned from a part; and, if one vessel be
obstructed from any cause, the current is simply diverted into another. The veins do
not present a true anastomosing plexus, such as exists in the capillary system, but simply
an arrangement by which the blood can readily find its way back to the heart, and by
which the vessels may accommodate themselves to the immense variations in the quan-
tity of their fluid contents. This, with the peculiar valvular arrangement which exists
in all but the veins of the cavities, provides against obstruction to the flow of blood
through, as well as from the capillaries, in which it seems essential to the proper nutri-
tion and function of parts that the quantity and course of the blood should be regulated
exclusively through the arterial system. Special allusion to the different venous anas-
tomoses belongs to descriptive anatomy. Physiologically, the communications between the
different veins are such that the blood can always find a way to the heart, and, once
fairly out of the capillaries, it cannot react and influence the circulation of fresh blood
in the tissues.

Collected in this way from all parts of the body, the blood is returned to the right
auricle, from the head and upper extremities by the superior vena cava, from the trunk
and lower extremities, by the inferior vena cava, and from the substance of the heart, by
the coronary veins.

Structure and Properties of the Veins. — The structure of the veins is somewhat more
complex and difficult of study than that of the arteries. Their walls, which are always
much thinner than the walls of the arteries, may be divided into quite a number of
layers ; but, for convenience of physiological description, we shall regard them as pre-
senting three distinct 'coats. These have properties which are tolerably distinctive,
although not as much so as the three coats of the arteries.

The internal coat of the veins is a continuation of the single coat of the capillaries
and of the internal coat of the arteries. It is a simple, homogeneous membrane, some-
what thinner than in the arteries, lined by a delicate layer of polygonal epithelium.

The middle coat is divided by some into two layers ; an internal layer, which is com-
posed chiefly of longitudinal fibres, and an external layer, in which the fibres have a
circular direction. These two layers are intimately adherent and are quite closely
attached to the internal coat. The longitudinal fibres are composed of connective-tissue
fibres mingled with a large number of the smallest variety of the elastic fibres. This
layer contains a large number of capillary vessels (vasa vasorum). The circular fibres
are composed of elastic tissue, some of the fibres of the same variety as is found in the
longitudinal layer, some of medium size, and some in the form of the " fenestrated mem-
brane." In addition, there are inelastic fibres interlacing in every direction and mingled

STRUCTURE AND PROPERTIES OF THE VEINS. 95

with capillary blood-vessels, and the unstriped or involuntary muscular fibres. In the
human subject, in the veins of the dura and pia mater, the bones, and the retina, the
vena cava descendens, the thoracic portion of the vena cava ascendens, the external and
internal jugulars, and the subclavian veins, there are no muscular fibres in the middle coat.
In the larger veins, such as the abdominal vena cava, the iliac, crural, popliteal, mesen-
teric, and axillary veins, the fibres are both circular and transverse. In the smaller
veins, the fibres are circular.

The external coat of the veins is composed of white fibrous tissue, like the cor-
responding coat of the arteries. In the largest veins, particularly those of the abdominal
cavity, this coat contains a layer of longitudinal unstriped muscular fibres. In the veins
near the heart, are found a few striated fibres, which are continued on to the veins from
the auricles. In some of the inferior animals, as the turtle, these fibres are quite thick,
and pulsation of the veins in the immediate vicinity of the heart is very marked. In
nearly all veins, the external coat is several times thicker than the internal. This is
most marked in the larger veins, in which the middle coat, particularly the layer of
muscular fibres, is very slightly developed.

In what are called the venous sinuses, and in the veins which pass through bony
tissue, we have only the internal coat, to which are superadded a few longitudinal fibres,
the whole being closely attached to the surrounding parts. As examples of this, may be
mentioned the sinuses of the dura mater and the veins of the large bones of the skull.
In the first instance, there is little more than the internal coat of the vein firmly attached
to the surrounding layers of the dura mater. In the second instance, the same thin mem-
brane is adherent to canals formed by a layer of compact bony tissue. The veins are
much more closely adherent to the surrounding tissues than the arteries, particularly
when they pass between layers of aponeurosis.

The above peculiarities in the anatomy of the veins indicate considerable differences
in their properties as compared with the arteries. When a vein is cut across, its walls
fall together, if not supported by adhesions to surrounding tissues, so that its caliber is
nearly or quite obliterated. The yellow elastic tissue, which gives to the larger arteries
their great thickness, is very scanty in the veins, and the thin walls collapse when not
sustained by liquid in the interior of the vessels. Whenever the veins remain open after
saction, it is on account of their attachment to surrounding tissues and is not due to
the rigidity of the vessels themselves.

Although with much thinner and apparently weaker walls, the veins, as a rule, will
resist a greater pressure than the arteries. Observations on the relative strength of
the arteries and veins were made by Hales, but the most extended experiments on the
subject were made by Clifton Wintringham, in 1740. The latter observer ascertained
that the inferior vena cava of a sheep, just above the opening of the renal veins, was rup-
tured by a pressure of one hundred and seventy-six pounds, while the aorta, at a corre-
sponding point, yielded to a pressure of one hundred and fifty-eight pounds. The
strength of the portal vein was even greater, supporting a pressure of nearly five atmos-
pheres, bearing a relation to the vena cava of six to five; yet these vessels had hardly
one-fifth the thickness of the arteries. In the lower extremities in the human subject, the
veins are much thicker and stronger than in other situations, a provision against the
increased pressure to which they are habitually subjected in the upright posture. Win-
tringham noticed one singular exception to the general rule just given. In the vessels of
the glands and of the spleen, the strength of the arteries was much greater than that of
the veins. The splenic vein gave way under a pressure of little more than one atmos-
phere, while the artery supported a pressure of more than six atmospheres.

A little reflection on the influences to which the venous and arterial circulation are
subject will enable us to understand the physiological importance of the great difference
in the strength of the two varieties of vessels. It is true that in the arterial system thf
constant pressure is greater than in the veins; but it is nearly the same throughout the ar

96 CIRCULATION OF THE BLOOD.

terial system, and the immense extent of the outlet into the capillary system provides
against any very great increase in pressure, so long as the blood is in a condition which
enables it to pass into the capillaries. The muscular fibres of the left ventricle have but
a limited power, and when the pressure in the arteries is so great, as it sometimes is in
asphyxia, as to close the aortic valves so firmly that the force of the ventricle will not
open them, it cannot be increased. At the same time, it is being gradually relieved by the
capillaries, through which the blood slowly filters, even when completely unaerated. With
the veins it is different. The blood has a comparatively restricted outlet at the heart and
is received by the capillaries from all parts of the system. The vessels are provided with
numerous valves, which render a general backward action impossible. Thus, restricted
portions of the venous system, from pressure in the vessels, increase of fluid from absorp-
tion, accumulation by force of gravity, and other causes, may be subjected to great and
sudden variations in pressure. The great strength of these vessels enables them ordina-
rily to suffer these variations without injury ; although varicose veins in various parts
present examples of the effects of repeated and continued distention.

The veins possess a considerable degree of elasticity, although this property is not so
marked as it is in the arteries. If we include between two ligatures a portion of a vein
distended with blood and make a small opening in the vessel, the blood will be ejected
with some force, and the vessel becomes very much reduced in caliber.

It has been proven by direct experiment that the veins are endowed with the peculiar
contractility characteristic of the action of the unstriped muscular fibres. On the application
of galvanic or mechanical excitation, they contract slowly and gradually, the contraction
being followed by a correspondingly-gradual relaxation. There is never any rhythmical
or peristaltic movement in the veins, sufficient to assist the circulation. The only regular
movements which occur are seen in the vessels in immediate proximity to the right
auricle, which are provided with a few fibres similar to those which exist in the walls of
the heart.

Nerves, chiefly from the sympathetic system, have been demonstrated in the walls of
the larger veins but have not been followed out to the smaller ramifications.

Valves of the Veins. — The discovery of the valves of the veins has already been
alluded to in connection with the history of the discovery of the circulation. They had
undoubtedly been observed in various parts of the venous system, but Fabricius, the
greatest anatomist of his day, had the good fortune to demonstrate them to his illustrious
pupil, William Harvey, whose immortal discovery indicated their physiological importance.
Being ignorant of the observations of his predecessors on this subject, Fabricius an-
nounced himself as their discoverer and is generally so regarded. In all parts of the
venous system, except, in general terms in the abdominal, thoracic, and cerebral cavities,
there exist little membranous, semilnnar folds, resembling the aortic and pulmonic valves
of the heart. When distended, the convexities of these valves look toward the periph-
ery. In the great majority of instances, the valves exist in pairs, but they are occa-
sionally found in groups of three. They are formed in part of the lining membrane of
the veins, with fine fibres of connective tissue. There exists, also, a fibrous ring follow-
ing the line of attachment of the valvular curtains to the vein, which renders the vessel
much stronger and less dilatable here than in the spaces between the valves. The valves
are by far the most numerous in the veins of the lower extremities. They are generally
situated just below the point where a small vein empties into one of larger size, so that
the blood, as it passes in, finds an immediate obstacle to passage in the wrong direction,
The situation of the valves may be readily observed in any of the superficial veins. If
the flow of blood be obstructed, little knots will be formed in the congested vessels,
which indicate the position and action of the valves. The simple experiment of Harvey,
already referred to, presents a striking illustration of the action of the valves. When the
vein is thus congested and knotted, if the finger be pressed along the vessel in the direc-

VALVES OF THE VEINS.

97

FIG. 84.— Valves of the veins. (Copied and reduced from a figure in the original work of Fabricius, published in 16-7 )
A, B, vein; L, artery; D, E, F, G, II, I, valves; a, /3, y, S, e, venous branches.

7

98 CIRCULATION OF THE BLOOD.

tion of the blood-current, a portion situated between two valves maybe emptied of blood;
but it is impossible to empty any portion of the vessel by pressing the blood in the oppo-
site direction. On slitting open a vein, we observe the shape, attachment, and extreme
delicacy of structure of the valves. When the vessel is empty, or when fluid moves
toward the heart, they are closely applied to the walls ; but if liquid or air be forced in the
opposite direction, they project into its caliber, and, by the application of their free edges
to each other, effectually prevent any backward current. Fabricius noted the following
peculiarity in the arrangement of the valves : When closed, the application of their free
edges forms a line which runs across the vessel ; it is found that, in successive sets of
valves, these lines are at right angles to each other, so that if, in one set, this line have a
direction from before backward, in the sets above and below the lines run from side to
side.

There are certain exceptions to the general proposition that the veins of the great
cavities are not provided with valves. Valves are found in the portal system of some of
the inferior animals, as the horse. They do not exist, however, in this situation in the
human subject. Generally, in following out the branches of the inferior vena cava, no
valves are found until we come to the crural vein ; but occasionally there is a double
valve at the origin of the external iliac. In some of the inferior animals, there exists
constantly a single valvular fold in the vena cava at the openings of the hepatic, and one
at the opening of the renal vein. This is not constant in the human subject. Valves
are found in the spermatic, but not in the ovarian veins. A single valvular fold has
been described at the opening of the right spermatic into the vena cava. There are
two valves in the azygos vein near its opening into the superior vena cava. There
is a single valve at the orifice of the coronary vein. There are no valves at the
openings of the brachio-cephalic into the superior vena cava ; but there is a strong double
valve at the point where the internal jugular opens into the brachio-cephalic. Between
this point and the capillaries of the brain, the vessels are entirely deprived of valves,
except in very rare instances, when one or two are found in the course of the jugular.

In addition to the double, or more rarely triple valves which have just been described,
there is another variety, found in certain parts, at the point where a tributary vein opens
into a main trunk. This consists of a single fold, which is attached to the smaller vessel
but projects into the larger. Its action is to prevent regurgitation, by the same mech-
anism as that by which the ileo-cascal valve prevents the passage of matters from the
large into the small intestine. These valves are much less numerous than the first variety.

The veins form a system which is adapted to the return of blood to the heart in a
comparatively slow and unequal current. Distention of certain portions is provided for ;
and the vessels are so protected with valves, that whatever influences the current must
favor its flow in the direction of the heart.

Course of the Blood in the Veins.— The experiments of Hales and Sharpey, showing
that defibrinated blood can be made to pass from the arteries into the capillaries and out
at the veins by a pressure less than that which exists in the arterial system, and the
observations of Magendie upon the circulation in the leg of a living dog, showing that
ligation of the artery arrests the flow in the vein, points which have already been fully
discussed in treating of the causes of the capillary circulation, have established, beyond
question, the fact that the force exerted by the left ventricle is sufficient to account for
the venous circulation. The heart must be regarded as the prime cause of all movement
in these vessels. Regarding this as definitely ascertained, there remain to consider, in
the study of the course of the blood in the veins, the character of the current, the influence
of the vessels themselves, the question of the existence of forces which may assist
the ms a tergo from the heart, and circumstances which may interfere with the flow of
blood.

As a rule, in the normal circulation, the flow of blood in the veins is continuous. The

COURSE OF THE BLOOD IN THE VEINS. 99

intermittent impulse of the heart, which progressively diminishes as we recede from this
organ but is still felt even in the smallest arteries, is lost, as we have seen, in the capil-
laries. Here, for the first time, the blood moves in a constant current ; and, as the press-
ure in the arteries is continually supplying fresh blood, that which has circulated in the
capillaries is forced into the venous radicles in a steady stream. As the supply to the
capillaries of different parts is regulated by the action of the small arteries, and as this
supply is subject to great variations, there must necessarily be corresponding, variations
in the current in the veins and in the quantity of blood which these vessels receive. As we
should anticipate, then, the venous circulation is subject to very great variations arising
from irregularity in the supply of blood, aside from any action of the vessels themselves
or any external disturbing influences. Great variations in the venous current are observed
in the veins which collect the blood from the intestinal canal. During the intervals of
digestion, these vessels carry a comparatively small quantity of blood ; but, during diges-
tion, they are laden with, the fluids received by absorption, and the quantity is largely
increased.

It often happens that a vein becomes obstructed from some cause which is entirely
physiological, as the action of muscles. The immense number of veins, as compared with
the arteries, and their free communications with each other, provide that the current,
under these circumstances, is simply diverted, passing to the heart by another channel.
When any part of the venous system is distended, the vessels react on the blood and exert
a certain influence on the current, always pressing it toward the heart, for the valves
oppose a flow in the opposite direction.

The intermittent action of the heart, which pervades the whole arterial system, is
generally absorbed, as it were, in the passage of the blood through the capillaries; but,
when the arterioles of any part are very much relaxed, the impulse of the central organ
may extend to the veins. Bernard has shown this in the most striking manner, in his
well-known experiments on the circulation in the glands. When the glands are pouring
out their secretions, the quantity of blood which they receive is very much increased. It
is then furnished to supply material for the secretion, and not exclusively for nutrition.
If the vein be opened at such a time, it is found that the blood has not lost its arterial
character, that the quantity which escapes is increased, and that the flow is in an inter-
mittent jet, as from a divided artery. This is due to the relaxed condition of the arteri-
oles of the part, and the phenomenon thus observed constitutes the true venous pulse.
What thus occurs in a restricted portion of the circulatory system may take place in all
the veins, though in a less marked degree. Physicians have frequently noticed, after the
blood has been flowing for some time in the operation of venesection, that the color
changes from black to red, and the stream becomes intermittent, often leading the
operator to fear that he has pricked the artery. In all probability, this is due to
the relaxation of the arterioles as one of the effects of abstraction of blood, producing
the same condition that has been noted in some of the glands during their functional
activity. The hypothesis that it is due to an impulse from the adjacent artery is not ad-
missible. Except in the veins near the heart, any pulsation which occurs is to be attrib-
uted to the force of the heart, transmitted with unusual facility through the capillary
system. A nearly uniform current, however, is the rule, and a marked pulsation, the
rare exception.

Pressure of Blood in the Veins. — The pressure in the veins is always much less than
in the arteries. It is exceedingly variable in different parts of the venous system and in
the same part at different times. As a rule, it is in inverse ratio to the arterial pressure.
Whatever favors the passage of blood from the arteries into the capillaries lias a tendency
to diminish the arterial pressure, and, as it increases the quantity of blood which passes
into the veins, must increase the venous pressure.. The fnvr.t capacity of th3 vcr.ct» sys-
tem, its numerous anastomoses, the presence w Valves \vhiv'h, n-ay siuit o4! a nortion from

100 CIRCULATION OF THE BLOOD.

the rest, are circumstances which involve great variations in pressure in different vessels.
It has been ascertained that, as a rule, the pressure is diminished as we pass from the
periphery toward the heart. In an observation on the calf, Volkmann found that, with a
pressure of about 6'5 inches of mercury in the carotid, the pressure in the metatarsal vein
was I'l inch, and but G'36 in the jugular. Muscular effort has a marked influence on the
force of the circulation in certain veins and produces an elevation in the pressure. As
the reduced pressure in the veins is due, in a measure, to the great relative capacity of
the venous system and the free communications between the vessels, it would seem that,
if it were possible to reduce the capacity of the veins in a part and force all the blood to
pass to the heart by a single vessel corresponding to the artery, the pressure in this vessel
would be greatly increased. Poiseuille has shown this to be the fact by the experiment
of ligating all the veins coming from a part, except one which had the volume of the
artery by which the blood was supplied, forcing all the blood to return by this single
channel. This being done, he found the pressure in the vein immensely increased, becom-
ing nearly equal to that in the artery.

Rapidity of the Venous Circulation. — It is impossible to fix upon any definite rate as
representing the rapidity of the current of blood in the veins. It will be seen that various
circumstances are capable of increasing very considerably the rapidity of the flow in cer-
tain veins, and that, under certain conditions, the current in some parts of the venous
system is very much retarded. Undoubtedly, the general movement of blood in the veins
is very much slower than in the arteries, from the fact that the quantity of blood is greater.
If it be assumed that the quantity of blood in the veins is double that contained in the
arteries, the general average of the current would be diminished one-half. As we near
the heart, however, the flow becomes more uniform and progressively increases in rapidity.

As the effect of the heart's action upon the venous circulation is subject to so many
modifying influences through the small arteries and capillaries, and as there are other
forces influencing the current, which are by no means uniform in their action, with our
present knowledge, estimates of the general rapidity of the venous circulation or the
variations in different vessels would be founded on mere speculations.

Causes of the Venous Circulation.

In the veins, the blood is farthest removed from the influence of the contractions of
the left ventricle ; and, although these are felt, there are many other causes which com-
bine to carry on the circulation, and many influences by which it is retarded or ob-
structed.

The great and uniform force which operates on the circulation in these vessels is the
vis a tergo. We have repeatedly referred to the entire adequacy of the arterial pressure,
propagated through the capillaries, to account for the movement of blood in the veins,
provided there be no great obstacles to the current. There are no facts which lead us to
doubt the operation of this force as the prime cause of the venous circulation ; and the
only question which arises is whether there be any force exerted in the capillaries them-
selves which is superadded to the force of the heart. In discussing the capillary circu-
lation, we stated that there is no direct proof of the existence of a distinct " capillary
power " influencing the movement of blood in these vessels ; and consequently the
vis a tergo operating on the circulation in the veins must be attributed mainly to the ac-
tion of the left ventricle.

The other forces which concur to produce movement of blood in the veins are the
following :

1. Muscular action, by which many of the veins are at times compressed, thus forcing
the blood toward the heart, regurgitation being prevented by the action of the valves.

2. A euctioR'fcfc'e exerted by the act' on of the thorax in respiration, operating,
however, 'only WtheVeinfe In 'the '5 tnn'teui,<U"e rieighborhood of the chest.

COURSE OF BLOOD IX THE VEINS. 101

3. A possible influence from contraction of the coats of the vessels themselves.
This is marked in the veins near the heart in some of the inferior animals.

4. The force of gravity, which operates only on vessels which carry blood from above
downward to the heart, and a slight suction force which may be exerted upon the blood
in a small vein as it passes into a larger vessel in which the current is more rapid.

The obstacles to the venous circulation are : Pressure sufficient to obliterate the cali-
ber of a vessel, when, from the free communications with other vessels, the current is
simply diverted into another channel ; the expulsive efforts of respiration ; the contrac-
tions of the right side of the heart; and the force of gravity, which operates, in the
erect posture, on the current in all excepting the veins of the head, neck, and in parts
of the trunk above the heart.

Influence of Muscular Contraction. — That the action of muscles has considerable in-
fluence on the current of blood in the veins situated between them and in their sub-
stance, has long been recognized. It is exemplified in the operation of venesection,
when it is well known that the jet from the vein may be very much increased in force
by contraction of the muscles below the opening. This action is so marked, that the
parts of the venous system which are situated in the substance of muscles have been
compared by Chassaignac to a sponge full of liquid, vigorously pressed by the hand. It
must always be remembered, however, that, although the muscles are capable of acting
on the blood contained in veins in their substance with great vigor, the heart is fully
competent to carry on the venous circulation without their aid ; a fact which is exempli-
fied in a striking manner in the venous circulation in paralyzed parts.

It has been shown by actual observations with the ha3madynarnometer, that muscular
action is capable of immensely increasing the pressure in certain veins. The first defi-
nite experiments on this subject were made by Magendie, who showed a pressure of over
two inches of mercury produced by a general muscular contraction, on the passage of a
galvanic current from a needle plunged into the cervical region of the spinal marrow to
one fixed in the muscles of the thigh. The experiments of Bernard have shown this
more accurately. This physiologist found that the pressure in the jugular of a horse,
in repose, was 1*4 inch ; but the action of the muscles in raising the head increased it to
a little more than five inches, or nearly four times. These observations show at once
the great variations in the current and the important influence of muscular contraction
on the venous circulation.

In order that contractions of muscles shall assist the venous circulation, two things
are necessary :

1. The contraction must be intermittent. This is always the case in the voluntary
muscles. It is a view entertained by many that each muscular fibre relaxes immediately
after its contraction, which is instantaneous, and that a certain period of repose is neces-
sary before it can contract again. However this may be, it is well known that all
active muscular contraction, as distinguished from the efforts necessary to maintain the
body in certain ordinary positions, is intermittent and not very prolonged. Thus the
veins, which are partly emptied by the compression, are filled again during the repose of
the muscle.

2. There should be no possibility of a retrograde movement of the blood. This con-
dition is fulfilled by the action of the valves. Anatomical researches have shown that
these valves are most abundant in veins situated in the substance of or between the mus-
cles, and that they do not exist in the veins of the cavities, which are not subject to the
same kind of compression. It is thus that the blood is prevented from passing back-
ward toward the capillary system ; and, when the caliber of a vein is reduced by com-
pression, part of its contents must be forced toward the heart. This action of the valves
constitutes their most important function.

Milne-Edwards alludes to an important physiological bearing of the acceleration of

102 CIKCULATION OF THE BLOOD.

the venous circulation by contractions of muscles on their nutrition. It is apparently
necessary that the supply of blood should be increased in a muscle, in proportion to and
during its activity ; for at that time its disassimilation is undoubtedly augmented, and
there is an increased demand on the blood to supply the waste. It is apparently a pro-
vision of Nature that the activity of a muscle, facilitating the passage of blood in its
veins and consequently its flow from the capillaries, induces an increased supply of the
nutrient fluid. As the development of tissues is generally in proportion to their vascu-
larity, this may account for the increase in the development of muscles which is the al-
most invariable result of exercise.

Force of Aspiration from the Thorax.— During the act of inspiration, the enlarge-
ment of the thorax, by depression of the diaphragm and elevation of the ribs, affects
the movements of fluids in all the tubes in its vicinity. The air rushes in by the trachea
and expands the lungs, so that they follow the movements of the thoracic walls. The
flow of blood into the great arteries is somewhat retarded, as is indicated by a dimi-
nution in the arterial pressure ; and, finally, the blood in the great veins passes to the
heart with greater facility and in increased quantity. This last-mentioned phenomenon
can be readily observed, when the veins are prominent, in profound or violent inspira-
tion. The veins at the lower part of the neck are then seen to empty themselves of
blood during inspiration, and they become distended during expiration, producing a sort of
pulsation which is synchronous with respiration. This can always be observed after ex-
posure of the jugular in the lower part of the neck in an inferior animal. After this
operation, if we cause the animal to make violent respiratory efforts, the vein will be
almost emptied and collapsed with inspiration and turgid with expiration. The move-
ments of the veins near the thorax have long been observed and have been described
with tolerable accuracy. Direct observations on the jugulars show conclusively that the
influence of inspiration cannot be felt much beyond these vessels. They are seen to
collapse with each inspiratory act, a condition which limits this influence to the veins
near the heart. The flaccidity of the walls of the veins will not permit the extended
action of any suction force. If a portion of a vein removed from the body be attached
to the nozzle of a syringe and we attempt to draw a liquid through it, although the suc-
tion force be applied very gently, when the vessel has any considerable length its walls
will -be drawn together. In the circulation, the veins are moderately distended with
blood by the vis a tergo, and, to a certain extent, they are supported by connections with
surrounding tissues, so that the force of aspiration is felt farther than in any experiment
on vessels removed from the body. The blood, as it approaches the thorax, impelled by
other forces, is considerably accelerated in its flow ; but it is seen by direct observation,
that beyond a certain point, and that very near the chest, ordinary aspiration has no in-
fluence, and violent efforts rather retard than favor the venous current.

In the liver, the influence of inspiration becomes a very important element in the
mechanism of the circulation. This organ presents a vascular arrangement which is
exceptional. The blood, distributed by the arteries in a capillary plexus in the mucous
membrane of the alimentary canal and in the spleen, instead of being returned directly
to the heart by the veins, is collected into the portal vein, carried to the liver, and is there
distributed in a second set of capillary vessels. It is then collected in the hepatic veins
and carried by the vena cava to the heart. This double capillary plexus between the
left and the right side of the heart has been cited as an argument against the fact that the
left ventricle is capable of sending the blood through the entire circuit of the vascular
system. The three hepatic veins open into the inferior vena cava near the point where
it passes the diaphragm, where the force of aspiration from the thorax would materially
assist the current of blood. On following these vessels into the substance of the liver, it
is found that their walls are so firmly adherent to the tissue of the organ, that, when cut
across, they remain patulous; and it is evident that they remain open under all con-

FORCE OF ASPIRATION FROM THE THORAX. 103

ditions. The thorax can therefore exert a powerful influence upon the hepatic cir-
culation ; for it is only the flaccidity of the walls of the vessels which prevents this
influence from operating throughout the entire venous system. Although this must be a
very important element in the production of the circulation in the liver, the fact that the
blood circulates in this organ in the foetus before any movements of the thorax take
place shows that it is not absolutely essential. All the influences which we have thus
far considered are merely supplementary to the action of the great central organ of the
circulation.

A farther proof, if any were needed, of the suction force of inspiration is found in an
accident which is not infrequent in surgical operations in the lower part of the neck.
When the veins in this situation are kept open by a tumor or by induration of the sur-
rounding tissues, an inspiratory effort has occasionally been followed by the entrance of
air into the circulation, an accident which is liable to lead to the gravest results. This
occurs only when a divided vein is kept patulous ; and the accident proves both the
influence of inspiration on liquids in the veins near the chest and its restriction to the
vessels in this particular situation by the flaccidity of their walls.

A full discussion of the subject of air in the veins, which is of great pathological inter-
est, does not belong to physiology. The blood is capable of dissolving a certain quantity
of atmospheric air; and a small quantity, very gradually introduced into a vein, can be
disposed of in this way. When, however, a considerable quantity suddenly finds its way
into the venous system, the patient experiences a sense of mortal distress and almost
immediately falls into a state of insensibility. A peculiar whistling sound is heard when
the air passes in ; and, if the ear be applied to the chest, we distinguish the labored
efforts of the heart, accompanied by a loud churning sound. On opening the chest after
death, the right cavities of the heart are invariably found distended with air and blood,
the blood being frothy and florid. Generally the left side of the heart is nearly or quite
empty.

The production of death from air in the veins is purely mechanical. The air, finding
its way to the right ventricle, is mixed with the blood in the form of minute bubbles and
is carried into the pulmonary artery. Once in this vessel, it is impossible for it to pass
through the capillaries of the lungs, and death by suffocation is the inevitable result, if
the quantity of air be large. It is because no blood can pass through the lungs, that the
left cavities of the heart are usually found empty.

Air injected into the arteries produces no such serious effects as air in the veins. It
is arrested in the capillaries of certain parts and in the course of time is absorbed with-
out producing any injury.

Aside from the pressure exerted by the contraction of muscles and the force of as-
piration from the thorax, the influences which assist the venous circulation are very
slight. As far as the action of the coats of the vessels themselves is concerned, their
contraction, it must be remembered, is slow and gradual, like the contraction of the
arteries ; and it is hardly possible that, in the general venous system, this should operate at
all on the blood-current, beyond the simple influence of the reduction of the caliber of
the vessel. There is a slight contraction in the vense cavse in the immediate proximity
of the heart, which is very much more extended in many of the lower vertebrate ani-
mals and may be mentioned as having an influence, very insignificant it is true, on the
flow of blood from the great veins.

In the veins which pass from above downward, the force of gravity favors the flow
of blood. This is seen by the turgescence of the veins of the neck and face, when
the head is kept for a short time below the level of the heart. If the arm be elevatvd
above the head, the veins of the back of the hand will be much reduced in size, from the
greater facility with which the blood passes to the heart, while they are distended when
the hand is allowed to hang by the side and the blood has to mount up against the force
of gravity.

104 CIRCULATION OF THE BLOOD.

In the extreme irregularity in the rapidity of the circulation in different veins, it
must frequently happen that a vessel empties its blood into another of larger size, in
which the current is more rapid. In such an instance, as a physical necessity, the more
rapid current in the larger vessel exerts a certain suction force on the fluid in the vessel
which joins with it.

Function of the Valves of the Veins.

It is difficult to comprehend, at the present day, how any anatomist could have accu-
rately described the valves of the veins and yet have been ignorant of their function ; and
the fact that their use was not understood before the description of the circulation by Har-
vey shows the greatness of this as a discovery and the shallow character of any pretence
that men of science had any definite idea of the motion of the blood before his time.

With our present knowledge of the course of the blood, it is evident that the great
function of the valves is to present an obstacle to the reflux of blood toward the
capillary system ; and it only remains to study the conditions under which they are
brought into action.

There are two distinct conditions under which the valves of the veins may be closed.
One of them is the arrest of circulation, from any cause, in veins in which the blood has
to mount against the force of gravity ; and the other, compression of veins, from any
cause (generally from muscular contraction) which tends to force the blood from the
vessels compressed into others, when the valves offer an obstruction to a flow toward the
capillaries and necessitate a current in the direction of the heart. In the first of these
conditions, the valves are antagonistic to the force of gravity, and, when the caliber of
any vessel is temporarily obliterated, they aid in directing the current into anastomotic
vessels. It is but rarely, however, that they act thus in opposition to the force of grav-
ity ; and it is only when many of the veins of a part are simultaneously compressed that
they aid in diverting the current. When a single vein is obstructed, it is not probable
that the valves are necessary to divert the current into other vessels, for this would take
place in obedience to the vis a tergo ; but when many veins are obstructed in a depend-
ent part, and the avenues to the heart become insufficient, the numerous valves divide
the columns of blood, so that the pressure is equally distributed throughout the extent
of the vessels. For, it must be remembered, the strength of the walls diminishes as
we pass from the larger veins to the periphery, and the smallest vessels, which, were
it not for the valves, would be subjected to the greatest amount of pressure, are least
calculated to bear distention. This is but an occasional function which the valves are
called upon to perform ; and it is evident that their influence is only to prevent the
weight of the entire column of blood, in vessels thus obstructed, from operating on the
smallest veins and the capillaries. It cannot make the labor of the heart, when the
blood is again put in motion, any less than if the column were undivided, as this organ
must have sufficient power to open successively each set of valves, when, of course,
they cease to have any influence whatsoever.

It is in connection with the intermittent compression of the veins that the valves
have their principal and almost-constant function. Their situation alone would lead to
this supposition. They are found in greatest numbers throughout the muscular system,
having been demonstrated by Sappey in the smallest venules ; they are also found in the
upper parts of the body, where they certainly do not operate against the force of gravity ;
while they do not exist in the cavities, where the venous trunks are not subject to com-
pression. It has already been made sufficiently evident that the action of muscles sec-
onds most powerfully the contractions of the heart. The vis a tergo from the heart is,
doubtless, generally sufficient to turn this influence of muscular compression from the
capillary system, and the valves of the veins are open ; but they stand ready, neverthe-
less, to oppose any tendency to regurgitation.

In the action of muscles, the skin is frequently stretched over the part, and the cuta-

CONDITIONS WHICH IMPEDE THE VENOUS CIRCULATION. 105

neous veins are somewhat compressed. This may be seen in the hand, by letting it hang
by the side until the veins become somewhat swollen, and then contracting the muscles,
when the skin will become tense and the veins are very much less prominent. Here the
valves have an important action. The compression of the veins is much greater in the
substance of and between the muscles than in the skin ; but the blood is forced from the
muscles into the skin, and the valves act to prevent it from taking a retrograde course.
The fact that the contraction of muscles forces blood into the veins of the skin may be
seen by surrounding the upper part of the forearm with a moderately-tight ligature,
which will distend the cutaneous veins below. If we now contract the muscles vigor-
ously, the veins below will become sensibly more distended and knotted ; showing, at
once, the passage of blood into the skin and the action of the valves.

When a vein is distended by the injection of air or a liquid forced against the valves,
it is observed that, at the point where the convex borders of the valves are attached, the
vessel is not dilated as much as at other parts. This is due to the fact that the valves
are bordered with a fibrous ring which strengthens the vessel and prevents distention
at that point, which would otherwise separate the free borders of the valves and render
them insufficient.

A full consideration of the venous anastomoses belongs to descriptive anatomy.
Suffice it to say, in this connection, that they are very numerous and provide for a
return of the blood to the heart by a number of channels. The azygos vein, the veins
of the spinal canal, and veins in the walls of the abdomen and thorax, connect the infe-
rior with the superior vena cava. Even the portal vein has lately been shown to have
its communications with the general venous system. Thus, in all parts of the organism,
temporary compression of a vein only diverts the current into some other vessel, and
permanent obliteration of a vein produces enlargement of communicating branches, which
soon become sufficient to meet all the requirements of the circulation.

Conditions which impede the Venous Circulation.

Influence of Expiration. — The influence of expiration on the circulation in the veins
near the thorax is directly opposed to that of inspiration. As the act of inspiration has
a tendency to draw the blood from these vessels into the chest, the act of expiration
assists in forcing the blood out from the vessels of the thorax and opposes a flow in
the opposite direction. The effect of prolonged and violent expiratory efforts is very
marked, being followed by deep congestion of the veins of the face and neck and a sense
of fulness in the head, which may become very distressing. The opposition to the venous
current generally extends only to vessels in the immediate vicinity of the thorax, or, it
may be stated in general terms, to those veins in which the flow of blood is assisted by
the movements of inspiration ; but, while the inspiratory influence is absolutely confined
to a very restricted circuit of vessels, the obstructive influence of very violent and pro-
longed expiration may be extended very much farther, as is seen when the vessels of the
neck, face, and conjunctiva become congested in prolonged vocal efforts, blowing, etc.
The mechanism of this is not what we might at first be led to suppose; namely, a
mere reflux from the large trunks of the thoracic cavity. Were this the case, it would
be necessary to assume an insufficiency of certain valves, which does not exist. In
extreme congestion, reflux of blood may take place to a certain extent in the external
jugular, for this vessel has but two valves, which are not competent to prevent regurgi-
tation ; the chief cause of congestion, however, is due, not to regurgitation, but to accumu-
lation from the periphery and an obstruction to the flow of blood into the great vessels.

It is in the internal jugular that the influence of expiration is most important, both
from its great size in the human subject, as compared with the other vessels, and from
the importance and delicacy of the parts from which it collects the blood. At the open-
ing of this vessel into the innominate vein, is a pair of strong and perfect valves, which
effectually close the orifice when there is a tendency to regurgitation. These valves have

106 CIRCULATION OF THE BLOOD.

attracted much attention among physiologists since the discovery of the circulation has
made it evident how important they may be in protecting the brain from reflux of
blood. When the act of expiration arrests the onward flow in the veins near the thorax,
these valves are closed and effectually protect the brain from congestion by regurgita-
tion. The blood accumulates behind the valves, but the free communication of the inter-
nal jugular with the other veins of the neck relieves the brain from congestion, unless
the effort be extraordinarily violent and prolonged.

The above remarks with regard to the influence of expiration are applicable to vocal
efforts, violent coughing or sneezing, or any unusual muscular efforts, such as straining, in
which the glottis is closed.

Eegurgitant Venous Pulse.— In the inferior animals, like the dog, if the external
jugular be exposed, a distention of the vessel is seen to accompany each expiratory act.
This is sometimes observed in the human subject, when respiration is exaggerated, and
has been called improperly the venous pulse. There is no sufficient obstacle to the regur-
gitation of blood from the thorax into the external jugular, and distinct pulsations, syn-
chronous with the movements of respiration, may be produced in this way.

It is evident that there are various other circumstances which may impede the venous
circulation. Accidental compression may temporarily arrest the flow in any particular
vein. When the whole volume of blood is materially increased, as after a full meal with
copious ingestion of liquids, the additional quantity of blood accumulates chiefly in the
venous system and proportionately diminishes the rapidity of the venous circulation.

The force of gravity also has an important influence. It is much more difficult for the
blood to mount from below upward to the heart than to flow downward from the head
and neck. The action of this is seen if comparison be made between the circulation in
the arm elevated above the head and hanging by the side. In the one case the veins are
readily emptied and contain but little blood, and in the other the circulation is more
difficult and the vessels are moderately distended. The walls of the veins are thickest
and the valves are most numerous in parts of the body which are habitually dependent.
The influence of gravity is exemplified in the production of varicose veins in the lower
extremities. This disease is frequently induced by occupations which require constant
standing; but the exercise of walking, aiding the venous circulation, as it does, by the
muscular effort, has no sucli tendency.

Circulation in the Cranial Cavity. — In the encephalic cavity, there are certain pecu-
liarities in the anatomy of some of the vessels, with exceptional conditions of the blood
as regards atmospheric pressure, which have been considered capable of essentially modi-
fying the circulation. In the adult, the cranium is a closed, air-tight box, containing the
incompressible cerebral substance, and blood ; conditions which are widely different from
those presented in other parts of the system. On this account some have gone so far as
to consider that any change in the quantity of circulating fluid in the brain is a physical
impossibility. Pathological facts in opposition to such a view are so numerous and well
established that the question does not now demand extended discussion; but it is never-
theless true that there are anatomical peculiarities in these parts, the effects of which
on the circulation present important and interesting points for study.

In the brain, the venous passages which correspond to the great veins of other parts
are in the form of sinuses between the folds of the dura mater and are but slightly
dilatable. In the perfectly-consolidated adult head, the blood is not subjected to
atmospheric pressure, as in other parts, and the semisolids and liquids which com-
pose the encephalic mass cannot increase in size in congestion and diminish in anae-
mia. Notwithstanding these conditions, the fact remains, that examinations of the
vessels of the brain after death show great differences in the quantity of blood which

CIRCULATION IN THE CRANIAL CAVITY. 107

they contain. The question then arises as to what is displaced to make room for
the blood in congestion, and what supplies the place of the blood in anaemia. An
anatomical peculiarity, which has not yet been considered, offers an explanation of
these phenomena. Magendie has shown, by observations on living animals, confirmed
by dissections of the human body, that between the pia mater and the arachnoid of the
brain and spinal cord there exists a liquid, the cephalo-rachidian fluid, which is capable
of passing from the surface of the brain to the spinal canal and communicates with the
fluid in the ventricles. This he has conclusively demonstrated to be situated, not
between the layers of the arachnoid, as was supposed by Bichat, but between the inner
layer of this membrane and the pia mater. The communication between the cranial
cavity and the spinal canal is very free. This has been demonstrated by exposing the dura
mater of the brain and of the cord, making an opening in the membranes of the cord so
as to allow the liquid to escape (which it does in quite a forcible jet), when pressure on the
membranes of the brain not only accelerated the flow but pressed out a quantity of the liquid
after all that would escape spontaneously had been evacuated. It is easy to see one of
the physiological uses of this liquid. When the pressure of blood in the arteries leading
to the brain is increased or when there is an obstacle to its return by the veins, more or
less congestion takes place, and the blood forces the liquid from the cranial into the spinal
cavity ; the reverse taking place when the supply of blood to the brain is diminished.
The functions of all highly-organized and vascular parts seem to require certain varia-
tions in the supply of blood ; and there is no reason to suppose that the brain, in its
varied conditions of activity and repose, is any exception to this general rule, although
the physiological conditions of its vascularity are not easily studied.

Physiologists, even before the time of Haller, had noticed alternate movements of
expansion and contraction in the brain, connected with the acts of respiration. This is
observed in children before the fontanels are closed, and in the adult when the brain is
exposed by an injury or a surgical operation. The movements are, an expansion with the
act of expiration, which, in violent efforts, is sometimes so considerable as to produce
protrusion, and contraction with inspiration. Magendie also studied these movements,
which he explained in the following way : With the act of expiration, the flow of blood
in the arteries is favored, and the current in the veins is retarded. If the effort be
violent, the valve at the opening of the internal jugular may be closed. This act would
produce an expansion of the brain, not from reflux by the veins, but from the fact that
the flow into the chest is impeded, and the blood, while passing in more freely by the
arteries, is momentarily confined. With inspiration, the flow into the thorax is mate-
rially aided, and the brain is in some degree relieved of this expanding force.

Robin, His, and others have noted a peculiarity in the small vessels of the brain,
spinal cord, and pia mater, which is curious, but the physiological significance of which is
not yet apparent. These vessels are surrounded by a thin, amorphous sheath, which has
a diameter of from y^^- to ^7 of an inch greater than that of the vessel itself. Be-
tween this and the blood-vessel is a transparent liquid. This structure, which has been
observed in no other part of the circulatory system, is regarded by Robin as the com-
mencement of the lymphatics of the nervous centres. What effect this disposition of
the vessels may have upon the facility with which they may become dilated or contracted,
it is difficult to determine.

Circulation in Erectile Tissues. — In the organs of generation of both sexes, there
exists a tissue which is subject to great increase in volume and rigidity when in a state
of what is called erection. The parts in which the erectile tissue exists are, in the male,
the corpora cavernosa of the penis, the corpus spongiosum, with the glans penis; and, in
the female, the corpora cavernosa of the clitoris, the gland of the clitoris, and the bulb
of the vestibule. In addition, Rouget has lately demonstrated the presence of a struct-
ure analogous to erectile tissue in the body of the uterus and in a bulb annexed to the

108 CIRCULATION OF THE BLOOD.

ovary of the human female. He has shown by injections that the uterus is capable of
erection like the penis. In some other parts, such as the nipple and the mucous mem-
brane of the vagina, which are sometimes described as erectile, the peculiar vascular
arrangement which is characteristic of true erectile tissues is not found. In the nipple,
the hardness which follows gentle stimulation is simply the result of contraction of the
smooth muscular fibres with which this part is largely supplied, and it is analogous to the
elevation of the follicles of the skin from the same cause, in what is called goose-flesh.
In the vagina, congestion may occur, as in other mucous membranes, but there is no
proper erection.

The vascular arrangement in erectile organs, of which the penis may be taken as the
type, is peculiar to them and is not found in any other part of the circulatory system.
Taking the penis as an example, the arteries, which have an unusually-thick muscular
coat, after they have entered the organ, do not simply branch and divide dichotomously,
as in most other parts, but send off large numbers of arborescent branches, which imme-
diately become tortuous and are distributed in the cavernous and spongy bodies in nu-
merous anastomosing vessels, with but a single thin, homogeneous coat, like the true
capillaries. These vessels are larger, even, than the arterioles which supply them with
blood, some having a diameter of from ^V to TV of an inch. The cavernous bodies have
an external investment of strong fibrous tissue of considerable elasticity, which sends
bands, or trabeculao, into the interior, by which it is divided up into cells. The trabeculra
are composed of fibrous tissue mixed with a large number of smooth muscular fibres.
These cells lodge the blood-vessels, which ramify in the tortuous manner already indicated
and finally terminate in the veins. The anatomy of the corpora spongiosa is essentially
the same, the only difference being that the fibrous envelope and the trabecula3 are more
delicate and the cells are of smaller size.

Without going fully into the mechanism of erection, which comes more properly
under the head of generation, it may be stated in general terms that, during sexual
excitement, or when erection occurs from any cause, the thick muscular walls of the
arteries of supply relax and allow the arterial pressure to distend the capacious vessels
lodged in the cells of the cavernous and spongy bodies. This produces the characteristic
change in the volume and position of the organ. It is evident that erection depends upon
the peculiar arrangement of the blood-vessels, and is not simply a congestion, such as
could occur in any vascular part. During erection, there is not a stasis of blood; but,
if it continue for any length of time, the quantity which passes out of the part by the
veins must be equal to that which passes in by the arteries.

Derivative Circulation. — In some parts of the circulatory system, there exists a di-
rect communication between the arteries and the veins, so that all the blood does not
necessarily pass through the minute vessels which have been described as true capilla-
ries. This peculiarity, which had been noted by Todd and Bowman, Paget, and others,
has been closely studied by M. Sucquet, who was first led to investigate the subject by
noticing that by injecting a very small quantity of fluid, entirely insufficient to fill all
the capillaries of a member, it was returned by certain of the veins. On using a black,
solidifiable injection, he found that there were certain parts of the upper and lower ex-
tremities and the head which became colored by the injection, while other parts were
not penetrated. Following this out by dissection, he showed that, in the upper extrem-
ity, the skin of the fingers and part of the palm of the hand and the skin over the ole-
cranon are provided with vessels of considerable size, which allowed the fluid injected by
the axillary artery to pass directly into some of the veins, while in other parts the veins
were entirely empty. Extending his researches to the lower extremity, he found analo-
gous communications between the vessels in the knee, toes, and parts of the sole of the
foot. He also found communications in the nose, cheeks, lips, forehead, and ends of the
ears, parts which are particularly liable to changes in color from congestion of vessels.

PULMONARY CIRCULATION. 109

It is evident that, under certain circumstances, a larger quantity of blood than usual
may pass through these parts without necessarily penetrating the true capillaries and
thus exerting a modifying influence upon nutrition. The changes which are liable to oc-
cur in the quantity of blood, in the force of the heart's action, etc., may thus take place
without disturbing the circulation in the capillaries, a provision which the functions of
the parts would seem to demand.

Pulmonary Circulation. — The vascular system of the lungs merits the name, which
is frequently applied to it, of the lesser circulation. The right side of the heart acts
simultaneously with the left, but is entirely distinct from it, and its muscular walls are
very much less powerful. The pulmonary artery has thinner and more distensible coats
than the aorta and distributes its blood to a single system of capillaries, situated very
near the heart. We have seen that the orifice of the pulmonary artery is provided with
valves which prevent regurgitation into the ventricle. In the substance of the lungs,
the pulmonary artery is broken up into capillaries, most of them just large enough to
allow the passage of the blood-corpuscles in a single row. These vessels are provided
with a single coat and form a very close net-work surrounding the air-cells. From the
capillaries the blood is collected by the pulmonary veins and conveyed to the left auri-
cle. There is no great disparity between the arteries and veins of the pulmonary system
as regards capacity. The pulmonary veins in the human subject are not provided with
valves.

The blood in its passage through the lungs does not meet with the resistance which
is presented in the systemic circulation. This fact we have often noticed in injecting
defibrinated blood through the lungs of an animal just killed. We have also observed
that an injection passes through the lungs as easily when they are collapsed as when they
are inflated. The anatomy of the circulatory system in the lungs and of the right side
of the heart shows that the blood must pass through these organs with comparative fa-
cility. The power of the right ventricle is evidently less than half that of the left, and
the pulmonary artery will sustain a much less pressure than the aorta.

The two sides of the heart act simultaneously ; and at the same time that the blood
is sent by the left ventricle to the system it is sent by the right ventricle to the lungs.
Some physiologists have endeavored to measure the pressure of blood in the pulmonary
artery. The only experiments which have not involved opening the thoracic cavity, an
operation which must interfere materially with the pressure of blood in the pulmonary
artery, as it does with the general arterial pressure, are those of Chauveau and Faivre.
These observers measured the pressure by connecting a cardiometer with a trocar intro-
duced into the pulmonary artery of a living horse through one of the intercostal spaces,
and found it to be about one-third as great as the pressure in the aorta ; an estimate
which corresponds pretty nearly with the comparative power of the two ventricles, as
deduced from the thickness of their muscular walls.

Anatomy teaches us that the capillaries of the lungs have exceedingly delicate walls;
and it is evident that rupture of these vessels from exceesive action of the heart would
lead to grave results. It has already been noted that on the right side the lungs are pro-
tected by an insufficiency of the auriculo-ventricular valves, which does not exist on the
left side, allowing a certain degree of regurgitation when the heart is acting with un-
usual force, and thus relieving, to a certain extent, the pulmonary system. This was
pointed out by Mr. King, of London, and is called the safety-valve function of the right
ventricle. We have noticed, in the heart of the ox, a similar difference between the
aortic and the pulmonic semilunar valves. If these be exposed on both sides by cutting
away portions of the ventricles, and if a current of liquid be forced against them through
the vessels, the aortic valves will be found to entirely prevent the passage of the liquid,
even under very great pressure, while the pulmonic valves permit regurgitation under
a comparatively inconsiderable force. A little reflection will make it evident that,

HO CIRCULATION" OF THE BLOOD.

when the heart is acting with undue vigor, it is quite as important to relieve the lungs
by a certain amount of regurgitation from the pulmonary artery as by insufficiency of
the tricuspid valves. This insufficiency is important, both at the auriculo-ventricular
and the pulmonic orifices, in protecting the delicate structure of the lungs from the varia-
tions in force to which the action of both ventricles is constantly liable.

On microscopical examination of the circulation in the lower animals, as the frog, the
movement of blood in the capillaries of the lungs does not present any differences from
the capillary circulation in other parts, except that the vessels seem more crowded with
corpuscles and there is no " still layer " next their walls.

There are no forces of any importance which are superadded to the action of the
right ventricle in the production of the arterial, capillary, or venous circulation in the
lungs ; but there are certain conditions which may obstruct the flow of blood through
these parts. We have already noted the effect of introduction of air into the veins in
blocking up the capillaries of the lungs and preventing the passage of blood. It is a view
pretty generally entertained that in asphyxia the non-aeration of the blood obstructs the
pulmonary circulation. We have already considered this subject rather fully in treating
of the general effects of arrest of respiration on the circulation. The celebrated experi-
ments of Bichat demonstrated the passage of black blood through the lungs in asphyxia
and its presence in the arterial system. The experiments of Dalton and others have
shown that, in this condition, the obstruction to the circulation occurs first in the sys-
temic capillaries, and the distention is propagated backward through the great vessels
and the left cavities of the heart to the right side. When the heart is exposed in a living
animal and artificial respiration is kept up, temporary arrest of the respiration produces
engorgement and labored action of both ventricles. There are no observations which show
that increase of pressure in the pulmonary artery is the first and the immediate result
of asphyxia. It is true that, after death, the right side oY the heart is engorged ; but it
is well known, from observations after death and experiments on living animals, that the
tonic contraction of the arteries is competent to empty the blood into the veins ; and
the facts just stated regarding the insufficiency of the pulmonic semilunar valves explain
how the right side of the heart may become engorged as the result of obstruction to the
blood-current in the left side. Established facts seem to show that asphyxia does not
primarily affect the pulmonary circulation, but that it is possible for venous blood to
pass through the lungs without undergoing arterialization.

Circulation in the Walls of the Heart. — The fact that the contractions of the muscu-
lar walls of the heart, by which the blood is discharged from the ventricles into the
great arteries, necessarily compress the vessels in the substance of the heart itself
would lead us to expect certain peculiarities in the cardiac circulation. Notwithstanding
this, however, in a series of experiments by Prof. II. Newell Martin, published in 1881, it
was shown that the pressure of blood in the coronary arteries in the dog, during the ven-
tricular systole, is sufficient to supply the arteries in the substance of the heart with blood
precisely as it is supplied to the general arterial system. In a number of experiments, in
which simultaneous traces of the pulse-bents were obtained, it was found that the coro-
nary and carotid pulses were practically synchronous.

General Rapidity of the Circulation.

Several questions of considerable physiological interest arise in connection with the
general rapidity of the circulation :

1. It would be interesting to determine, if possible, what length of time is occupied
by the blood in its passage through the entire circuit of both the lesser and the greater
circulation.

2. What is the time required for the passage of the entire mass of blood through the
heart ?

GENERAL EAPIDITY OF THE CIRCULATION. m

3. What influence has the number of pulsations of the heart on the general rapidity
of the circulation ?

The first of these questions is the one which has been most satisfactorily answered by
experiments on living animals. In 1827, Hering, a German physiologist, performed the
experiment of injecting into the jugular vein of a living animal a harmless substance,
which could be easily recognized by its chemical reactions, and noted the time which
elapsed before it could be detected in the blood of the vein of the opposite side. This
gave the first correct idea of the rapidity of the circulation ; for, although the older
physiologists had studied the subject, their estimates were founded on calculations which
had no accurate basis and gave very varied results. The experiment of Hering, as modi-
fied by Bernard, is often roughly performed as a physiological demonstration. The follow-
ing is Bernard's method of making this demonstration : In a good-sized dog, expose both
external jugular veins as largely as possible. Place a serre-fine upon one jugular at its
superior portion, press out the blood below and isolate a portion free from blood, by
means of another serre-fine placed on the vein about an inch below the first. Fill this
isolated portion of the vein with a strong solution of ferrocyanide of potassium in
water, which is injected by means of a hypodermic syringe. The serre-finea are then
suddenly removed and the salt immediately begins to circulate in the vessels. The blood
is then collected from the opposite jugular at intervals of five seconds. The specimens
of blood are then boiled with a little water and the addition of a small quantity of sul-
phate of soda, filtered, and the clear fluid is tested with a drop of persulphate of iron,
which gives a blue reaction when the ferrocyanide is present. When the experiment is
carefully performed, the blue color appears in the extract of blood drawn about ten sec-
onds after removal of the serre-fines. In making the test, the addition of a drop of nitric
acid before the persulphate of iron is added will render the blue reaction much more
prompt and distinct.

The experiments of Hering were evidently conducted with great care and accuracy.
He drew the blood at intervals of five seconds after the commencement of the injection, and
thus, by repeated observations, ascertained pretty nearly the rapidity of a circuit of blood
in the animals upon which he experimented. Yierordt collected the blood as it flowed,
in little vessels fixed on a disk revolving at a known rate, which gave more exactness
to the observations. The results obtained by these two observers were nearly identical.

The length of time occupied by a portion of blood in making a complete circuit of
the vascular system, in the human subject, is only to be deduced from observations on
the inferior animals ; but, before this application is made, it will be well to examine the
objections, if any exist, to the experimental procedure above described.

The only objection which could be made is, that a saline solution, introduced into the
torrent of the circulation, would have a tendency to diffuse itself throughout the whole
mass of blood, it might be, with considerable rapidity. This objection to the observa-
tions of Hering has been made by Matteucci and is considered by him as fatal to their
accuracy. It certainly is an element which should be taken into account ; but, from the
definite data which have been obtained concerning the rapidity of the arterial circula-
tion and the inferences which are unavoidable with regard to the rapidity of the venous
circulation, it would seem that the saline solution must be carried on by the mere rapid-
ity of the arterial flow to the capillaries, which are very short, taken up from them, and
carried on by the veins, and thus through the entire circuit, before it has had time to
diffuse itself to any considerable extent. It is not apparent how this objection can be
overcome, for a substance must be used which will mix with the blood, otherwise it
could not pass through the capillaries.

There seems no reason why, with the above restrictions, the results obtained by
Hering should not be accepted, and their application be made to the human subject.

Hering found that the rapidity of the circulation in different animals was in inverse
ratio to their size and in direct ratio to the rapidity of the action of the heart.

112 CIRCULATION" OF THE BLOOD.

The following are the mean results in certain of the domestic animals, taking the
course from jugular to jugular, when the blood passes through the lungs and through the
capillaries of the face and head :

In the Horse, the circulation is accomplished in 27'3 seconds.
" Dog, " " 15-2 "

" Goat, " " 12-8 "

" Kabbit, " " 6-9 "

Applying these results to the human subject, taking into account the size of the body
and the rapidity of the heart's action, the duration of the circuit from one jugular to
the other may be estimated at 21'4 seconds, and the general average through the entire
system, at 23 seconds. This is simply approximative ; but the results in the inferior ani-
mals may be received as very nearly, if not entirely accurate.

Estimates of the time required for the passage of the whole mass of blood through
the heart are even less definite than the estimate of the general rapidity of the circula-
tion. To arrive at any satisfactory result, it is necessary to know the entire quantity of
blood in the body and the exact quantity which passes through the heart at each pulsa-
tion. If we divide the whole mass of blood by the quantity discharged from the heart
with each ventricular systole, we ascertain the number of pulsations required for the
passage of the whole mass of blood through the heart ; and, knowing the number of
beats per minute, we can ascertain the length of time thus occupied. The objection to
this kind of estimate is the inaccuracy of the data respecting the quantity of blood in
the system as well as the quantity which passes through the heart with each pulsation.
Nevertheless, an estimate can be made, which, if it be not entirely accurate, cannot be
very far from the truth.

The entire quantity of blood, according to estimates which seem to be based on the
most reliable data, is about one-eighth the weight of the body, or eighteen pounds, in a
man weighing one hundred and forty-four. The quantity discharged at each ventricular
systole is estimated by Valentin at five ounces, and by Volkmann, at six ounces. In
treating of the capacity of the different cavities of the heart, it has been noted that the
left ventricle, when fully distended, contains from five to seven ounces. Assuming that,
at each systole, the left ventricle discharges all its blood, except perhaps a few drops,
and that this quantity in an ordinary-sized man is five ounces (for in the estimates of
Eobin and Hiffelsheim, the cavities were fully distended, and contained more than under
the ordinary conditions of the circulation), it would require fifty-eight pulsations for the
passage through the heart of the entire mass of blood. Assuming the pulsations to be
seventy-two per minute, this would occupy about forty-eight seconds.

The almost instantaneous action of certain poisons, which must act through the blood,
confirms our ideas with regard to the rapidity of the circulation. The intervals between
the introduction of some agents, strychnine for example, into the circulation, and the
characteristic effects on the system, have been carefully noted by Blake, whose observa-
tions coincide pretty closely in their results with the experiments of Hering.

The relation of the rapidity of the circulation to the frequency of the heart's action is
a question of considerable interest, which was not neglected in the experiments of Hering.
It is evident that, if the charge of blood sent into the arteries be the same, or nearly the
same, under all circumstances, any increase in the number of pulsations of the heart would
produce a corresponding acceleration of the general current of blood. But this is a propo-
sition which cannot be taken for granted ; and there are many facts which favor a con-
trary opinion. It may be enunciated as a general rule that when the acts of the heart
increase in frequency they diminish in force ; which renders it probable that the ventricle
is most completely distended and emptied when its action is moderately slow. When,
however, the pulse is very much accelerated, the increased number of pulsations of the
heart might be sufficient to overbalance the diminished force of each act and would thus

PHENOMENA IN THE CIRCULATORY SYSTEM AFTER DEATH. 113

actually increase the rapidity of the circulation. Hering has settled these questions ex-
perimentally. His observations were made on horses, by increasing the frequency of
the pulse, on the one hand, physiologically, by exercise, and on the other hand, patho-
logically, by inducing inflammatory action. He found, in the first instance, that, in a
horse, with the heart beating at the rate of thirty-six per minute, with eight respiratory
acts, ferrocyauide of potassium injected into the jugular appeared in the vessel on the
opposite side after an interval of from twenty to twenty-five seconds. By exercise, the
number of pulsations was raised to one hundred per minute, and the rapidity of the cir-
culation was from fifteen to twenty seconds. The observations were made with an
interval of twenty-four hours. The same results were obtained in other experiments.
Here there is a considerable increase in the rapidity of the circulation following a physio-
logical increase in the number of beats of the heart; but the value of each beat is materi-
ally diminished; otherwise, the rapidity of the current would be increased about three
times, as the pulse became three times as frequent. In its tranquil action, with the pulse
at thirty-six, the heart contracted thirteen times during one circuit of blood ; while it
required twenty-nine pulsations to send the blood over the same course, after exercise,
with the pulse at one hundred; showing a diminution in the value of the ventricular sys-
tole of more than one-half. In animals suffering under inflammatory fever, either spon-
taneous or produced by irritants, the same observer found a diminution in the rapidity
of the circulation, accompanying acceleration of the pulse. In one observation, inflam-
mation was produced in the horse by the injection of amn\onia into the pericardium. At
the commencement of the experiment, the pulse was from seventy-two to eighty-four
per minute, and the duration of the circulation was about twenty-five seconds. The next
day, with the pulse at ninety, the circulation was accomplished in from thirty-five to
forty seconds; and the day following, with the pulse at one hundred, the rapidity of the
circulation was diminished to from forty to forty-five seconds.

If we be justified in applying the above-mentioned observations to the human subject
(and there is no reason why this should not be done), it is shown that, when the pulse is
accelerated in disease, the value of the contractions of the heart, as represented by the
quantity of blood discharged, bears an inverse ratio to their number and is so much
diminished as absolutely to produce a current of less rapidity than normal.

With regard to the relations between the rapidity of the heart's action and the gen-
eral rapidity of the circulation, the following conclusions may be given as the results of
experimental inquiry:

1. In physiological increase in the number of beats of the heart, as the result of exer-
cise, for example, the general circulation is somewhat increased in rapidity, though not
in proportion to the increase in the pulse.

2. In pathological increase of the heart's action, as in febrile movement, the rapidity
of the general circulation is generally diminished, it may be, to a very great extent.

3. Whenever the number of beats of the heart is considerably increased from any
cause, the quantity of blood discharged at each ventricular systole is very much dimin-
ished, either from lack of complete distention or from imperfect emptying of the cavities.

Phenomena in the Circulatory System after Death. — We do not believe that any one
has proven the existence of a force in the capillaries or the tissues (capillary power) which
materially assists the circulation during life or produces any movement immediately after
death ; and we shall not, therefore, discuss the extraordinary post-mortem phenomena
of circulation, particularly those which have been observed by Dr. Dowler in subjects
dead of yellow fever. But nearly every autopsy shows that, after death, the blood does
not remain equally distributed in the arteries, capillaries, and veins. Influenced by
gravitation, it accumulates in and discolors the most dependent parts of the body. The
arteries' are always found empty, and all the blood in the body accumulates in the venous
system and capillaries ; a fact which was observed by the ancients and gave rise to the
8

114 RESPIRATION.

belief that the arteries, as their name implies, were air-bearing tubes. This has long
engaged the attention of physiologists, who have attempted to explain it by various
theories. "Without discussing the views on this subject anterior to our knowledge of the
great contractile power of the arteries as compared with other vessels, we may cite the
following experiment of Magendie as offering a satisfactory explanation. If the artery
and vein of a limb be exposed in a living animal and all the other vessels be tied, com-
pression of the artery does not immediately arrest the current in the vein, but the blood
will continue to flow until the artery is entirely emptied. The artery, when relieved
from the distending force of the heart, reacts on its contents by virtue of its contractile
coat and completely empties itself of blood. An action similar to this takes place after
death throughout the entire arterial system. The vessels react on their contents and
gradually force all the blood into and through the capillaries, which are very short, to
the veins, which are capacious, distensible, and but slightly contractile. This begins
immediately after death, while the irritability of the muscular coat of the arteries remains,
and is seconded by the subsequent cadaveric rigidity, which affects all the involuntary,
as well as the voluntary muscular fibres. Once in the venous system, the blood cannot
return on account of the valves. Thus, after death, the blood is found in the veins and
capillaries of dependent parts of the body.

CHAPTER IV.

RESPIRA TION— RESPIRA TOR F M 0 VEMENTS.

General considerations— Physiological anatomy of the respiratory organs— Eespiratory movements of the larynx-
Epiglottis— Trachea and bronchial tubes— Parenchyma of the lungs— Movements of respiration— Inspiration-
Muscles of inspiration— Expiration— Influence of the elasticity of the pulmonary structure and walls of the chest
upon expiration — Muscles of expiration — Action of the abdominal muscles in expiration — Types of respiration —
Frequency of the respiratory movements— Eelations of inspiration and expiration to each other— The respiratory
sounds— Capacity of the lungs and the quantity of air changed in the respiratory acts— Kesidual air— Eeserve
air — Tidal, or breathing air — Complemental air — Extreme breathing capacity — Eelations in volume of the expired
to the inspired air — Diffusion of air in the lungs.

THE characters of the blood are by no means identical in the three great divisions of
the vascular system ; but physiologists have thus far been able to investigate only the dif-
ferences which exist between arterial and venous blood, for the capillaries are so short,
communicating directly with the arteries on the one side and the veins on the other, that
it is impossible to obtain a specimen of true capillary blood. In the capillaries, how-
ever, the nutritive fluid, which is identical in all parts of the arterial system, under-
goes a remarkable change, which renders it unfit for nutrition. Thus modified it is
known as venous blood ; and, as we have seen, the only office of the veins is to
carry it back to the right side of the heart, to be sent to the lungs, where it loses
the vitiating materials it has collected in the tissues, takes in a fresh supply of
oxygen, and goes to the left, or systemic heart, again prepared for nutrition. As the
processes of nutrition vary in different parts of the organism, there are of necessity cor-
responding variations in the composition of the blood throughout the venous system.

The important principles which are given off by the lungs are exhaled from the
blood; and the gas which disappears from the air is absorbed by the blood, mainly by
its corpuscular elements.

A proper supply of oxygen is indispensable to nutrition and even to the compara-
tively-mechanical process of circulation ; but it is no less necessary to the nutritive pro-
cesses that carbonic acid, which the blood acquires in the tissues, should be given off.

Respiration may be defined strictly as the process by which the various tissues and
organs receive and appropriate oxygen.

GENERAL CONSIDERATIONS. 115

As it is almost exclusively through the blood that the tissues and organs are supplied
with oxygen, and as the blood receives and exhales most of the carbonic acid, the respira-
tory process may be said to consist chiefly in the change of venous into arterial blood.
But experiments have demonstrated that the tissues themselves, detached from the body
and placed in an atmosphere of oxygen, will absorb this gas and exhale carbonic acid.
Under these circumstances, they certainly respire ; and it is evident, therefore, that, in
this process, the intervention of the blood is not an absolute necessity.

The tide of air in the lungs does not constitute respiration, as we now understand it.
These organs merely serve to facilitate the introduction of oxygen into the blood and the
exhalation of carbonic acid* If the system be drained of blood, or if the blood be
rendered incapable of interchanging its gases with the air, respiration ceases, and all the
phenomena of asphyxia are presented, although air be introduced into the lungs with
perfect regularity. It must be remembered that the essential processes of respiration
take place in all the tissues and organs of the system and not in the lungs. Respiration
is a process similar to what are known as the processes of nutrition ; and, although it is
much more active and uniform than the ordinary nutritive acts, it is inseparably con-
nected with, and strictly a part of the general process. As, in the nutrition of the sub-
stance of tissues, the nitrogenized principles of the blood united with inorganic matters
are used up, transformed into the tissue itself, finally changed into excrementitious prod-
ucts, such as urea or cholesterine, and discharged from the body, so the oxygen of the
blood is appropriated, and carbonic acid, which is an excrementitious product, is produced,
whenever tissues are worn out and regenerated. There is a necessary and inseparable
connection between all these processes ; and they must be considered, not as distinct
functions, but as different parts of the one great function of nutrition. As we are as
yet unable to follow out all the intermediate changes which take place between the
appropriation of nutritive materials from the blood and the production of effete or ex-
crementitious substances, it is impossible to say precisely how oxygen is used by the
tissues and how carbonic acid is produced. "We only know that more or less oxy-
gen is necessary for the nutrition of all tissues, in all animals, high or low in the scale,
and that the tissues produce a certain quantity of carbonic acid. The fact that oxygen is
consumed with much greater rapidity than any other nutritive principle and that the
production of carbonic acid is correspondingly active, as compared with other effete
products, points pretty conclusively to a connection between the absorption of the one
principle and the production of the other.

In some of the lowest of the inferior animals, there is no special respiratory organ,
the interchange of gases being effected through the general surface. Higher in the ani-
mal scale, special organs are found, which are called gills when the animals live under
water and respire the air which is in solution in the water, and lungs when the air is
introduced in a gaseous form. Animals possessed of lungs have a tolerably-perfect cir-
culatory apparatus, so that the blood is made to pass continually through the respiratory
organs. In the human subject and the warm-blooded animals generally, the lungs are
very complex and present an immense surface by which the blood is exposed to the air,
separated from it simply by a delicate and permeable membrane. These animals are like-
wise provided with a special heart, which has the function of carrying on the pulmonary
circulation. Although respiration is carried on to some extent by the general surface, the
lungs are the important and essential onrans in which the interchange of gases takes place.

The essential conditions for respiration in animals which have a circulating nutritive
fluid are: air and blood, separated by a membrane which will allow the passage of gases.
The effete products of respiration in the blood pass out and vitiate the air. The air is
deprived of a certain portion of its oxygen, which passes into the blood, to be conveyed
to the tissues. Thus the air must be changed to supply fresh oxygen and get rid of the
carbonic acid. The rapidity of this change is in proportion to the nutritive activity of
the animal and the rapidity of the circulation of the blood.

116 KESPIRATIOK

In treating in detail of the function of respiration, it will be convenient to make the
following division of the subject:

1. The mechanical phenomena of respiration ; or the processes by which the fresh air
is introduced into the lungs (inspiration), and the vitiated air is expelled (expiration).

2. The changes which the air undergoes in respiration.

3. The changes which the blood undergoes in respiration.

4. The relations of the consumption of oxygen and the production of carbonic acid to
the general process of nutrition.

5. The respiratory sense ; a want, on the part of the system, which induces the re-
spiratory acts (besoin de respirer).

6. Cutaneous respiration.

7. Asphyxia.

The study of these questions will be facilitated by a brief consideration of some
points in the anatomy of the respiratory organs.

Physiological Anatomy of the Respiratory Organs.

Passing backward from the mouth to the pharynx, two openings are observed;
a posterior opening, which leads to the oesophagus, and an anterior opening, the opening
of the larynx, which is the commencement of the passages devoted exclusively to respi-
ration. The structure of the oesophagus and of the air-tubes is entirely different. The
oesophagus is flaccid and destined to receive and convey to the stomach the articles of
food, which are introduced by the constrictions of the muscles above. The trachea and
its ramifications are exclusively for the passage of air, which is taken in by a suction
force produced by the enlargement of the thorax. The act of inhalation requires that
the tubes should be kept open by walls sufficiently rigid to resist the external pressure
of the air.

Beginning our description with the larynx, it is seen that the cartilages of which it is
composed are sufficiently rigid and unyielding to resist the pressure produced by any in-
spiratory effort. Across its superior opening are the vocal chords, which are four in num-
ber and have a direction from before backward. The two superior are called the false vocal
chords, because they are not concerned in the production of the voice. The two inferior
are the true vocal chords. They are ligamentous bands covered by folds of mucous mem-
brane, which is quite thick on the superior chords and very thin and delicate on the in-
ferior. Anteriorly, they are attached to a fixed point between the thyroid cartilages, and
posteriorly, to the movable arytenoid cartilages. Air is admitted to the trachea through
an opening between the chords, which is called the rima glottidis. Little muscles, arising
from the thyroid and cricoid and attached to the arytenoid cartilages, are capable of
separating and approximating the points to which the vocal chords are attached posteri-
orly, so as to open and close the rima glottidis.

If the glottis be exposed in a living animal, certain regular movements are presented,
which are synchronous with the acts of respiration. The larynx is opened at each inspira-
tion by the action of the muscles referred to above, so that the air has a free entrance to
the trachea. At the termination of the inspiratory act, these muscles are relaxed, the
vocal chords fall together by their own elasticity, and, in expiration, the chink of the
glottis returns to the condition of a narrow slit. These respiratory movements of the
glottis are constant and are essential to the introduction of air in proper quantity into the
lungs. The expulsion of air from the lungs is rather a passive process and tends in it-
self to separate the vocal chords; but inspiration, which is active and more violent, were
it not for the movements of the glottis, would have a tendency to draw the vocal chords
together. The muscles which are concerned in producing these movements are animated
by the inferior laryngeal branches of the pneumogastric nerves. If these nerves be
divided, the movements of the glottis are arrested, and respiration is very seriously inter-

PHYSIOLOGICAL ANATOMY OF THE RESPIRATORY ORGANS. 117

fered with. This is particularly marked in young animals, in which the walls of the
larynx are comparatively yielding, when the operation is frequently followed by immedi-
ate death from suffocation. The movements of the glottis enable us to understand how
foreign bodies of considerable size are sometimes accidentally introduced into the air-
passages. The respiratory movements of the larynx are entirely distinct from those con-
cerned in the production of the voice and are simply for the purpose of facilitating the
entrance of air in respiration.

Attached to the anterior portion of the larynx, is the epiglottis, a little, leaf-shaped
lamella of fibro-cartilage, which, during ordinary respiration, projects upward and lies
against the posterior portion of the tongue. During the act of deglutition, respiration is
momentarily interrupted, and the air-passages are protected by the tongue, which presses
backward, carrying the epiglottis before it and completely closing the opening of the

FIG. 35.— Trachea and bronchial lubes. (Sappey.)

1, 2, larynx; 3,3, trachea; 4, bifurcation of the trachea; 5, right bronchus; 6, left bronchus ; 7, bronchial division to
the upper lobe of the right lung; 8, division to the middle lobe; 9, division to the lower lobe; 10. division to
the upper lobe of the left lung; 11, division to the lower lobe; 12, 12, 12, 12, ultimate ramifications of the
bronchi; 13, 13, 13, 13, lungs, represented in contour; 14, 14, summit of the lungs; 15, 15, base of the lungs.

larynx. Physiologists have questioned whether the epiglottis be necessary to the com-
plete protection of the air-passages ; and, repeating the experiments of Magendie, it has
been frequently removed from the lower animals without apparently interfering with the
proper deglutition of solids or liquids. We have been satisfied, from actual experiment,
that a dog will swallow liquids and solids immediately after the ablation of the epiglottis,
without allowing any to pass into the trachea ; but it becomes a question whether this
experiment can be absolutely applied to the human subject. In a case of loss of the

118

EESPIBATION.

entire epiglottis, which was observed in the Bellevue Hospital, the patient experienced
slight difficulty in swallowing, from the passage of little particles into the larynx, which
produced cough. This case seemed to show that the presence of the epiglottis, in the
human subject at least, is necessary to the complete protection of the air-passages in
deglutition.

Passing down the neck from the larynx toward the lungs, is a tube, from four to four
and a half inches in length and about three-quarters of an inch in diameter, which is
called the trachea. It is provided with cartilaginous rings, from sixteen to twenty in
number, which partially surround the tube, leaving about one-third of its posterior por-
tion occupied by fibrous tissue mixed with a certain number of non-striated muscular
fibres. Passing into the chest, the trachea divides into the two primitive bronchia, the
right being shorter, larger, and more horizontal than the left. These tubes, provided, like
the trachea, with imperfect cartilaginous rings, enter the lungs, divide and subdivide, until
the minute ramifications of the bronchial tree open directly into the air-cells. After
penetrating the lungs, the cartilages become irregular and are in the form of oblong,
angular plates, which are so disposed as to completely encircle the tubes. In tubes of
very small size, these plates are fewer than in the larger bronchia, until, in tubes of a
less diameter than ^ of an inch, they are lost altogether.

i. — Lungs, anterior view. (Sappey.)
I upper lobe, of the, left lung; 2, lower lobe; S, fissure; 4, notch corresponding to the apex of t?ie heart; 5.
pericardium; 6, upper lobe of the right lung; 7, middle lobe; 8, lower lobe; S, fissure; 10, fissure; 11,
diaphragm ; 12, anterior mediastinum ; 13, thyroid gland ; 14, middle cervical aponeurosis ; 15, process of attach-
ment of the mediastinum to the pericardium; 16, 16, seventh ribs; 17, 17, transversales musclea; 18, linea alba.

PHYSIOLOGICAL ANATOMY OF THE RESPIRATORY ORGANS. 119

The walls of the trachea and bronchial tubes are composed of two distinct mem-
branes ; an external membrane, between the layers of which the cartilages are situated,
and a lining mucous membrane. The external membrane is composed of inelastic and
elastic fibrous tissue. Posteriorly, in the space not covered by cartilaginous rings, these
fibres are mixed with a certain number of unstriped, or involuntary muscular fibres, which
exist in two layers ; a thick internal layer, in which the fibres are transverse, and a thinner
longitudinal layer, which is external. This collection of muscular fibres is sometimes
called the trachealis muscle. Throughout the entire system of bronchial tubes, there
are circular fasciculi of muscular fibres lying just beneath the mucous membrane, with a
number of longitudinal elastic fibres. The character of the bronchi abruptly changes
in tubes less than ^ of an inch in diameter. They lose4 the cartilaginous rings, and
the external and the mucous membranes become so closely united that they can no
longer be separated by dissection. The circular muscular fibres continue down to the air-
cells. The mucous membrane is smooth, covered by ciliated epithelium, the movements
of the cilia being always from within outward, and it is provided with numerous mucous
glands. These glands are of the racemose variety and, in the larynx, are of considerable
size. In the trachea and bronchi, racemose glands exist in the membrane on the posterior
surface of the tubes ; but anteriorly are small follicles, terminating in a single, and some-
times a double, blind extremity. These follicles are lost in tubes measuring less than ^
of an inch in diameter.

FIG. 87. — Bronchia and lungs, posterior view. (Sappey.)

1, 1, summit of the lunQs; 2, 2, base of the lung* ; 8, trachea ; 4. right bronchus ; 5, diriaion to the upper lob*
of the lung; 0, dirlnion to the lower lobe ; 7, left bronchus ; 3. division to the upper Job, ; '.), ilirlxiiin to the.
lower lobe; 10, left branch of the pulmonary artery : 11. risrht braiich ; 12, left auricle of the heart: \A. K-ft MI-
perior pulmonary vein ; 14, left inferior pulmonary vein ; 15. ritrht superior pulmonary vein ; 1(5, right inferior pul-
monary vein; 17, inferior vena cava; IS, left ventricle of the heait; ID, right ventricle.

It is the anatomy of the parenchyma of the lungs which possesses the most physio-
logical interest, for here the essential processes of respiration take place. When mod-
erately inflated, the lungs have the appearance of irregular cones, with rounded apices,
and concave bases resting upon the diaphragm. They fill all of the cavity of the chest
which is not occupied by the heart and great vessels, and are completely separated from
each other by the mediastinum. In the human subject, the lungs are not attached to the

120

RESPIRATION".

thoracic walls, but are closely applied to them, each covered by a reflection of the serous
membrane which lines the cavity of the corresponding side. Thus they necessarily fol-
low the movements of expansion and contraction of the thorax. Deep fissures divide
the right lung into three lobes and the left lung into two. The surface of the lungs is
divided into irregularly-polygonal spaces, from £ of an inch to an inch in diameter,
which mark what are sometimes called the pulmonary lobules; although this term is in-
correct, as each of these divisions includes quite a number of the true lobules.

Following out the bronchial tubes from the diameter of -fa of an inch, the smallest,
which are from T|-o to TV of an inch in diameter, open into a collection of oblong vesicles,

which are the air-cells. Each collection
of vesicles constitutes one of the true pul-
monary lobules and is from T^ to -^ of
an inch in diameter. After entering the
lobule, the tube forms a sort of tortuous
central canal, sending off branches which
terminate in groups of from eight to fif-
teen pulmonary cells. The cells are a
little deeper than they are wide and have
each a rounded, blind extremity. Some
are smooth, but many are marked by
little circular constrictions, or rugae. In
the healthy lung of the adult, after death,
they measure from ^^ to T£7 or -fa of an
inch in diameter, but are capable of very
great distention. The smallest cells are
in the deep portions of the lungs, and the
largest are situated near the surface.
There are considerable variations in the
size of the cells at different periods of
life. The smallest cells are found in young
children, and they progressively increase
in size with age. The walls of the air-
cells contain numerous small elastic fibres,
which do not form distinct bundles for
each air-cell, but anastomose freely with
each other, so that the same fibres belong
to two or more cells. This structure is peculiar to the parenchyma of the lungs and
gives to these organs their great distensibility and elasticity, properties which play an im-
portant part in expelling the air from the chest, as a consequence simply of cessation
of the action of the inspiratory muscles. Interwoven with these elastic fibres, is the
richest plexus of capillary blood-vessels found in the economy. The vessels are larger
than the capillaries in other situations, and the plexus is so close that the spaces between
them are narrower than the vessels themselves. When distended, the blood-vessels form
the greatest part of the walls of the cells.

Lining the air-cells, are very thin scales of pavement-epithelium, from ^Vo to ^-^ of
an inch in diameter, which are applied directly to the walls of the blood-vessels. The
epithelium here does not seem to be regularly desquamated, as in other situations. Ex-
amination of injected specimens shows that the blood-vessels are so situated between the
cells, that the blood in the greater part of their circumference is exposed to the action of
the air.

The entire mass of venous blood is distributed in the lungs by the pulmonary artery.
Arterial blood is conveyed to these organs by the bronchial arteries, which ramify and
subdivide on the bronchial tubes and follow their course into the lungs, for the nourish-

FIG. 38. — Mould of a terminal bronchus and a growp of
air-cells moderately distended by injection, from, the
human subject, (Robin.)

MOVEMENTS OF RESPIRATION. 121

ment of these parts. It is possible that the tissue of the lungs may receive some nourish-
ment from the blood conveyed there by the pulmonary artery ; but, as this vessel does
not send any branches to the bronchial tubes, it is undoubtedly the bronchial arteries
which supply the material for their nutrition and for the secretion of the mucous glands.
This is one of the anatomical reasons why inflammatory conditions of the bronchial tubes
do not extend to the parenchyma of the lungs, and vice versa.

FIG. 39. — Section of the parenchyma of the human lung, injected through the pulmonary artery. (Schulze.)
a, a, c, c, walls of the air-cells; 6, small arterial branch.

The foregoing anatomical sketch shows the admirable adaptation of the trachea and
bronchial tubes to the passage of the air by inspiration to the deep portions of the lungs,
and the favorable conditions which it there meets with for an interchange of the elements
of the air and blood. It is also evident, from the enormous number of air-cells, that the
respiratory surface must be immense.1

Movements of Respiration.

In man and in the warm-blooded animals generally, inspiration takes place as a con-
sequence of enlargement of the thoracic cavity and the entrance of a quantity of air
through the respiratory passages corresponding to the increased capacity of the lungs.
In the mammalia, the chest is enlarged by the action of muscles ; and, in ordinary respi-
ration, inspiration is an active process, while expiration is comparatively passive.

A glance at the physiological anatomy of the thorax in the human subject makes it
evident that the action of certain muscles will considerably increase its capacity. In the
first place, the diaphragm mounts up into its cavity in the form of a vaulted arch. By
contraction of its fibres, it is brought nearer a plane, and thus the vertical dianii-tor of
the thorax is increased. The walls of the thorax are formed by the dorsal vertebra and

» Hales estimated the combined surface of the air-cells at 289 square feet; Koill at about 15-2 square foot: find
Liebcrkiihn, at 1,500 square feet. There are not sufficient data on this point for us to form any thin<r like a reliable
estimate. It is simply evident that the extent of surface must be very proat. In pnsslnsr from flu- l<>\vvr to tho
hig-her orders of animals, it is seen that Nature provides for the necessity of an increase in the activity of the respira-
tory process, by a diminished size and a multiplication of tho air-cells.

122

EESPJRATIOK

ribs posteriorly, by the upper ten ribs laterally, and by the sternum and costal cartilages
anteriorly. The direction of the ribs, their mode of connection with the sternum by the
costal cartilages, and their articulation with the vertebral column, are such that, by their
movements, the antero-posterior and transverse diameters of the chest may be consider-
ably modified.

Inspiration.

The ribs are somewhat twisted upon themselves and have a general direction forward
and downward. The first rib is nearly horizontal, but the obliquity of the ribs progressively
increases from the upper to the lower parts of the chest. They are articulated with the
bodies of the vertebra?, so as to allow of considerable motion. The upper seven ribs are
attached by the costal cartilages to the sternum, these cartilages running upward and

FIG. 40.— Thorax, anterior view. (Sappey.)

1, 2, 3, sternum ; 4, circumference of the upper portion of
the thorax: 5, circumference of the base of the
thorax; 6, first rib; 7, second rib; 8, 8, last five ster-
nal ribs; 9, upper three false ribs; 10, last two, or
floating ribs ; 11, costal cartilages.

FIG. 41,— Thorax, posterior mew. (Sappey.)
1, 1, spinous processes of the dorsal vertebrae ; 2, 2,
laminsn of the vertebrae ; 3, 3, transverse processes ;
4. 4, dorsal portions of the ribs ; 5, 5, angles of the
ribs.

inward. The cartilages of the eighth, ninth, and tenth ribs are joined to the cartilage
of the seventh. The eleventh and twelfth are floating ribs and are attached only to the
vertebras.

It may be stated, in general terms, that inspiration is effected by descent of the dia-
phragm and elevation of the ribs ; and expiration, by elevation of the diaphragm and
descent of the ribs.

Arising severally from the lower border of each rib and attached to the upper border
of the rib below, are the eleven external intercostal muscles, the fibres of which have
an oblique direction from above downward and forward. Attached to the inner bor-
ders of the ribs are the internal intercostals, which have a direction from above downward
and backward, nearly at right angles to the fibres of the external intercostals. There are
also a number of muscles attached to the thorax and spine, thorax and head, upper part
of humerus, etc., which are capable of elevating either the entire chest or the ribs.
These must act as muscles of inspiration, when the attachments to the thorax become
the movable points. Some of them are called into action during ordinary respiration ;
others act as auxiliaries when respiration is a little exaggerated, as after exercise, and are

MUSCLES OF INSPIRATION. 123

called ordinary auxiliaries ; while others, which ordinarily have a different function, are
only brought into play when respiration is excessively difficult, and are called extraordi-
nary auxiliaries.

The following are the principal muscles concerned in inspiration :

Muscles of Inspiration.

Ordinary Respiration.
Muscle. Attachments.

Diaphragm Circumference of lower border of thorax.

Scalenus anticus Transverse processes of third, fourth, fifth, and sixth cer-
vical vertebrae tubercle of first rib.

Scalenus medius Transverse processes of lower six cervical vertebras

upper surface of first rib.

Scalenus posticus , Transverse processes of lower two or three cervical ver-
tebrae outer surface of second rib.

External intercostals Outer borders of the ribs.

Sternal portion of internal interco^tals . .Borders of the costal cartilages.

Twelve levatores costarum Transverse processes of dorsal vertebrae ribs, between

the tubercles and angles.

Ordinary Auxiliaries.

Serratus posticus superior Ligamentum nuchae, spinous processes of last cervical

and upper two or three dorsal vertebrae upper bor-
ders of second, third, fourth, and fifth ribs, just beyond
the angles.

Sterno-mastoideus Upper part of sternum mastoid process of temporal

bone.

Extraordinary Auxiliaries.

Levator anguli scapuke Transverse processes of upper three or four cervical

vertebrae posterior border of superior angle of

scapula.

Trapezius (superior portion) Ligamentum nuchae and seventh cervical vertebra

upper border of spine of scapula.

Pectoralis minor Coracoid process of scapula anterior surface and up-
per margins of third, fourth, and fifth ribs, near the
cartilages.

Pectoralis major (inferior portion) Bicipital groove of humerus costal cartilages and low-
er part of sternum.

Serratus magnus Inner margin of posterior border of scapula external

surface and upper border of upper eight ribs.

Action of the Diaphragm. — The descriptive and general anatomy of the diaphragm
gives a pretty correct idea of its functions in respiration. It arises, anteriorly, from the
inner surface of the ensiform cartilage, laterally, from the inner surface of the lower
borders of the costal cartilages and the six or seven inferior ribs, passes over the qnadra-
tus lumborum by the external arcuate ligament, and the psoas magnus by the internal
arcuate ligament, and has two tendinous slips of origin, called crune of the diapliniirm,
from the bodies of the second, third, and fourth lumbar vertebra and the interrortebral
cartilages on the right side, and the second and third lumbar vertebra) and the interver-
tebral cartilages on the left side. From this origin, which extends around the lower cir-
cumference of the thorax, it mounts into the cavity of the chest, forming a vaulted
arch, or dome, with its concavity toward the abdomen and its convexity toward the
lungs. In the central portion, there is a tendon of considerable size and shaped some-

124: RESPIRATION.

thing like the club on a playing-card, with middle, right, and left leaflets. The remain-
der of the organ is composed of radiating fibres of voluntary muscular tissue. The
oesophagus, aorta, and inferior vena cava pass through the diaphragm from the thoracic
to the abdominal cavity, by three openings.

The opening for the oesophagus is surrounded by muscular fibres, by which it is par-
tially closed when the diaphragm contracts in inspiration, as the fibres simply surround
the tube, and none are attached to it.

FIG. 42.— Diaphragm. (Sappey.)

1, 2, 3, central ten don ; 4, right pillar ; 5, left pillar ; 6, 7, processes "between the pillars ; 8, 8, openings for the splanch-
nic nerves ; 9, fibrous arch passing over the psoas magnus ; 10, fibrous arch passing over the quadratus lumbo-
rum ; 11, muscular fibres arising from these two arches ; 12, 12, muscular fibres arising from the lower six ribs ;
13, fibres from the ensiform cartilage; 14, opening for the vena cava ; 15, opening for the oasophagus ; 16, open-
ing for the aorta; 17, 17, part of the transversalis muscle; 18, 18, aponeurosis; 19, 19, quadratus lumborum;
20, 20, psoas magnus; 21, fourth lumbar vertebra.

The orifice for the aorta is bounded by the bone and aponeurosis posteriorly, and in
front, by a fibrous band to which the muscular fibres are attached, so that their contrac-
tion has a tendency rather to increase than to diminish the caliber of the vessel.

The orifice for the vena cava is surrounded entirely by tendinous structure, and con-
traction of the diaphragm, although it might render the form of the orifice more nearly
circular, can have no effect upon its caliber.

The action of the diaphragm can be easily studied in the inferior animals by vivisec-
tions. If the abdomen of a cat, which, from the conformation of the parts, is well adapted
to this experiment, be largely opened, we can observe the descent of the tendinous por-
tion and the contraction of the muscular fibres. The action of this muscle may be ren-
dered more apparent by compressing the walls of the chest with the hands, so as to
interfere somewhat with the movements of the ribs. By putting a strong ligature around
the spinal column and soft parts just below the diaphragm and cutting off the lower
half of the body, as was done by the assistant to the chair of physiology in the Bellevue
Hospital Medical College, Dr. 0. F. Roberts, the movements of the diaphragm may be
very beautifully exhibited in class-demonstrations.

In ordinary respiration, the descent of the diaphragm and its approximation to a
plane are the chief phenomena observed ; but, as there is a slight resistance to the depres-
sion of the central tendon, it is probable that there is also a certain amount of elevation

MUSCLES OF INSPIRATION. 125

of the inferior ribs, the diaphragm assisting, in a limited degree it is true, the action
of the external intercostals.

The phenomena referable to the abdomen, which coincide with the descent of the
diaphragm, can easily be observed in the human subject. As the diaphragm is depressed,
it necessarily pushes the viscera before it, and inspiration is therefore accompanied by
protrusion of the abdomen. This may be rendered very marked by a forced or deep
inspiration.

The action of the diaphragm may be illustrated by a very simple yet striking experi-
ment. In an animal just killed, after opening the abdomen, if we take hold of the struct-
ures which are attached to the central tendon and make traction, we imitate, in a rough
way, the movements of the diaphragm in respiration, and the air will pass into the lungs,
sometimes with a distinctly-audible sound.

The effects of the action of the diaphragm upon the size of its orifices are chiefly
limited to the cesophageal opening. The anatomy of the parts is such that contraction
of the muscular fibres has a tendency to close this orifice. When we come to treat of
the digestive system, we shall see that the contraction of the diaphragm is auxiliary
to the action of the muscular walls of the oesophagus itself, by which the cardiac open-
ing of the stomach is regularly closed during inspiration. This may become important
when the stomach is much distended ; for descent of the diaphragm compresses all the
abdominal organs and might otherwise cause regurgitation of food.

The contractions of the diaphragm are animated almost exclusively, if not exclu-
sively, by the phrenic nerve ; a nerve which, having the office of supplying the most
important respiratory muscle, derives its filaments from a number of sources. It arises
from the third and fourth cervical nerves, receiving a branch from the fifth and some-
times from the sixth ; it passes through the chest, penetrates the diaphragm, and is dis-
tributed to its under surface. This nerve was the subject of numerous experiments by
the early physiologists, who were greatly interested in the minuti® of the action of the
diaphragm and of other muscles, in respiration. Its galvanization produces convulsive con-
tractions of the diaphragm, and its section paralyzes the muscle almost completely. It
was noticed by Lower, that after section of both phrenic nerves the movements of the
abdomen were reversed, and it became retracted in inspiration. This is explained and
illustrated by voluntary suspension of the action of the diaphragm and exaggeration of the
costal movements. As the ribs are raised, the atmospheric pressure causes the diaphragm
to mount up into the cavity of the thorax, and of course the abdominal organs follow.

From the great increase in the capacity of the chest produced by the action of the
diaphragm and its constant and universal action in respiration, it must be regarded as by
far the most important and efficient of the muscles of inspiration.

Hiccough, sobbing, laughing, and crying, are due mainly to the action of the dia-
phragm, particularly hiccough and sobbing, which are produced by spasmodic contrac-
tions of this muscle, generally beyond the control of the will.

Action of the Muscles which elevate the Ribs. — Scalene Muscles.— In ordinary respira-
tion, the ribs and the entire chest are elevated by the combined action of a number of
muscles. The three scalene muscles are attached to the cervical vertebra and the first
and second ribs. These muscles, which act particularly upon the first rib, must ele-
vate with it, in inspiration, the rest of the thorax. The articulation of the first rib
with the vertebral column is very movable, but it is joined to the sternum by a very
short cartilage, which allows of very little movement, so that its elevation necessarily
carries with it the sternum. This movement increases both the transverse :md antero-
posterior diameters of the thorax, from the mode of articulation and direction of the
ribs, which are somewhat rotated as well as rendered more horizontal.

Intercostal Muscles. — Concerning the mechanism of the action of these muscle?, there
is great difference of opinion among physiologists; so much, indeed, that the author of

126 RESPIRATION.

a late elaborate work assumes that the question is still left in considerable uncertainty.
The most extended researches on this point are those of Beau and Maissiat (Archives
generates de medecine, 1843), and Sibson (Philosophical Transactions, 1846). The latter
seern to settle the question of the mode of action of the intercostals and explain satis-
factorily certain points which even now are not generally appreciated. More recently,
Onimus has shown, by experiments upon a decapitated animal, that the external inter-
costals raise, and the internal intercostals depress the ribs, thus confirming the views of
Sibson.

We shall first note the changes which take place in the direction of the ribs and their
relation to each other in inspiration, before considering the way in which these move-
ments are produced.

In the dorsal region, the spinal column forms an arch with its concavity toward the
chest, and the ribs increase in length progressively, from above downward, to the deep-
est portion of the arch, where they are longest and then become progressively shorter.
According to Sibson, " during inspiration the ribs approach to or recede from each other
according to the part of the arch with which they articulate ; the four superior ribs ap-
proach each other anteriorly and recede from each other posteriorly ; the fourth and
fifth ribs, and the intermediate set (sixth, seventh, and eighth), move further apart to a
moderate, the diaphragmatic set (four inferior), to a great extent. The upper edge of
each of these ribs glides toward the vertebra in relation to the lower edge of the rib
above, with the exception of the lowest rib, which is stationary." These movements
increase the antero-posterior and transverse diameters of the thorax. As the ribs are
elevated and become more nearly horizontal, they must push forward the lower portion
of the sternum. Their configuration and mode of articulation with the vertebrae are
such, that they cannot be elevated without undergoing a considerable rotation, by which
the concavity looking directly toward the lungs is increased, and with it the lateral

diameter of the chest. All the intercostal spaces posteriorly
are widened in inspiration.

The ribs are elevated by the action of the external inter-
costals, the sternal portion of the internal intercostals, and
the levatores costarum. The external intercostals are situ-
ated between the ribs only, and are wanting in the region
of the costal cartilages. As the vertebral extremities of the
ribs are the pivots on which these levers move, and as the
sternal extremities are movable, the direction of the fibres
of the intercostals from above downward and forward
renders elevation of the ribs a necessity of their contrac-
tion, if it can be assumed that the first rib is fixed or at
least does not move downward. The scalene muscles ele-
vate the first rib in ordinary inspiration; and, in deep in-

. 4Z.-ElwaUon of the ribs in spiration, this takes place to such an extent as to palpably
inspiration. (Bceiard ) carrv with it the sternum and the lower ribs. Theoreti-

Ine dark lines represent the ribs, * . , , . ,

sternum, and costal cartilages in cally, then, the external intercostals can do nothing but
render the ribs more nearly horizontal.

If the external intercostals be exposed in a living animal, the dog, for example, in
which the costal type of respiration is very marked, close observation can hardly fail to
convince any one that these muscles enter into action in inspiration. This fact has
been observed by Sibson and many other physiologists. If attention be directed to the
sternal portion of the internal intercostals, situated between the costal cartilages, their
fibres having a direction from above downward and backward, it is equally evident that
they enter into action with inspiration. By artificially inflating the lungs after death,
Sibson confirmed these observations and showed that, when the lungs are filled with
air, the fibres of these muscles are shortened. In inspiration, the ribs are all separated

MUSCLES OF INSPIRATION. 127

posteriorly ; but laterally and anteriorly, some are separated (all below the fourth), and
some are approximated (all above the fourth). Thus all the interspaces, except the
anterior portion of the upper three, are widened in inspiration. Sibson has shown, by
inflation of the chest, that, although the ribs are separated from each other, the attach-
ments of the intercostals are approximated. The ribs, from an excessively oblique posi-
tion, are rendered nearly horizontal ; and consequently the inferior attachments of the
intercostals are brought nearer the spinal column, while the superior attachments to the
upper borders of the ribs are slightly removed from it. Thus these muscles are short-
ened. If, by separating and elevating the ribs, the muscles be shortened, shortening of
the muscles will necessarily elevate and separate the ribs. In the three superior inter-
spaces, the constant direction of the ribs is nearly horizontal, and the course of the
intercostal fibres is not so oblique as in those situated between the lower ribs. These
spaces are narrowed in inspiration. The muscles between the costal cartilages have
a direction opposite to that of the external intercostals and act upon the ribs from the
sternum, as the others do from the spinal column. The superior interspace is narrowed,
and the remainder are widened, in inspiration.

Levatores Costarum. — The action of these muscles cannot be mistaken. They have
immovable points of origin, the transverse processes of twelve vertebrae from the last
cervical to the eleventh dorsal, and, spreading out like a fan, are attached to the upper
edges of the ribs between the tubercles and the angles. In inspiration, they* contract
and assist in the elevation of the ribs. They are more developed in man than in the
inferior animals.

Auxiliary Muscles of Inspiration. — The muscles which have just been considered are
competent to increase the capacity of the thorax sufficiently in ordinary respiration;
there are certain muscles, however, which are attached to the chest and the upper part
of the spinal column, or upper extremities, which may act in inspiration, although ordi-
narily the chest is the fixed point and they move the head, neck, or arms. These
muscles are brought into action when the movements of respiration are exaggerated.
When this exaggeration is but slight and physiological, as after exercise, certain of them
(the ordinary auxiliaries) act for a time, until the tranquillity of the movements is
restored. But when there is obstruction in the respiratory passages or when respiration
is excessively difficult from any cause, threatening suffocation, all the muscles which can
by any possibility raise the chest are brought into action. The principal ones are put
down in the table under the head of extraordinary auxiliaries. Most of these muscles
can voluntarily be brought into play to raise the chest, and the mechanism of their
action can in this way be demonstrated.

Serratus Posticus Superior.— This muscle arises from the ligamentum nuchae, the
spinous processes of the last cervical and the upper two or three dorsal vertebra?, its fibres
passing obliquely downward and outward, to be attached to the upper borders of the
second, third, fourth, and fifth ribs just beyond their angles. By reversing its action, as
we have reversed the description of its origin and insertions, it is capable of increasing
the capacity of the thorax.

Sterno-mastoideus. — That portion of the muscle which is attached to the mastoid
process of the temporal bone and the sternum, when the head is fixed, is capable of act-
ing as a muscle of inspiration. It does not act in ordinary respiration, but its contrac-
tions can be readily observed whenever respiration is hurried or exaggerated.

The following muscles, as a rule, act as muscles of inspiration only when respiration
is exceedingly difficult or labored. In certain cases of capillary bronchitis, for example,
the anxious expression of the countenance betrays the sense of impending suffocation ;
the head is thrown back and fixed; the shoulders are braced; and every available muscle
in brought into action to raise the walls of the thorax.1

1 Under these circumstances, some muscles which we have not thought it necessary to enumerate may act in-
directly as muscles of inspiration.

128 RESPIRATION.

Lenator Anguli Scapula and Superior Portion of the Trapezius. — Movements of the
scapula have often been observed in very labored respiration. Its elevation during in-
spiration is effected chiefly by the levator anguli scapulae and the upper portion of the
trapezius. The former muscle arises from the transverse processes of the upper three or
four cervical vertebrae and is inserted into the posterior border of the scapula below the
angle. It is a thick, flat muscle and, when the neck is the fixed point, assists in the ele-
vation of the thorax by raising the scapula. The trapezius is a broad, flat muscle, aris-
ing from the occipital protuberance, part of the superior curved line of the occipital
bone, the ligamentum nuchaa, and the spinous processes of the last cervical and all
the dorsal vertebras, to be inserted into the upper border of the spine of the scapula.
Acting from its attachments to the occiput, the ligamentum nuchae, the last cervical
vertebra, and perhaps one or two of the dorsal vertebrae, this muscle may elevate the
scapula and assist in inspiration.

Pectoralis Minor and Inferior Portion of the Pectoralis Major. — These muscles act
together to raise the ribs in difficult respiration. The pectoralis minor is the more effi-
cient. Tracing it from its attachment to the coracoid process of the scapula, its fibres
pass downward and forward to be attached by three indigitations to the external surface
and upper margins of the third, fourth, and fifth ribs just posterior to the costal cartilages.
With the coracoid process as the fixed point, this muscle is capable of powerfully assist-
ing in the elevation of the ribs. That portion of the pectoralis major which is attached
to the lower part of the sternum and costal cartilages is capable of acting from its in-
sertion into the bicipital groove of the humerus, when the shoulders are fixed, in concert
with the pectoralis minor. In great dyspnoea, it is frequently observed that the shoulders
are braced, the pectorals acting vigorously to raise the walls of the chest.

Serratus Magnus. —This is a broad, thin muscle covering a great portion of the lat-
eral walls of the thorax. Attached to the inner margin of the posterior border of the
scapula, its fibres pass forward and downward and are attached to the external surface
and upper borders of the eight superior ribs. Acting from the scapula, this muscle is
capable of assisting the pectorals in raising the ribs and becomes a powerful auxiliary in
difficult inspiration.

We have thus considered the functions of the principal inspiratory muscles, without
taking up those which have an insignificant or undetermined action. In many animals,
the nares are considerably distended in inspiration; and, in the horse, which does
not respire by the mouth, these movements are as essential to life as the respiratory
movements of the larynx. In man, as a rule, the nares undergo no movement unless
respiration be somewhat exaggerated. In very difficult respiration, the mouth is opened
at each inspiratory act. We have not thought it necessary to treat of the action of those
muscles which serve to fix the head, neck, or shoulders in dyspnoea.

The division into muscles of ordinary inspiration, ordinary auxiliaries, and extraor-
dinary auxiliaries, must not be taken as absolute. In the male, in ordinary respiration,
the diaphragm, intercostals, and levatores costarum are the great inspiratory muscles,
and the action of the scaleni, with the consequent elevation of the sternum, is commonly
very slight or may be wanting. In the female, the movements of the upper parts of
the chest are very marked, and the scaleni, the serratus posticus superior, and sometimes
the sterno-mastoid, are brought into action in ordinary respiration. In the various types
of respiration, the action of the muscles engaged in ordinary respiration necessarily pre-
sents considerable variations.

Expiration.

The air is expelled from the lungs, in ordinary expiration, by a simple and compara-
tively-passive process. The lungs contain a great number of elastic fibres surrounding
the air-cells and the smallest ramifications of the bronchial tubes, which give them great
elasticity. We can form an idea of the extent of elasticity of these organs, by simply
removing them from the chest, when they collapse and become many times smaller than

MUSCLES OF INSPIRATION. 129

the cavity which they before had completely filled. The thoracic walls are also very
elastic, particularly in young persons. After the muscles which increase the capacity
of the thorax cease their action, the elasticity of the costal cartilages and the tonicitv
of the muscles which have been put on the stretch will restore the chest to what we may
call its passive dimensions. This elasticity is likewise capable of acting as an inspiratory
force when the chest has been compressed in any way. There are also certain muscles,
the action of which is to draw the ribs downward and which, in tranquil respiration,
are antagonistic to those which elevate the ribs. Aside from this, many operations, such
as speaking, blowing, singing, etc., require powerful, prolonged, or complicated acts of
expiration, in which numerous muscles are brought into play.

Expiration may be considered as depending upon two causes, as follows :

1. The passive influence of the elasticity of the lungs and thoracic walls.

2. The action of certain muscles, which either diminish the transverse and antero-
posterior diameters of the chest by depressing the ribs and sternum, or the vertical di-
ameter, by pressing up the abdominal viscera behind the diaphragm.

Influence of the Elasticity of the Pulmonary Structure and Walls of the Chest. —
It is easy to understand the influence of the elasticity of the pulmonary structure in ex-
piration. From the collapse of the lungs when openings are made in the chest, it is seen
that, even after the most complete expiration, these organs have a tendency to expel
part of their gaseous contents, which cannot be fully satisfied until the chest is opened.
They remain partially distended, from the impossibility of collapse of the thoracic walls
beyond a certain point ; and, by virtue of their elasticity, they exert a suction force
upon the diaphragm, causing it to form a vaulted arch, or dome above the level of the
lower circumference of the chest. When the lungs are collapsed, the diaphragm hangs
loosely between the abdominal and thoracic cavities. In inspiration and in expiration,
then, the relations between the lungs and diaphragm are reversed. In inspiration, the
descending diaphragm exerts a suction force on the lungs, drawing them downward ; in
expiration, the elastic lungs exert a suction force upon the diaphragm, drawing it up-
ward. This antagonism is one of the causes of the great power of the diaphragm as an
inspiratory muscle.

The elasticity of the lungs operates chiefly upon the diaphragm in reducing the capa-
city of the chest; for the walls of the thorax, by virtue of their own elasticity, have a
reaction which succeeds the movements produced by the inspiratory muscles. A simple
experiment, which we have often performed in public demonstrations, illustrates the
expiratory influence of the elasticity of the lungs. If, in an animal just killed, we
open the abdomen, seize hold of the vena cava as it passes through the diaphragm, and
make traction, we imitate the action of this muscle sufficiently to produce at times an
audible inspiration ; on loosing our hold, we have expiration, as it is in a measure accom-
plished in natural respiration, by virtue of the resiliency of the lungs, carrying the dia-
phragm up into the thorax. Although this is the main action of the lungs themselves
in expiration, their relations to the walls of the thorax are important. By virtue of
their elasticity, they assist the passive collapse of the chest. When they lose this prop-
erty to any considerable extent, as in vesicular emphysema, they offer a notable resistance
to the contraction of the thorax ; so much, indeed, that in old cases of this disease the
movements are much restricted, and the chest presents a characteristic rounded and dis-
tended appearance.

Little more need be said concerning the passive movements of the thoracic walls.
When the action of the inspiratory muscle ceases, the ribs regain their oblique direction,
the intercostal spaces are narrowed, and the sternum, if it have been elevated and drawn
forward, falls back to its place simply by virtue of the elasticity of the parts.

Action of Muscles in Expiration. — The following are the principal muscles concerned
in expiration :
9

130 RESPIRATION.

Muscles of Expiration.

Ordinary Respiration.

Muscle. Attachments.

Osseous portion of internal intercostal s . .Inner borders of the ribs.

Infracostales Inner surfaces of the ribs.

Triangularis sterni Ensiform cartilage, lower borders of sternum, lower three

or four costal cartilages cartilages of the second,

third, fourth, and fifth ribs.

Auxiliaries.

Obliquus externus External surface and inferior borders of eight inferior

ribs anterior half of the crest of the ileum, Pou-

part's ligament, linea alba.

Obliquus internus Outer half of Poupart's ligament, anterior two-thirds of

the crest of the ileum, lumbar fascia cartilages of

four inferior ribs, linea alba, crest of the pubis, pec-
tineal line.

Transversalis Outer third of Poupart's ligament, anterior two-thirds of

the crest of the ileum, lumbar vertebras, inner surface

of cartilages of six inferior ribs crest of the pubis,

pectineal line, linea alba.

Sacro-lumbalis Sacrum angles of six inferior ribs.

Internal Intercostals. — The internal intercostals have different functions in different
parts of the thorax. They are attached to the inner borders of the ribs and costal carti-
lages. Between the ribs, they are covered by the external intercostals, but, between the
costal cartilages, they are covered simply by aponeurosis. Their direction is from above
downward and backward, nearly at right angles to the external intercostals. The function
of that portion of the internal intercostals situated between the costal cartilages has al-
ready been noted. They assist the internal intercostals in elevating the ribs in inspiration.
Between the ribs, these muscles are directly antagonistic to the external intercostals.
They are more nearly at right angles to the ribs, particularly in that portion of the tho-
rax where the obliquity of the ribs is greatest. The observations of Sibson have shown
that they are elongated when the chest is distended, and shortened when the chest is
collapsed. This fact, taken in connection with experiments on living animals, shows
that they are muscles of expiration. Their contraction tends to depress the ribs and
consequently to dimmish the capacity of the chest. If we bring an animal, a dog fur
example, completely under the influence of ether, expose the walls of the chest, dissect off
the fascia from some of the external intercostals, and then remove carefully a portion of
one or two of these muscles so as to expose the fibres of the internal intercostal s, it is
not difficult, on close examination, to observe the antagonism between the two sets of
muscles ; one being brought into action in inspiration and the other, in expiration.

Infracostales. — These muscles, situated at the posterior part of the thorax, are vari-
able in size and number. They are most common at the lower part of the chest. Their
fibres arise from the inner surface of one rib to be inserted into the inner surface of the
first, second, or third rib below. The fibres follow the direction of the internal intercos-
tals, and, acting from their lower attachments, their contractions assist these muscles in
drawing the ribs downward.

Triangularis Sterni. — There has never been any doubt concerning the expiratory func-
tion of the triangularis sterni. From its origin, the ensiform cartilage, lower borders of
the sternum, and lower three or four costal cartilages, it acts upon the cartilages of the
second, third, fourth, and fifth ribs, to which it is attached, drawing them downward and
thus diminishing the capacity of the chest.

TYPES OF RESPIRATION. 131

The above-mentioned muscles are called into action in ordinary tranquil respiration,
and their sole function is to diminish the capacity of the chest. In labored or difficult
expiration, and in the acts of blowing, phonation, etc., other muscles, which are called
auxiliaries, play a more or less important part. These muscles all enter into the forma-
tion of the walls of the abdomen, and their general action in expiration is to press the
abdominal viscera and diaphragm into the thorax and diminish its vertical diameter.
Their action is voluntary ; and, by an effort of the will, it may be opposed more or less
by the diaphragm, by which means the duration or intensity of the expiratory act is regu-
lated. They are also attached to the ribs or costal cartilages, and, while they press the
diaphragm upward, depress the ribs and thus diminish the antero-posterior and transverse
diameters of the chest. In this action, they may be opposed by the voluntary contraction
of the muscles which raise the ribs, also for the purpose of regulating the character of the
expiratory act. The importance of this kind of action in declamation, singing, blowing,
etc., is evident; and the skill exhibited by vocalists and performers on wind instruments
shows how delicately this may be regulated by practice.

In labored respiration in disease and in the hurried respiration which follows violent
exercise, the auxiliary muscles of expiration, as well as of inspiration, are called into
action to a considerable extent.

Olliquus Externus. — This muscle, in connection with the obliquus internus and trans-
versalis, is efficient in forced or labored expiration, by pressing the abdominal viscera
against the diaphragm. Its fibres run obliquely from above downward and forward.
Acting from its attachments to the linea alba, the crest of the ileum, and Poupart's liga-
ment, by its attachment to the eight inferior ribs, it draws the ribs downward.

Olliquus Internus. — This muscle also acts in forced expiration, by compressing the ab-
dominal viscera. The direction of its fibres is from below upward and forward. Acting
from its attachments to the crest of the ileum, Poupart's "ligament, and the lumbar fascia,
by its attachments to the cartilages of the four inferior ribs, it draws them downward.
The direction of the fibres of this muscle is the same as that of the internal intercostals.
By its action the ribs are drawn inward as well as downward.

Transversalis. — The expiratory action of this muscle is mainly in compressing the ab-
dominal viscera.

Sacro-lumbalis. — This muscle is situated at the posterior portion of the abdomen and
thorax. Its fibres pass from its origin at the sacrum, upward and a little outward, to be
inserted into the six inferior ribs at their angles. In expiration it draws the ribs down-
ward, acting as an antagonist to the lower levatores costarum.

There are some other muscles which may be brought into action in forced expiration,
assisting in the depression of the ribs, such as the serratus posticus inferior, the superior
fibres of the serratus magnus, the inferior portion of the trapezius, but their function is
unimportant.

Types of Respiration. — In the expansive movements of the chest, although all the
muscles which have been classed as ordinary inspiratory muscles are brought into action
to a greater or less extent, the fact that certain sets may act in a more marked manner
than others has led physiologists to recognize different types of respiration. The three
following types are generally given in works on physiology :

1. The Abdominal type. — In this, the action of the diaphragm and the consequent
movements of the abdomen are most prominent.

2. The Inferior Costal type. — In this, the action of the muscles which expand the
lower part of the thorax, from the seventh rib inclusive, is most prominent.

3. The Superior Costal type. — In this, the action of the muscles which dilate the thorax
above the seventh rib and which elevate the entire chest is most prominent.

The abdominal type is most marked in children under the age of three years, irrespec-
tive of sex. In them, respiration is carried on almost exclusively by the diaphragm.

132 RESPIRATION.

At a variable period after birth, a difference in the types of respiration in the sexes
begins to show itself. In the male, the abdominal conjoined with the inferior costal type
is predominant, and this continues through life. In the female, the inferior costal type
is insignificant, and the superior costal type predominates. Observers differ in their state-
ments of the period of life when this distinction in the sexes becomes apparent. Without
discussing the nice question as to the exact age when this difference in the sexes first
makes its appearance, it may be stated, in general terms, that, shortly before the age of
puberty in the female, the superior costal type becomes more marked and soon predomi-
nates ; while, in the male, respiration continues to be carried on mainly by the diaphragm
and lower part of the chest.

The cause of the excessive movements of the upper part of the chest in the female has
been the subject of considerable discussion. It is evident that it is not due to the mode
of dress now so general in civilized countries, which confines the lower part of the chest
and would render movements of expansion somewhat difficult, for the same phenomenon
is observed in young girls and others who have never made use of such appliances. But
there is evidently a physiological condition, the enlargement of the uterus in gestation,
which, at certain times, would nearly arrest all respiratory movements, except those
of the upper part of the chest. The peculiar mode of respiration in the female is a pro-
vision of Nature against the mechanical difficulties which would otherwise follow the
physiological enlargement of the uterus. In pathology it is observed that, in consequence
of this peculiarity, females are able to carry, without great inconvenience, immense quan-
tities of water in the abdominal cavity ; while a much smaller quantity, in the male, pro-
duces great distress from difficulty of breathing.

Frequency of the Respiratory Movements. — In counting the respiratory acts, it is de-
sirable that the subject be unconscious of the observation, otherwise their normal char-
acter is apt to be disturbed. Of all who have written on this subject, Hutchinson pre-
sents the most numerous and convincing collection of facts. This observer ascertained
the number of respiratory acts per minute, in the sitting posture, in 1,897 males. The
results of his observations, with reference to frequency, are given in the following table:

Respirations per minute. Number of cases.
From 9 to 16... 79

16 239

17 105

18 195

19 74

20 561

21 129

22 143

23 42

24 243

24 to 40 87

Although this table shows considerable variation in different individuals, the great
majority (1,781) breathed from sixteen to twenty-four times per minute. Nearly a third
breathed twenty times per minute, a number which may be taken as the average.

The relations of the respiratory acts to the pulse are quite constant in health. It has
been shown by Hutchinson that the proportion in the great majority of instances is one
respiratory act to every four pulsations of the heart. The same proportion generally
obtains when the pulse is accelerated in disease, except when the pulmonary organs are
involved.

Age has an influence on the frequency of the respiratory acts, corresponding with
what we have already noted with regard to the pulsations of the heart.

EESPIRATORY SOUNDS. 133

Quetelct gives the following as the results of observations on 300 males :

44 respirations per minute, soon after birth ;

26, at the age of five years ;

20, at the age of fifteen to twenty years ;

19, at the age of twenty to twenty-five years ;

16, about the thirtieth year ;

18, from thirty to fifty years.

The influence of sex is not marked in very young children. The same observer noted
no difference between males and females at birth ; but in young women the respirations
are a little less frequent than in young men of the same age.

The various physiological conditions which have been noted as affecting the pulse
have a corresponding influence on respiration. In sleep, the number of respiratory acts
is diminished by about twenty per cent. (Quetelet). Muscular effort accelerates the re-
spiratory movQi&Qnts par i pass u with the movements of the heart.

delations of Inspiration and Expiration to each other— The Respiratory Sounds.— In
ordinary respiration, inspiration is produced by the action of muscles, and expiration, in
greatest part, by the passive reaction of the elastic walls of the thorax and the lungs.
The inspiratory and expiratory acts do not immediately follow each other. Commencing
with inspiration, it is found that this act maintains about the same intensity from its be-
ginning to its termination; there is then a very brief interval, when expiration follows,
which has its maximum of intensity at the commencement of the act and gradually dies
away.1 Between the acts of expiration and inspiration is an interval, which is somewhat
longer than that which occurs after inspiration.

The duration of expiration is generally somewhat greater than that of inspiration,
although they may be nearly, or in some instances quite equal. After from five to eight
ordinary respiratory acts, an effort generally occurs which is rather more profound than
the rest, and by which the air in the lungs is more effectually changed. The temporary
arrest of the acts of respiration in violent muscular efforts, in straining, in parturition,
etc., is familiar to all.

Ordinarily respiration is not accompanied by any sound which can be heard without
applying the ear directly, or by the intervention of a stethoscope, to the respiratory
organs; except when the mouth is closed and breathing is carried on exclusively
through the nasal passages, when a soft, breezy murmur accompanies both acts. If the
mouth be sufficiently opened to admit the free passage of air, no sound is to be heard in
health. In sleep, the respirations are unusually profound; and, if the mouth be closed,
the sound is rather more intense.

Snoring, a peculiar sound, more or less marked, which sometimes accompanies the
respiratory acts during sleep, occurs when the air passes through both the mouth and the
nose. It is more marked in inspiration, sometimes accompanying both acts, and sometimes
it is not heard in expiration. It is not necessary to describe the characters of a sound
so familiar. Snoring is an idiosyncrasy with many individuals, although those who do not
snore habitually may do so when the system is unusually exhausted and relaxed. It only
occurs when the mouth is open, and the sound is produced by vibration and a sort Oi
flapping of the velum pendulum palati, between the two currents of air from the mouth
and nose, together with a vibration in the column of air itself.

Applying the stethoscope over the larynx or trachea, a sound is heard, of a distinctly
and purely tubular character, accompanying both acts of respiration. In inspiration,
according to Dr. Austin Flint, " it attains its maximum of intensity quickly after the de-
velopment of the sound and maintains the same intensity to the close of the act, when
the sound abruptly ends, as if suddenly cut off." After a brief interval, the sound of ex-

» In listening to the respiratory murmur over the substance of the lungs, the expiratory follows the inspiratory
sound without an interval. The interval between the acts of inspiration and expiration is only appreciated as the air
passes in and out at the mouth.

134 KESPIRATION.

piration follows. This is also tubular in quality ; it soon attains its maximum of intensity,
but, unlike the sound of inspiration, gradually dies away and is lost imperceptibly. It is
seen that these phenomena correspond with the nature of the two acts of respiration.

Sounds approximating in character to the foregoing are heard over the bronchial
tubes before they penetrate the lungs.

Over the substance of the lungs, a sound may be heard entirely different in its char-
acter from that heard over the larynx, trachea, or bronchial tubes. In inspiration, the
sound is much less intense than over the trachea and has a breezy, expansive, or what
is called in auscultation a vesicular character. It is much lower in pitch than the trachea!
sound. It is continuous and rather increases in intensity from its commencement to its
termination, ending abruptly, like the tracheal inspiratory sound. The sound is produced
in part by the movement of air in the small bronchial tubes, but chiefly by the expansion
of the innumerable air-cells of the lungs. It is followed, without an interval, by the sound
of expiration, which is shorter, one-fifth to one-fourth as long, lower in pitch, and very
much less intense. A sound is not always heard in expiration.

The variations in the intensity of the respiratory sounds in different individuals are
very considerable. As a rule they are more intense in young persons ; which has given
rise to the term puerile respiration, when the sounds are exaggerated in parts of the lung,
in certain cases of disease. The sounds are generally more intense in females than in
males, particularly in the upper regions of the thorax.

It is difficult by any description or comparison to convey an accurate idea of the
character of the sounds heard over the lungs and air-passages, and it is superfluous to
make the attempt, when they can be so easily studied in the living subject.

Coughing, Sneezing, Sighing, Yawning, Laughing, Soiling, and Hiccough. — These
peculiar acts demand a few words of explanation. Coughing and sneezing are gen-
erally involuntary acts, produced by irritation in the air-tubes or nasal passages, al-
though coughing is often voluntary. In both of these acts, there is first a deep in-
spiration, followed by a convulsive action of the expiratory muscles, by which the
air is violently expelled with a characteristic sound, in the one case by the mouth,
and in the other by the mouth and nares. Foreign bodies lodged in the air-passages
are frequently expelled in violent fits of coughing. In hypersecretion of the bron-
chial mucous membrane, the accumulated mucus is carried by the act of coughing
either to the mouth or well into the larynx, whence it is expelled by the act of ex-
pectoration. When either of these acts is the result of irritation from a foreign sub-
stance or secretions, it may be modified or partly smothered by the will, but is not com-
pletely under control. The exquisite sensibility of the mucous membrane at the summit
of the air-passages, under most circumstances, protects them from the entrance of foreign
matters, both liquid and solid ; for the slightest impression received by the membrane
gives rise to a violent and involuntary cough, by which the offending matter is removed.
The glottis is also spasmodically contracted.

In sighing, a prolonged and deep inspiration is followed by a rapid and generally an
audible expiration. This occurs, as a general rule, once in from five to eight respiratory
acts, for the purpose of changing the air in the lungs more completely, and it is due to an
exaggeration of the cause which gives rise to the ordinary acts of respiration. When due
to depressing emotions, it has the same cause; for, at such times, respiration is less
effectually performed. Yawning is an analogous process, but differs from sighing in the
fact that it is involuntary and cannot be produced by an effort of the will. It is charac-
terized by a wide opening of the mouth and a very profound inspiration. Yawning is
generally assumed to be an evidence of fatigue, but it often occurs from a sort of con-
tagion. When not the result of imitation, it has the same exciting cause as sighing, viz.,
deficient oxygenation of the blood, and it is followed by a sense of satisfaction, which shows
that it meets some decided want on the part of the system.

CAPACITY OF THE LUNGS. 135

Laughing and sobbing, though expressing opposite conditions, are produced by very
much the same mechanism. The characteristic sounds accompanying these acts are the
result of short, rapid, and convulsive movements of the diaphragm, accompanied by con-
tractions of the muscles of the face, which produce the expressions characteristic of
hilarity or grief. Although to a certain extent under the control of the will, these acts are
mainly involuntary. Violent and convulsive laughter may be excited in many individuals
by titillation of certain portions of the surface of the body. Laughter and sometimes
sobbing, like yawning, may be the result of involuntary imitation.

Hiccough is a peculiar modification of the act of inspiration, to which it is exclusively
confined. It is produced by a sudden, convulsive, and entirely involuntary contraction
of the diaphragm, accompanied by a spasmodic constriction of the glottis. The contrac-
tion of the diaphragm is more extensive than in laughing and sobbing and occurs only
once every four or five respiratory acts. The causes which give rise to hiccough are nu-
merous, and many of them are referable to the digestive system. Among these may be
mentioned the rapid ingestion of a quantity of dry food or of effervescing or alcoholic
drinks. It occurs frequently in cases of disease.

Capacity of the Lungs, and the Quantity of Air changed in the Respiratory

Acts.

The volume of air ordinarily contained in the lungs is about two hundred cubic
inches; but it is evident, from the simple experiment of opening the chest, when the
elastic lungs collapse and expel a certain quantity of air which cannot be removed while
the lungs are in situ, that a part of the gaseous contents of these organs necessarily
remains after the most complete and forcible expiration. After an ordinary act, there is
a certain quantity of air in the lungs which can be expelled by a forced expiration. In
ordinary respiration, a comparatively small volume of air is introduced with inspiration,
which is expelled by the succeeding expiration.1 By the extreme action of all the inspi-
ratory muscles in a forced inspiration, a supplemental quantity of air may be introduced
into the lungs, which then contain much more than they ever do in ordinary respiration.
For convenience, many physiologists have adopted the following names, which are
applied to these various volumes of air :

1. Residual Air ; that which is not and cannot be expelled by a forced expiration.

2. Reserve Air ; that which remains after an ordinary expiration, deducting the
residual air.

3. Tidal, or ordinary Breathing Air ; that which is changed by the ordinary acts
of inspiration and expiration.

4. Complemental Air ; the excess over the ordinary breathing air. which may be
introduced by a forcible inspiration.

The questions relating to the above divisions of the respired air have been made the
subject of numerous investigations; but, although at first it might seem easy to deter-
mine all of them by a sufficient number of experiments, the necessary observations are
attended with considerable difficulty, and the sources of error are numerous. In measur-
ing the air changed in ordinary breathing, it has been found that the acts of respiration
are so easily influenced by the mind and it is so difficult to experiment on any individual
without his knowledge, that the results of many good observers are not to be relied
upon. This is one of the most important of the questions under consideration. The
difficulties in the way of estimating with accuracy the residual, reserve, or complemental
volumes, will readily suggest themselves. The observations on these points, which may
be taken as the most definite and exact, are those of Herbst, of Gottingen, and Ilutchin-
son, of England. Those of the last-named observer are exceedingly elaborate and were

1 Experiments have shown that a certain volume of air is lost in the lungs, the expired air being a little less in
volume than the quantity inspired (from fa to 5'5). This is not taken into account in this connection.

136 EESPIRATIOK

made on an immense number of subjects of both sexes and of all ages and occupations.
They are generally accepted by physiologists as the most extended and accurate.

Residual Air. — Perhaps there is not one of the questions under consideration more
difficult to answer definitely than that of the quantity of air which remains in the lungs
after a forced expiration ; but it fortunately is not one of any great practical importance.
The residual air remains in the lungs as a physical necessity. The lungs are always, in
health, in contact with the walls of the thorax; and, when this cavity is reduced to its
smallest dimensions, it is impossible that any more air should be expelled. The volume
which thus remains has been variously estimated at from forty cubic inches (Fontana) to
two hundred and twenty cubic inches (Jurin). Dr. Hutchinson, who has carefully con-
sidered this point, estimates the residual volume at about one hundred cubic inches, but he
states that it varies very considerably in different individuals. Taking every thing into
consideration, we may assume this estimate to be as nearly correct as any. It is certain
that the lungs of a man of ordinary size, at their minimum of distention, contain more
than forty cubic inches of air; and, from measurements of the capacity of the thorax,
deducting the estimated space occupied by the heart and vessels and the parenchyma
of the lungs, it is shown that the residual air cannot amount to any thing like two hun-
dred cubic inches.

There is no special division of the function of respiration connected with the residual
air. It remains in the lungs merely as a physical necessity, and its volume must not be
taken into account in considering the volumes which are changed in any of the opera-
tions connected with breathing.

Reserve Air. — This name is appropriately given to the volume of air which may be
expelled and changed by a voluntary effort, but which remains in the lungs, added to the
residual air, after an ordinary act of expiration. It may be estimated, without any
reference to the residual air, by forcibly expelling air from the lungs, after an ordinary
expiration. The average volume is one hundred cubic inches.

The reserve air is more or less changed whenever we experience a necessity for a
more complete renovation of the contents of the lungs than ordinary. It is encroached
upon in the unusually profound inspiration and expiration which occur every five or six
acts. It is used in certain prolonged vocal efforts, in blowing, etc. Added to the residual
air, it constitutes the minimum capacity of the lungs in ordinary respiration. As it is
continually receiving watery vapor and carbonic acid, it is always more or less vitiated,
and, when reenforced by the breathing air, which enters with inspiration, is continually
in circulation, in obedience to the law of the diffusion of gases. Those who are in the
habit of arresting respiration for a time, as pearl-divers, learn to change the reserve air
as completely as possible by several forcible acts and then fill the lungs with fresh air.
In this way they are enabled to suspend the respiratory acts for from one to two minutes
without inconvenience. The introduction of fresh air with each inspiration, and the
constant diffusion which is going on and by which the proper quantity of oxygen finds
its way to the air-cells, give, in ordinary breathing, a composition to the air in the
deepest portions of the lungs which insures a constant aeration of the blood.

Tidal, or Ordinary Breathing Air. — The volume of air which is changed in the
ordinary acts of respiration is subject to immense physiological variations, and the
respiratory movements, as regards intensity, are so easily influenced by the mind, that
great care is necessary to avoid error in estimating the volume of ordinary breathing air.
The estimates of Herbst and of Hutchinson are the results of very extended observations
made with great care and are generally acknowledged to be as nearly accurate as pos-
sible. As a mean of these observations, it has been found that the average volume of
breathing air, in a man of ordinary stature, is twenty cubic inches. According to Hutch-

EXTREME BREATHING CAPACITY. 137

inson, in perfect repose, when the respiratory movements are hardly perceptible, not
more than from seven to twelve cubic inches are changed ; while, under excitement, he
has seen the volume increased to seventy-seven cubic inches. Of course the latter is
temporary. Herbst noted that the breathing volume is constantly increased in pro-
portion to the stature of the individual and bears no definite relation to the apparent
capacity of the chest.

Complemental Air. — The thorax may be so enlarged by an extreme voluntary in-
spiratory effort as to contain a quantity of air much larger than after an ordinary in-
spiration. The additional volume of air thus taken in may be estimated by measuring
all the air which can be expelled from the lungs after the most profound inspiration, and
deducting the sum of the reserve air and breathing air. This quantity has been found
by Hutchinson to vary in different individuals, bearing a close relation to stature. The
mean complemental volume is one hundred and ten cubic inches.

The complemental air is drawn upon whenever an effort is made which requires a
temporary arrest of respiration. Brief and violent muscular exertion is generally pre-
ceded by a profound inspiration. In sleep, as the volume of breathing air is somewhat
increased, the complemental air is encroached upon. A part or the whole of the com-
plemental air is also used in certain vocal efforts, in blowing, in yawning, in the deep
inspiration which precedes sneezing, in straining, etc.

Summary. — In a healthy male of medium stature, the residual air, which cannot be
expelled from the lungs, amounts to about one hundred cubic inches.

The reserve air, which can be expelled but which is not changed in ordinary respi-
ration, amounts to about one hundred cubic inches.

The tidal air, which is changed in ordinary respiration, amounts to about twenty
cubic inches.

The complemental air, which may be taken into the lungs after the completion of an
ordinary act of inspiration, amounts to about one hundred and ten cubic inches.

Extreme Breathing Capacity. — By the extreme breathing capacity is meant the vol-
ume of air which can be expelled from the lungs by the most forcible expiration, after
the most profound inspiration. This has been called by Dr. Hutchinson the vital capa-
city, as signifying " the volume of air which can be displaced by living movements."
Its volume is equal to the sum of the reserve air, the breathing air, and the complemental
air, and represents the extreme capacity of the chest, deducting the residual air. Its
physiological interest is due to the fact that it can readily be determined by an appro-
priate apparatus, the spirometer, and comparisons can thus be made between different
individuals, both healthy and diseased. The number of observations on this point made
by Dr. Hutchinson is enormous, amounting in all to little short of five thousand.

The extreme breathing capacity in health is subject to variations which have been
shown to bear a very close relation to the stature of the individual. Hutchinson com-
mences with the proposition that, in a man of medium height (five feet eight inches), it
is equal to two hundred and thirty cubic inches. He has shown that the extreme breath-
ing capacity is constant in the same individual, and that it is not to be increased by habit
or practice.

The most striking result of the experiments of Dr. Hutchinson, with regard to the
modifications of the vital capacity, is that it bears a definite relation to stature, without
being affected in a very marked degree by weight or the circumference of the chest.
This is especially remarkable, as it is well known that height does not depend so much
upon the length of the body as upon the length of the lower extremities.

It has been ascertained that for every inch in height, between five and six feet, the
extreme breathing capacity is increased eight cubic inches.

138

RESPIRATION.

The following table shows the mean results of the immense number ot observations
on which this conclusion is based :

Progression of the Vital Capacity Volume icith the Stature.

Height.

Series from
observations on
1,012 cases.

OQ « T*

O

Series in
arithmetical
progression.

6 feet 0 inches ) K c . , . ,
ti i > 5 teet 1 men

1st result.

2d result.

176'0

1*74-0

52 \

lu i : [«.«"*.« ...

188'5

191-0

190*0

! , *

(-5 " 5 " .

206'0

207'0

206*0

5 6 ' j

5 ' 6 * IK ti tt

222fO

228'0

292-0

58 i

6" A '
/ 5 « 9 c

237-5

241-0

238'0

5 " 10 ^
5 « 10 « Is « n u

254'5

258-0

254*0

6 " 0 " J

Mean of all Heights. .

214'0

217'0

214-0

Age has an influence, though less marked than stature, upon the extreme breathing
capacity. As the result of 4,800 observations (males), it was ascertained that the volume
increases with age up to the thirtieth year, and progressively decreases, with tolerable
regularity, from the thirtieth to the sixtieth year. These figures, though necessarily sub-
ject to certain individual variations, may be taken as the basis for examinations of the
extreme breathing capacity in disease, which frequently give important information.
Of course, the breathing capacity is modified by any abnormal condition which interferes
with the mobility of the thorax or the dilatability of the lungs.

Relations in Volume of the Expired to the Inspired Air. — A certain proportion of the
inspired air is lost in respiration, so that the air expired is always a little less in volume
than that which is taken into the lungs. All the older experimenters, except Magendie,
were agreed upon this point. The loss was put by Davy at TV, and by Cuvier at -fa of
the amount of air introduced. Observations on this point, to be exact, must include a
considerable number of respiratory acts; and, from the difficulty of continuing respira-
tion in a perfectly regular and normal manner when the attention is directed to that
function, the most accurate results may probably be obtained from experiments on the
lower animals. Despretz caused six young rabbits to respire for two hours in a confined
space containing two hundred and ninety-nine cubic inches of air, and ascertained that
the volume had diminished sixty-one cubic inches, or a little more than one-fiftieth. We
may take the approximations of Davy and Cuvier, as applied to the human subject, as
nearly correct, and assume that, in the lungs, from -fa to -fa of the inspired air is lost.

Diffusion of Air in the Lungs. — When it is considered that, with each inspiration, but
about twenty cubic inches of fresh air is introduced, sufficient only to fill the trachea and
larger bronchial tubes, it is evident that some forces must act by which this fresh air
finds its way into the air-cells and the vitiated air is brought into the larger tubes, to be
expelled with the succeeding expiration. The expired air may become so charged with
noxious gases, by holding the breath for a few seconds, that, when collected in a receiver
under water, it is incapable of supporting combustion.

DIFFUSION OF AIR IN THE LUNGS. 139

The interchange between the fresh air in the upper portions of the respiratory appa-
ratus and the air in the deeper parts of the lungs is constantly going on, in obedience to
the well-known law of the diffusion of gases, aided by the active currents or impulses
produced by the alternate movements of the chest. When two gases, or mixtures of
gases, of different densities are brought in contact with each other, they diffuse or mingle
with great rapidity, until, if undisturbed, the whole mass has a uniform density and com-
position. This has been shown to take place between very light and very heavy gases
in opposition to the laws of gravity, and even when two reservoirs are connected by a
small tube many feet in length, though then it proceeds quite slowly. In the respiratory
apparatus, at the termination of inspiration, the atmospheric air, composed of a mixture
of oxygen and nitrogen, is introduced into the tubes with a considerable impetus and is
brought into contact with the gas in the lungs, which is much heavier, as it contains a
considerable quantity of carbonic acid. Diffusion then takes place, aided by the elastic
lungs, which are gradually forcing the gaseous contents out of the cells, until a certain
portion of the air loaded with carbonic acid finds its way to the larger tubes, to be
thrown off in expiration, its place being supplied by the fresh air.

In obedience to the law established by Graham, that the diffusibility of gases is in-
versely proportionate to the square root of their densities, the penetration of atmos-
pheric air, which is the lighter gas, to the deep portions of the lungs would take place
with greater rapidity than the ascent of the air charged with carbonic acid; so that
eighty-one parts of carbonic acid should be replaced by ninety-five of oxygen. It is
found, indeed, that the volume of carbonic acid exhaled is always less than the volume
of oxygen absorbed. This diffusion is constantly going on, so that the air in the pul-
monary vesicles, where the interchange of gases with the blood takes place, maintains a
pretty uniform composition. The process of aeration of the blood, therefore, has none
of that intermittent character which attends the muscular movements of respiration,
which would undoubtedly occur if the entire gaseous contents of the lungs were changed
with every respiratory act.

CHAPTER V.

CHANGES WHICH THE AIR AND THE BLOOD UNDERGO IN RESPIRATION.

Composition of the air— Consumption of oxygen— Exhalation of carbonic acid— Influence of age— Relations between
the quantity of oxygen consumed and the quantity of carbonic acid exhaled— Exhalation of watery vapor— Ex-
halation of ammonia— Exhalation of organic matter— Exhalation of nitrogen— Changes of the blood in respira-
tion (haematosis) — Difference in color between arterial and venous blood — Comparison of the gases in venous
and arterial blood— Analysis of the blood for gases— Relative quantities of oxygen and carbonic acid in venous
and arterial blood— Nitrogen of the blood— Condition of the gases in the blood— Mechanism of the interchange
of gases between the blood and the air in the lungs— Relations of respiration to nutrition, etc.— Views of physi-
ologists anterior to the time of Lavoisier — Relations of the consumption of oxygen to nutrition — Relations of
the exhalation of carbonic acid to nutrition— Essential processes of respiration— The respiratory sense, or want
on the part of the system which induces the respiratory movements — Respiratory efforts before birth — Cuta-
neous respiration — Asphyxia.

FROM the allusions which we have already made to the general process of respiration,
it is apparent that, before the discovery of the nature of the gases which compose the
air and those which are exhaled from the lungs, it was impossible for physiologists to
have any correct ideas of the nature of this important function. It is not surprising that
the ancients, observing the regular introduction of air into the lungs and noting the fact
that the air is generally much cooler than the body, supposed the great object of respi-
ration to be the cooling of the blood. It is also evident that no definite knowledge of
any of the processes of respiration could exist prior to the discovery of the circulation

140 EESPIRATION.

of the blood and our knowledge of the composition of the air and the properties of
oxygen.

The discovery of the properties of oxygen and carbonic acid, although bearing upon the
great question under consideration, were simply isolated facts and failed to develop any
definite idea of the changes of the air and blood in respiration. The application of these
facts was made by the great chemist, Lavoisier, who was the first to employ the delicate
balance in chemical investigation, and whose observations mark the beginning of an
accurate knowledge of the function of respiration. With the balance, Lavoisier showed
the nature of the oxides of the metals ; he discovered that carbonic acid is formed by a
union of carbon and oxygen ; and, noting the consumption of oxygen and the produc-
tion of carbonic acid in respiration, advanced, for the first time, the view that the one
was employed in the production of the other. Although, as would naturally be expected,
the doctrines of this great observer have been modified with the advances in science, he
developed facts which will stand forever, and which have served as the starting-point of
all our knowledge on this subject. From that time, physiologists began to regard respi-
ration as consisting in the appropriation of oxygen and the exhalation of carbonic acid ;
and now the seat of this process is simply changed from the lungs to the tissues. From the
limited knowledge of the intimate phenomena of nutrition which obtained in his day,
Lavoisier could not be expected to entertain any other view than that the carbonic acid
produced was the result of a direct union of oxygen writh carbon in the blood. It is
only since investigations have made manifest the great complexity of the processes of
nutrition, that some are unwilling to believe that carbonic acid is produced in so simple
a way as it appeared to Lavoisier.

Composition of the Air. — Pure atmospheric air is a mechanical mixture of 79*19 parts
of nitrogen with 20'81 parts of oxygen (Dumas and Boussingault). It contains, in addi-
tion, a very small quantity of carbonic acid, about one part in 2,000 by volume. The air
is never free from moisture, which is very variable in quantity, being generally more
abundant at a high than at a low temperature. In 1840, Schonbein discovered in the
air a peculiarly odorous principle called ozone, which he conceived to be a compound of
oxygen and hydrogen, but which is now pretty well shown to be an allotropic form of
oxygen. Oxygen obtained by decomposing water by the Voltaic pile is in this condition.
It exists in very small quantity in the air, and, as far as we know, plays no important
part in the function of respiration. Its chief interest has been in its theoretical rela-
tions to epidemic diseases. Floating in the atmosphere, are a number of excessively-
minute organic bodies. Various odorous and other gaseous matters may be present as
accidental constituents of the atmosphere.

In considering the function of respiration, it is not necessary to take account of any
of the constituents of the atmosphere except oxygen and nitrogen, the others being
either inconstant or existing in excessively minute quantity. It is necessary to the regu-
lar performance of the function, that the air should contain about four parts of nitrogen
to one of oxygen and have about the density which exists on the general surface of the
globe. When the density is very much increased, as in mines, respiration is usually
more or less disturbed. By exposure to a rarefied atmosphere, as in the ascent of high
mountains or in aerial voyages, respiration may be very seriously interfered with, from the
fact that less oxygen than usual is presented to the respiratory surface and the reduced
atmospheric pressure diminishes the capacity of the blood for holding gases in solution.

Magendie and Bernard, in experimenting on the minimum proportion of oxygen in
the air which is capable of sustaining life, found that a rabbit, confined under a bell-
glass, with an arrangement for removing the carbonic acid and water exhaled as fast as
they were produced, died of asphyxia when the quantity of oxygen became reduced to
from three to five per cent.

A few experiments are on record in which the human subject and animals have been

CONSUMPTION OF OXYGEN.

made to respire for a time pure oxygen. Although this is the gas which is essential in
ordinary respiration, the process being carried on about as well in a mixture of oxygen
with hydrogen as with nitrogen, the functions do not seem to be much altered when the
pure gas is taken into the lungs. Allen and Pepys confined animals for twenty-four
hours in an atmosphere of pure oxygen without any notable results; but, as is justly
remarked by Longet, these experiments do not show that it would be possible to respire
unmixed oxygen indefinitely without inconvenience. As it exists in the air, oxygen is
undoubtedly in the best form for the permanent maintenance of the respiratory func-
tion. The blood seems to have a certain capacity for the absorption of oxygen, which is
not increased when the pure gas is respired.

The only other gas which has the power of maintaining respiration, even for a time,
is nitrous oxide. This is absorbed by the blood-corpuscles with great avidity, and, for a
time, it produces an exaggeration of the vital processes, with delirium, etc. — properties
which have given it the common name of the laughing gas ; but this condition is fol-
lowed by anaesthesia, and finally asphyxia, probably because the gas has such an affinity
for the blood-corpuscles as to remain to a certain extent fixed, interfering with that inter-
change of gases which is essential to life. Notwithstanding this, experimenters have
confined with impunity rabbits and other animals in an atmosphere of nitrous oxide for
a number of hours. In all cases they became asphyxiated, but in some instances were
restored on being brought again into the ordinary atmosphere.

Other gases which may be introduced into the lungs either produce asphyxia, nega-
tively, from the fact they are not absorbed by the blood and are incapable of carrying on
respiration, like hydrogen or nitrogen, or positively, by a poisonous effect on the system.
The most important of the gases which act as poisons are, carbonic oxide, sulphuretted
hydrogen, and arseniuretted hydrogen. It is somewhat uncertain whether carbonic acid
exert its deleterious influence as a poison or as merely taking the place of the oxygen in
the blood-corpuscles. It is easily displaced from the blood by oxygen, and therefore
does not seem to possess the properties of a poison, like carbonic oxide and some other
gases, which become fixed in the blood and are not readily displaced when fresh air is
introduced into the lungs.

Consumption of Oxygen. — The determination of the quantity of oxygen which is re-
moved from the air by the process of respiration is a question of great physiological
interest and one which engaged largely the attention of Lavoisier and those who have
followed in his line of observation. On this point, there is an accumulated mass of
observations, which are comparatively unimportant from the fact that they were made
before the means of analysis of the gases were as perfect as they now are. Although
many of the results obtained by the older experimenters are interesting and instructive
as showing the comparative quantities of oxygen consumed under various physiological
conditions, they are not to be compared with the more recent observations. In the
observations of Regnault and Eeiset, the animal to be experimented upon was enclosed
in a receiver filled with air, a measured quantity of oxygen was introduced as fast as it
was consumed by respiration, and the carbonic acid was constantly removed and care-
fully estimated. In most of the experiments, the confinement did not appear to inter-
fere with the functions of the animal, which ate and drank in the apparatus and was in
as good condition at the termination as at the beginning of the observation. This method
is much more accurate than that of simply causing an animal to breathe in a confined
space, when the consumption of oxygen and accumulation of carbonic acid and other
matters must interfere more or less with the proper performance of the respiratory func-
tion. As employed by Regnault and Reiset, it is only adapted to experiments on animals
of small size. These give but an approximate idea of the processes as they take place in
the human subject, as it is natural to suppose that the relative quantities of gases con-
sumed and produced in respiration vary in different orders of animals.

142 RESPIRATION.

In the researches on respiration by Dr. Max Pettenkofer, the conditions for accurate
observation on the human subject seem to have been fulfilled. Dr. Pettenkofer con-
structed a chamber large enough to admit a man and allow perfect freedom of motion,
eating, sleeping, etc., into which air could be constantly introduced in definite quantity,
and from which the products of respiration were constantly removed and estimated. An
incomplete series of observations is published, which has particular reference to the prod-
ucts of respiration ; and, thus far, the subject of consumption of oxygen has not been fully
considered. This method was adapted to the human subject on a small scale in 1843, by
Scharling, but there was no arrangement for estimating the quantity of oxygen furnished.

Estimates of the absolute quantities of oxygen consumed, or of carbonic acid ex-
haled, based on analyses of the inspired and expired air, calculations from the average
quantity of air changed with each respiratory act, and the average number of respirations
per minute, are by no means so reliable as analyses showing the actual changes in the air,
like those of Regnault and Reiset, provided the physiological conditions be fulfilled.
When there is so much multiplication and calculation, a very slight and perhaps unavoid-
able inaccuracy in the quantities consumed or produced in a single respiration will make
an immense error in the estimate for a day or even an hour. Bearing in mind all these
sources of error, from the experiments of Valentin and Brunner, Dumas, Regnault and
Reiset, and others, a sufficiently-accurate approximation of the proportion of oxygen
consumed by the human subject may be formed. The air, which contains, when inspired,
20-81 parts of oxygen per 100, is found on expiration to contain but about 16 parts per
100. In other words, the volume of oxygen absorbed in the lungs is five per cent, or -£$
of the volume of air inspired. It is interesting and useful to extend this estimate as far
as possible to the quantity of oxygen absorbed in a definite time ; for the regulation of
the supply of oxygen where many persons are assembled, as in public buildings, hospi-
tals, etc., is a question of great practical importance. Assuming that the average respira-
tions per minute are eighteen, and that, with each act, twenty cubic inches of air are
changed, fifteen cubic feet of oxygen are consumed in the twenty-four hours, which repre-
sent three hundred cubic feet of pure air. This is the minimum quantity of air which is
actually used, making no allowance for any increase in the intensity of the respiratory
processes, which is liable to occur from various causes. To meet all the respiratory exi-
gencies of the system, in hospitals, prisons, etc., it has been found necessary to allow at
least eight hundred cubic feet of air for each person, unless the situation be such that the
air is changed with unusual frequency ; for, beside the actual loss of oxygen in the respired
air, constant emanations from both the pulmonary and cutaneous surfaces are taking
place, which should be removed. In some institutions as much as twenty-five hundred
cubic feet of air is allowed to each person.

The quantity of oxygen consumed is subject to great variations, depending upon tem-
perature, the condition of the digestive system, muscular activity, etc. The following
conclusions, the results of the observations of Lavoisier and Seguin, give at a glance tho
variations from the above-mentioned causes :

"1. A man, in repose and fasting, with an external temperature of 90° Fahr., con-
sumes 1,465 cubic inches of oxygen per hour.

"2. A man, in repose and fasting, with an external temperature of 59° Fahr., con-
sumes 1,627 cubic inches of oxygen per hour.

"3. A man, during digestion, consumes 2,300 cubic inches of oxygen per hour.

"4. A man, fasting, while he accomplishes the labor necessary to raise, in fifteen
minutes, a weight of 7,343 kil. (about 16 Ib. 3 oz. av.) to the height of 656 feet, consumes
3,874 cubic inches of oxygen per hour.

"5. A man, during digestion, accomplishing the labor necessary to raise, in fifteen
minutes, a weight of 7,343 kil. (about 16 Ib. 3 oz. av.) to the height of 700 feet, consumes
5,568 cubic inches of oxygen per hour.1'

All who have experimented on the influence of temperature upon the consumption of

CONSUMPTION OF OXYGEN. 143

oxygen, in the warm-blooded animals and in the human subject, have noted a marked in-
crease at low temperatures. Immediately after birth, the consumption of oxygen in the
warm-blooded animals is relatively very slight. Buffon and Legallois have shown that,
just after birth, dogs and other animals will live for half an hour or more under water ; and
cases are on record where life has been restored in newly-born children after seven, and,
it has been stated, after twenty-three hours of asphyxia. (Milne-Edwards.) During the
first periods of existence, the condition of the newly-born approximates to that of a cold-
blooded animal. The lungs are relatively very small, and it is some time before they fully
assume their function. The muscular movements are hardly more*than is necessary to take
the small amount of nourishment consumed at that period, and nearly all of the time is
passed in sleep. There is also very little power of resistance to low temperature. Although
accurate researches regarding the comparative quantities of oxygen in the venous and
arterial blood of the foetus are wanting, it has been frequently observed that the differ-
ence in color is not so marked as it is after pulmonory respiration becomes established.
The direct researches of "W. F. Edwards have shown that the absolute consumption of
oxygen by very young animals is very small ; and the observations of Legallois on rabbits,
made every, five days during the first month of existence, show a rapidly-increasing de-
mand for this principle with age.

Eegnault and Reiset have shown that the consumption of oxygen is greater in lean
than in very fat animals, provided they be in perfect health. They have also shown that
the consumption is much greater in carnivorous than in herbivorous animals ; and, in ani-
mals of different sizes, it is relatively much greater in those which are very small. In
small birds, such as the sparrow, the relative quantity of oxygen absorbed was ten
times greater than in the fowl.

During sleep the quantity of oxygen consumed is considerably diminished ; and in hi-
bernation it is so small, that Spallanzani could not detect any difference in the composi-
tion of the air in which a marmot, in a state of torpor, had remained for three hours.
In experiments on a marmot in hibernation, Regnault and Reiset observed a reduction
in the quantity of oxygen consumed to about •£$ of the normal standard.

It has been shown by experiments, that the consumption of oxygen bears a pretty
constant ratio to the production of carbonic acid ; and, as the observations upon the influ-
ence of sex, number of respiratory acts, etc., on the activity of the respiratory processes,
have been made chiefly with reference to the carbonic acid exhaled, we shall consider
these influences in connection with the products of respiration.

Experiments on the effect of increasing the proportion of oxygen in the air have led
to varied results in the hands of different observers. Regnault and Reiset, whose
observations on this point are generally accepted, did not discover any increase in the
consumption of oxygen when this gas was largely in excess in the atmosphere.

The results of confining an animal in an atmosphere composed of twenty-one parts of
oxygen and seventy-nine parts of hydrogen are very curious and instructive. When
hydrogen is thus substituted for the nitrogen of the air, the consumption of oxygen is
largely increased. Regnault and Reiset attribute this to the superior refrigerating power
of the hydrogen ; but a more rational explanation would seem to be in its superior
diffusibility. Hydrogen is the most diffusible of all gases ; and, when introduced into the
lungs in place of the nitrogen of the air, the vitiated air, charged with carbonic acid,
is undoubtedly more readily removed from the deep portions of the lungs, giving place
to the mixture of hydrogen and oxygen. It is probably for this reason that the
quantity of oxygen consumed is increased. It is probable that the nitrogen of the air
plays an important part in the phenomena of respiration by virtue of its degree of
diffusibility.

In view of the great variations in the consumption of oxygen dependent on different
physiological conditions, such as digestion, exercise, temperature, etc., it is impossible to
fix upon any number which will represent, even approximatively, the average quantity

144 EESPIEATIOK

consumed per hour. The estimate arrived at by Longet, from a comparison of the re-
sults obtained by different reliable observers, is perhaps as near the truth as possible.
This estimate puts the hourly consumption at from 1,220 to 1,525 cubic inches, "in an
adult male, during repose and in normal conditions of health and temperature."

In passing through the lungs, the air, beside losing a proportion of its oxygen,
undergoes the following changes :

1. Increase in temperature.

2. Gain of carbonic acid.

3. Gain of watery vapor.

4. Gain of ammonia.

5. Gain of a small quantity of organic matter.

6. Gain, and occasionally loss, of nitrogen.

The elevation in temperature of the air which has passed through the lungs has been
carefully observed by Dr. Grehant. He found that, with an external temperature of 72°
Fahr., respiring seventeen times per minute, the air taken in by the nares and expired by
the mouth, through an apparatus containing a thermometer carefully protected from ex-
ternal influences, marked a temperature of 95*4°. Taking in the air by the mouth, the
temperature of the expired air was 93°. At the commencement of the expiration, Dr.
Grehant noted a temperature of 94°. After a prolonged expiration, the temperature
was 96°. In these observations, the temperature taken beneath the tongue was 98°.

Exhalation of Carbonic Acid. — The production of carbonic acid in the respiratory
process is as universal as the consumption of oxygen. Experiments have shown that all
animals during life exhale this principle, as well as all tissues, so long as they retain their
irritability. This takes place, not only when the animals or tissues are placed in an
atmosphere of oxygen or common air, but, as was observed by Spallanzani, in an
atmosphere of pure nitrogen or hydrogen. This fact has since been noted by W. F.
Edwards, J. Muller, G. Liebig, Bert, and others.

The study of the exhalation of carbonic acid presents several problems of great
physiological interest :

1. What is the absolute quantity of carbonic acid exhaled by the lungs in a given
time?

2. What are the variations in the exhalation of this principle due to physiological
influences ?

3. What is the relation between the quantity of carbonic acid produced and the
quantity of oxygen consumed ?

On account of the variations in the quantities of carbonic acid exhaled at different
periods of the day, and particularly the great influence of the rapidity of the respiratory
movements, it is exceedingly difficult to fix upon any number that will represent the
average proportion of this gas contained in the expired air. The same influences were
found affecting the consumption of oxygen, and the same difficulties were experienced
in forming an estimate of the proportion of this gas consumed. As we assumed, after
a comparison of the results obtained by different observers, that the volume of oxygen
consumed is about five per cent, of the entire volume of air, it may be stated, as an
approximation, that, in the intervals of digestion, in repose, and under normal conditions
as regards the frequency of the pulse and respiration, the volume of carbonic acid
exhaled is about four per cent, of the volume of the expired air. As the volume of
oxygen which enters into the composition of a definite quantity of carbonic acid is pre-
cisely equal to the volume of the carbonic acid, it is seen that a certain quantity of
oxygen disappears in respiration and is not represented in the carbonic acid exhaled.

There are great differences in the proportion of carbonic acid in the expired air,
depending upon the time during which the air has remained in the lungs. This interest-

EXHALATION OF CARBONIC ACID. 145

ing point lias been studied by Vierordt, in a series of ninety-four experiments made upon
his own person, with the following results:

"When the respirations are frequent, the quantity of carbonic acid expelled at each
expiration is much less than in a slow expiration ; but the quantity of carbonic acid pro-
duced during a given time by frequent respirations is greater than that which is thrown
off by slow expirations."

The air which escapes during the first period of an expiration is naturally less rich in
carbonic acid than that which is last expelled and comes directly from the deeper por-
tions of the lungs. Dividing, as nearly as possible, the expiration into two equal parts,
Vierordt found, as the mean of twenty-one experiments, a percentage of 3*72 in the
first part of the expiration and 5'44 in the second part.

Temporary arrest of the respiratory movements, as we should expect, has a marked
influence in increasing the proportion of carbonic acid in the expired air; although the
absolute quantity exhaled in a given time is diminished. In a number of experiments
on his own person, Vierordt ascertained that the percentage of carbonic acid becomes
uniform in all parts of the respiratory organs, after holding the breath for forty seconds.
Holding the breath after an ordinary inspiration, for twenty seconds, the percentage
of carbonic acid in the expired air was increased T73 over the normal standard; but the
absolute quantity exhaled was diminished by 2*642 cubic inches. After taking the
deepest possible inspiration and holding the breath for one hundred seconds, the per-
centage was increased 3 '08 above the normal standard ; but the absolute quantity was
diminished more than fourteen cubic inches. Allen and Pepys state that air which has
passed nine or ten times through the lungs contains 9 '5 per cent, of carbonic acid.

Vierordt gives the following formula as representing the influence of the frequency of
the respirations on the production of carbonic acid: Taking 2-5 parts per hundred as
representing the constant value of the gas exhaled by the blood, the increase over this
proportion in the expired air is in exact ratio to the duration of the contact of the air
and blood.

The absolute quantity of carbonic acid exhaled in a given time is a more important
subject of inquiry than the proportion contained in the expired air ; for the latter is con-
stantly varying with every modification in the number and extent of the respiratory acts,
and the volume of breathing air is subject to great fluctuations and is very difficult of
determination.

Among the most reliable observations on the quantity of carbonic acid exhaled by the
human subject in a definite time and the variations to which it is subject, are those of
Andral and Gavarret and of Dr. Edward Smith. The observations of Lavoisier and S6guin,
Front, Davy, Dumas, Allen and Pepys, Scharling, and others, have none of them seemed
to fulfil the necessary experimental conditions so completely. Scharling's method was to
enclose his subject in a tight box, with a capacity of about twenty-seven cubic feet, to
which air was constantly supplied ; but the observations were comparatively few, being
made on only six persons. In his observations, the quantities of gas exhaled must have
been considerably modified by the elevation of temperature and exhalation of moisture in
so small a space. The mental condition of the subject of an experiment has an influence
upon the products of respiration, and the function is sometimes modified from the mere
fact that an experiment is being performed ; an influence which Scharling did not foil to
recognize, but which frequently cannot be guarded against.

The observations of Andral and Gavarret were made on sixty-two persons of both
sexes and different ages and under absolutely identical conditions as regards digestion,
time of the day, barometric pressure, and temperature. The products of respiration wore
collected in the following way : A thin mask of copper covering the face and large
enough to contain an entire expiration was fitted to the face by its edges, which were
provided with India-rubber so as to make it air-tight. At the upper part was a plate of
glass for the admission of light, and at the lower part, an opening, which allowed the
10

146 RESPIRATION.

entrance of air but was provided with a valve preventing its escape. By another open-
ing, the mask was connected by a rubber tube with three glass balloons, capable of hold-
ing 8,544 cubic inches, in which a vacuum had been previously established. With the mask
fixed upon the face, and a stopcock opened, connected with the balloons, so as to gradu-
ate the current of air, the subject respires freely in the current which comes from the
exterior into the receivers. In this way, although the quantity of air respired is not meas-
ured, the vacuum in the receivers draws in the products of respiration. The current will
continue for from eight to thirteen minutes and is so regulated that the air is respired
but once. The quantity of carbonic acid in the receivers represents the quantity pro-
duced during the time that the experiment has been going on. By carefully fulfilling all
the physiological conditions, regulating the number of respirations, as far as possible, to
the normal standard, different observations on the same subject, at different times and under
the same conditions, were attended with results so nearly identical as to give every con-
fidence in the accuracy of the process. But even then, these observers recognized such
immense variations in the exhalation of carbonic acid with the constantly-varying physi-
ological conditions, that they did not feel justified in taking their observations as a basis
for calculations of the entire quantity exhaled in the twenty-four hours.

The results of the above-mentioned observations on the male, between the ages of six-
teen and thirty, between 1 and 2 P. M., under identical conditions of the digestive and
muscular systems, each experiment lasting from eight to thirteen minutes, showed an
exhalation of about 1,220 cubic inches of carbonic acid per hour.

Dr. Edward Smith, in his elaborate paper on the phenomena of respiration, employed
a very rigorous method for the estimation of the carbonic acid exhaled. He used a mask,
fitting closely to the face, which covered only the air-passages. The air was admitted after
being measured by passing through an ordinary dry gas-meter. The expired air was passed
through a drying apparatus, and the carbonic acid was absorbed by a solution of potash,
arranged in a number of layers so as to present a surface of about seven hundred square
inches, and carefully weighed. This apparatus was capable of collecting all the carbonic
acid exhaled in an hour. The estimate was made for eighteen waking hours and six hours
of sleep. The observations for the eighteen hours were made on four persons; namely,
Dr. Smith, get. 38 years, weighing 196 pounds, 6 feet high, with a vital capacity of 280
cubic inches ; Mr. Moul, ret. 48 years, 5 feet 9£ inches high, 1V5 pounds weight ; Dr.
Murie, set. 26 years, 5 feet 7|- inches high, 133 pounds weight, vital capacity 250 cubic
inches ; Prof. Frankland, set. 33 years, 5 feet 10£ inches high, and 136 pounds weight.
Breakfast was taken at 8^ A. M., dinner at 1^, tea at 5|-, and supper at 8^ p. M. The ob-
servations occupied ten minutes and were made every hour and half-hour for eighteen
hours. The average for the eighteen hours gave 20,082 cubic inches of carbonic acid for
the whole period. Observations during the six hours of sleep showed a total exhalation
of 4,126 cubic inches. This, added to the quantity exhaled during the day, gives as the
total exhalation in the twenty-four hours, during complete repose, 24,208 cubic inches
(about 14-24 cubic feet), containing T144 oz. av. of carbon. Considering the great varia-
tions in the exhalation of carbonic acid, this estimate can be nothing more than an ap-
proximation. One of the great modifying influences is muscular exertion, by which the
production of carbonic acid is largely increased. This would indicate a larger quantity
during ordinary conditions of exercise, and a much larger quantity in the laboring classes.
Dr. Smith gives the following approximate estimates of these differences :

In quietude 7'144 oz. av. of carbon.

Non-laborious class 8'68 " "

Laborious class 11'7 " "

In studying the variations in the exhalation of carbonic acid, important information
has been derived from experiments by many observers on the inferior animals, as well as
from the observations of Dumas, Prout, Scharling, Pettenkofer, and others, on the

EXHALATION OF CARBONIC ACID. 147

human subject. The principal conditions which influence the exhalation of this principle
are the following : Age and sex ; activity or repose of the digestive system ; form of
diet; sleep; muscular activity ; fatigue; moisture and surrounding temperature; season
of the year.

Influence of Age. — In treating of the consumption of oxygen, it was stated that, during
the first few days of extra-uterine existence, the demand for oxygen on the part of the
system is very slight. At this period there is a correspondingly-feeble exhalation of
carbonic acid. It is well known that, during the first hours and days after birth, the new
being has little power of generating heat, needs constant protection from changes in tem-
perature, and the voluntary movements are very imperfect. During the first few days,
indeed, the infant does little more than sleep and take the small quantity of colostrum
which is furnished by the mammary glands of the mother. While the animal functions
are so imperfectly developed and until the nourishment becomes more abundant and the
child begins to increase rapidly in weight, the quantity of carbonic acid exhaled is very
small.

After the respiratory function has become fully established, it is probable, from the
greater number of respiratory movements in early life, that the production of carbonic
acid, in proportion to the weight of the body, is greater in infancy than in adult life.
Direct observations, however, are wanting on this point.

The observations of Andral and Gavarret show the comparative exhalation of carbonic
acid in the male, from the age of twelve to eighty-two, and give the results of a single
observation at the age of one hundred and two years. They show an increase in the
absolute quantity exhaled, from the age of twelve to thirty-two; a slight diminution,
from thirty-two to sixty ; and a considerable diminution, from sixty to eighty-two. These

results are given in the following table:

Carbonic acid exhaled per hour

In boys from twelve to sixteen years 915 cubic inches.

In young men from seventeen to nineteen years 1,220 " "

In men from twenty-five to thirty-two years. 1,343 " "

In men from thirty-two to sixty years 1,220 " "

In men from sixty-three to eighty-two years 933 " "

In an old man of one hundred and two years 671

Taking into consideration the increase in the weight of the body with age, it is evident
that the respiratory activity is' much greater in youth than in adult life. Andral and
Gavarret do not give the weight of the subjects of their observations, but, as the weight
generally does not diminish after maturity, there can be no doubt that there is a rapid
diminution in the relative quantity of carbonic acid produced in old age.

Scharling, in a series of observations on a boy nine years of age and weighing 48-5
pounds, an adult of twenty-eight, and one of thirty-five years, the latter weighing 163'6
pounds, showed that the respiratory activity in the child was nearly twice as great, in
proportion to his weight, as the average in the adults. It is seen, from the observations
of Andral and Gavarret, that the absolute increase in the exhalation of carbonic acid from
childhood to adult life is very slight in comparison with the natural increase in the
weight of the body; showing that, proportionately, the exhalation of carbonic acid is
greater in early life.

Influence of Sex. — All observers have found a marked difference between the sexes, in
favor of the male, in the proportion of carbonic acid exhaled. Andral and Gavarret noted
an absolute difference of about forty-five cubic inches per hour but did not take into
consideration the differences in the weight of the body. Scharling, taking the proportion
exhaled to the weight of the body, noted a marked difference in favor of the male.

The difference in the degree of muscular activity in the sexes is sufficient to account
for the greater evolution of carbonic acid in the male, for this principle is exhaled in pro-
portion to the muscular development of the individual ; but there is an important differ-

148 RESPIRATION.

ence connected with the variations with age, which depends upon the condition of the
generative system of the female.

The absolute increase in the evolution of carbonic acid with age, in the female, is
arrested at the time of puberty and remains stationary during the entire menstrual
period, provided the menstrual flow occur with regularity. During this time, the average
exhalation per hour is 714 cubic inches. After the cessation of the menses, the quantity
gradually increases, until, at the age of sixty, it amounts to 915 cubic inches per hour.
From the age of sixty to eighty-two, the quantity diminishes to 793, and finally to 670
cubic inches.

When the menses are suppressed, there is an increase in the exhalation of carbonic
acid, which continues until the flow becomes reestablished. In a case of pregnancy
observed by Scharling, the exhalation was increased to about 885 cubic inches.

Influence of Digestion. — Almost all observers agree that the exhalation of carbonic
acid is largely increased during digestion. Lavoisier and Seguin found that, in repose
and fasting, the quantity exhaled per hour was 1,210 cubic inches, which was raised to
1,800 and 1,900 during digestion. Numerous experiments on animals have confirmed
this statement. A very interesting series of observations on this point was made by
Vierordt upon his own person. Taking his dinner at from 12 '30 to 1 P. M., having noted
the frequency of the pulse and respirations and the exhalation of carbonic acid at 12, he
found, at 2 p. M., the pulse and respirations increased in frequency, the volume of expired
air augmented, and that the carbonic acid exhaled had increased from 15*77 to 18'22 cubic
inches per minute. In order to ascertain that this variation did not depend upon the
time of day independently of the digestive process, he made a comparison at 12 M.. at 1
and at 2 p. M. without taking food, which showed no notable variation, either in the
pulse, number of respirations, volume of expired air, or quantity of carbonic acid exhaled.
There can be no doubt that the exhalation of carbonic acid is notably increased during
the functional activity of the digestive system.

The effect of inanition is to gradually diminish the exhalation of carbonic acid. Bidder
and Schmidt noted the daily production of carbonic acid in a cat which was subjected to
eighteen days of inanition, at the end of which time it died. The quantity diminished
gradually from day to day, until, just before death, it was reduced a little more than one-
half. Dr. Smith noted, in his own person, the influence of a fast of twenty-seven hours.
There was a marked diminution in the quantity of air respired, in the quantity of vapor
exhaled, in the number of respirations, and in the rapidity of the pulse. The exhalation
of carbonic acid was diminished one-fourth. An interesting point in this observation was
the fact that the quantity was as small four and a half hours after eating as at the end
of the twenty-seven hours. " An increase of carbonic acid in the absence of food, at or
near the period when it is usually increased by food," was also noted in the experiment
by Dr. Smith.

Influence of Diet. — Eegnault and Reiset, in their experiments on animals, studied the
effect of different kinds of diet upon the relations of the quantity of oxygen absorbed to
the carbonic acid exhaled. About the only conclusive and extended series of investiga-
tions on the influence of diet upon the absolute quantity of carbonic acid exhaled are
those of Dr. Smith. This observer made a large number of experiments on the influence
of various kinds of food and extended his inquiries into the influence of certain beverages,
such as tea, coffee, cocoa, malt and fermented liquors. "We have already fully described
the method employed in these experiments, and the conclusions, which are of great
interest and importance, are very exact and reliable.

Dr. Smith divides food into two classes, one which increases the exhalation of carbonic
acid, which he calls respiratory excitants, and the other, which diminishes the exhalation,
he calls non-exciters.

The following are the results of a large number of carefully-conducted observations
upon four persons:

EXHALATION OF CARBONIC ACID. 149

" The excito-respiratory are nitrogeneous food, milk and its components, sugars, rum,
beer, stout, the cereals, and potato.

" The non-exciters are starch, fat, certain alcoholic compounds, the volatile elements
of wines and spirits, and coffee-leaves.

" Respiratory excitants have a temporary action ; but the action of most of them
commences very quickly, and attains its maximum within one hour.

" The most powerful respiratory excitants are tea and sugar ; then coffee, rum, milk,
cocoa, ales, and chiccory ; then casein and gluten, and lastly, gelatin and albumen. The
amount of action was not in uniform proportion to their quantity. Compound aliments,
as the cereals, containing several of these substances, have an action greater than that
of any of their elements.

" Most respiratory excitants, as tea, coffee, gluten, and casein, cause an increase in
the evolution of carbon greater than the quantity which they supply, while others, as
sugar, supply more than they evolve in this excess, that is, above the basis. No sub-
stance containing a large amount of carbon evolves more than a small portion of that
carbon in the temporary action occurring above the basis-line, and hence a large portion
remains unaccounted for by these experiments."

The comparative observations of Dr. Smith upon the four persons who were the sub-
jects of experiment demonstrated one very important fact ; namely, that the action of
different kinds of food upon respiration is modified by idiosyncrasies and the tastes of
different individuals. For example, in experiments on his own person, certain articles
which were agreeable to him excited the exhalation of carbonic acid ; but in experi-
menting with the same articles upon Mr. Moul, to whom they were distasteful, he found
the respiratory action diminished.

Quite a number of observers have noted the influence of alcohol upon the products
of respiration ; but the results of experiments have not been entirely uniform. Prout
observed a constant diminution in the quantity of carbonic acid exhaled, under the in-
fluence of alcohol. This has been confirmed by the observations of Horn, Vierordt, and
many others; but Hervier and Saint-Lager assert that the use of alcohol increases the
exhalation of carbonic acid. In the experiments of Prout, a small quantity of wine taken
fasting caused the proportion of carbonic acid in the expired air to fall immediately
from 4 to 3 parts per 100. During the four hours following, it oscillated between 3*40,
3*10, and 3. The administration of a second dose, followed by some symptoms of in-
toxication, diminished the proportion to 2'70 per 100. Dr. Fyfe, of Edinburgh, showed
that the depressing effects of an alcoholic excess were continued into the following day.
Dr. Fyfe also noted a fact, important in this connection, namely, that the prolonged use
of nitric acid and the condition of the system induced by the administration of mer-
curials were attended with a considerable diminution in the daily amount of carbonic
acid exhaled by the lungs. In addition, Prout demonstrated that the exhalation of car-
bonic acid was diminished by the use of a concentrated infusion of tea, and Horn noted
the same effect attending slight narcotism produced by smoking tobacco.

The observations of Dr. Smith, which were all made fasting, show a certain variation
in the effects of different alcoholic beverages. His results are briefly the following :

" Brandy, whiskey, and gin, and particularly the latter, almost always lessened the
respiratory changes recorded, while ruin as commonly increased them. Rum-and-milk
had a very pronounced and persistent action, and there was no effect on the sensorium.
Ale and porter always increased them, while sherry wine lessened the quantity of air
inspired, but slightly increased the carbonic acid evolved.

"The volatile elements of alcohol, gin, rum, sherry, and port-wine, when inhaled,
lessened the quantity of carbonic acid exhaled, and usually lessened the quantity of air
inhaled. The effect of fine old port-wine was very decided and uniform ; and it is
known that wines and spirits improve in aroma and become weaker in alcohol by age.
The excito-respiratory action of rum is probably not due to its volatile elements."

150 RESPIRATION.

From these facts, it would seem that the most constant effect of alcohol and of alcoholic
liquors, such as wines and spirits, is to diminish the exhalation of carbonic acid. This
effect is almost instantaneous, when the articles are taken into the stomach fasting ; and
when taken with the meals, the increase in carbonic acid which habitually accompanies
the process of digestion is materially lessened. Rum, which Dr. Smith found to be a
respiratory excitant, is an exception to this rule. Malt liquors seem to increase the ex-
halation of carbonic acid. "With regard to alcohol itself, Dr. Smith says: "The action
of pure alcohol was much more to increase than to lessen the respiratory changes, and
sometimes the former effect was well pronounced."

Eegarding as one of the great sources of carbonic acid the development of this prin-
ciple in the tissues, whence it is taken up by the blood, Dr. Smith attributes the grateful
and soothing influence of tea, coffee, eau sucree, and the other beverages which he classes
as respiratory excitants, to their action in facilitating the removal of this principle from
the system. The presence of carbonic acid in the tissues and in the blood produces a
sense of malaise, or depression, which we should suppose would be relieved by any thing
which facilitates its elimination. It is undoubtedly this indefinite sense of discomfort
which induces the act of sighing, by which the air in the lungs is more effectually reno-
vated. This view is sustained by the fact that intellectual fatigue and mental emotions
diminish the exhalation of carbonic acid. Apjohn cites an instance in which the pro-
portion of carbonic acid in the expirations was reduced to 2'9 parts per 100 under the
influence of mental depression.

We have already alluded to the modification in the exhalation of carbonic acid pro-
duced by tobacco.

Influence of Sleep. — All who have directed attention to the influence of sleep upon
the respiratory products have noted a marked diminution in the exhalation of carbonic
acid ; but we again recur to the experiments of Dr. Smith for exact information on this
point. Dr. Smith estimated the quantity of carbonic acid exhaled during six hours of
sleep, at night, at 4,126 cubic inches. According to this observer, the quantity during
the night is to the quantity during the day, in complete repose, as ten is to eighteen.
During a light sleep, the exhalation was 10'32, and during profound sleep, 9 '52 cubic
inches per minute.

We have alluded to the great diminution in the quantity of oxygen consumed in hiber-
nating animals while in a torpid condition. Eegnault and Reiset found that a marmot
in hibernation consumed only ^ of the oxygen which he used in his active condition.
In the same animal they noted an exhalation of carbonic acid equal to but little more
than half the weight of oxygen absorbed ; so that in this condition the diminution in the
exhalation of carbonic acid is proportionately even greater than in the consumption of
oxygen.

Influence of Muscular Activity, — Nearly all observers are agreed that there is a con-
siderable increase in the exhalation of carbonic acid during and immediately following
muscular exercise. In insects, Mr. Newport has found that a greater quantity is some-
times exhaled in an hour of violent agitation than in twenty-four hours of repose. In a
drone, the exhalation in twenty-four hours was 0'30 of a cubic inch, and during vio-
lent muscular exertion the exhalation in one hour was 0'34. Lavoisier recognized the
great influence of muscular activity upon the respiratory changes. In treating of the
consumption of oxygen, we have quoted his observations on the relative quantities of air
vitiated in repose and activity.

Vierordt, in a number of observations on the human subject, ascertained that moder-
ate exercise increased the average quantity of air respired per minute by nearly nineteen
cubic inches, and that there was an increase of T197 cubic inch per minute in the ab-
solute quantity of carbonic acid exhaled.

The following results of the experiments of Dr. Edward Smith on the influence of
exercise are very definite and satisfactory :

EXHALATION OF CARBONIC ACID. 151

In walking at the rate of two miles an hour, the exhalation of carbonic acid during
one hour was equal to the quantity produced during If hour of repose with food, and 2.V
hours of repose without food.

Walking at the rate of three miles per hour, one hour was equal to 2£- hours with,
and 3,V hours without food.

One hour's labor at the tread-wheel, while actually working the wheel, was equal to
4V hours of rest with food, and 6 hours without food.

The various observers we have cited have remarked that, when muscular exertion is
carried so far as to produce great fatigue and exhaustion, the exhalation of carbonic acid
is notably diminished.

Influence of Moisture and Temperature. — Lehmann has shown that the exhalation of
carbonic acid is much greater in a moist than in a dry atmosphere. This conclusion
was the result of a number of experiments on birds and animals confined in air at differ-
ent temperatures and different degrees of moisture. He found that 35£ oz. av. weight of
rabbits, at a temperature of about 100° Fahr., exhaled during an hour before noon, in a
dry air, about 15 cubic inches of carbonic acid ; while, in a moist air at the same tempera-
ture, the exhalation was about 22 cubic inches.

Disregarding observations on the influence of temperature in cold-blooded animals as
inapplicable to the human subject, it has been ascertained that the exhalation of carbonic
acid is much greater at low than at high temperatures, within the limits of heat and cold
that are easily borne by the human subject ; thus following the rule which governs the
consumption of oxygen.

The experiments of Vierordt on the human subject show that there is an increase in
the exhalation of carbonic acid of about one-sixth, under the influence of a moderate
diminution in temperature. In these observations, the low temperatures ranged between
3T'5° and 59°, and the high temperatures between 60'5° and 75'5° Fahr. He found the
quantity of air taken into the lungs slightly increased at low temperatures. The abso-
lute quantity of carbonic acid .exhaled per minute was 18-27 cubic inches for the low
t3iuperatures, and 15'73 cubic inches for the high temperatures.

Influence of the Season of the Year. — It has been pretty well established by the re-
searches of Dr. Smith, that spring is the season of the greatest, and fall the season of
the least activity of the respiratory function.

The months of maximum are: January, February, March, and April.

The months of minimum are: July, August, and a part 'of September.

The months of decrease are: June and July.

The months of increase are : October, November, and December.

W. F. Edwards, in 1819, showed in a marked manner the influence of the seasons
upon the respiratory phenomena in birds. In a series of very curious observations, which
he repeatedly verified, it was demonstrated that the increase in the activity of respiration
during the winter was to a certain extent independent of the immediate influence of the
surrounding temperature. In the month of January, he confined six yellow-hummers in
a receiver containing 71 '4 cubic inches of air, carrying the temperature from 69° to 70°
Fahr. The mean duration of their life was 62 minutes 25 seconds. In the months of
August and September, he repeated the experiment on thirteen birds of the same species,
at the same temperature. The mean duration of life was 82 minutes. These experiments
have an important bearing on our views concerning the essential nature of the respira-
tory function. They seem to indicate that the respiratory processes are intimately con-
nected with nutrition. Like the other nutritive phenomena, they undoubtedly vary at
different seasons of the year and are to a certain extent independent of sudden and
transitory conditions. During the winter, more air is habitually used than in summer,
and the respiratory processes cannot be immediately brought down to the summer
standard by a mere elevation of temperature.

Observations on the influence of barometric pressure are not sufficiently definite in
their results to warrant any exact conclusions.

152 RESPIRATION,

Some physiologists have attempted to fix certain hours of the day when the exhalation
of carbonic acid is at its maximum or at its minimum ; but the respiratory activity is
influenced by such a variety of conditions, that it is impossible to do this with any degree
of accuracy.

Relations between the Quantity of Oxygen consumed and the, Quantity of

Carbonic Acid exhaled.

Oxygen unites with carbon in certain proportions to form carbonic-acid gas, the vol-
ume of which is precisely equal to the volume of the oxygen which enters into its com-
position. In studying the relations of the volumes of these gases in respiration, we have
a guide in the comparison of the volumes of the inspired and expired air. It is now
generally recognized that the volume of air expired is less, at an equal temperature, than
the volume of air inspired. Assuming, then, that the changes in the expired air, as re-
gards nitrogen and all gases except oxygen or carbonic acid, are insignificant, it must be
admitted that a certain quantity of the oxygen consumed by the economy is unaccounted
for by the oxygen which enters into the composition of the carbonic acid exhaled. "We
have already noted that from TV to ^ff, or about 1*4 to 2 per cent, of the inspired air is
lost in the lungs ; or it may be stated, in general terms, that the oxygen absorbed is equal
to about five per cent, of the volume of air inspired, and the carbonic acid exhaled, only
about four per cent. A certain amount of the deficiency in volume of the expired air is
to be accounted for, then, by a deficiency in the exhalation of carbonic acid.

The experiments of Eegnault and Iteiset, to which frequent reference has been made,
have a most important bearing on the question under consideration. As these observers
were able to accurately measure the entire quantities of oxygen consumed and carbonic
acid produced in a given time, the relation between the two gases was kept constantly in
view. They found great variations in this relation, mainly dependent upon the regimen
of the animal. The total loss of oxygen was found to be much greater in carnivorous
than in herbivorous animals ; and, in animals that could be subjected to a mixed diet, by
regulating the food, this was made to vary between the two extremes. The mean of
seven experiments on dogs showed that, for every 1,000 parts of oxygen consumed, 745
parts were exhaled in the form of carbonic acid. In six experiments on rabbits, the
mean was 919 for every 1,000 parts of oxygen.

In animals fed on grains, the proportion of carbonic acid exhaled was greatest, some-
times passing a little beyond the volume of oxygen consumed.

" The relation is nearly constant for animals of the same species which are subjected
to a perfectly uniform alimentation, as is easy to realize as regards dogs ; but it varies
notably in animals of the same species, and in the same animal, submitted to the same
regimen, but in which we cannot regulate the alimentation, as in fowls."

When herbivorous animals were entirely deprived of food, the relation between the
gases was the same as in carnivorous animals.

The final result of the experiments of Regnault and Keiset was, that the "relation
between the oxygen contained in the carbonic acid and the total oxygen consumed, varies,
in the same animal, from 0-62 to T04, according to the regimen to which it is subjected."
These observations on animals have been confirmed in the human subject by M. Doyere,
who found a great variation in the relations of the two gases in respiration ; the volume
of carbonic acid exhaled varying between 1-087 and 0-862 for 1 part of oxygen consumed.

The destination of the oxygen which is not represented in the carbonic acid exhaled
is obscure. Some have thought that it unites with hydrogen to form water ; but there is
no satisfactory evidence of the formation of water in the economy, and researches have
failed to show that there is more thrown off from the body than is taken in with food and
drink.

The variations in the relative volumes of oxygen consumed and carbonic acid produced

EXHALATION OF WATEKY VAPOR. 153

in respiration are not favorable to the hypothesis that the carbonic acid is the result of a
direct action of oxygen upon carbonaceous matters. We should hardly expect a definite
relation to exist between these two gases in respiration, when we find carbonic acid ex-
haled in the absence of oxygen.

Many of the points which we have considered with relation to the variations in the
exhalation of carbonic acid have been investigated by experiments in Pettenkofer's cham-
ber, and the results very nearly correspond with the observations of Scharling, Smith, and
others which we have quoted.

Sources of Carbonic Acid in the Expired Air. — All the carbonic acid in the expired
air comes from the venous blood, where it exists in two forms; in a free state in simple
solution, or at least in a state of very feeble combination, and in union with bases, form-
ing the carbonates and bicarbonates. That which exists in solution in the blood is simply
exhaled. The alkaline carbonates and bicarbonates of the blood, coming to the lungs,
meet with pneumic acid (discovered by Verdeil in 1851), and are decomposed, giving rise
to a farther evolution of gas. It is pneumic acid which gives the constant acid reaction
to the tissue of the lungs. This principle is found in the pulmonary parenchyma at all
periods of life, from which it may be extracted by the proper manipulations and obtained
in a crystalline form. Its quantity is not very great. The lungs of a female who suffered
death by decapitation contained about 0'77 of a grain.

The action of pneumic acid upon the bicarbonates in the blood has been illustrated
in a marked manner by Bernard. When bicarbonate of soda is injected into the jugular
of a living animal, a rabbit, for example, it is decomposed as fast as it gets to the lungs,
and carbonic acid is evolved. This experiment produces no inconvenience to the animal
when the bicarbonate is introduced slowly ; but, when it is injected in large quantity,
the evolution of gas in the lungs is so great as to fill the pulmonary structure and even
the heart and great vessels, and death is the result.

Exhalation of Watery Vapor. — The fact that the expired air contains a considerable
quantity of watery vapor has long been recognized ; and most of the earlier experimenters
who directed their attention to the phenomena of respiration made the estimation of the
quantity exhaled, and the laws which regulate pulmonary transpiration, the subject of
investigation. It is evident that there must be many circumstances materially influencing
this process, such as the hygrometric condition of the atmosphere, temperature, extent
of respiratory surface, etc., which are of sufficient importance to demand special con-
sideration. In many points of view, also, it is interesting to know the absolute quantity
of aqueous exhalation from the lungs.

When the surrounding atmosphere has a temperature below 40° or 43° Fahr., a distinct
cloud is produced by the condensation of the vapor of the breath. By breathing upon
any polished surface, it is momentarily tarnished by the condensed moisture. Although the
fact that watery vapor is contained in the breath is thus easily demonstrated, the estimation
of its absolute quantity presents difficulties which were not overcome by the older physi-
ologists. With the present improved methods of analysis, however, there are many very
accurate means of estimating watery vapor. One method is by the use of Liebig's bulbs
filled with sulphuric acid, or tubes filled with chloride of calcium, both of which sub-
stances have a great avidity for water. From a large number of observations on his own
person and eight others, collecting the water by sulphuric acid, Valentin made the fol-
lowing estimate of the weight of water exhaled from the lungs in twenty-four hours :

In his own person, the exhalation in twenty-four hours was 6,055 grains.

In a young man of small size, the quantity was 5,042 grains.

In a student rather above the ordinary height, the quantity was 11,930 grains.

The mean of his observations gave a daily exhalation of 8,333 grains, or about \\
Ib. av.

154 RESPIRATION.

The extent of respiratory surface has a very marked influence on the quantity of
watery vapor exhaled. This fact is very well shown by a comparison of the exhalation
in the adult and in old age, when the extent of respiratory surface is much diminished-
Barral found the exhalation in an old man less than half that of the adult. It is evident
that the absolute quantity of vapor exhaled is increased when respiration is accelerated.
The quantity of water in the blood also exerts an important influence. Valentin found
that the pulmonary transpiration was more than doubled in a man immediately after
drinking a large quantity of water.

The vapor in the expired air is derived from the entire surface which is traversed in
respiration, and not exclusively from the air-cells. The air which passes into the lungs
derives a certain amount of moisture from the mouth, nares, and trachea. The great vas-
cularity of the mucous membranes in these situations as well as of the air-cells, and the
great number of mucous glands which they contain, serve to keep the respiratory sur-
faces constantly moist. This is important, for only moist membranes allow the free
passage of gases, which is of course essential to the process of respiration.

Exhalation of Ammonia, Organic Matter, etc. — Ammonia has long been recognized
as an exhalation from the human body in health, from the skin as well as the lungs. Dr.
Eichardson calls attention, in his essay on the " Coagulation of the Blood," to the obser-
vations of Mr. Reade, Dr. Reuling, Viale and Latini, and others, on this point. Reuling
has shown that the quantity of ammonia in the expired air is increased in certain diseases,
particularly in uraemia. Its characters in the expired air are frequently so marked, that
patients who are entirely unacquainted with the pathology of urremia sometimes recog-
nize an ammoniacal odor in their own breath.

The pulmonary surface exhales a small quantity of organic matter. This has never
been collected in sufficient quantity to enable us to recognize in it any peculiar or dis-
tinctive properties, but its presence may be demonstrated by the fact that a sponge com-
pletely saturated with the exhalations from the lungs, or the vapor from the lungs
condensed in a glass vessel, will undergo putrefaction, which is a property distinctive
of organic substances.

It is well known that certain substances which are only occasionally found in the
blood may be eliminated by the lungs. Certain odorous principles in the breath are
pretty constant in those who take liquors habitually in considerable quantity. The odor
of garlics, onions, turpentine, and many other principles which are taken into the stom-
ach, may be recognized in the expired air.

The action of the lungs in the elimination of certain gases, which are poisonous in
very small quantities when they are absorbed in the lungs and carried to the general
system in the arterial blood, is very well shown by the experiments of Bernard. Sulphu-
retted hydrogen, which produces death in a bird when it exists in the atmosphere in the
proportion of one to eight hundred, may be taken in solution into the stomach with
impunity and even be injected into the venous system; in both instances being elimi-
nated by the lungs with great promptness and rapidity. The lungs, while they present
an immense and rapidly absorbing surface for volatile poisonous substances, are capable
of relieving the system of some of these substances by exhalation when they find their
way into the veins.

Exhalation of Nitrogen. — The most accurate direct experiments, particularly those of
Regnault and Reiset, show that the exhalation of a small quantity of nitrogen is a pretty
constant respiratory phenomenon. From a large number of experiments on dogs, rabbits,
fowls, and birds, these observers came to the conclusion that, when animals are subjected
to their habitual regimen, they exhale a quantity of nitrogen equal in weight to from Ti-g-
to -fa of the weight of oxygen consumed. In birds, during inanition, they sometimes
observed an absorption of nitrogen, but this was rarely seen in mammals. Boussingault,

CHANGES IN THE BLOOD IN RESPIRATION. 155

estimating the nitrogen taken into the body and comparing it with the entire quantity
discharged, arrived at the same results in experiments upon a cow. Barral, by the same
method, confirmed these observations by experiments on the human subject. Notwith-
standing the conflicting testimony of the older physiologists, there can now be no doubt
that, under ordinary physiological conditions, there is an exhalation by the lungs of a
small quantity of nitrogen.

Changes of the Blood in Respiration (Hcematosis).

It is to be expected that the blood, receiving, on the one hand, all the products of
digestion, and, on the other, the products of disassimilation or decay of the tissues, con-
nected with the lymphatic system, and exposed to the action of the air in the lungs,
should present important differences in composition in different parts of the vascular
system.

In the first place, there is a marked difference in color, composition, and properties,
between the blood in the arteries and in the veins; the change from venous to arterial
blood being effected almost instantaneously in its passage through the lungs. The blood
which goes to the lungs is a mixture of the fluid collected from all parts of the body ; and
we have seen that it presents great differences in its composition in different parts of the
venous system. In some veins it is almost black, and in some, nearly as red as in the
arteries. In the hepatic vein it contains sugar, and its nitrogenized constituents and cor-
puscles are diminished ; in the portal vein, during digestion, it contains materials absorbed
from the alimentary canal ; and, finally, there is every reason to suppose that parts which
require different materials for their nutrition and produce different excrementitious prin-
ciples exert different influences on the constitution of the blood which passes through
them. After this mixture of different kinds of blood has been collected in the right side
of the heart and passed through the lungs, it is returned to the left side and sent to the
system, thoroughly changed and renovated, and, as arterial blood, it has a nearly uniform
composition, as far as can be ascertained, in all parts of the system. The change, there-
fore, which the blood undergoes in its passage through the lungs, is the transformation
of the mixture of venous blood from all parts of the organism into a fluid of uniform
character, which is capable of nourishing and sustaining the function of every tissue and
organ of the body.

The capital phenomena of respiration, as regards the air in the lungs, are loss of oxygen
and gain of carbonic acid, the other phenomena being accessory and comparatively un-
important. As the blood is capable of holding gases in solution, in studying the essential
changes which this fluid undergoes in respiration, we look for them in connection with
the proportions of oxygen and carbonic acid before and after it has passed through the
lungs. In respiration, the most marked effect on the venous blood is change in color.

Difference in Color between Arterial and Venous Blood. — "We have already considered
this in treating of the properties of the blood, and shall take up in this connection only
the cause of the remarkable change in the color of the blood in the lungs. This change
is instantaneous, and, long before the discovery of oxygen by Priestley, was recognized
by Lower, Goodwyn, and others, as due to the action of the air.

The influence of air in changing the color of venous blood may be noted in blood
which has been drawn from the body, as is exemplified by the red color of that portion
of a clot, or the surface of defibrinated venous blood, which is exposed to the air. If we
cut into a clot of venous blood, the interior is almost black, but it becomes red on ex-
posure to the air for a very few seconds.

"We have been in the habit of illustrating the physiological influence of the air on
venous blood by the following simple experiment : Removing the lungs of an animal (a
dog) just killed, the nozzle of a syringe is secured in the pulmonary artery by a ligature,
and a canula, connected with a rubber tube which empties into a glass vessel, is secured

156 RESPIRATION.

in the pulmonary vein. Adapting a bellows to the trachea, we imitate the process of
respiration ; and, if defibrinated venous blood be carefully injected through the lungs, it
will be returned by the pulmonary vein, presenting the bright-red color of arterial blood.
"When the artificial respiration is interrupted, the blood passes through the lungs without
change.1 In exposing the thoracic organs and keeping up artificial respiration, repeating
the celebrated experiment of Robert Hook, made before the Royal Society, in 1664, we
can see, through the thin walls of the auricles, the red color of the blood on the left side
contrasting with the dark venous blood on the right.

Since the discovery of oxygen, it has been ascertained that this is the only constituent
of the air which is capable of arterializing the blood. Priestley showed that venous blood
is not changed in color by nitrogen, hydrogen, or carbonic acid ; while all these gases,
by displacing oxygen, will change the arterial blood from red to black.2

The elements of the blood which absorb the greater part of the oxygen are the red
corpuscles. While the plasma will absorb, perhaps, twice as much gas as pure water, it
has been shown by Magnus and by Gay-Lussac that the corpuscles will absorb from ten to
thirteen times as much. By some the proportion is put much higher. According to the
late researches of Fernet, which have been confirmed by Lothar Meyer, the volume of
oxygen fixed by the corpuscles is about twenty-five times that which is dissolved in the
plasma.

Comparison of the Gases in Venous and Arterial Blood. — The demonstration of the
fact that free oxygen and carbonic acid exist in the blood, with a knowledge of the rela-
tive proportion of these gases in the blood before and after its passage through the lungs,
is a point hardly second in importance to the relative composition of the air before and
after respiration. The idea enunciated by Mayow, about two hundred years ago, that
"there is something in the air, absolutely necessary to life, which is conveyed into the
blood," except that the vivifying principle is not named or its other properties described,
expresses what we now consider one of the great objects of respiration. This is
even more strictly in accordance with facts than the idea of Lavoisier, who supposed
that all the chemical processes of respiration took place in the lungs. Mayow also de-
scribed the evolution of gas from blood placed in a vacuum. Many observers have since
succeeded in extracting gases from the blood by various processes. Sir Humphry Davy
induced the evolution of carbonic acid by raising arterial blood to the temperature of 200°
Fahr., and venous blood to a temperature of 112°; Stevens and others disengaged gas
by displacement with hydrogen, nitrogen, or the ordinary atmosphere; but, notwith-
standing this, before the experiments of Magnus, in 1837, many denied the existence in
the blood of any free gas whatsoever.

Analysis of the Blood for Oases. — There were certain grave sources of error in the
method employed by Magnus, which render his observations of little value, except as
demonstrating that oxygen, carbonic acid, and nitrogen may be extracted by the air-
pump from both arterial and venous blood. The only source of error in the results
which he fully recognized lay in the difficulty in extracting the entire quantity of gas in
solrtion ; but a careful study of his essay shows another element of inaccuracy which is
even more important. The relative quantities of oxygen and carbonic acid in any single

1 This demonstration is very striking, especially if we use a syringe with a double nozzle, one point secured in the
pulmonary artery, and the other simply carrying the blood by a rubber tube into a glass vessel. Eeceiving the blood
which passes through the lungs and that which simply passes through the tube, into two tall glass vessels, the one
is of a bright red, and the other retains its dark color. In preparing for the experiment it is necessary, immediately
after removing the lungs from the animal, to inject them with o, little defibrinated blood, so as to remove the coagu-
lating blood from the pulmonary capillaries, whi:-h would otherwise become obstructed. The injection should be
made gently and crradually, to avoid extra vasatic n. Defibrinated ox-blood may be used. The most convenient way
to secure the canulffl in the vessels is to push them into the pulmonary artery through the right ventricle, and into
the pulmonary vein through the left auricle.

2 Carbonic oxide and nitrous oxide have a strong affinity for the blood-corpuscles and become fixed in them, the
former giving the blood a vivid red color. Sugar and many salts will also redden venous blood. These agents, how-
ever, do not impart the physiological properties of arterial blood.

ANALYSIS OF THE BLOOD FOR GASES. 157

specimen of blood present great variations, dependent upon the length of time that the
blood has been allowed to stand before the estimate of the gases is made. As it is im-
possible to make this estimate immediately after the blood is drawn, on account of the
froth produced by agitation with a gas when the method by displacement is employed,
and the bubbling of the gas when extracted by the air-pump, this objection is fatal. It
is necessary to wait until the froth has subsided before attempting to make an accurate
estimate of the volume of gas given off. The following observation of Magnus illus-
trates this fact. The observation was on the human blood, six hours after it had been
thoroughly mixed with hydrogen :

Blood of Man. Carbonic Acid.

4-077 cubic inches. '013 cubic inches.

3-650 " 0-781 "

3-838 " 1-355 "

After twenty -four hours, at the end of which time the blood had no odor :

4-077 cubic inches. 1-517 cubic inches.

3-650 " 1-456 "

3-833 " 2-075 "

The excess of carbonic acid found twenty-four hours after over the quantity found
six hours after, in the first and third specimens, is a little more than fifty per cent., while
in the second specimen it is very nearly one hundred per cent. In these analyses, the pro-
portion of oxygen is not given. The question naturally arises as to the source of the car-
bonic acid which was evolved during the last eighteen hours of the observation. This is
evident, when we consider one of the important properties of the blood. A number of
years ago, Spallanzani demonstrated that, in common with other parts of the body, fresh
blood removed from the body has, of itself, the property of consuming oxygen ; and
W. F. Edwards has shown that the blood will exhale carbonic acid. In 1856, Harley,
by a series of ingenious experiments, found that blood, kept in contact with air in a
closed vessel for twenty -four hours, consumed oxygen and gave off carbonic acid. More
recently, Bernard has shown that, for a certain time after the blood is drawn from the
vessels, it will continue to consume oxygen and exhale carbonic acid. If all the carbonic
acid be removed from a specimen of blood by treating it with hydrogen, and if it be
allowed to stand for twenty-four hours, another portion of gas can be removed by again
treating it with hydrogen, and still another quantity by treating it with hydrogen a third
time. From these facts it is clear that, in the experiment of Magnus, the excess of car-
bonic acid involved a post-mortem consumption of oxygen ; and no analyses made in the
ordinary way, by displacement with hydrogen or by the air-pump, in which the blood
must necessarily be allowed to remain in contact with oxygen for a number of hours, can
be accurate. The only process which can give us a rigorous estimate of the relative quan-
tities of oxygen and carbonic acid in the blood is one in which the gases can be esti-
mated without allowing the blood to stand, or in which the formation of carbonic acid
in the specimen, at the expense of the oxygen, is prevented. All others will give a less
quantity of oxygen and a greater quantity of carbonic acid than exists in the blood cir-
culating in the vessels or immediately after it is drawn from the body.

A solution of this important and difficult problem in the analysis of the blood has been
attained by Bernard. This observer made a great number of experiments in the hope of
discovering some means by which the post-mortem consumption of oxygen by the blood-
corpuscles could be arrested. He found, finally, that carbonic oxide, one of the most active
of the poisonous gases, had a remarkable affinity for the blood-corpuscles. When taken
into the lungs, it is absorbed by and becomes fixed in the corpuscles, effectually prevent-
ing the consumption of oxygen and the production of carbonic acid, which normally

158 RESPIRATION'.

takes place in the capillary system and which is one of the indispensable conditions of
nutrition. The mechanism of poisoning by the inhalation of this gas is by its fixation in
the blood-corpuscles, their consequent paralysis, and the arrest of their function as re-
spiratory organs. As it is the continuance of this transformation of oxygen into carbonic
acid, after the blood is drawn from the vessels, which interferes with the ordinary analy-
sis of the blood for gases, we might expect to extract all the oxygen if we could imme-
diately saturate the blood with carbonic oxide. The preliminary experiments of Ber-
nard on this point are conclusive. He ascertained that, by mixing carbonic oxide in suf-
ficient quantity with a specimen of fresh arterial blood, in about two hours, all the oxy-
gen which it contained was displaced. Introducing a second quantity of carbonic oxide
after two hours, and leaving it in contact with the blood for an hour, a quantity of oxy-
gen was removed so small that it might almost be disregarded. A third experiment on
the same blood failed to disengage any oxygen or carbonic acid.

The view entertained by Bernard of the action of carbonic oxide in displacing the
oxygen of the blood is, that the former gas has a remarkable affinity for the blood-corpus-
cles, in which nearly all the oxygen is contained, and when brought in contact with
them unites with the organic matter, setting free the oxygen, in the same way that the
acid entering into the composition of a salt is set free by any other acid which has a
stronger affinity for the base. There is every reason to suppose that this view is correct,
as carbonic oxide is much less soluble than oxygen and as it has the property of dis-
engaging this gas only from the blood, leaving the other gases still in solution.

As carbonic oxide displaces the oxygen alone, it is necessary to resort to some other
process, in addition to this, to disengage the other gases contained in the blood. It is
only necessary to arrest the action of the corpuscles upon the oxygen, and then the
gases may be set free by the air-pump or any method which may be convenient. The
method adopted by Lothar Meyer, Bernard, Ludwig, and Grebant for the disengagement
of all the gases contained in the blood is first to displace the oxygen by carbonic oxide,
using about two-thirds of gas by volume to one-third of blood, then to attach the tube
to a column of mercury and subject the blood to the barometric vacuum, which sets free
the carbonic acid and the nitrogen. The results obtained by this method correspond
with our ideas concerning the nature of the respiratory process; and analyses of the
blood taken at different periods show variations in the quantities of oxygen in the ar-
terial, and carbonic acid in the venous blood, corresponding with some of the variations
which we have noted in the loss of oxygen and gain of carbonic acid in the air in res-
piration.

In drawing the blood for analysis, Bernard takes the fluid directly from the vessels by
a syringe and passes it under mercury into a tube, in such a way that it does not come in
contact with the air. In this tube, which is graduated, the blood is brought in contact
with carbonic oxide, which displaces the oxygen from the corpuscles and prevents the
formation of carbonic acid at the expense of a portion of the oxygen. The tube is then
connected with an apparatus by which the atmospheric pressure is removed. In this way,
nearly all the gases contained in the blood are disengaged ; but, according to most ob-
servers, a small quantity of carbonic acid remains in the blood in combination. This may
be removed by the introduction into the apparatus of a small quantity of tartaric acid.
It is justly remarked by Bert, in his admirable work on respiration, that, as the appa-
ratus for the exhaustion of air has been made more and more nearly perfect, the quantity
of carbonic acid in combination has seemed less and less. By far the greatest quantity of
the excrementitious carbonic acid in the blood is extracted by the removal of atmospheric
pressure in the most carefully-perfected apparatus.

The analyses of Bernard, who obtained from fifteen to twenty per cent, of oxygen in
volume from the arterial blood, show the great imperfection of the process employed by
Magnus, who obtained from the arterial blood of horses and calves a mean of but 2*44
per cent, of oxygen. It does not seem necessary, therefore, to discuss the criticisms of

ANALYSIS OF THE BLOOD FOR GASES. 159

the results obtained by Magnus which were made by Gay-Lussac and Magendie, soon
after their publication, and more recently by Harley and others.

Bernard's experiments were made chiefly on dogs and had special reference to the
proportion of oxygen in the blood. In two specimens taken from a dog in good con-
dition, a specimen of arterial blood, drawn from the vessels by a syringe and put in con-
tact with carbonic oxide without being exposed to the air, was found to contain 18'28
per cent., and a specimen of venous blood, taken in the same way, 8'42 per cent., in vol-
ume, of oxygen. The proportion of gases in the blood is found to vary very considerably
under different conditions of the system, particularly with reference to the digestive
process. The following are the general results of later observations, showing the differ-
ences and variations in the proportions of all the gases in arterial and venous blood.

Arterial blood, while an animal is fasting, contains from nine to eleven parts per
hundred of oxygen. In full digestion, the proportion is raised to seventeen, eighteen, or
even twenty parts per hundred. The proportion varies in different animals, being much
greater, for example, in birds than in mammals.

The quantity of carbonic acid is even more variable than the quantity of oxygen.
During digestion there are from five to six parts per hundred of free carbonic acid in the
arterial blood. During the intervals of digestion this quantity is reduced to almost noth-
ing; and, after fasting for twenty-four hours, frequently not a trace is to be discovered.1

Venous blood always contains a large quantity of carbonic acid, both free in solution
and combined with bases. The quantity varies considerably in different parts of the venous
system. It is well known that the venous blood coming from some glands is dark during
the intervals of secretion and nearly as red as arterial blood during their functional activ-
ity. In the venous blood from the submaxillary gland of a dog, Bernard found 18-07 per
cent, of carbonic acid during repose and 10*14 per cent, during secretion. The blood
coming from the muscles is the darkest in the body and contains the greatest quantity of
free carbonic acid. The quantity of free carbonic acid is immensely increased in the ve-
nous blood during digestion. It is owing to this fact that the gas then exists in quantity
in the arterial blood. Bearing in mind the fact that the proportion of gases in the arte-
rial and venous blood varies considerably under different conditions of the system and
that it is variable in the blood of different veins, we rnay take the following, which we
quote from Bert, as the average results obtained by the most recent German observers:

Oxygen. Carbonic Acid, Carbonic Acid, Carbonic Acid, Nitrogen. Total gas

disengaged in combi- total. in volume

by a vacuum. nation. per 100.

"Arterial blood.. 15'03 27'99 1'15 29'14 TOO 45'77

Venous blood . . 8"17 31'27 2'38 33'65 1-37 43'19

"If we now examine the blood coming from different parts of the body, we find that
the blood of the hepatic veins is poorer in oxygen and richer in carbonic acid than the
general venous blcod ; that the blood of the portal vein presents the same characters to
a higher degree ; that the blood of the muscles in contraction presents the same relations
as compared with the blood of muscles in repose or paralyzed ; that, on the other hand,
the blood of the glands has more oxygen during their activity than during their repose.

"If we compare the venous blood of the right side of the heart with the arterial
blood of the left side, we find that the latter is richer in oxygen and poorer in carbonic
acid. In examining this more closely, we see that the difference in the oxygen is greater
than in the carbonic acid ; this being in accordance with the well-known fact that ani-
mals absorb more oxygen than is equivalent to the carbonic acid exhaled."

These facts coincide with the views which are now held regarding the essential pro-
cesses of respiration. The blood going to the lungs contains carbonic acid and but a small
proportion of oxygen. In the lungs, carbonic acid is given off, appearing in the expired
air, and the oxygen which disappears from the air is carried away by the arterial blood.

1 These results are quoted from Bernard and were given in his lectures delivered at the College of France in the
summer of 1861.

160 BESPIRATIOK

Schoffer, in 1860, demonstrated the remarkable fact that the presence of the red blood-
corpuscles greatly facilitates the extraction of carbonic acid from the blood, showing
that much more carbonic acid could be extracted, by means of a vacuum, from the entire
blood than from blood-serum. These observations were confirmed, in 1864, by Preyer
and by Pfliiger, who regarded the blood-corpuscles as playing the part of a feeble acid in
the process of extraction of carbonic acid. The researches of Preyer, in 1866, show
that carbonic acid is extracted more easily from arterial than from venous blood ; and, as
a result of his observations, he concludes that it is the combination of oxygen with the
coloring matter of the blood which operates as an acid in the processes for the analysis
of the blood for carbonic acid.

Nitrogen of the Blood. — As far as is known, nitrogen has no very important office in
the process of respiration. There is sometimes a slight exhalation of this gas by the
lungs, and analyses have demonstrated its existence in solution in the blood. Magnus
found generally a larger proportion in the arterial than in venous blood, although, in one
instance, there was a larger proportion in the venous blood. It is not absolutely certain
whether the nitrogen which exists in the blood be derived from the air or from the
tissues. Its almost constant exhalation in the expired air would lead to the supposition
that it is produced in small quantity in the system or supplied by the food. There is no
evidence that nitrogen enters into combination with the blood-corpuscles; it exists sim-
ply in solution in the blood, which is capable of absorbing about ten times as much as
pure water. Nothing is known with regard to the relations of the free nitrogen of the
blood to the processes of nutrition.

Condition of the Gases in the Blood. — It is now pretty generally admitted that the
oxygen of the blood exists, not in simple solution, but in a condition of feeble combina-
tion with certain of the constituents of the blood-corpuscles, particularly the coloring
matter. In studying the composition of the corpuscles, we have seen that, when air is
admitted to venous blood, oxygen unites with the hasmaglobine, forming oxyhsema-
globine. Carbonic oxide, which has a great affinity for the corpuscles, displaces almost
immediately all the oxygen which the blood contains. When the corpuscles are de-
stroyed, as they may be readily by receiving fresh blood into a quantity of pure water,
the red color is instantly changed to black.

Carbonic acid is more easily exhaled from the blood than oxygen. It was this
principle which was obtained by those who first succeeded in extracting gas from the
blood. While there is every reason to suppose that oxygen is in combination with the
blood-corpuscles, carbonic acid seems to be in a condition of simple solution and is con-
tained more especially in the plasma. What may be considered as the free carbonic acid
of the blood behaves in all regards like a gas simply held in solution. The view that it is
held in solution chiefly in the plasma is sustained by the fact that serum will absorb
more carbonic acid than an equal volume of defibrinated blood.

Liebig has shown that the phosphate of soda, one of the constituents of the blood,
influences to a remarkable degree the quantity of carbonic acid which can be held in
solution by any liquid. One hundredth of a part of this salt in pure water will double
its capacity for dissol\7ing carbonic acid. When blood is in contact with a certain
quantity of air, oxygen is consumed and carbonic acid is exhaled. The fact that car-
bonic oxide, which has such a remarkable affinity for the corpuscles, displaces oxygen
almost exclusively, is another argument in favor of the view that the carbonic acid is
contained mainly in the plasma.

The carbonic acid which is formed in the tissues and is taken up by the blood in its
passage through the capillaries exists in this fluid in two forms : one, in simple solution,
chiefly in the plasma, and the other, in a state of such loose chemical combination in
the bicarbonates that it may be disengaged by displacement by another gas and is

CONDITION OF THE GASES IN THE BLOOD. 161

readily set free by pneumic acid. This gas is a product of excretion and is not engaged
in any of the vital functions; while oxygen, which has an all-important function to per-
form, unites immediately with the blood-corpuscles and is not easily disengaged except
when it undergoes transformation in the process of nutrition. In addition to this
excrementitious carbonic acid, there is another portion which is a permanent constituent
of the blood, in the carbonates, and cannot be set free without the use of reagents.

Nitrogen exists in the blood in the same condition of solution in the plasma as
carbonic acid.

Mechanism of the Interchange of Gases between the Blood and the Air in the Lungs. —
The gases from the air pass into the blood, and the gases of the blood are exhaled
through the delicate membrane which separates these two fluids, in accordance with
laws which are now well understood. The first to point out the power of gases thus
to penetrate and pass through membranes was the late Dr. J. K. Mitchell, of Philadel-
phia. His attention was first directed to this subject by noticing the escape of gas from
gum-elastic balloons filled with hydrogen. Observations on the lungs of the snapping
turtle filled with air and placed in an atmosphere of carbonic acid or nitrous oxide,
showed a very rapid passage of gas from the exterior to the interior. Dr. Mitchell
recognized the passage of gases through membranes into liquids and the exhalation of
gases which were in solution in these liquids. He noted this action in the absorption of
oxygen and the exhalation of carbonic acid in the lungs, although he fell into the error of
supposing that there was no carbonic acid in solution in the blood and that it was ex-
haled as soon as formed. A few years later, Dr. Rogers, of Philadelphia, enclosed a
fresh pig's bladder, filled with venous blood, in a bell-glass of oxygen. In two hours a
quantity of oxygen had been consumed and a large quantity of carbonic acid had made
its appearance.

We have already seen that the blood is exposed to the air in the lungs, separated
from it only by a very delicate membrane, over an immense surface. The membrane,
far from interfering with the interchange of gases, actually favors it ; and thus, in
obedience to the laws which regulate endosmosis between gases and liquids, the oxygen
is continually passing into the blood and the free carbonic acid is exhaled.

General Differences in the Composition of Arterial and Venous Blood. — All observers
agree that there are certain marked differences in the composition of arterial and venous
blood, aside from their free gases. The arterial blood contains less water and is richer
in organic and most inorganic constituents than the venous blood. It also contains a
larger proportion of corpuscles. It is more coagulable and offers a larger and firmer
clot than venous blood. The only principles which are constantly more abundant in
venous blood are water and the alkaline carbonates. According to Longet, 10,000 parts
of venous blood contained 12 -3 parts of carbonic acid combined, and the same quantity
of arterial blood contained but 8'3 parts. The deficiency of water in the blood which
comes from the lungs is readily explained by the escape of watery vapor in the expired air.

An important distinction between arterial and venous blood is one to which we have
already incidentally alluded ; viz., that the former has a uniform composition in all parts
of the arterial system, while the composition of the latter varies very much in the blood
coming from different organs. Arterial blood is capable of carrying on the processes of
nutrition, while venous blood is not and cannot even circulate freely in the systemio
capillaries.

Relations of Respiration to Nutrition, etc.— It has been demonstrated that all tissues,
so long as they retain their absolute integrity of composition, have the property of appro-
priating oxygen and exhaling carbonic acid, independently of the presence of blood; and
that the arterial blood carries oxygen from the lungs to the tissues, there gives it up, and
receives carbonic acid, which is carried by the venous blood to the lungs, to be exhaled.
11

162 RESPIRATION.

From this fact alone, it is more than probable that respiration is inseparably connected
with the general act of nutrition. Its processes must be studied, therefore, as they take
place in the tissues and organs of the body. In the present state of the science, the
questions which naturally arise in connection with the essential processes of respiration
are the following :

1. In what way is oxygen consumed in the system ?

2. How is carbonic acid produced by the system?

3. What is the nature of the processes which take place between the disappearance
of oxygen and the evolution of carbonic acid ?

When these questions are satisfactorily answered, we shall understand the essence of
respiration; but, in reasoning on this subject, we must not fall into the error of assimilat-
ing the respiratory phenomena too closely to those with which we are acquainted as
they occur in inorganic bodies. It must be remembered that in the organism we are
dealing with principles which have the remarkable property of self-regeneration, and
which, as a simple condition of normal existence, consume oxygen, when it is presented
to them, and exhale carbonic acid. Without a proper supply of oxygen, the tissues die,
lose these peculiar properties, and finally disappear by putrefactive decomposition. This
consumption of oxygen cannot be regarded in any other light than as the appropriation,
by a living part, of an element necessary to supply waste, in the same way as those ma-
terials which are ordinarily called nutritive are appropriated. That waste is continually
going on there can be no doubt; and, as the production of urea, creatine, creatinine,
cholesterine, etc., is, to a certain extent, independent of the absorption of food, so the
production of carbonic acid is in a certain degree independent of the absorption of oxy-
gen. How different are these phenomena from those which attend the combinations and
decompositions of inorganic matters ! As an example, let oxygen be brought in contact,
under proper conditions, with iron. Under these circumstances, a union of iron and
oxygen takes place, and a new substance, oxide of iron, is formed, which has peculiar
and distinct properties. In the same way, carbonic acid may be disengaged from its
combinations by the action of a stronger acid, which unites with the base and forms a
new substance in no way resembling the original salt. To make the contrast still more
striking, let fat be heated in oxygen or in the air until it undergoes combustion; it is
then changed into carbonic acid and water, by a definite chemical reaction, and is utterly
destroyed as fat.

In the living body the organic nitrogenized principles are in a condition of continual
change, breaking down and forming various excrementitious principles, at the head of
which may be placed carbonic acid. It is essential to life that these principles be main-
tained in their chemical integrity, which requires a supply of fresh matter as food, and,
above all, a supply of oxygen. We put ourselves in the position of ignoring well-estab-
lished facts and principles when we assimilate without reserve the process of the con-
sumption of oxygen and production of carbonic acid by living organic bodies, to simple
combustion of sugar or fat. The ancients saw that the breath was warmer than the sur-
rounding air, that in the lungs the air took heat from the body, and, as they knew of no
other changes in the air produced by respiration, they assumed that its object was simply
to cool the blood. Lavoisier discovered that the air, containing oxygen, lost a portion
of this principle in respiration and gained carbonic acid and watery vapor. He saw that
this might be imitated by the combustion of hydro-carbons, such as exist in the blood.
He called respiration a slow combustion and regarded as its principal office the mainte-
nance of animal temperature. When it was shown by analyses of the blood for gases,
that oxygen is not consumed in the lungs, but is taken up by the circulating fluid and
carried all over the body, and that carbonic acid is brought from all parts by the blood
to the lungs, these facts, taken in connection with the fact that the tissues have the prop-
erty of consuming oxygen and exhaling carbonic acid, led physiologists to change the
location of the combustive process from the lungs to the tissues.

RELATIONS OF RESPIRATION TO NUTRITION. 163

We cannot stop at this point. Now it is known that the organic principles of the
body, which form the basis of all tissues and organs, are continually undergoing change
as a condition of existence ; that they do not unite with any substance in definite chemi-
cal proportions, but that their particles, after a certain period of existence, degenerate
into excrementitious substances and are regenerated by an appropriation and change of
materials furnished by the blood. As far as the respiration of these parts is concerned,
we can only say, that, in this process, carbonic acid is produced and oxygen is consumed.
These facts show that respiration is essentially a phenomenon of nutrition, possessing a
degree of complexity certainly equal to that of the other nutritive processes. It must
be acknowledged that thus far its cause and intimate nature have eluded investigation.
In respiration by the tissues, no one has yet been able to give the cause of the absorption
of oxygen or the exhalation of carbonic acid, or to demonstrate the condition in which
oxygen exists when once appropriated, or the particular changes which take place and
the principles which are lost, in the formation of carbonic acid.

The views of physiologists with regard to the essential processes of respiration, be-
fore the time of Lavoisier, have barely an historical interest at the present day, except
the remarkable idea of Mayow, which comprehended nearly the whole process and
which was unnoticed for about a hundred years. It is not our object to dwell upon the
various theories which have been advanced from time to time, or even to fully discuss, in
this connection, the combustion-theory as proposed by Lavoisier and modified by Liebig
and others. Although this theory is nominally received by many physiologists of the pres-
ent day, it will be found that most of them, in accordance with the facts which have
since been developed, really regard respiration as connected with nutrition. They only
differ from those who reject the combustion-theory, in their definition of the term com-
bustion. Lavoisier regarded respiration as a slow combustion of carbon and hydrogen ;
and, if every rapid or slow combination of oxygen with any other body be considered a
combustion, this view is absolutely correct and was proven when it was shown that
oxygen united with any of the tissues. Longet says that since the time of Lavoisier it is
agreed to give the above signification to the word combustion; but this must simply be
for the purpose of retaining the name applied by Lavoisier to the respiratory process,
while its signification is altered to suit the facts which have since taken their place in
science. There is no doubt that combustion is generally regarded as signifying the direct
and active union of oxygen with certain principles which commonly contain carbon and
hydrogen; and the immediate products of this union are carbonic acid, water, and, inci-
dentally, heat and light. It is certain that oxygen does not unite in the body directly
with carbon and hydrogen, although it is consumed and carbonic acid and water are pro-
duced in respiration. Important intermediate phenomena take place, and we do not
therefore fully express the respiratory process by the term combustion. The researches
of Spallanzani, W. F. Edwards, Collard de Martigny, and others, who have demonstrated
the abundant exhalation of carbonic acid by animals and by tissues deprived of oxygen,
show that it is not a product of combustion of any of the principles of the organism.
Rejecting this hypothesis as insufficient to explain the intimate nature of the respira-
tory process, it remains to be seen how satisfactorily, in the present state of the science,
it is possible to answer the several questions we have proposed.

1. In what way is the oxygen consumed in the system? Oxygen taken from the air
is immediately absorbed by, and enters into the composition of the red corpuscles. Part
of the oxygen disappears in the red corpuscles themselves, and carbonic acid is given
off. To how great an extent this takes place it is impossible to say ; but it is evident,
even from a study of the methods of analysis of the blood for gases, that the property
of absorbing oxygen and giving off carbonic acid, which Spallanzani demonstrated to
belong to the tissues, is possessed as well by the red corpuscles. During life it is not
possible to determine how far this takes place in the blood and how far in the tissues.
The theory has been proposed that all the respiratory change takes place in the blood as

164 EESPIEATION.

it circulates ; but the avidity of the tissues for oxygen and the readiness with which
they exhale carbonic acid leave no room for doubt that much of this change is effected
in their substance.

Oxygen, carried by the blood to the tissues, is appropriated and consumed in their
substance, together with the nutritive materials with which the circulating fluid is
charged. We are acquainted with some of the laws which regulate its consumption but
have not been able to follow it out and ascertain the exact nature of the changes which
take place. All that we can say definitely on this point is, that it unites with the organic
principles of the system, satisfying the "respiratory sense" and supplying an imperative
want which is felt by all animals and which extends to all parts of the organism. After
being absorbed, it is lost in the intricate processes of nutrition. There is no evidence in
favor of the view that oxygen unites directly with carbonaceous matters in the blood
which it meets in the lungs, and, by direct union with carbon, forms carbonic acid.

2. How is carbonic acid produced by the system? That carbonic acid makes its
appearance in the blood itself, produced in the red corpuscles, has been abundantly proven
by observations already cited, although it is impossible to determine to what extent this
takes place during life. It is likewise a product of the physiological decomposition of
the tissues, whence it is absorbed by the blood circulating in the capillaries and conveyed
by the veins to the right side of the heart. It has been experimentally demonstrated
that its production is not immediately dependent upon the absorption of oxygen, for its
formation continues in an atmosphere of hydrogen or of nitrogen. It is most reasonable
to consider the carbonic acid thus formed as a product of excretion or disassimilation,
like urea, creatine, or cholesterine. The fact that it may easily be produced artificially,
out of the body, does not demonstrate that its formation in the body is as simple as when
it is formed by the process of combustion. We may be able at some future time to pro-
duce artificially all the excrementitious principles, as has already been done in the case
of urea; but we are hardly justified in supposing that the mode of formation of carbonic
acid, as one of the phenomena of nutrition, is precisely the same as when it is made by
our chemical manipulations.

As expressing nearly all that is known, even at the present day, regarding the mode
of formation of carbonic acid in the economy, we may take the following concluding
passage from the paper of Collard de Martigny, published in 1830 :

" The carbonic acid expired is a product of assimilative decomposition, secreted in
the capillaries and excreted by the lungs."

The carbonic acid thus produced is taken up by the blood, part of it in a free state in
solution, particularly in the plasma, and a part which has united with the carbonates to
form bicarbonates. Carried thus to the lungs, the free gas is removed by simple dis-
placement, and that which exists in combination is set free by the acids found in the
pulmonary substance.

3. What is the nature of the intermediate processes, from the disappearance of
oxygen to the evolution of carbonic acid? A definite answer to this question would
complete our knowledge of the respiratory process ; but this, in the present state of the
science, we are not prepared to give. We can only repeat what has already been so
frequently referred to, that oxygen must be considered as a nutritive principle, and
carbonic acid, as a product of excretion. The intermediate processes belong to the general
function of nutrition, with the intimate nature of which we are unacquainted. We
have not sufficient evidence for supposing that this process is identical witli what is
generally known as combustion.

The Respiratory Sense, or Want on the part of the System which induces the
Respiratory Movements. (Besoin de respirer.)

We are all familiar with the peculiar and distressing sense of suffocation which
attends an interruption in the respiratory process. Under ordinary conditions, the act

THE RESPIRATORY SENSE. 165

of breathing takes place without our knowledge ; but even when the air is but little
vitiated, when its entrance into the lungs is slightly interfered with, or when a consider-
able portion of the pulmonary structure is involved in disease, we experience a certain
sense of uneasiness and become conscious of the necessity of respiratory efforts. This
gradually merges into the sense of suffocation, and, if the obstruction be sufficient, is fol-
lowed by convulsions, insensibility, and finally by death.

Although we are not sensible of any want of air under ordinary conditions, it was
proven by the celebrated experiment of Robert Hook, in 1664, that there is a want
always felt by the system, and that, if this want be effectually supplied, no respiratory
movements will take place. We have often repeated the experiment demonstrating this
fact. If a dog be brought completely under the influence of ether, the chest and abdo-
men opened, and artificial respiration be carefully kept up by means of a bellows fixed in
the trachea, even after the animal has come from under the influence of the anaesthetic so
as to look around and wag his tail when spoken to, he will frequently cease all respiratory
movements when the air is adequately supplied to the lungs ; but if the artificial respi-
ration be interrupted or imperfectly performed, the animal almost immediately feels the
want of air, and the respiratory muscles are thrown into violent contraction.

It is generally admitted, indeed, that there exists in the system what may appropri-
ately be regarded as a respiratory sense, or, as it is called by the French, besoin de respirer,
which operates upon the respiratory nervous centre and gives rise to the involuntary
movements of respiration, and that this sense is exaggerated by any thing which inter-
feres with respiration, and is then conveyed to the brain, where it is appreciated as
dyspnoea and finally as the overpowering sense of suffocation. An exaggeration of the
respiratory sense constitutes a sense of oppression, which is referred to the lungs ; but it
cannot be assumed, from sensations only, that the sense of want of air is really situated
in the lungs. The question of its seat and its immediate cause is one of the most inter-
esting of the physiological points connected with respiration.

Many physiologists accept the view of Marshall Hall, that the respiratory sense has its
origin in the lungs, is carried to the medulla oblongata by the pulmonary branches of the
pneumogastric nerves, and is due to the accumulation of carbonic acid in the pulmonary
vesicles; but there are facts in physiology and pathology which are inconsistent with
such an exclusive view.

In cases of disease of the heart, when the system is imperfectly supplied with oxygen-
ated blood, the sense of suffocation is frequently most distressing, although the lungs be
unaffected and receive a sufficient supply of pure air. This and other similar facts led
Berard to adopt the view that the respiratory sense has its point of departure in the right
cavities of the heart and is due to their distention as the result of obstruction to the pas-
sage of blood through the lungs. John Reid thought it was due in a measure to the cir-
culation of venous blood in the medulla oblongata. Volkmann, in 1841, advanced the
view that the sense of want of air is dependent upon a deficiency of oxygen in the tissues,
producing an impression which is conveyed to the medulla oblongata by the nerves of
general sensibility. By a series of experiments, this observer disproved the view that

I this sense resides in the lungs and is transmitted along the pneumogastric nerves ; and,
by exclusion, he located it in the general system. In the hope of settling some of these
questions, we instituted, in 1861, a series of experiments upon the situation and cause
of the respiratory sense. In these observations, the following facts, some of which had
been previously noted, were demonstrated :
1. If the chest be opened in a living animal, and artificial respiration be carefully per-
formed, inflating the lungs sufficiently but cautiously and taking care to change the air in
the bellows every few moments, as long as this is continued, the animal will make no
ivsj'irutory effort ; showing that, for the time, the respiratory sense is abolished.

2. When the artificial respiration is interrupted, the respiratory muscles are thrown
into contraction, and the animal makes regular, and at last violent efforts. If we now

166 KESPIRATIOK

expose an artery and note the color of the blood as it flows, it will be observed that the
respiratory efforts commence only when the blood in the vessel begins to be dark. When
artificial respiration is resumed, the respiratory efforts cease only when the blood becomes
red in the arteries.

3. If, while artificial respiration is being regularly performed, a large artery be opened
and the system be thus drained of blood, when the haemorrhage has proceeded to a cer-
tain extent, the animal makes respiratory efforts, which become more and more violent,
until they terminate, just before death, in general convulsions.

These facts, which may be successively observed in a single experiment, remain pre-
cisely the same if we previously divide both pneumogastric nerves in the neck ; showing
that these are by no means the only nerves which convey the respiratory sense to the
medulla oblongata.

The conclusion which may legitimately be drawn from the above-mentioned facts is
that the respiratory sense does not originate in the lungs, for it operates when the lungs
are regularly filled with pure air, if the system be drained of the oxygen-carrying fluid.

In 1877, we repeated and extended the experiments just mentioned (New York Medical
Journal, November, 1877). The new experiments were made upon dogs, in the follow-
ing way : The animals were brought under the influence of ether, the chest was opened,
and artificial respiration was carried on by means of a bellows fixed in the trachea. The
great vessels given off from the arch of the aorta were isolated so that they could be sep-
arately constricted at will. In a number of experiments upon different animals, the in-
nominate artery and the left subclavian were constricted, and the animal began to make
respiratory efforts in from two minutes and five seconds to two minutes and eight sec-
onds after, although artificial respiration was kept up constantly and efficiently. The
animals made no respiratory efforts when the vessels given off from the arch of the aorta
were left free and when the aorta was tied in the chest, which cut off the supply of blood
from the trunk and the lower extremities. In the experiments in which the vessels
going to the head and upper extremities were constricted, the respiratory efforts always
ceased when the vessels were freed.1

In our experiments upon the location of the sense of want of air, made in 1861, we
thought that they proved experimentally that the sense of want of air is due to a
deficiency in oxygen in the system at large. The main features of the experiments made
at that time have been already stated. Our object in making these new experiments was
to study the effects of cutting off the supply of oxygenated blood from different parts.
It may be assumed that the sole respiratory nervous centre is in the medulla oblongata,
and we endeavored to devise some means of cutting off the arterial supply of blood from
this part. Animals respire when all of the encephalic centres have been destroyed ex-
cept the medulla oblongata, so that it is improbable that cutting off the supply of blood
from the brain would affect the muscles of respiration, provided that artificial respiration
be efficiently maintained. Blood can get to the medulla oblongata from the internal
carotids, which are connected with the circle of Willis, from the vertebral arteries, which
unite to form the basilar artery, and perhaps from other vessels ; but it is certain that, if
all the arteries given off from the arch of the aorta be tied, the medulla must be deprived
of oxygenated blood.

In one experiment (1877), the innominate artery and the left subclavian artery were
constricted, and the animal made respiratory efforts in two minutes and eight seconds,
notwithstanding that artificial respiration was kept up.

In another experiment, the same vessels were constricted, and the animal made respir-
atory efforts in two minutes and five seconds.

In a third experiment, both subclavian arteries and both carotids were constricted,

1 The reader is referred to our original article for a complete account of the details of these experiments. In Her-
mann, Grurtdiss der Physiologic, Berlin, 1870, S. 160, and in Foster, Text-Book of Physiology, London, 1877, p.
254, the respiratory efforts are attributed to " an accumulation of carbonic acid and a paucity of available oxygen " in
the medulla oblongata, but this view lacked the positive experimental proof afforded by our experiments of 1S77.

SENSE OF SUFFOCATION. 167

and the animal made respiratory efforts in two minutes and seven seconds. Both vertebral
arteries and both carotids were constricted, and the animal made no respiratory efforts
for five minutes ; but respiratory efforts were made in one minute and thirty-five seconds
after both subclaviaus had been constricted in addition to the vertebrals and carotids.

It seems, from these experiments, that, in order to induce respiratory efforts in an
animal under the influence of ether and with the lungs supplied with air by artificial res-
piration, either the innominate artery and the left subclavian artery, or both subclavians,
both carotids, and both vertebral arteries, must be tied. In other words, according to
our view of the cause of these respiratory efforts, the supply of blood to the medulla ob-
longata cannot be cut off completely except by tying all the vessels given off from the
arch of the aorta.

As the result of these experiments, we must now modify the view advanced in 1861
as a conclusion from experiments then published, which we have maintained up to the
present time; viz., that the sense of want of air, which is the starting-point of the move-
ments of respiration, is due to want of oxygen in the general system. The experiments
made in 1861 were accurate, and the conclusions from them seemed to be legitimate ; but
these experiments were incomplete. Our more recent experiments, taken in connection
with the experiments of 1861, lead to the conclusion that the sense of want of air is due
to a want of circulation of oxygenated blood in the medulla oblongata.

If we regard the sense of want of air as due primarily to a deficiency of oxygen in
the medulla oblongata, which can hardly be doubted, it becomes an important and inter-
esting question to determine, whether the normal respiratory movements be actually re-
flex in their character, as has been generally supposed, or whether they be due to direct
excitation of the nerve-cells in the respiratory centre. The latter seems, at present, to
be the more reasonable supposition.

Sense of Suffocation. — "We must separate, to a certain extent, the respiratory sense
from the sense of distress from want of air, and its extreme degree, the sense of suffoca-
tion. The first is not a sensation, but an impression made upon the medulla oblongata,
giving rise to involuntary respiratory movements. The necessities for oxygen on the part
of the system regulate the supply of air to the lungs. We have already seen that, once in
every five to eight respirations, or when the respiratory movements are a little restricted
under the influence of depressing emotions, an involuntary deep or sighing inspiration is
made, for the purpose of changing the air in the lungs more completely. The increased
consumption of oxygen, and a certain amount of interference with the mechanical process
of respiration during violent muscular exercise put us " out of breath," and for a time
the respiratory movements are exaggerated. This is perhaps the first physiological way
in which the want of air is appreciated by the senses. A deficiency in hasmatosis, either
from a vitiated atmosphere, mechanical obstruction in the air-passages, or grave trouble
in the general circulation, produces all grades of sensations, from the slight oppression
which is felt in a crowded room, to the intense distress of suffocation. When ha3matosis
is but slightly interfered with, only an indefinite sense of oppression is experienced, and
the respiratory movements are a little increased, the most marked effect being an increase
in the number and extent of sighing inspirations.

Experiments have failed to show that either the respiratory sense or the sense of suf-
focation is due to irritation produced by carbonic acid in the non-oxygenated blood.

Respiratory Efforts before Birth.

It is generally admitted that one of the most important functions of the placenta, and
the one which is most immediately connected with the life of the fetus, is a respiratory
interchange of gases, analogous to that which takes place in the gills of aquatic animals.
The vascular prolongations from the fetus are continually bathed in the blood of the
mother, and this is the only way in which it can receive oxygen. Notwithstanding the

168 RESPIRATION.

statements of those who have been unable to note any difference in color between the
blood contained in the umbilical arteries and the vein, there are direct observations
showing that such a difference does exist. Legallois frequently observed a bright-red
color in the blood of the umbilical vein ; and, on alternately compressing and releasing the
vessel, he saw the blood change in color successively from red to dark and from dark to red.
Zweifel has demonstrated the presence of oxyhsemaglobine in the blood of the umbilical
vessels by means of the spectroscope, thus showing that it contains oxygen. As oxygen is
thus adequately supplied to the system, the foetus is in a condition similar to that of the
animals in which artificial respiration was effectually performed. The want of oxygen is
fully met, and therefore no respiratory efforts take place. Respiratory movements will
take place, however, even in very young animals, when there is a deficiency of oxygen
in the system. It has been observed that the liquor amnii occasionally finds its way into
the respiratory passages of the foetus, where it could only enter during efforts at respira-
tion. Winslow, in the latter part of the last century, first noticed respiratory efforts in
the foetuses of cats and dogs in the uterus of the mother during life ; and many others
have observed that, when foetuses are removed from vascular connection with the moth-
er, they wrill make vigorous efforts at respiration. This fact we have frequently had oc-
casion to demonstrate in making operations upon pregnant animals. After the death of
the mother, the foetus always makes a certain number of distinct and unmistakable respi-
ratory efforts, which follow each other at regular intervals.

From what has been experimentally demonstrated with regard to the seat and cause
of the respiratory sense after birth, it is evident that want of oxygen is the cause of re-
spiratory movements in the foetus. When the circulation in the maternal portion of the
placenta is interrupted from any cause, or when the blood of the foetus is obstructed in
its course to and from the placenta, the impression due to want of oxygen is made upon
the medulla oblongata, and efforts at respiration are the result. This cannot be due to
an accumulation of carbonic acid in the lungs, and it is entirely consistent with our views
with regard to the seat of the respiratory sense.

Cutaneous Respiration.

This mode of respiration, although very important in many of the lower orders of ani-
mals, is insignificant in the human subject and is even more slight in animals covered
with hair or feathers. Still, an appreciable quantity of oxygen is absorbed by the skin
of the human subject, and an amount of carbonic acid, which is proportionately larger,
is exhaled. Exhalation of carbonic acid, which is connected rather with the functions
of the skin as a general eliminating organ and is by no means an essential part of the re-
spiratory process, will be more fully considered under the head of excretion. Carbonio,
acid is given off with the general emanations from the surface, being found at the same
time in solution in the urine and in most of the secretions. It is well known that death
follows the application of an impermeable coating to the entire cutaneous surface ; but
this is by no means due to a suppression of its respiratory function alone. The skin has
other offices, particularly in connection with regulation of the animal temperature, which
are infinitely more important.

An estimate of the extent of the cutaneous, as compared with pulmonary respiration,
has been made by Scharling, by comparing the relative quantities of carbonic acid exhaled
in the twenty-four hours. According to this observer, the skin performs from ^ to £r of
the respiratory function. It is exceedingly difficult to collect all the carbonic acid given
off by the skin under perfectly normal conditions. In some recent observations by Au-
bert, the estimate is very much lower than that given by Scharling.

Asphyxia.

The effects of cutting off the supply of oxygen from the lungs are mainly referable to
the circulatory system and have already been considered under the head of the influ-

ASPHYXIA. 169

ence of respiration upon the circulation. It will be remembered that, in asphyxia the
non-aerated blood passes with so much difficulty through the systemic capillaries as
finally to arrest the action of the heart. It is the experience of those who have experi-
mented on this subject, that the movements of the heart, once arrested in this way, can-
not be restored, but that while the slightest regular movements continue, its functions
will gradually return if air be readmitted to the lungs.

A remarkable power of resisting asphyxia exists in newly-born animals that have
never breathed. This was noticed by Haller and others and has been the subject of nu-
merous experiments, among which we may mention those of Buffon, Legallois, and "W. F.
Edwards. Legallois found that young rabbits would live for fifteen minutes deprived of
air by submersion, but that this power of resistance diminished rapidly with age. "W.
F. Edwards has shown that there exists a great difference in this regard in different
classes of animals. Dogs and cats, which are born with the eyes shut and in which there
is at first a very slight development of animal heat, will show signs of life after submer-
sion for more than half an hour ; while Guinea-pigs, which are born with the eyes open,
are much more active, and produce a greater amount of heat, will not live more than
seven minutes. The cause of this peculiarity has been attributed to the existence of
the foramen ovale, enabling the blood to get to the system without passing through
the lungs, by those who regard the arrest of the circulation in asphyxia as due to ob-
struction to the pulmonary circulation ; but this explanation is not sufficient, as blood
passes easily through the lungs in asphyxia and is obstructed only in the systemic capil-
laries. The true explanation seems to be that, in most warm-blooded animals, during the
very first periods of extra-uterine life, the demands on the part of the system for oxygen
are comparatively slight. At this time, there is very little activity in the processes of
nutrition, and the actual consumption of oxygen and exhalation of carbonic acid are
much below the usual regular standard in animals of this class. In fact, their condition is
somewhat like that of cold-blooded animals. The actual difference in the consumption
of oxygen immediately after birth and at the age of a few days is sufficient to explain
the remarkable power of resisting asphyxia just after birth.

One of the most interesting questions, in a practical point of view, connected with
the subject of asphyxia, is the effect on the system of air vitiated from breathing in a
confined space. There are here several points which present themselves for considera-
tion. The effect of respiration on the air is to take away a certain proportion of oxygen
and to add certain principles which are regarded as deleterious. The emanation which is
generally regarded as having the most decided influence upon the system is carbonic acid.
A careful review of the most reliable observations on this subject shows that the in-
fluence of carbonic acid is generally very much over-estimated. In poisoning by char-
coal-fumes, it is generally carbonic oxide which is the active principle. Regnault and
Reiset exposed dogs and rabbits for many hours to an atmosphere containing twenty-
three parts per hundred of carbonic acid artificially introduced, and thirty to forty parts
of oxygen, without any ill effects. They took care, however, to keep up a constant sup-
ply of oxygen. These experiments are at variance with the results obtained by others,
but Regnault and Reiset explain this difference by the supposition that the gases in other
observations were probably impure, containing a little chlorine or carbonic oxide. There
is no reason to doubt, from the high reputation of these observers for skill and accuracy,
that their experiments are perfectly reliable ; and, in that case, they prove that carbonic
acid does not act upon the system as a poison. This view is sustained by the observa-
tions of Bernard with carbonic oxide, which is known to be excessively poisonous. In
animals killed by this gas, the blood, both venous and arterial, is of a bright-red color,
which is due to the fixation of the gas by the blood-corpuscles. In this way, the red
corpuscles, which act normally as respiratory agents carrying oxygen to the tissues, are
paralyzed, and the animal dies from asphyxia. We have already referred to this remark-
able affinity of the red corpuscles for carbonic oxide and its action in arresting the trans-

170 RESPIRATION".

formation of oxygen into carbonic acid in the blood, in treating of the different methods
of analysis of the blood for gases, and have shown that this gas is the proper agent to
use in the method of analysis by displacement.

In breathing in a confined space, the distress and the fatal results are produced, in
all probability, more by animal emanations and a deficiency of oxygen than by the pres-
ence of carbonic acid. When the latter gas is removed as fast as it is produced, the effects
of diminution in the proportion of oxygen are soon very marked, and they progressive-
ly increase until death occurs. Bernard has shown that birds enclosed in a confined space,
from which the carbonic acid is carefully removed, will gradually consume oxygen, un-
til, when death occurs, the proportion is reduced to from three to five parts per hun-
dred. When the carbonic acid is allowed to remain, the increased density of the atmos-
phere interferes with the diffusion between the gases of the blood and the air, and death
supervenes with greater rapidity.

The influence on animals of emanations from the lungs and general surface is un-
doubtedly very considerable ; and this fact, which almost all have experienced more or
less, has been fully and painfully illustrated in several instances of large numbers of per-
sons confined without proper change of air. Overcrowding is one of the most prolific
sources of disease among the poorer classes of society ; and there are many forms of dis-
ease prevalent in large cities, that are almost unknown in the rural districts and that can
be alleviated only by proper sanitary regulations, which, unfortunately, are often very
difficult to enforce.

In crowded assemblages, the slight diminution of oxygen, the elevation of temperature,
increase in moisture, and particularly the presence of organic emanations, combine to
produce unpleasant sensations. The terrible effects of this carried to an extreme degree
were exemplified in the confinement of the one hundred and forty-six English prisoners,
for eight hours only, in the "Black Hole" of Calcutta, a chamber eighteen feet square,
with only two small windows, and those obstructed by a veranda. Out of this number,
ninety-six died in six hours, and one hundred-and twenty-three, at the end of the eight
hours. Many of those who immediately survived died afterward of putrid fever. This
frightful tragedy has frequently been repeated on emigrant and slave ships, by confining
great numbers in the hold of the vessel, where they were entirely shut out from the
fresh air. This subject possesses great pathological interest ; the effects of an insufficient
supply of air and the accumulation in the atmosphere of animal emanations being very
important in connection with the cause and prevention of many diseases.

The condition of the system has a marked and important influence on the rapidity
with which the effects of vitiated atmosphere are manifested, as we should anticipate
from what we know of the variations in the consumption of oxygen under different con-
ditions. As a rule, the immediate effects of confined air are not so rapidly manifested in
weak and debilitated persons as in those who are active and powerful. It has sometimes
been observed, in cases where a male and female have attempted suicide together by the
fumes of charcoal, that the female may be restored some time after life is extinct in the
male. This is probably owing to the greater demand for oxygen on the part of the male.

The following interesting fact is reported by Bernard, showing the relative power of
resisting asphyxia in health and disease :

" Two young persons were in a chamber warmed by a stove fed with coke. One of
them was seized with asphyxia and fell unconscious. The other, at that time suffering
with typhoid fever and confined to the bed, resisted sufficiently to be able to call for help.
We know already that this resistance to toxic influences is manifested in animals, when
they are made sick ; we here have the proof of the same phenomenon in man. As for tlie
one who, in good health, had experienced the effects of the commencement of poisoning,
she had a paralysis of the left arm, which was not completely cured at the end of six
months."

When poisoning by confined air is gradual, the system becomes somewhat accustomed

ALIMENTATION. 171

the toxic influence, the temperature of the body is lowered, and an animal will live in
aa atmosphere which will produce instantaneous death in one that is fresh and vigorous.
Bernard has made a number of curious and instructive experiments on this point. In
one of them a sparrow was confined under a bell-glass for one hour and a half, at the
end of which time another was introduced, the first being still quite vigorous. The second
became instantly much distressed and died in five minutes; but, ten minutes after, the
sparrow which had been confined for more than an hour and a half was released and flew
away. The points to which we have alluded have been confirmed and the observations
somewhat extended by the more recent researches of Bert. This is simply demonstrating,
with experimental accuracy, a fact of which we are all conscious; for it is well known
that, going from the fresh air into a close room, we experience a malaise which is not
felt by those who have been in the room for a length of time and whose emanations have
vitiated the atmosphere.

CHAPTER VI.

ALIMENTATION.

Appetite— Circumstances which modify the appetite— Influence of habit— Hunger— Seat of the sense of hunger-
Thirst — Seat of the sense of thiret— Duration of life in inanition — Division of alimentary principles— Nitrogen-
ized alimentary principles — Non-nitrogenized alimentary principles — Inorganic alimentary principles — Water —
Alcohol— Distilled liquors— Wines, malt liquors, etc.— Coffee— Tea— Chocolate— Condiments and flavoring articles
— Quantity and variety of food necessary to nutrition — Necessity of a varied diet.

IN the organism of animals, every part is continually undergoing what may be called
physiological decay ; the organic nitrogenized principles are being constantly transformed
into effete matter; and, as these constituents never exist without inorganic principles, with
which they are closely and inseparably united, it is found that the products of their decay
are always discharged from the body in combination with inorganic matters. This pro-
cess of molecular change is a necessary and an inevitable condition of life. Its activity may
be increased or retarded by various means, but it cannot be arrested. The excremen-
titious principles which are thus formed are produced constantly by the tissues and must
be continually removed from the organism, otherwise they accumulate and induce serious
toxic conditions. Examples of this are found in those diseases of the kidneys which in-
terfere with the elimination of urea, producing ura3mic poisoning, and in diseases of the
liver which interfere with the elimination of cholesterine, giving rise to cholesteraemia.

It is evident, from the amount of matter that is daily discharged from the body,
that the process of disassimilation, as it is called, must be very active. Its constant
operation necessitates a constant appropriation of new matter by the parts, in order that
they may maintain their integrity of composition and be always ready to perform their
functions in the economy. The blood contains all the principles necessary for the regen-
eration of the organism. Its inorganic constituents are generally found in the form in
which they exist in the substance of the tissues ; but the organic principles of the parts
are formed in the substance of the tissues themselves, by a transformation of material
furnished by the blood. The physiological decay of the organism is, therefore, being
constantly repaired by the blood ; but, in order to keep the great nutritive fluid from
becoming impoverished, the materials which it is constantly losing must be supplied from
some source out of the body, and this necessitates the ingestion of matters which are
known as food. Food is taken into the body in obedience to a want on the part of the
system, which is expressed by the sensation of hunger, when it relates to solid or semi-
solid matters, and thirst, when it relates to water. As these sensations constitute the
first cause of the introduction of materials capable of regenerating the blood, their

172 ALIMENTATION.

consideration naturally precedes the study of digestion, the process by which the articles
of food are prepared for absorption and appropriation by the circulating fluid.

Hunger and Thirst.

The term hunger may be applied to all degrees of that peculiar want felt by the sys-
tem which induces the ingestion of nutritive principles. Its first manifestations are, per-
haps, best expressed by the term appetite ; a sensation by no means disagreeable, and
one which may be excited by the sight, smell, or even the recollection 'of savory articles,
at times when it does not absolutely depend on a want in the system. In the ordinary
and moderate development of the appetite, it is impossible to say that the sensation is
referable to any distinct part or organ. It is influenced in some degree by habit ; in
many persons, the feeling being experienced at or near the hours when food is ordinarily
taken. If not soon gratified, the appetite is rapidly intensified until it becomes actual
hunger. Except when the quantity of food taken is unnecessarily large, the appetite
simply disappears on the introduction of food into the stomach and gives place to the
sense of satisfaction which accompanies the undisturbed and normal action of the diges-
tive organs ; or, in those who are in the habit of engaging in absorbing occupations at
that time, the only change experienced is the absence of desire for food. The sense of
oppression and fulness which attends over-distention of the stomach is simply superadded
to the feeling of satisfaction of the appetite, of which it is not a necessary part.

In man, the appetite is usually manifested in a marked degree at least twice, and
generally three times in the twenty-four hours. In this country, food is commonly
taken three times daily. In childhood, when the system demands material, not only for
the repair of worn-out parts but for growth, food is generally taken oftener and in
larger relative quantity than in the adult. The infant should satisfy the appetite at least
six or seven times in the twenty-four hours ; and nothing has a more serious influence
upon the development of the growing child than bad quality or a restricted quantity of
food.

It has been observed that children and old persons do not endure deprivation of food
so well as adults. This fact was noted by M. Savigny, in the case of the wreck of the
frigate Medusa. After the wreck, one hundred and fifty persons, of all ages, were
exposed on a raft for thirteen days with hardly any food. Out of this number only
fifteen survived, among them M. Savigny ; and the children, young persons, and the aged,
were the first to succumb.

Important modifications in the appetite are due to temperature. In cold climates,
and during the winter season in all climates, the desire for food is notably increased, and
the tastes are somewhat modified. Animal food, and particularly fats, are more agree-
able at that time, and the quantity of nutriment which is demanded by the system is
then considerably greater. In many persons, the difference in the appetite in warm and
cold seasons is very marked.

Exercise and occupation, both mental and physical, when not pushed to the point of
ex'i mstion, increase the desire for food and undoubtedly facilitate digestion. Certain
armies, especially the vegetable bitters, taken into the stomach immediately before the
time when food is habitually taken, frequently have the same effect; while other articles,
which do not satisfy the requirements of the system, have a tendency to diminish the
desire for food. Many articles of the materia medica, especially preparations of opium,
have, in some persons, a marked influence in diminishing the appetite. The abuse of
alcoholic stimulants will sometimes take away all desire for food. "When hunger is
pressing, it has been observed that tobacco, in those who are accustomed to its use, will
frequently allay the sensation for a time. When the system has been badly nourished
from any cause, as after prolonged abstinence or in recovery from an exhausting dis-
ease, hunger is generally pressing and almost constant; and this continues until the
organism has regained its normal condition. Under these circumstances, the ingestion

HUNGER AND THIRST. 173

of food, even in unusually large quantity, has but a momentary effect in appeasing the
appetite ; showing that, although the feeling of satiety which follows the introduction of a
sufficient quantity of food into the stomach is experienced, the system still feels the want
of nourishment, and this want is expressed by an almost immediate recurrence of the
appetite.

If food be not taken in obedience to the demands of the system as expressed by the
appetite, the sensation of hunger becomes most distressing. It is then manifested by a
peculiar and indescribable sensation in the stomach, which soon becomes developed into
actual pain. This is generally accompanied by intense pain in the head and a feeling of
general distress, which soon render the satisfaction of this imperative demand on the
part of the system the absorbing idea of existence. Starvation overcomes, in many
instances, every moral and intellectual feeling and gives full play to the purely animal
instincts. Furious delirium frequently supervenes after a fe\v days of complete absti-
nence ; and this is generally the immediate precursor of death. It is unnecessary to cite
any of the numerous instances in which murder and cannibalism are resorted to when
starvation is imminent ; suffice it to say, that the extremity of hunger or of thirst, like
the sense of impending suffocation, is a demand on the part of the system so imperative,
that it must be satisfied if within the range of possibility. There have been instances of
sublime resignation in the face of this terrible agony, but these are rare in comparison
with the examples of frightful expedients to satisfy the demands of Nature.

The question of the seat of the sense of hunger is one of considerable physiological
interest. When we say that it is instinctively referred to the stomach, it is simply
expressing the fact that the sensation is of a nature to demand the introduction of food
into the alimentary canal. The sense of the want of air demands the introduction of fresh
air into the lungs ; but, though air be inspired, if any thing interfere with its passage to
the system by the blood, the demand for oxygen is unsatisfied. It has been shown that the
real seat of the respiratory sense is in the general system, and that this is referred to the
lungs because it is necessarily by the introduction of air into these organs that the want
is met. The same principle is manifested, in a manner no less distinct, with regard to
the ingestion and assimilation of food. When the system is suffering from defective
nutrition, as after prolonged abstinence or during recovery from diseases which have
been accompanied by lack of assimilation, the mere filling of the stomach produces a
sensation of repletion of this organ, but the sense of hunger is not relieved ; but if, on the
other hand, the nutrition be active and sufficient, the stomach is frequently entirely
empty for a considerable time without the development of the sense of hunger. The
following observation bears strongly on this point : In a dog with a fistula into the gall-
bladder, the bile-duct having been tied and partly exsected, digestion was so much inter-
fered with that death from inanition took place in thirty-eight days ; and, although the
animal took food abundantly, the appetite was voracious and never satisfied. The same
phenomenon has sometimes been observed in cases of diabetes accompanied with great
deficiency of assimilation. The appetite is preserved and hunger is felt by persons who
suffer from extensive organic disease of the stomach, and the sensation has been occa-
sionally relieved by nutritious enemata or by injections into the veins.

An interesting and curious case has been reported by Prof. Busch, of Bonn, which
points almost conclusively to a want of assimilation of nutritive matter by the gen-
eral system as the main cause of the sensation of hunger. In this case, which will be
more fully detailed hereafter, there existed a fistula into what appeared to be the upper
third of the small intestine. The patient was a woman, thirty-one years of age, who,
in the sixth month of her fourth pregnancy, received the injury which resulted in the
fistulous opening, by being tossed by a bull, one of the horns penetrating the abdomen.
She was seen by Prof. Busch six weeks after the injury, at which time every thing taken
into the stomach passed at the upper opening of the fistula. Although the patient took
food in large quantity, she became extremely emaciated and weak. " The patient at

174 ALIMENTATION.

first had a most voracious appetite ; she never felt satisfied. She continued to eat, even
when the first portions of food which she had taken were escaping through the opening.
She would then say that she felt better, but was still hungry. Prof. Busch infers that
hunger is composed of two separate sensations — one general, the other local ; the former
resulting from the want of material to supply the waste of tissue." Such facts render
it certain that the appetite and the sense of hunger are expressions of a general want on
the part of the system, referred by our sensations to the stomach, but really located in
the general system. This want can only be completely satisfied by the absorption of
digested alimentary matter by the blood and its assimilation by the tissues.

The sense of hunger is undoubtedly appreciated by the cerebrum, and it has been a
question whether there be any special nerves which have the function of conveying this
impression to the great nervous centre. The nerve which would naturally be supposed to
possess this function is the pneumogastric ; but, notwithstanding certain observations to
the contrary, it has been proven that section of both of these nerves by no means abolishes
the desire for food. Longet has observed that dogs eat, apparently with satisfaction,
after section of the glosso-pharyngeal and lingual nerves. This observer is of the opinion
that the sensation of hunger is conveyed to the brain through the sympathetic system.
Although there are various considerations which render this somewhat probable, it is
not apparent how it could be demonstrated experimentally. It is undoubtedly the sym-
pathetic system of nerves which presides specially over nutrition ; and hunger, which
depends upon deficiency of nutrition, is certainly not conveyed to the brain by any of the
cerebro- spinal nerves.

Thirst is the special sensation which induces the ingestion of water. In its moderate
development, this is usually an indefinite feeling, accompanied with more or less sense
of dryness and heat of the throat and fauces, and sometimes, after the ingestion of a
quantity of very dry food, by a peculiar sensation referred to the stomach. When the
sensation of thirst has become intense, the immediate satisfaction which follows the
ingestion of a liquid, particularly water, is very great. Thirst is very much under the
influence of habit, some persons experiencing a desire to take liquids only two or three
times daily, while others do so much more frequently. The sensation is also sensibly
influenced by the condition of the atmosphere, as regards moisture, by exercise, and
by other circumstances which influence the discharge of water from the body, particularly
by the skin. A copious loss of blood is always followed by great thirst. This we have
frequently noticed in the inferior animals. After an operation involving haemorrhage,
they nearly always drink with avidity as soon as released. In diseases which are charac-
terized by increased discharge of liquids, thirst is generally excessive.

The demand on the part of the system for water is much more imperative than for
solids; in this respect being only second to the demand for oxygen. Animals will live
much longer deprived of solid food but allowed to drink freely than if deprived of both
food and drink. A man, supplied with dry food but deprived of water, will not survive
more than a few days. Water is necessary to the function of nutrition, and acts, more-
over, as a solvent in removing from the S3rstem the products of disassimilation.

After deprivation of water for a considerable time, the intense thirst becomes most
agonizing. The dryness and heat of the throat and fauces are increased and accom-
panied by a distressing sense of constriction. A general febrile condition supervenes, the
blood is diminished in quantity and becomes thickened, the urine is scanty and scalding,
and there seems to be a condition of the principal viscera approaching inflammation.
Death takes place in a few days, generally preceded by delirium.

The sensation of thirst is instinctively referred to the mouth, throat, and fauces; but
it is not necessarily appeased by the passage of water over these parts, and it may be
effectually relieved by the introduction of water into the system by other channels, as by
injecting it into the veins. Bernard has demonstrated, by the following experiment, that
water must be absorbed before the demands of the system can be satisfied : He made an

HUNGER AND THIRST. 175

opening into the oesophagus of a horse, tied the lower portion, and allowed the animal
to drink after he had been deprived of water for a number of hours. The animal drank
an immense quantity, but the water did not pass into the stomach, and the thirst was
not relieved. He modified this experiment by causing dogs to drink with a fistulous
opening into the stomach by which the water was immediately discharged. They con-
tinued to drink without being satisfied, until the fistula was closed and the water could
be absorbed. We have often repeated the latter experiment in public demonstrations. In
one of these particularly, the animal drank repeatedly until he had taken several quarts
of water, only ceasing from fatigue and soon recommencing ; but, so soon as the fistula
was closed, he drank a moderate quantity and was satisfied.

In a case reported by Dr. Gairdner, of Edinburgh, in the human subject, all the
liquids swallowed passed out at a wound in the neck by which the oesophagus had been cut
across. The thirst in this case was insatiable, although buckets-full of water were taken in
the day ; but, on injecting water, mixed with a little spirit, into the stomach, the sen-
sation was soon relieved. This observation was made in 1820, long before the experi-
ments just referred to upon the inferior animals.

Although the sensation of thirst is referred to special parts, it is an expression of the
want of fluids in the system and is to be effectually relieved only by the absorption of
fluids by the blood. There are no nerves belonging to. the cerebro-spinal system which
have the office of carrying this sensation to the brain, division of which will abolish the
desire for liquids. Experiments show that no effectual relief of the sensation is afforded
by simply moistening the parts to which the heat and dryness are referred. As a demand
on the part of the system, it is entirely analogous to the sense of want of air and of
hunger, differing only in the way in which it is manifested.

After a certain period of inanition, febrile movement and general agitation occur,
and there is almost always disturbance of the mental faculties, amounting sometimes to
furious delirium. Frequently, however, the delirium is of a mild character, with hallu-
cinations. There are cases in which there is no marked mental disturbance, but these
are generally in persons who voluntarily suffer starvation.

The length of time that life continues after complete deprivation of food and drink is
very variable. The influences of age and obesity have already been referred to. With-
out citing the numerous individual instances of starvation in the human subject which
have been reported, it may be stated, in general terms, that death occurs after from five
to eight days of total deprivation of food. In 1816, one hundred and fifty persons,
wrecked on the frigate Medusa, were exposed on a raft in the open sea for thirteen days.
At the end of this time only fifteen were found alive. One of the survivors, M. Savigny,
gave, in an inaugural thesis, a very instructive and accurate account of this occurrence,
which has been very generally quoted in works of physiology. Authentic instances are
on record in which life has been prolonged much beyond the period above mentioned ; but
they generally occurred in persons who were so situated as not to suffer from cold,
which the system, under this condition, has very little power to resist. In these cases,
also, there was no muscular exertion, and water was generally taken in abundance. All
of these circumstances have an important influence in prolonging life.

Berard quotes the example of a convict who died of starvation after sixty-three days,
but in this case water was taken. An instance of eight miners who survived after five
days and sixteen hours of almost complete deprivation of food is referred to in works
upon physiology. Berard also quotes from various authors instances of deprivation of
food for periods varying from four months to sixteen years; but these accounts are not
properly authenticated and are discredited by physiologists. They generally occurred in
hysterical females, and their consideration belongs to psychology rather than to physi-
ology. According to Chossat, death from starvation occurs after a loss of four-tenths of
the weight of the body, the time of death being variable in different classes of animals.

From thirty to thirty-five days may be taken as the average duration of life in dogs

176 ALIMENTATION.

deprived entirely of food and drink. This fact it is important to bear in mind in con-
nection with observations on the nutritive value of different articles of food.

Alimentation.

Under the name of aliment, in its widest signification, it is proposed to include all
articles composed of or containing elements in a form which enables them to be used
for the nourishment of the body, either by being themselves appropriated by the or-
ganism, by influencing favorably the process of nutrition, or by retarding disassimila-
tion. Those principles which are themselves appropriated may be called direct aliments ;
and those which simply assist nutrition without contributing reparative material,
together with those which retard disassimilation, may be termed accessory aliments.
By this definition of aliment, nothing is excluded which contributes to nutrition. The
air must be considered in this light, as well as water and all articles which are com-
monly called drinks.

In the various articles used as food, nutritious elements are frequently combined with
each other and with indigestible and non-nutritious matters. The elements of the
food which are directly used in nutrition are the true alimentary principles, embracing,
thus, only those principles which are capable of absorption and assimilation. The
ordinary food of the warm-blooded animals contains alimentary principles united with
innutritious substances from which they are separated in digestion. This necessitates a
complicated digestive apparatus. In some of the inferior animals, the quantity of nu-
tritious material forms so small a part of the food that the digestive apparatus is even
more complicated than in the human subject. This is especially marked in the herbivora,
the flesh of which forms an important part of the diet of man. In addition to what are
distinctly recognized as alimentary principles, food contains many substances having an
important influence on nutrition, which have never been isolated and analyzed, but
which render it agreeable. Many of these principles are developed in the process of
cooking. They will be considered, as far as practicable, in connection with the different
articles of diet.

The alimentary principles belong to the inorganic, vegetable, and animal kingdoms,
and are generally divided into the following classes:

1. Organic nitrogenized principles (albumen, fibrin, caseine, musculine, etc.), belong-
ing to the animal kingdom, and vegetable nitrogenized principles, such as gluten and
legumine.

2. Organic non-nitrogenized principles (sugars, fats, and starch).

3. Inorganic principles.

Nitrogenized Alimentary Principles.

In the nutrition of certain classes of animals, these principles are derived exclusively
from the animal kingdom, and in others, exclusively from the vegetable kingdom^ but
in man, who is omnivorous, both animals and vegetables contribute nitrogenized material.
In both animal and vegetable food, these principles are always found combined with
inorganic matters (water, chloride of sodium, the phosphates, sulphates, etc.), and fre-
quently with non-nitrogenized principles (sugar, starch, and fat).

Musculine. — Of the different nitrogenized principles used as food, musculine, albumen,
caseine, and fibrin are the most important. Musculine, the organic principle which forms
the bulk of the muscular substance, is perhaps the most important and abundant article
of this class. This substance is always united with more or less inorganic matter, which
cannot be separated without incineration. The flesh of different animals presents wide
differences in general appearance, in nutritive properties, and in flavor, which become
more marked after the formation of the odorous, empyreiimatic substances which are

NITROGENIZED ALIMENTARY PRINCIPLES. 177

developed in cooking; but the organic principle of all of them is musculine. Muscular
tissue is rendered much more digestible by cooking, a process which serves to disin-
tegrate, to a certain extent, the intermuscular areolar tissue and facilitates the action of
the digestive fluids. The savors developed in this process have a decidedly favorable
influence on the secretion of the gastric juice. It is doubtful whether pure musculine
would be capable of supporting life for a long period ; but the muscular tissue has been
shown by experiment to be sufficient for the purposes of nutrition, in the carnivora, and
it undoubtedly is in man.

Of all kinds of muscular tissue, beef possesses the greatest nutritive power. Other
varieties of flesh, even that of birds, fishes, and animals in a wild state, do not present
an appreciable difference, as far as can be ascertained by chemical analysis ; but when
taken daily for a long time, they become distasteful, the appetite fails, and the system
seems to demand a change of diet. The flesh of carnivorous animals is rarely used as
food; and animals that feed upon animal as well as vegetable food, such as pigs or
ducks, acquire a disagreeable flavor when the diet is not strictly vegetable.

Albumen.— This is an alimentary principle hardly second in importance to musculine.
As an article of diet, it is chiefly found in the white of egg, where it exists in great
quantity and is combined with a variety of inorganic substances. Although an important
alimentary principle, it cannot meet all the nutritive requirements of the organism.
Numerous observations on the inferior animals have shown that pure albumen will not
sustain life. The egg of the fowl, however, containing, in addition to albumen, a large
quantity of inorganic matter, the fatty matter of the yolk, and other 'organic principles,
is a most nutritious article of food. The albuminoid matters constitute the great
nutritive nitrogenized principles of the blood and are the substances into which all the
principles of this class which exist in food are converted before they are applied to the
nutrition of the tissues.

Gaseine. — At a certain period of life, caseine constitutes essentially the sole nitrogenized
article of food. It is found only in milk, and it exists largely in the great variety of
cheeses, which are manufactured from milk. In addition to caseine, milk contains butter,
sugar, and a variety of inorganic principles. Milk is capable of supplying material for
the nourishment of all parts of the organism, caseine furnishing the nitrogenized prin-
ciple. In the form of cheese, caseine constitutes an important article of food.

Fibrin. — Fibrin is by no means so important an article of diet as those just considered,
and it very seldom forms any considerable part of our food The aame may be said of
some other principles of this class, such as globuline, which is the organic principle of the
blood-corpuscles, vitelline, a principle peculiar to the yolk of the egg, osteine and car-
tilagine. The last two substances are generally taken after they have undergone peculiar
modifications in cooking, when they are known by other names.

Gelatine and Chondrine, etc. — After prolonged boiling, the organic principles of the
bones, integuments, areolar tissue, tendons, and other structures composed of the white
fibrous tissue, are dissolved and transformed into a new substance which is called gelatine.
Cartilage treated in the same way is in great part converted into chondrine. The prin-
ciples thus formed are soluble in hot water, rendering it slightly viscid, but on cooling the
whole mass becomes of a more or less gelatinous consistence, according to the quantity of
gelatine that is present. A considerable quantity of inorganic matter, particularly phos-
phate of lime, is always present in combination with gelatine.

Gelatine and chondrine present slight differences as regards their chemical reactions,
in other respects being nearly identical. The sulphate of alumina, alum, and the sulphate
of iron, will precipitate chondrine but have no influence on a solution of gelatine. Tan-
12

178 ALIMENTATION.

nin, or infusion of galls, added to a solution of gelatine, produces a brownish precipitate.
This reaction is marked in a solution containing but one part of gelatine to five thousand
parts of water. Both gelatine and chondrine are of indefinite chemical composition and un-
crystallizable. By the action of sulphuric acid, gelatine is transformed into a crystallizable
substance called glycocolle, which has a sweetish taste, is soluble in water, and is insoluble
in alcohol and ether. According to some, this is capable of being separated into alcohol
and carbonic acid by fermentation.

A great deal of interest was at one time attached to gelatine as an article of food,
from the fact that it is formed and extracted from parts, particularly the bones, which
were before regarded as comparatively useless. Indeed, the experiment of diminishing
the quantity of meat and supplying in its place the extract of bones was made in several
hospitals and manufacturing establishments in France ; but this change in diet led so uni-
versally to complaints of insufficiency of food, that experiments were soon instituted with
a view of determining whether gelatine really possessed any nutritive power. Without
entering into a full discussion of these experiments, it may be stated that the introduction
of gelatine as an article of diet, to the exclusion of other principles which were known to
be nutritive, was always followed by loss of weight and the indications of more or less de-
fective nutrition. In other words, the introduction of gelatine did not permit any diminu-
tion in the quantity of ordinary articles of food. The whole question was finally settled
by the researches of Magendie, the reporter of the French committee on gelatine, in 1841.
This report embodied the results of numerous experiments on the effects of various nitro-
genized principles, but the conclusions with regard to gelatine were very striking. "When
taken alone, it was distasteful in the highest degree, even to animals on the verge of
starvation ; even the agreeable jelly formed of different parts of the pig and the giblets
of fowl, prepared by the charcutiers of Paris, which were at first taken by the animals
with apparent satisfaction, was refused after a few days ; and, when animals were con-
fined exclusively to this article, death took place about the twentieth day, with all the
symptoms of inanition.

The flavor of meat was formerly supposed to depend chiefly on a peculiar principle,
called, by Th6nard, osmazome. This name is now seldom used, as the substance which
was so called is known to be composed of various empyreumatic nitrogenized products,
with lactic acid, the lactate of soda, the inosate of potash, creatine, creatinine, and
other principles the nature of which has not been determined .

Most of the vegetable articles of food contain more or less nitrogenized matters
which resemble very closely their analogues in the animal kingdom. Some of these vege-
table principles resemble those above considered so closely that they have 'been called
respectively, vegetable albumen, fibrin, and caseine. They all, however, present certain
distinguishing peculiarities.

Vegetable Albumen. — In the juice of most vegetables which are used as food, there
exists a substance, coagulable by heat and by alcohol, and having the same composition as
ordinary albumen with the exception of the equivalents of phosphorus and sulphur.
This is found most abundantly in the juice of turnips, carrots, cabbages, and vegetables of
this class. In wheaten flour, which contains nearly all classes of alimentary principles,
it is also found, but in small quantity.

There is every reason to suppose that, as nutritive principles, vegetable and animal
albumen are nearly identical. Many of the largest and strongest animals are nourished
exclusively from the vegetable kingdom. The human subject and many of the inferior
animals may be nourished at will by vegetable or by animal food. There is, however,
always a physiological difference in the various nitrogenized principles, which is not ap-
preciable by chemical analysis. The flesh of the carnivora, when used as food, is not the
same as the flesh of the herbivora; and the quality of the meat may be modified in many
animals by changing them from vegetable to animal food. Although the muscular tissue

NITROGENIZED ALIMENTARY PRINCIPLES. 179

of one animal may be used for the nourishment of another, the flesh of an animal thus
nourished is not an appropriate food for man. We should live upon vegetable principles ;
taking them in part directly, and in part indirectly, or after they have been prepared and
assimilated by animals. As a rule, the nutritive principles in vegetables are relatively
less abundant than in animal food, and the indigestible residue is therefore greater; but
man, and even the carnivorous animals, may be nourished for an indefinite period by ap-
propriate articles derived from the vegetable kingdom.

Vegetable Fibrin and Caseine. — Many of the vegetable juices contain a spontaneously-
coagulable substance which has been called vegetable fibrin. This is particularly abun-
dant in the cereals. What has been said concerning fibrin as an alimentary principle is
applicable to this substance. Its proportion in vegetables is small, unless we consider as
vegetable fibrin, gluten, one of the most abundant and important of the nutritive principles
contained in ordinary flour.

A principle may be extracted from beans, peas, and other vegetables of this class,
which is thought by many to be identical, in all respects, with caseine and has been
called vegetable caseine. The article called tao-foo, made by the Chinese from peas, is
apparently identical with cheese. The peas are reduced to a pulp by boiling and the
vegetable caseine is coagulated by rennet,being afterward treated in the same way as the
analogous substance manufactured from milk. Vegetable and animal caseine have, as far
as we know, identical physiological relations. Vegetable caseine is sometimes called
legumine. It is sparingly soluble in water, is insoluble in alcohol, is not coagulated by
heat, and is precipitated by the mineral acids and some of the mercurial and calcareous
salts. It is dissolved by the vegetable acids.

Another substance, supposed by some to be identical with vegetable caseine, is aman-
dine. This is found widely distributed in the vegetable kingdom, but it hardly presents
points of distinction from legumine, sufficient to mark it as a distinct principle.

Gluten. — In many of the vegetable grains known as cereals, there exists, in variable
proportions, a highly-nutritive nitrogenized substance called gluten. This is found in
great abundance (from ten to thirty-five per cent.) in wheat. Its proportion in other
grains is insignificant. It may be easily extracted from ordinary wheaten flour, by knead-
ing under a stream of water, when the starch, a little sugar, vegetable albumen, mucilage,
and some soluble matters are removed, and the gluten remains in the form of an adhesive,
elastic, grayish-white mass. Gluten is capable of acting as a ferment, transforming starch
first into dextrine and then into sugar. It is the substance which gives the peculiar con-
sistence and porous character to bread.

The nutritive power of gluten is so great, and it contains such a variety of alimentary
principles, that dogs are well nourished and can live indefinitely on it when taken as the
sole article of food. This experiment was actually made by the gelatine committee ; and
the fact will be easily understood when we consider that it is a compound of no less
than three distinct nitrogenized principles, together with fatty and inorganic matters.
In one of the methods of treatment of diabetes mellitus, in which all saccharine and
amylaceous matters are excluded from the food, it has been found difficult to nourish the
body sufficiently and give proper variety to the diet without bread ; and, under these
circumstances, the use of bread composed almost exclusively of gluten has been nighty
successful. With proper care, a bread can be made in this way, which is eminently
nutritive and not unpalatable.

Gluten obtained by washing flour under a stream of water contains vegetable fibrin,
vegetable albumen, and a substance soluble in alcohol, called glutine. This latter sub-
stance is found in quantity only in wheaten flour.

In the different articles of food belonging to the vegetable kingdom, there are un-
doubtedly many nitrogenized matters with the distinguishing properties of which we

180 ALIMENTATION.

are not yet familiar. In their relations to the body as alimentary principles, these would
not possess much practical interest, even if they had all been isolated and studied ; for all
articles of this class are apparently transformed into the same nutritive principles,
namely, the albuminoid constituents of the blood.

Noyi-Nitrogenized Alimentary Principles.

The important principles belonging to the class of non-nitrogenized matters are the
sugars, starch, and fat. From the fact that these are supposed by some to be exclusively
concerned in keeping up the animal temperature by the oxidation of carbon, they are
frequently spoken of as the carbonaceous or calorific elements of food. They are some-
times called hydro-carbons.1

In many respects there are marked and important differences between the nitro-
genized and non-nitrogenized articles of food ; and whether or not these differences relate
to the nutrition of the organism is a question which will be considered in its appropriate
place. The production of animal heat, which is supposed by some to be due entirely to
the action of non-nitrogenized substances, is closely connected with the function of nutri-
tion, and all that is at present known of this general process must be taken into con-
sideration in connection with calorification. It is certain, however, that all alimentary
and proximate principles which contain nitrogen, excluding the inorganic and some
crystallizable organic substances, have very different properties from those which contain
no nitrogen. While the nitrogenized principles are in a state of continual change, so that
it is impossible to fix upon any formula as representing their exact ultimate composition,
the non-nitrogenized principles are not changed, unless by the influence of some other sub-
stance known as a ferment, and have a distinct and definite chemical composition. The
latter not only differ greatly from the nitrogenized principles, but most of the individual
articles of this class present distinctive peculiarities in their general properties, reactions,
and ultimate composition. Treating of them as alimentary principles, we have now only
to do with their general properties and the changes which they may be made to under-
go out of the body.

Sugar. — A great many varieties of sugar occur in food, and this principle may be
derived from both the animal and the vegetable kingdom. The most common varieties
derived from animals are sugar of milk, and honey, beside a small quantity of liver-sugar,
which is taken whenever the liver is used for food. The sugars derived from the vege-
table kingdom are cane-sugar, under which head may be classed all varieties of sugar
except that obtained from fruits, and grape-sugar, which comprises all the varieties exist-
ing in fruits. In addition, an impure, uncrystallizable residue, obtained in the manu-
facture of the different varieties of cane-sugar, called molasses, is a common article of
food. The following are the formulas for the different varieties of sugar in a crystalline
form :

Cane- Sugar, da Hn On

Milk-Sugar, da H12 O]2

Grape-Sugar (Glucose), da Hu OJ4

All varieties of sugar have a peculiar sweet taste ; they are soluble in water and in
alcohol; they are inflammable, leaving an abundant carbonaceous residue and giving off
a peculiar odor of caramel ; they are capable of being converted, in contact with fer-
ments or with nitrogenized principles, into alcohol and carbonic acid and into lactic
acid; they are also capable of other modifications when treated with the mineral acids,
or with alkalies, which are interesting more in a chemical than a physiological point of
view. Of all the varieties of sugar, that made from the sugar-cane is the most soluble,

1 The name hydro-carbon is strictly applicable only to the sugars and starch, which are, chemically, hydrates of
carbon, containing as they do, carbon, with hydrogen and oxygen in the proportions to form water.

NON-NITROGENIZED ALIMENTARY PRINCIPLES.

181

the sweetest, and the most agreeable. Beet-root sugar, so extensively used in France, is
perhaps as agreeable, but is not so sweet.

Much of the sugar used in the nutrition of the organism is formed in the body from
the digestion of starch. This transformation of starch may be effected artificially. The
sugar thus formed is called glucose and is identical in composition with grape-sugar.
Except in the milk during lactation, this is the only form in which sugar exists in the
organism, all the sugar of the food being converted into glucose before it is taken into
the blood.

Starch. — A non-nitrogenized principle, closely resembling sugar in its ultimate com-
position (da IIio Oio), is contained in abundance in a great number of vegetables. It is
found particularly in the cereals (wheat, rye, corn, barley, rice, and oats), in the potato,
chestnuts, and in the grains of leguminous plants (beans, peas, lentils, and kidney-beans), in
the tuberous roots of the yam, tapioca, and sweet-potato, in the roots of the Maranta
arundinacea,1 in the sago-plant, and in the bulbs of orchis. In the cereals, after desicca-
tion, the proportion of starch is, in general terms, between sixty and seventy parts per
hundred. It is most abundant in rice, which contains, after desiccation, 88*65 parts per
100.

Starch may be separated from many plants by simple washing, but in others, in which
it exists in connection with a considerable proportion of gluten, a more elaborate process
is employed in commerce. The different varieties of manufactured starch, such as corn-
starch, potato-starch, arrow-root, tapioca, and sago, differ only in the presence of a
minute quantity of odorous and flavoring principles.

When extracted in a pure state, starch is in the form of granules, varying in size from
Ttfwo- to TTO °f an inch, and presenting, in most varieties, certain peculiarities of form.
The granule is frequently marked by a
little conical excavation called the hilum,
and the starch-substance is arranged in the
form of concentric laminas, the outlines
of which are frequently quite distinct.
When starch is rubbed between the fingers,
these little hard bodies give it rather a
gritty feel and produce a crackling sound.
The different varieties of starch may be
recognized microscopically by the peculiar
appearance of the granules.

The presence of even a minute quan-
tity of starch in any mixture which is not
alkaline may be readily determined by
the addition of iodine, which unites with
the starch, producing an intense-blue color.
The color may be destroyed by the addi-
tion of an alkali or by the application of pI0. 44.— Arrow-root xtarch-granuleK ; magnified 370

heat. It may be restored, however, by

the addition of an acid or, in the latter

instance, it returns when the mixture is allowed to cool, if the temperature have not

been carried to 212° Fahr.

Starch is insoluble in water, but, when boiled with several times its volume of water,
the grannies swell up, become transparent, and finally fuse together, mingling with the
water and giving it a mucilaginous consistence. The mixture on cooling forms a jelly-
like mass of greater or less consistence. This change in starch is called hydration and
is interesting as one of the transformations which takes place in the process of digestion,

1 The creeping roots from which the substance known as arrow-root is manufactured.

diameters. (From a photograph taken at the United
States Army Medical Museum.)

182 ALIMENTATION.

when starch is taken uncooked. This change is generally effected, however, in the pro-
cess of cooking.

The most interesting properties ot starch are connected with its transformation, first
into dextrine and finally into glucose. This always takes place in digestion, before starch
can be absorbed. In the digestive apparatus, the change into sugar is almost instan-
taneous, and the intermediate substance, dextrine, is not recognized. By boiling starch
for a number of hours with dilute sulphuric acid, it gradually loses its property of striking
a blue color with iodine, and is transformed, without any change in chemical composition,
into the soluble substance called dextrine. If the action be continued, it assumes four atoms
of water and is converted into glucose. If dextrine be perfectly pure, no coloration is
produced by the addition of iodine, but it ordinarily contains starch imperfectly trans-
formed, and iodine produces a reddish color. The change of starch into dextrine may be
effected by a dry heat of about 400° Fahr., a process which is commonly employed in
commerce. The most effectual method of producing this transformation of starch, aside
from the process of digestion, is by the action of a peculiar vegetable substance called
diastase. This substance is produced in the process of germination of many of the vege-
tables containing starch.1 One part of diastase will effect the transformation of one hun-
dred parts of starch, which would require thirty times the quantity of sulphuric acid.
What has been said regarding sugar as an alimentary principle will apply to starch.
Although an abundant and important article of diet, it is insufficient of itself for the pur-
poses of nutrition.

Vegetable Principles resembling Starch. — In certain vegetables, substances isomeric
with starch, but presenting slight differences as regards general properties and reactions,
have been described, but they possess no very great interest as alimentary principles and
demand only a passing mention. These are, inuline, lichenine, cellulose, pectose, mannite,
mucilages, and gums. Inuline is found in certain roots. It is capable of being converted
into sugar but does not pass through the intermediate stage of dextrine. It differs from
starch in being very soluble in hot water and in striking a yellow instead of a blue color
with iodine. Lichenine is found in many kinds of edible mosses and lichens. It differs
from starch only in its solubility.

Cellulose is a substance, generally regarded as identical in all plants, which forms the
basis of the walls of the vegetable cells. It exists in greater or less abundance in all
vegetables. It is less easily acted upon by acids than starch, but is capable, when treated
with concentrated sulphuric acid, of being converted first into dextrine, and finally into
sugar. It is only in soft and recent vegetable products that it can be regarded as an ali-
mentary principle.

Pectose is a principle which exists, mingled with cellulose, in unripe fruits, carrots,
turnips, and some other vegetables of this class. Its composition has not been deter-
mined. In ripe fruits, it is found transformed into a soluble substance called pectine.
This transformation may be effected artificially by the action of acids and heat. Pectine
may be precipitated in a gelatinous form by alcohol from the juices of fruits.

Mannite is a sweetish principle found in manna, mushrooms, celery, onions, and
asparagus. Manna in tears is composed of this principle in nearly a pure state. It is
perhaps more analogous to sugar than to starch, but it is not capable of fermentation and
has no influence on polarized light.

Gums and mucilages may enter to a certain extent into the composition of food, but
they can hardly be considered as alimentary principles. Gums are found exuding from
certain trees, first in a fluid state, but becoming hard on exposure to the air. A viscid,
stringy mucilage is found surrounding many grains, such as the flax-seed and quince-seeds,
and exists in various kinds of roots and leaves. Both gums and mucilages mix readily

1 Diastase is a white, amorphous, nitrogenized substance, insoluble in alcohol, soluble in water, and is extracted
from barley, oats, grain, and potatoes, in process of germination. Its action upon starch is most energetic at from 150*
to 167° Fahr.

FATS AND OILS.

183

with water, giving it a consistence called mucilaginous. They have the same composition
as starch.

Experiments have shown that gum passes through the alimentary canal unchanged
and has no nutritive power. It is said that gummy exudations from trees form an im-
portant part of the food of certain savage African tribes ; but it must be remembered
that in this condition the exudation is impure and contains many other substances. Gum
is mentioned in this connection from the fact that it is frequently used in the treatment
of disease and is thought by many to possess nutritive properties.

Fats and Oils. — Fatty or oily matters, derived from both the animal and the vegetable
kingdom, constitute an important division of the articles of food. As a proximate prin-
ciple, fat is found in all parts of the body, with the exception of the bones, teeth, and
fibrous tissues. It necessarily constitutes an important part of all animal food and is
taken in the form of adipose tissue, infiltrated in the various tissues in the form of globules
and granules of oil, and in suspension in the caseine and water in milk. Animal fat is a
mixture of oleine, margarine, and stearine, in varied proportions, and possesses a con-
sistence which depends upon the relative quantities of these principles. More or less fat
always enters into the composition of food, but, as a rule, it is more abundantly taken in
cold than in warm climates. The ordinary diet of the Greenlander contains what would
be considered in temperate climates as an enormous quantity of fat and oil, frequently in
a disgusting form, and often taken unmixed with other articles.

The different varieties of animal fats do not demand special consideration as articles
of diet. Butter, an important article of food, is somewhat different from the fat extracted
from adipose tissue, but most varieties of fat lose their individual peculiarities in the pro-
cess of digestion and are apparently identical when they find their way into the lacteal
vessels.

FIG. 45._ Crystals of margarine and mar-
garic acid. (Funke.) a, a, a, margarine ;
&, margaric acid.

FIG. 46.— Crystals of stearine and stearic
acid. (Funke.) a, a, a, stearine; &,
stearic acid.

In the vegetable kingdom, fat is particularly abundant in seeds and grains, but it
exists in quantity in some fruits, as the olive. Here it is generally called oil. Its pro-
portion in linseed is 20 per cent. ; in rape-seed, 35 to 40 per cent. ; in hemp-seed, 25 per
cent. ; and in poppy-seed, 47 to 50 per cent. It exists in considerable proportion in nuts
and in certain quantity in the cereals, particularly Indian corn. Its proportion in the
different varieties of wheat is from 1'87 to 2'61 per cent. ; in rye, 2'25 per cent. ; in
barley, 2'76 per cent. ; in oats, 5'5 per cent. ; in Indian corn, 8-8 per cent. ; and in rice,
0'8 per cent. The above is the proportion in the grains after desiccation.

Fat, both animal and vegetable, may be either liquid or solid. It has a peculiar oily

184 ALIMENTATION".

ieel, a neutral reaction, and is insoluble in water and soluble in alcohol (particularly hot
alcohol), chloroform, ether, benzine, and solutions of soaps. The solid varieties are exceed-
ingly soluble in the oils. Treated with alkalies, at a high temperature and in the presence
of water, the fats are decomposed into fatty acids and glycerine, the acid uniting with the
base to form a soap. Alkaline, mucilaginous, and some animal fluids (particularly the
pancreatic juice) are capable of holding fat in a state of minute and permanent subdivision
and suspension, forming what are known as emulsions.

The composition of many of the fats and oils has never been definitely ascertained, on
account of the difficulty in obtaining them in a state of absolute purity. They contain
carbon, hydrogen, and oxygen, but the latter elements do not exist in the proportions to
form water.

As alimentary principles, fats and oils are undoubtedly of great importance. They
are supposed by many to be particularly concerned in the function of calorification. It
has been proven by repeated experiments that fat, as a single article of diet, is insufficient
for the purposes of nutrition.

Inorganic Alimentary Principles.

Physiological chemistry has shown that all the organs, tissues, and fluids of the
body contain inorganic matter in greater or less abundance. The same is true of vege-
table products. All the organic nitrogenized principles contain mineral substances which
cannot be removed without incineration and which must be considered as actually part
of their substance. When new organic matter is appropriated by the tissues to supply
the place of that which has become effete, the mineral substances are deposited with
them ; and the organic principles, as they become effete or are transformed into excre-
mentitious substances and discharged from the body, are always thrown off in connection
with the mineral substances which enter into their composition. This constant dis-
charge of inorganic principles, forming, as they do, an essential part of the organism,
necessitates their introduction with the food, in order to maintain the normal constitu-
tion of the parts. As these principles are as necessary to the proper constitution of the
body as any other, they must be considered as belonging to the class of alimentary sub-
stances.

Water. — This is one of the most important of the proximate principles of the organ-
ism, is found in every tissue and part without exception, is introduced with all kinds
of food, and is the basis of all drinks. As a rule, it is taken in greater or less quantity
in a nearly pure state. Although, as a drink, water should be colorless, odorless, and
nearly tasteless, it always contains more or less saline and other matters in solution,
with a certain quantity of air. The air and gases may be evolved by boiling or removing
the atmospheric pressure. Pure water does not exist in Nature. Even rain-water always
contains' salts and frequently a little ammonia and organic matter. The waters of the
mineral springs, which are so abundant in parts of this country, are very rich in saline
constituents and generally contain a notable quantity of carbonic acid ; but the consid-
eration of their properties does not belong to physiology. The demand on the part of
the system for water is regulated, to a certain extent, by the quantity discharged from
the organism, and this is subject to great variations. The quantity taken as drink also
depends very much on the constitution of the food as regards the water which enters into
its composition.

Chloride of Sodium. — Of all saline substances, chloride of sodium is the one most
widely distributed in the animal and the vegetable kingdom. It exists in all varieties of
food ; but the quantity which is taken in combination with other principles is usually
insufficient for the purposes of the economy, and common salt is generally added to cer-
tain articles of food as a condiment, when it improves their flavor, promotes the secre-

ALCOHOL

185

tion of certain of the digestive fluids, and meets a positive nutritive demand on the part
of the system. Numerous experiments and observations have shown that a deficiency
of chloride of sodium in the food has an unfavorable influence on nutrition.

Phosphate of Lime. — This is almost as common a constituent of vegetable and animal
food as chloride of sodium. It is seldom taken except in combination, particularly with
the nitrogenized alimentary principles. Its importance as an alimentary principle has
been experimentally demonstrated, it having been shown that, in animals deprived as
completely as possible of this substance, the nutrition of the body, particularly in parts
which contain it in considerable quantity, as the bones, is seriously affected.

Iron. — Hasmaglobine, the coloring matter of the blood, contains, intimately united
with organic matter, a considerable proportion of iron. Examples of anemia, which
are daily met with in practice and are almost always relieved in a short time by the ad-
ministration of iron, are proof of the importance of this substance as an alimentary
principle. The quantity of iron which is discharged from the body is very slight, a
trace only being discoverable in the urine. A small quantity of iron is frequently intro-
duced in solution in the water taken as drink, and it is a constant constituent of milk
and eggs. When its supply in the food is insufficient, it is necessary, in order to restore
the processes of nutrition to their normal condition, to administer it in some form, until
its proportion in the organism reaches the proper standard.

It is hardly necessary even to enumerate the other inorganic alimentary principles, as
nearly all are in a state of such intimate combination with nitrogenized principles that
they may be regarded as part of their substance. Suffice it to say, that all the inorganic
matters which exist in the organism as proximate principles are found in the food. That
these are essential to nutrition, cannot be doubted ; but it is evident that, by themselves,
they are incapable of supporting life, as they cannot be converted into either nitrogen-
ized or non-nitrogenized organic principles.

Alcohol.

All distilled and fermented liquors and wines contain a greater or less proportion of
alcohol. As these are so generally used as beverages, and as the effects of their exces-
sive use are so serious, the influence of alcohol upon the organism has become one of the
most important questions connected with alimentation. In the discussion of this subject,
it is not proposed to enter into the great moral questions involved, but to consider, from
a purely physiological point of view, the immediate and remote influences of the various
alcoholic beverages upon nutrition and the animal functions. Some alcoholic beverages
influence the functions solely through the alcohol which they contain ; while others, as
beer and porter, with a comparatively small proportion of alcohol, .contain a consider-
able quantity of solid matters which may act as alimentary principles.

Alcohol (04H8O2), from its composition, is to be classed with the non-nitrogenized
principles, more especially the fats, in which the hydrogen and oxygen do not exist in
the proportion to form water. We have seen that sugar and fat are essential to proper
nutrition and that they undergo important changes in the organism. Alcohol is capable
of being absorbed and taken into the blood ; and it becomes a question of great interest
to determine whether it be consumed in the economy or whether it be discharged un-
changed by the various emunctories.

Alcohol has long since been recognized in the expired air after it has been taken into
the stomach ; and late researches have confirmed the earlier observations with regard to
its elimination in its original form and have shown that, after it has been taken in quan-
tity, it exists in the blood and all the tissues and organs, particularly the liver and ner-

186 ALIMENTATION.

vous system.1 Lallemand, Perrin, and Duroy have stated, also, that there is a consider-
able elimination of alcohol by the lungs, skin, and kidneys ; but the accuracy of the ex-
periments by which these results were arrived at has lately been questioned. The re-
cent observations of Drs. Anstie and Dupre have, indeed, thrown great doubt upon the
chromic-acid test for alcohol, which was employed by the French observers above men-
tioned. Anstie and Dupr6 have clearly shown that the color-test applied to the urine of
persons who do not drink alcohol at all not only acts with chromic acid in the same
way as does alcohol, but that the substance in the urine, whatever it may be, " is capa-
ble of being similarly oxidized into an acid which is apparently identical with acetic acid,
and similarly converted to iodoform by boiling with iodine and an alkali." Nevertheless,
when alcohol has been taken in narcotic doses, there is a certain amount of alcoholic elimi-
nation in the urine, as was shown long ago by Percy. We are not, however, considering
at present the elimination of alcohol when the ingestion of this principle has been pushed
to extreme intoxication, but only the question whether moderate doses of alcohol be
eliminated in totality or be consumed in the organism in the same way as sugar or albu-
men. It is possible to administer, for example, such quantities of sugar that a certain
amount will pass off in the urine ; and no one supposes that moderate quantities of sugar
are not consumed in the organism. As the result of the final experiments of Anstie, it
is absolutely certain that most of the alcohol which is taken in quantities not sufficient
to produce alcoholic intoxication is consumed in the organism, and but a trivial amount
is thrown off, either in the urine, the faeces, the breath, or the cutaneous transpiration.
This question is of the greatest importance with regard to the moderate use of alcohol
under normal conditions, and especially in its bearing upon the therapeutical action of
the various alcoholic drinks administered in cases of disease.

Taken in moderate quantity, alcohol generally produces a certain amount of nervous
exaltation, which gradually passes off. In some individuals the mental faculties are
sharpened by alcohol, while in others they are blunted. There is nothing, indeed, more
variable than the immediate effects of alcohol on different persons. In large doses, the
effects are the well-known phenomena of intoxication, delirium, more or less anesthesia,
coma, and sometimes, if the quantity be excessive, death. As the rule, the mental exal-
tation produced by alcohol is followed by reaction and depression, except in debilitated
or exhausted conditions of the system, when the alcohol seems to supply a decided
want.

The views of physiologists concerning the influence of a moderate quantity of alcohol
on the nervous system are somewhat conflicting. That it may temporarily give tone and
vigor to the system when the energies are unusually taxed, cannot be doubted ; but this
effect is not produced in all individuals. The constant use of alcohol may create an ap-
parent necessity for it, producing a condition of the system which must be regarded as
pathological.

The immediate effects of the ingestion of a moderate quantity of alcohol, continued
for a few days, are decided. It notably diminisbes the exhalation of carbonic acid and
the discharge of other excrementitious principles, particularly urea. These facts have
long since been experimentally demonstrated. The proper amount of mental and physi-
cal exercise, tranquillity of the nervous system, and all circumstances which favor the
vigorous nutrition and development of the organism physiologically increase, rather than
diminish, the amount of the excretions, correspondingly increase the demand for food,
and, if continued, are of permanent benefit. Alcohol, on the other hand, diminishes the
activity of nutrition. If its use be long continued, the assimilative powers of the system

1 It was formerly a question considerably discussed whether alcohol exist in the brain and in the fluid found in the
ventricles, in intoxicated persons. This was settled by Percy, who found alcohol in the brain, liver, and sometimes
in the urine, in dogs poisoned with alcohol and in men who had died after excessive drinking. In these experi-
ments, the presence of alcohol was determined by distillation, the distilled substances being inflammable and capable
of dissolving camphor.— PERCY, Prise Thesis. An Experimental Inquiry concerning the Presence of Alcohol in
the Ventricles of the Brain, etc., London, 1839.

ALCOHOL. 187

become so weakened that the proper quantity of food cannot be appropriated, and alcohol
is craved to supply a self-engendered want. The organism may, in many instances, be
restored to its physiological condition by discontinuing the use of alcohol ; but it is gen-
erally some time before the nutritive powers become active, and alcohol, meanwhile,
seems absolutely necessary to existence.

Under ordinary conditions, when the organism can be adequately supplied with food,
alcohol is undoubtedly injurious. When the quantity of food is insufficient, alcohol may
supply the want for a time and temporarily restore the powers of the body ; but the
effects of its continued use, conjoined with insufficient nourishment, show that it can-
not take the place of assimilable matter. These effects are too well known to the
physician, particularly in hospital-practice, to need farther comment. Notwithstand-
ing these undoubted physiological facts, alcohol, in some form, is used by almost every
people on the face of the earth, civilized or savage. "Whether this be in order to
meet some want occasionally felt by and peculiar to the human organism, is a ques-
tion upon which physiologists have found it impossible to agree. That alcohol, at
certain times, taken in moderation, soothes and tranquillizes the nervous system and
relieves exhaustion dependent upon unusually severe mental or physical exertion, cannot
be doubted. It is by far too material a view to take of existence, to suppose that the
highest condition of man is that in which the functions, possessed in common with the
lower animals, are most perfectly performed. Inasmuch as temporary insufficiency of
food, great exhaustion of the nervous system, and various conditions in which alcohol
seems to be useful, must of necessity often occur, it is hardly proper that this agent
should be utterly condemned ; but it is the article, par excellence, which is liable to abuse,
and the effects of which on the mind and body, when taken constantly in excess, are
most serious.

Although alcohol imparts a genial warmth when the system is suffering from ex-
cessive cold, it is not proven that it enables men to endure a very low temperature for a
great length of time. This end can be effectually accomplished only by an increased
quantity of food. The testimony of Dr. Hayes, the Arctic explorer, is very strong upon
this point. He says : " While fresh animal food, and especially fat, is absolutely essen-
tial to the inhabitants and travellers in Arctic countries, alcohol is, in almost any shape,
not only completely useless but positively injurious. . . . Circumstances may occur
under which its administration seems necessary; such, for instance, as great pros-
tration from long-continued exposure and exertion, or from getting wet; but then it
should be avoided, if possible, for the succeeding reaction is always to be dreaded ; and,
if a place of safety is not near at hand, the immediate danger is only temporarily
guarded against, and becomes, finally, greatly augmented by reason of decreased vitality.
If given at all, it should be in very small quantities frequently repeated, and continued
until a place of safety is reached. I have known the most unpleasant consequences to
result from the injudicious use of whiskey for the purpose of temporary stimulation,
and have also known strong able-bodied men to have become utterly incapable of resist-
ing cold in consequence of the long-continued use of alcoholic drinks."

It is not demonstrated that alcohol increases the capacity to endure severe and pro-
tracted bodily exertion. Its influence as a therapeutic agent, in promoting assimilation
in certain conditions of defective nutrition, in relieving shock and nervous exhaustion, in
sustaining the powers of life in acute diseases characterized by rapid emaciation and
abnormally active disassimilation, etc., is undoubted; but the consideration of these
questions does not belong to physiology.

Coffee.

Coffee is an article consumed daily by many millions of human beings in all quarters
of the globe. In armies it has been found almost indispensable, enabling men on moderate
rations to perform an amount of labor which would otherwise be impossible. After

188 ALIMENTATION.

exhausting efforts of any kind, there is no article which relieves the overpowering sense
of fatigue so completely as coffee. Army-surgeons say that at night, after a severe
march, the first desire of the soldier is for coffee, hot or cold, with or without sugar, the
only essential being a sufficient quantity of the pure article. This has been the universal
experience in the late civil war; the rations of coffee issued by the United States Govern-
ment being abundant and pure, though not, of course, of the quality possessing the most
delicate flavor. Almost every one can bear testimony from personal experience to the
effects of coffee in relieving the sense of fatigue after mental or bodily exertion and in
increasing the capacity for labor, especially mental, by producing wakefulness and clear-
ness of intellect. From these facts, the importance of coffee, either as an alimentary
article or as taking the place, to a certain extent, of aliment, is apparent.

Except in persons who, from idiosyncrasy, are unpleasantly affected by it, coffee,
taken in moderate quantity and at proper times, produces an agreeable sense of tran-
quillity and comfort, with, however, no disinclination to exertion, either mental or
physical. Its immediate influence upon the system, which is undoubtedly stimulant, is
peculiar and is not followed by reaction or unpleasant after-effects. Habitual use renders
coffee almost a necessity, even in those who are otherwise well nourished and subjected to
no extraordinary mental or bodily strain. Taken in excessive quantity, or in those unac-
customed to its use, particularly when taken at night, it produces persistent wakeful-
ness. These effects are so well known that it is often taken for the purpose of prevent-
ing sleep.

Experimental researches have shown that the use of coffee permits a reduction in
the quantity of food, in workingraen especially, much below the standard which would
otherwise be necessary to maintain the organism in proper condition. In the observa-
tions of De Gasparin upon the regirnen of the Belgian miners, it was found that the
addition of a quantity of coffee to the daily ration enabled them to perform their arduous
labors on a diet which was even below that found necessary in prisons and elsewhere
where this article was not employed. Numerous experiments have shown that coffee
diminishes the absolute quantity of urea discharged by the kidneys. In this respect, as
far as has been ascertained, the action of coffee is like that of alcohol and may reason-
ably be supposed to retard disassimilation, with the important difference that it is
followed by no unfavorable after-effects and can be used in moderation for an indefinite
time with advantage.

A study of the composition of coffee shows a considerable proportion of what must
be considered as alimentary matter. The following is the result of the analyses of Payen :

Composition of Coffee.

Cellulose 34-000

Water (hygroscopic) 12-000

Fatty substances 10 to 13-000

Glucose, dextrine, indeterminate vegetable acid 15'500

Legumine, caseine, etc lO'OOO

Chlorolignate of potash, and caffeine , 3'5 to S'OOO

Nitrogenized organic matter 3'000

Free caffeine 0*800

Concrete, insoluble essential oil O'OOl

Aromatic essence, of agreeable odor, soluble in water 0-002

Mineral substances; potash, magnesia, lime, phosphoric, silicic, and sulphuric acid and

chlorine.. 6'697

100-000

The above is the composition of raw coffee, but the berry is seldom used in that
form, being usually subjected to torrification before an infusion is made. The roasting

COFFEE, TEA, AND CHOCOLATE.

189

should be conducted slowly and gently, until the grains assume a chestnut-brown color.
During this process, the grains are considerably swollen, but they lose from sixteen to
seventeen per cent, in weight. A peculiar aromatic principle is also developed by roasting.
If the torrification be pushed too far, much of the agreeable flavor is lost, and an acrid
empyreumatic principle is produced. An infusion of fifteen hundred grains of roasted
and ground coffee in about a quart of boiling water, the infusion made by simple per-
colation, contains about three hundred grains of the soluble principles. According to
Payen, this contains about one hundred and forty grains of nitrogenized matters and
one hundred and fifty-three grains of fatty, saccharine, and saline substances. There is
every reason to suppose that that these principles are assimilated; and an infusion of
coffee, with milk and sugar, presents, therefore, a considerable variety and quantity of
alimentary matter. The peculiar stimulant effects of coffee are probably due to the
caffeine and volatile oil.

In the countries where coffee is grown, the leaves of the shrub, roasted and made into
an infusion, are quite commonly used. Their effects upon the system are similar to those
of coffee, and it is said that the natives prefer the leaves to the berry.

Tea.

An infusion of the dried and prepared leaves of the tea-plant is perhaps as common a
beverage as coffee, and, taking into consideration its immense consumption in China and
Japan, it is actually used by a greater number of persons. Its effects upon the system are
similar to- those of coffee, but are generally not so marked. Ordinary tea, taken in
moderate quantity, like coffee, relieves fatigue and increases mental activity, but does not
usually induce such persistent wakefulness.

It is unnecessary to describe all the varieties of tea in common use. There are, how-
ever, certain varieties, called green teas, which present important differences, as regards
composition and physiological effects, from the black teas, which are more commonly
used. The following is a comparative analysis of these two varieties by Mulder:

Composition of Tea.

CONSTITUENTS.

CHINESE.

JAVANESE.

Hyson.

Congou.

Hyson.

Congou.

Volatile oil

0-79

2-22
0-28
2-22
8'56
17-80
0-43
22-80

23-60
3-00
17-08

0-60
1-84

3-64
7-28
12-88
0-46
19-88
1-48
19-12
2-80
28-32
~98'30
5-24

0-98
3-24
0-32
1-64
12-20
17-56
0-60
21-68

20-36
3-64
18-20
100-42
4-76

0-65
1-28

2-44
11-08
14-80
0-65
18-64
1-64
18-24
1-28
27-00

Chlorophylle. .

Wax. . .....

Resin

Gum

Tannin

Theine

Extractive

Apotheme

Extract obtained by hydrochloric acid

Albumen

Fibrous matter

Salts included in the above

98-78
5-56

97-70
5-36

Both tea and coffee possess peculiar organic principles. The active principle of tea is
called theine, and the active principle of coffee, caffeine. As they are supposed to be
particularly active in producing the peculiar effects upon the nervous system which are
characteristic of both tea and coffee, there is good reason to suppose that they are nearly
identical in their physiological effects. Theine (or caffeine) exists in greater proportion
in tea than in coffee ; but, as a rule, much more soluble matter is employed in the prepara-
tion of coffee, which may account for its more marked effects upon the system.

190 ALIMENTATION.

Green tea, especially in those unaccustomed to its use, frequently produces nervous
tremor, wakefuiness, and disturbed sleep — when sleep can be obtained — palpitations, and
other disturbances usually termed nervous. In some persons these unpleasant effects may
be overcome by habit ; and many constantly use a mixture of equal parts of black and
green tea with no unpleasant effects. The peculiar effects of green tea are attributed to
the volatile oil, which it contains in great abundance.

Tea is prepared for drinking by rapidly making an infusion of the leaves with hot
water. The aroma is impaired by boiling. The proportion generally used is about
three hundred grains of tea to a quart of water. The tea is first covered with boiling
water and allowed to steep, or " draw," for from ten to fifteen minutes, in a warm
place; boiling water is then added in the quantity desired. Green tea, treated in this
way, yields about twenty per cent, of soluble matters, and black tea, about twenty-
three per cent.

Chocolate.

Chocolate is made from the seeds of the cocoa-tree, roasted, deprived of their husks,
and ground with warm rollers into a pasty mass with sugar, flavoring substances being
sometimes added. It is then made into cakes, cut into small pieces or scraped to a pow-
der, and boiled with milk or milk and water, when it forms a thick, gruel-like drink,
which is highly nutritive and has some of the exhilarating properties of coffee or tea.
Beside containing a large proportion of nitrogenized matter resembling albumen, the
cocoa-seed is particularly rich in fatty matter and contains a peculiar principle, theobro-
mine, analogous to caffeine and theine, which is supposed to possess similar physiological
properties.

The following is an analysis by Payen of the cocoa-seeds freed from the husks but
not roasted. Torrification has the effect of developing the peculiar aromatic principle,
and moderating the bitterness, which is always more or less marked :

Composition of Kernels of Cocoa.

Fatty matter (cocoa-butter) 48 to 50

Albumen, fibrin, and other nitrogenized matter 21 " 20

Theobromine 4 " 2

Starch (with traces of saccharine matter) 11 " 10

Cellulose 3 " 2

Coloring matter, aromatic essence . traces.

Mineral substances 3 to 4

Hygroscopic water 10 " 12

100 100

It is evident, from the above table, that cocoa with milk and sugar, the ordinary form
in which chocolate is taken, must form a very nutritious mixture. Taken with a little
bread, it readily relieves hunger and supplies nearly all the principles absolutely necessary
to nutrition. Its influence as a stimulant, supplying the place of matter which is directly
assimilated and retarding disassimilation, is dependent, if it exist at all, upon the theobro-
mine ; but its stimulating properties are slight as compared with those of coffee and tea.

A drink called cocoa is sometimes made of the seeds roasted entire and mixed with a
little starchy matter, but this is not so delicate in flavor as chocolate. A brown, mucilagi-
nous infusion is sometimes made of the husks (shells). This has a slight chocolate-flavor,
but it does not possess the nutrient properties of the kernels of cocoa.

Condiments and Flavoring Articles.

The refinements of modern cookery involve the use of numerous articles which can-
not be classed as alimentary principles. Pepper, capsicum, vinegar, mustard, spices, and

QUANTITY OF FOOD NECESSARY TO NUTRITION. 191

articles of this class, which are so commonly used, with the various compound sauces
have no decided influence on nutrition, except in so far as they promote the secretion of
the digestive fluids. Common salt, however, as we have already seen, is very important,
and this has been considered under the head of inorganic alimentary principles. The
various flavoring seeds and leaves, truffles, mushrooms, etc., have no physiological impor-
tance except as they render articles of food more palatable.

Quantity and Variety of Food necessary to Nutrition.

The inferior animals, especially those not subjected to the influence of man, regulate
by instinct the quantity and kind of food which they consume. The same is true of man
during the earliest periods of his existence ; but, later in life, the diet is variously modi-
fied by taste, habit, climate, and what may be termed artificial wants. It is usually a
safe rule to follow the appetite with regard to quantity, and the tastes, when they are
not manifestly vitiated or morbid, with regard to variety. The cravings of Nature indi-
cate when to change the form in which nutriment is taken ; and that a sufficient quan-
tity has been taken is manifested by a sense, not exactly of satiety, but of evident satis-
faction of the demands of the system. During the first periods of life, the supply must
be a little in excess of the actual loss, in order to furnish materials for growth ; during
the later periods, the quantity of nitrogenized matter assimilated is somewhat less than
the loss ; but, in adult age, the system is maintained at a tolerably definite standard by
the assimilation of material about equal in quantity to that which is discharged in the
form of excretions.

Although the loss of substance by disassimilation creates and regulates the demand for
food, it is an important fact, never to be lost sight of, that the supply of food has a very
great influence upon the quantity of the excretions. As an illustration of this, we may
take the influence of food upon the exhalation of carbonic acid ; and this is but an
example of what takes place with regard to other excretions. The quantity of the
excretions is even more strikingly modified by exercise, which, within physiological
limits, increases the vigor of the system, provided the increased quantity of food required
be supplied.

While a certain amount of waste of the system is inevitable, it is a conservative pro-
vision of Nature, that, when the supply of new material is diminished, life is preserved —
not, indeed, in all its vigor — by a corresponding reduction in the quantity of excre-
tions ; and, in the same way, the forces are retained after complete deprivation of food
much longer than if disassimilation proceeded always with the same activity.

As regards the quantity of food necessary to maintain the system in proper condition,
it is evident that this must be greatly modified by habit, climate, the condition of the
muscular system, age, sex, etc., as well as idiosyncrasies.

The daily loss of substance which must be supplied by material introduced from with-
out is very great. A large portion of this discharge takes place by the lungs, and a con-
sideration of the mode of introduction of gaseous principles to supply part of this waste be-
longs to the subject of respiration. The most abundant discharge which is compensated by
absorption from the alimentary canal is that of water, both in a liquid and vaporous con-
dition. The entire quantity of water daily removed from the system has been estimated
at about four and a half pounds, and it is probable that about the same quantity is intro-
duced in the form of drink and as a constituent of the so-called solid articles of food.
The quantity which is taken in the form of drink varies with the character of the food.
When the solid articles contain a large proportion of water, the quantity of drink may be
diminished ; and it is possible, by taking a large quantity of the watery vegetables, to
exist entirely without drink. There is no article more frequently taken than water
merely as a matter of habit, any excess being readily removed by the kidneys, skin, and
lungs. Prof. Dalton estimates the daily quantity necessary for a full-grown, healthy
male, at fifty-two fluid ounces, or 3'38 Ibs. avoirdupois.

192 ALIMENTATION.

The quantity of solid food necessary to the proper nourishment of the body is shown
by estimating the solid matter in the excretions ; and the facts thus ascertained corre-
spond very closely with the quantity of material which the system has been found to
actually demand. The estimates of Payen, the quantity of carbon and of nitrogenized
matter in a dry state being given, are generally quoted and adopted in works on physiol-
ogy. According to this observer, the following are the daily losses of the organism:

Carbon (or its equivalent). . . . j *«T "C-^ [ 4'794'M «"• <10'98 °z' »•)

Nitrogenized substances ...... (with 308*68 grs. of nit.) 2,006 '42 grs. ( 4'58 oz. av.)

6,800'96 grs. (15-51 oz. av.)

From this he estimates that the normal ration, supposing the food to consist of lean
meat and bread, is as follows :

Nitrogenized substances. Carbon.

Bread ............. 15,434 grs. (35'27 oz.) = 1,080*38 grs. and 4,630-2 grs.

Meat .............. 4,412-12 grs. (10'09 oz.) = 930-05 grs. and 485'55 grs.

19,846-12 grs. (45'36 oz.) 2,010'43 grs. 5,115'75 grs.

This daily ration, which is purely theoretical, is shown by actual observation to be
nearly correct. Prof. Dalton says: " From experiments performed while living on an
exclusive diet of bread, fresh meat, and butter, with coffee and water for drink, we have
found that the entire quantity of food required during twenty-four hours by a man in
full health and taking free exercise in the open air, is as follows :

Meat .......................................... 16 ounces, or TOO Ib. avoirdupois.

Bread ......................................... 19 " " 1-19 "

Butter or fat ................................... 3£ " " 0'22 " "

Water.. . .' ..................................... 52 fluid oz. " 3'38 "

That is to say, rather less than two and a half pounds of solid food, and rather over
three pints of liquid food."

Bearing in mind the great variations in the nutritive demands of the system in differ-
ent persons, it may be stated, in general terms, that, in an adult male, from ten to twelve
ounces of carbon and from four to five ounces of nitrogenized matter (estimated dry)
are discharged from the organism and must be replaced by the ingesta ; and this de-
mands a daily consumption of from two to three pounds of solid food, the quantity of
food depending, of course, greatly on its proportion of solid, nutritive principles.

It is undoubtedly true that the daily ration has frequently been diminished consider-
ably below the physiological standard in charitable institutions, prisons, etc. ; but, when
there is complete inactivity of body and mind, this produces no other effect than that of
slightly diminishing the weight and strength. The system then becomes reduced with-
out any actual disease, and there is simply a diminished capacity for labor. But in the
alimentation of large bodies of men subjected to exposure and frequently called upon
to perform severe labor, the question of food is of vital importance, and the men collec-
tively are like a powerful machine in which a certain quantity of material must be fur-
nished in order to produce the required amount of force. This important physiological
fact is most strikingly exemplified in armies ; and the history of the world presents few
examples of warlike operations in which the efficiency of the men has not been impaired
by insufficient food.

The influence of diet upon the capacity for labor was well illustrated by a compari-
son of the amount of work accomplished by English and French laborers in 1841, on
a railroad from Paris to Eouen. The French laborers engaged on this work were

NECESSITY OF A VARIED DIET. 193

able at first to perform only about two-thirds of the labor accomplished by the English.
It was suspected that this was due to the more substantial diet of the English, which
proved to be the fact ; for, when the French laborers were subjected to a similar regi-
men, they were able to accomplish an equal amount of work. In all observations of this
kind, and they are very numerous, it has been shown that an animal diet is much more
favorable to the development of the physical forces than one consisting mainly of vege-
tables.

Climate has an important influence on the quantity of food demanded by the system.
It is generally acknowledged that the consumption of all kinds of food is greater in cold
than in warm climates, and almost every one has experienced in his own person a con-
siderable difference in the appetite at different seasons of the year. Travelers' accounts
of the quantity of food taken by the natives of the frigid zone are almost incredible.
They speak of men consuming over a hundred pounds of meat in a day ; and a Russian
admiral, Saritcheff, mentions an instance of a man who, in his presence, ate at a single
meal a mess of boiled rice and butter weighing twenty-eight pounds. Although it is
difficult to regard these statements with entire confidence, the general opinion that the
appetite is greater in cold than in warm climates is undoubtedly well founded. Dr.
Hayes, the Arctic explorer, states, from his personal observation, that the daily ration
of the Esquimaux is from twelve to fifteen pounds of meat, about one-third of which is
fat. On one occasion he saw an Esquimau consume ten pounds of walrus-flesh and
blubber at a single meal, which lasted, however, several hours. The continued low
temperature he found had a remarkable effect on the tastes of his own party. With the
thermometer ranging from — 60° to — 70° Fahr., there was a continual craving for a
strong animal diet, particularly fatty substances. Some members of the party were in
the habit of drinking the contents of the oil-kettle with evident relish.

Necessity of a Varied Diet.

In considering the nutritive value of the various alimentary principles, the fact that
no single one of them is capable of supplying all the material for the regeneration of the
organism has frequently been mentioned. The normal appetite, which is our best guide
as regards the quantity and the selection of food, indicates that a varied diet is necessary
to proper nutrition. This fact is also exemplified in a marked degree in long voyages
and in the alimentation of armies, when, from necessity or otherwise, the necessary
variety of aliment is not presented. Analytical chemistry fails to show why this change
in alimentary principles is necessary, or in what the deficiency in a single kind of diet
consists; but it is nevertheless true that, after the organic constituents of the organism
have appropriated the nutritious elements of particular kinds of food for a certain time,
they lose the power of inducing the changes necessary to proper nutrition, and a supply
of other material is imperatively demanded. This fact is particularly well marked when
the diet consists in great part of salted meats, although it is also the case when any single
variety of fresh meat is constantly used. After long confinement to a diet restricted as
regards variety, a supply of other material, such as fresh vegetables, the organic acids,
and articles which are called generally anti-scorbutics, becomes indispensable ; otherwise,
the modifications in nutrition and in the constitution of the blood incident to the scor-
butic condition are almost sure to be developed.

It is thus apparent that adequate quantity and proper quality of food are not all
that are required in alimentation ; and those who have the responsibility of n-irnlating
the diet of a large number of persons must bear in mind the foot that the organism de-
mands considerable variety. Fresh vegetables, fruits, etc., should be taken at the proper
seasons. It is almost always found, when there is of necessity some sameness of diet,
that there is a general craving for particular articles, and these, if possible, should be
supplied. This was frequently exemplified in the late war. At times when the diet was
13

194 ALIMENTATION.

necessarily somewhat monotonous, there was an almost universal craving for onions and
raw potatoes, which were found by the surgeons to be excellent anti-scorbutics.

With those who supply their own food, the question of variety of diet generally
regulates itself; and in institutions, it is a good rule to follow as far as possible the
reasonable tastes of the inmates. In individuals, particularly females, it is not uncommon
to observe marked disorders in nutrition attributable to want of variety in the diet as
well as to an insufficient quantity of food, as a matter of education or habit.

The physiological effects of a diet restricted to a single alimentary principle or to a
few articles have been pretty closely studied both in the human subject and in the inferior
animals. Magendie demonstrated long ago that animals subjected to a diet composed
exclusively of non-nitrogenized articles die in a short time with all the symptoms of
inanition. The same result followed in dogs confined to white bread and water; but
these animals lived very well on the military brown bread, as this contains a greater
variety of alimentary principles. Facts of this nature were multiplied by the "gelatine
commission," and the experiments were extended to nitrogenized substances and articles
containing a considerable variety of alimentary principles. In these experiments, it was
shown that dogs could not live on a diet of pure musculine, the appetite entirely failing, at
from the forty-third to the fifty -fifth day. They were nourished perfectly well by gluten,
which, as we have seen, is composed of a number of different alimentary principles.
Among the conclusions arrived at by this commission, which bear particularly on the
questions under consideration, were the following:

" Gelatine, albumen, fibrin, taken separately, do not nourish animals except for a very
limited period and in a very incomplete manner. In general, these substances soon
excite an insurmountable disgust, to the point that animals prefer to die of hunger rather
than touch them.

" The same principles artificially combined and rendered agreeably sapid by season-
ing are accepted more readily and longer than if they were isolated, but ultimately they
have no better influence on nutrition, for animals that take them, even in considerable
quantity, finally die with all the signs of complete inanition.

u Muscular flesh, in which gelatine, albumen, and fibrin are united according to the
laws of organic nature, and when they are associated with other matters, such as fat,
salts, etc., suffices, even in very small quantity, for complete and prolonged nutri-
tion."

In Burdach's treatise on physiology, is an account of some interesting experiments by
Ernest Burdach on rabbits, showing the influence of a restricted diet upon nutrition.
Three young rabbits from the same litter were experimented upon. One was fed with
potato alone and died on the thirteenth day with all the appearances of inanition.
Another fed on barley alone died in the same way during the fourth week. The third
was fed alternately day by day with potato and barley, for three weeks, and afterward
with potato and barley given together. This one increased in size and was perfectly
well nourished.

In 1769, long before any of the above-mentioned experiments were performed, Dr.
Stark, a young English physiologist, fell a victim at an early age to ill-judged experiments
on his own person on the physiological effects of different kinds of food. He lived for
forty -four days on bread and water, for twenty-nine days on bread, sugar, and water, and
for twenty-four days on bread, water, and olive-oil; until finally his constitution became
broken, and he died from the effects of his experiments.

DIGESTION. 195

CHAPTEK VII.

DIGESTION, MASTICATION, INSALIVATION, AND DEGLUTITION.

General arrangement of the digestive apparatus— Prehension of solids and liquids— Mastication— Physiological anat-
omy of the teeth — Anatomy of the maxillary bones — Temporo-maxillary articulation — Muscles of mastication

Muscles which depress the lower jaw — Action of the muscles which elevate the lower jaw and move it laterally
and antero-posteriorly— Action of the tongue, lips, and cheeks in mastication— Summary of the process of masti-
cation— Parotid saliva — Submaxillary saliva — Sublingual saliva — Fluids from the smaller glands of the mouth,
tongue, and fauces — Mixed saliva — Quantity of saliva — General properties and composition of the saliva — Action
of the saliva on starch— Mechanical functions of the saliva— Deglutition— Physiological anatomy of the parts con-
cerned in deglutition — Muscles of the pharynx — Muscles of the soft palate — Mucous membrane of the pharynx —
(Esophagus— Mechanism of deglutition— First period of deglutition— Second period of deglutition— Protection of
the posterior nares during the second period of deglutition— Protection of the opening of the larynx— Function
of the epiglottis — Study of deglutition by autolaryngoscopy — Third period of deglutition— Intermittent contrac-
tion of the lower third of the oesophagus — Nature of the movements of deglutition — Deglutition of air.

THE inorganic alimentary principles are, with few exceptions, introduced in the form
in which they exist in the blood and require no preparation or change before they are
absorbed ; but the organic nitrogenized principles are always united with more or less
matter possessing no nutritive properties, from which they must be separated, and, even
when pure, they always undergo certain changes before they become part of the great
nutritive fluid. The non-nitrogenized principles also undergo changes in constitution or
in form preparatory to absorption. With the varied forms in which food is taken by
different animals, we find great differences in the arrangement of the digestive apparatus,
from the simple pouch with a single orifice, which constitutes the entire digestive system
of many of the infusorial animalcules, to the immense length of intestine, with its numer-
ous glandular appendages, found in the mammalia. In the higher classes of animals,
great differences exist in the anatomy of the digestive organs, particularly as regards the
length and capacity of the alimentary canal. In the carnivora, in which the food con-
tains comparatively little indigestible residue, the intestine is but three or four times the
length of the body (i. e. from the mouth to the anus), and the colon, which receives the
residue of digestion, is of small capacity ; while in the herbivora, in which the bulk of
food, compared with its nutritious principles, is enormous, there are frequently four dis-
tinct cavities to the stomach, and the intestine is ten, twelve, and in some (the sheep)
twenty-eight times the length of the body, with a colon of very large size. The food of
man is derived from both the animal and the vegetable kingdom, and, in relative length
and capacity, the alimentary canal is between that of the carnivora and the herbivora,
being from six to seven times the length of the body.

A full meal probably occupies from two to four hours in its digestion, this depending,
of course, upon the kind of food, the fineness of its comminution by mastication, etc. The
matters taken into the stomach consist generally of all varieties of alimentary principles,
and they are exposed to certain mechanical processes in the mouth and alimentary canal
and to the action of various secreted fluids.

In the mouth, the food is divided, as occasion demands, by the incisor teeth, and
is then passed, by the action of the cheeks and tongue, between the molars, whore it is
subjected to mastication. During this process, it is mixed with the various fluids which
compose the saliva and becomes more or less coated with the tenacious secretions of the
mucous follicles of the buccal cavity. It is, or should be, reduced in the mouth to a pul-
taceous mass, with which the saliva, particularly that from the parotid gland, is thoroughly
incorporated. The secretion of the submaxillary and the sublingual gland, being more
viscid, has a tendency to coat the exterior of the alimentary bolus.

By the action of the tongue, the alimentary bolus, after mastication, is passed back to

196

DIGESTION.

the pharynx, where, by the successive action of the constrictor muscles, it is forced
into the oesophagus. This tube leads from the pharynx to the stomach and is provided
with thick muscular walls, by the contraction of which the food is passed into this cavity,
which serves at once as a receptacle for the food and an important active organ in
digestion.

FIG. 47. — Stomach, liver, small intestine, etc. (Sappey.)

1, inferior surface of the liver ; 2, round ligament of the liver; 8, gall-bladder; 4, superior surface of the right
lobe of tlie liver ; 5, diaphragm; 6, lower portion of the oesophagus; 7, stomach; 8, gastro-hepatic omentum; 9,
spleen; 10, gastro-splenic omentum ; 11, duodenum ; 12,12,8mallintestine; IS, caecum; 14, appendix ve,r~
miformis ; 15, 15, transverse colon ; 16, sigmoid flexure of the colon; 17, urinary bladder.

The stomach is covered externally by the general peritoneal covering of the abdominal
organs. It is provided with a mucous membrane, which secretes the gastric juice and
absorbs the water with inorganic and other principles in solution. The stomach also has
muscular walls, composed of unstriped muscular fibres arranged in two principal layers.
Nearly all the principles contained in food are modified by the gastric juice, and some are
completely liquefied and absorbed in the stomach. By the action of the gastric juice, the
food, comminuted and incorporated with the fluids of the mouth, is farther reduced to a
pultaceous mass, which was formerly called the chyme, the muscular movements of the
stomach turning it over and over, so that it becomes thoroughly incorporated with the
fluids. These movements have a tendency to force the food, as it becomes sufficiently
liquefied, into the small intestine ; and a collection of circular muscular fibres, called
sometimes the pyloric muscle, stands at the pylorus as a guard, allowing the liquid por-
tions to pass gradually through, but sending back the larger masses to be farther acted
upon in the stomach. By these movements, a great portion of the food, prepared by the

PREHENSION OF SOLIDS AND LIQUIDS. 197

action of the stomach, is slowly forced into the small intestine. This tube, from fifteen
to twenty leet in length, is covered with peritoneum and loosely bound to the spinal
column by the mesentery, which is formed of the two folds of the peritoneum and is
sufficiently long to allow of free movements of the intestines over each other and in the
abdominal cavity, except the first few inches, where it is pretty firmly attached to the
posterior abdominal wall. The small intestine commences by a dilated portion eight or
ten inches in length, called the duodenum. The remainder is divided into the jejunum
and the ileum. The former embraces the upper two-fifths of the intestine, but there is
no distinct line of separation between it and the ileum. The mucous membrane lining
the small intestine is thick, provided with an immense number of villi, and, particularly
in the upper portion, is thrown into transverse folds, which are called the valvulaa con-
niventes. The valvular conniventes disappear in the lower part of the ileum. They are
peculiar to the human subject. Thickly set in the upper part of the duodenum and scat-
tered through its lower portion and the upper part of the jejunum, are small compound
follicles called the glands of Brunner ; and throughout the whole of the intestine are
simple follicles, called the follicles of Lieberkuhn. These glandular organs secrete the
intestinal juice. As the food passes from the stomach into the intestine, it imbibes
the bile and pancreatic juice, which are poured into the duodenum, as well as the intes-
tinal juice.

Between the mucous membrane of the small intestine and the peritoneum, are two
layers of unstriped muscular fibres, by the progressive peristaltic action of which the
food is passed slowly on toward the large intestine. The alimentary principles, liquefied
and prepared by digestion, are gradually absorbed by the blood-vessels of the intestinal
mucous membrane and by the lacteals.

The indigestible residue of the food is passed by peristaltic action into the large intes-
tine. This portion of the alimentary canal is from four to six feet in length ; and, like
the small intestine, it has a peritoneal, mucous, and muscular coat. Under ordinary con-
ditions the large intestine is not concerned in digestion. It simply retains the residue of
food, with certain excrementitious substances, until its contents are expelled by the act
of defsecation.

Prehension of Solids and Liquids.

The different modes of prehension form a very interesting part of the physiology of
digestion in the inferior animals ; but, in the human subject, the process is so simple and
well known that it demands nothing more than a passing mention. The mechanism of
sucking in the infant and of drinking is a little more complicated. In sucking, the lips
are closed around the nipple, the velum pendulum palati is applied to the back of the
tongue so as to close the buccal cavity posteriorly, and the tongue, acting as a piston,
produces a tendency to a vacuum in the mouth, by which the liquids are drawn in with
considerable force. This may be done independently of the act of respiration, which is
necessarily arrested only during deglutition ; for the mere act of suction has never any
thing to do with the condition of the thoracic walls. The mechanism of drinking from
a vessel is essentially the same. The vessel is inclined so that the lips are kept covered
with the liquid and are closed around the edge. By a gentle, sucking action the liquid is
then introduced. This is the ordinary mechanism of drinking; but sometimes the head
is thrown back and the liquid is poured into the mouth, as in "tossing off" the contents
of a small vessel as a wine-glass.

Mastication.

In the human subject, mechanical division of food in the mouth is neither so com-
pletely and laboriously effected as in the herbivora, particularly the ruminants, nor is the
process so rapid and imperfect as in the carnivora. In order that digestion may take
place in a perfectly natural manner, it is necessary that the food, as it is received into
the stomach, should be so far comminuted and incorporated with the fluids of the mouth

198

DIGESTION.

as to be readily acted upon by the gastric juice ; otherwise stomach-digestion is pro-
longed and difficult. Non-observance of this physiological law is a frequent cause of
what is generally called dyspepsia. In animals that do not masticate, as in some which
live exclusively on flesh, the process of stomach-digestion is much more prolonged than in
the human subject, even when the diet is the same ; and it is found that while man must,
as a rule, take food two or three times in the day, the carnivorous animals are generally
best nourished when food, in proper quantity, is taken but once in the twenty-four hours.
In the carnivora, the proportionate quantity of food is greater than in man, and diges-
tion is much more prolonged.

The comparative anatomy of the organs of mastication makes it evident that the
human race is designed to live on a mixed diet ; but experience has shown that man can
be nourished for an indefinite period on a diet composed exclusively of either animal
or vegetable principles.

Physiological Anatomy of the Organs of Mastication. — In the adult, each jaw is pro-
vided with sixteen teeth, all of which are about equally well developed. The canines,
so largely developed in the carnivora but which are rudimentary in the herbivora, and

FIG. 48. — Permanent teeth. (Le Bon.)
The external portions of the maxillary bones have been removed to show the roots of the teeth.

the incisors and molars, so perfectly developed in the herbivora, are, in man, of nearly
the same length. Each tooth presents for anatomical description a crown, a neck, and
a root, or fang. The crown is that portion which is entirely uncovered by the gums ;
the root is that portion embedded in the alveolar cavities of the maxillary bones; and

MASTICATION. 199

the neck is the portion, sometimes slightly constricted, situated between the crown and
the root, covered by the edge of the gum. Thin sections of the teeth show that they
are composed of several distinct structures.

Enamel of the Teeth. — The crown is covered by the enamel, which is by far the
hardest structure in the economy. This is white and glistening and is thickest on the
lower portion of the tooth, especially over the surfaces which, from being opposed to
each other on either jaw, are most exposed to wear. It here exists in several concentric
layers. The incrustation of enamel becomes gradually thinner toward the neck, where
it ceases. -Microscopical examination shows that the enamel is made up of pentagonal or
hexagonal rods, one end resting upon the subjacent structure, and the other, when there
exists but a single layer of enamel, terminating just beneath the cuticle of the teeth.
The hardness of the enamel varies in different persons. In some it is so soft that in mid-
dle life it becomes worn away from the opposing surfaces, and occasionally the teeth are
worn down almost to the gums ; while in others the enamel remains over the crown of
the tooth even in old age.

The exposed surfaces of the teeth are still farther protected by a membrane, from
sirornr ^° TTFOT °f an inch in thickness, closely adherent to the enamel, called the cuticle
of the enamel. This delicate membrane may be demonstrated in thin sections of young
teeth by the addition, under the microscope, of weak hydrochloric acid. The acid at-
tacks the enamel, producing little bubbles of gas which press out the membrane from
the edge of the preparation and thus render it apparent. The cuticle presents a strong
resistance to reagents and is undoubtedly very useful in protecting the teeth from the
action of acids which may find their way into the mouth.

Dentine. — The largest portion of the teeth is composed of a peculiar structure called
dentine, or ivory. In many respects, particularly in its composition, this resembles
bone ; but it is much harder, and does not possess the lacunae and canaliculi which are
characteristic of the true osseous structure. The dentine bounds and encloses the cen-
tral cavity of the tooth, extending in the crown to the enamel and in the root, to the
cement. It is formed of a homogeneous fundamental substance, which is penetrated
by an immense number of canals radiating from the pulp-cavity toward the exterior.
These are called the dentinal tubules or canals. They are from ?5^66 to A2^06 of an
inch in diameter, with walls of a thickness a little less than their caliber. Their course
is slightly wavy or spiral. Commencing at the pulp-cavity, into which these canals open
by innumerable little orifices, they are found to branch and occasionally anastomose,
their communications and branches becoming more numerous as they approach the ex-
ternal surface of the tooth. The canals of largest diameter are found next the pulp-cav-
ity, and they become smaller as they branch. The structure which forms the walls of
these tubules is somewhat denser than the intermediate portion, which is sometimes
called the inter-tubular substance of the dentine ; but, in some portions of the tooth, the
tubules are so numerous that their walls touch each other, and there is, therefore, no
inter-tubular substance. Near their origin and near the peripheral terminations of the
dentinal tubules, are sometimes found solid globular masses of dentine, called dentine-
globules, which irregularly bound triangular or stellate cavities of very variable size.
These cavities have been considered as lacunas, like the lacunae of true bone ; but this
view is not held by the best and most recent observers. Sometimes these cavities are
very numerous and form regular zones near the peripheral termination of the tubules.
The dentine is sometimes marked by concentric lines, indicating a lamellated arrange-
ment. In the natural condition, the dentinal tubules are filled with a clear liquid, which
penetrates from the vascular structures in the pulp-cavity.

Cement. — Covering the dentine of the root, is a thin layer of true bony structure,
called the cement, or crusta petrosa. This is thickest at the summit and the deeper por-
tions of the root, where it is sometimes lamellated, and it becomes thinner near the neck.
It finally becomes continuous with the enamel of the crown, so that the dentine is every-

200

DIGESTION.

where completely covered. The cement contains true bone-lacunfe and canaliculi, and, in
very old teeth, a few Haversian canals, except near the neck, where the layer is very thin.
It is closely adherent to the dentine and to the periosteum lining the alveolar cavities.

Pulp- Cavity. — In the interior of each tooth, extending from the apex of the root or
roots into the crown, is the pulp-cavity, which contains a collection of minute blood-
vessels and nervous filaments, held together by longitudinal fibres of white fibrous tis-
sue. This is the only portion of the tooth endowed with sensibility. Its blood-vessels
and nerves penetrate by a little orifice at the extremity of the root.

The dentine and enamel of the teeth must be regarded as perfected structures ; for,
when the second or permanent teeth are lost, they are never reproduced, and when these
parts are invaded by wear or by decay, they are incapable of regeneration. The integrity

of the pulp, even, is not necessary to the
stability of the teeth ; for examples are
numerous in which the pulp loses its
vitality from various causes, and yet the
tooth remains and is as serviceable as
ever, being only discolored by the decom-
position of the structures in the pulp-
cavity, which can neither escape nor
become absorbed.

The descriptive anatomy of the teeth
in the human subject shows how well
calculated they are to perform their va-
ried functions, and how admirably they
are adapted to a diet composed of articles
derived from both the animal and the
vegetable kingdom. The thirty-two per-
manent teeth are divided as follows :

1. Eight incisors, four in each jaw,
called the central and lateral incisors.

2. Four canines, or cuspidati, two in
each jaw, just back of the incisors. The
upper canines are sometimes called the
eye-teeth, and the lower canines, the
stomach-teeth.

3. Eight bicuspid — the small, or false
molars— just back of the canines ; four
in each jaw.

4. Twelve molars, or multicuspid,
situated just back of the bicuspid ; six
in each jaw.

The incisors are wedge-shaped, flat-
tened antero-posteriorly, and bevelled
at the expense of the posterior face, giv-
ing them a sharp, cutting edge, which is
sometimes perfectly straight but is gen-
erally more or less rounded. The upper
incisors are generally larger and strong-
er than the lower. In the upper jaw the central incisors are larger than the lateral ;
while in the lower jaw the lateral incisors are larger than the central. Each of the incisors
has but a single root. The special function of the incisor teeth is to divide the food -as it
is taken into the mouth. The permanent incisors make their appearance from the sev-
enth to the eighth year.

FIG. 49.— Tooth of the cat, in situ. fWaldeyer.)
1, enamel; 2, dentine; 3, cement; 4, periosteum of the alveo-
lar cavity ; 5, lower jaw ; 6, pulp-cavity.

MASTICATION.

201

The canines are more conical and pointed than the incisors and have longer and
larger roots, especially those in the upper jaw. Their roots are single. They are used
to some extent, in connection with the incisors, in dividing the food ; but they have no
prominent function in tearing the food, as in the carnivora, in which they are extraor-
dinarily developed. The permanent canines make their appearance from the eleventh
to the twelfth year.

The bicuspid teeth are shorter and thicker than the canines. Their opposed surfaces
are rather broad and are marked by two eminences. The upper bicuspids are somewhat
larger than the lower. The roots are single, but in the upper jaw they are slightly bifur-
cated at their extremities. They are used, with the true molars, in triturating the food.
The permanent bicuspids make their appearance from the ninth to the tenth year.

The molar teeth, called respectively — counting from before backward — the first, sec-
ond, and third molars, are the largest of all and are, par excellence, the teeth used in
mastication. Their form is that of a cube, rounded laterally and provided with four or
five eminences on their opposed surfaces. The first molars are the largest. They have
generally three roots in the upper jaw and two in the lower, although they sometimes
have four or even five roots. The second molars are but little smaller than the first
and resemble them in nearly every particular. The third molars, called frequently the
wisdom-teeth, are much smaller than the others and are by no means so useful in masti-
cation. In the upper jaw the root is grooved or imperfectly divided into three branches;
but in the lower jaw it generally has two distinct branches. The first molars are the
first of the permanent teeth, making their appearance between the sixth and the seventh
year. The second molars appear from the twelfth to the thirteenth year ; and the third
molars, from the seventeenth to the twenty-first year, and sometimes even much later.
In some instances the third molars are never developed.

The upper jaw has ordinarily a somewhat longer and broader arch than the lower ;
so that when the mouth is closed the teeth are not brought into exact apposition, but the
upper teeth overlap the lower teeth both in front and laterally. The lower teeth are all
somewhat smaller than the corresponding teeth
in the upper jaw and generally make their ap-
pearance a little earlier.

The physiological anatomy of the maxillary
bones and of the temporo-maxillary articulation
necessarily precedes the study of the muscles of
mastication and the mechanism of their action.

The superior maxillary bones are immovably
articulated with the other bones of the head and
do not usually take any active part in mastica-
tion ; but their inferior borders, with the upper
teeth embedded in the alveolar cavities, present
fixed surfaces against which the food is pressed
by the action of the muscles which move the lower
jaw.

The inferior maxilla is a single bone. Its
body is horizontal, of a horseshoe shape, and, in
the alveolar cavities in its superior border, are
embedded the lower teeth. Below the teeth,
both externally and internally, are surfaces for the attachments of the muscles concerned
in the various movements of the jaw, and for one of the muscles of the tongue.

Behind the body of the inferior maxilla, on either side, is a vertical portion called the
minus. In the adult, this forms nearly a right angle with the body, making what is called
the angle of the jaw. Superiorly, the ramus terminates in two processes, separated by a
deep groove called the sigmoid notch. The posterior process is the condyle, or condyloid

Fio. 50. — Inferior maxilla. (Sappey.)
1, body; 2, ramus; 8, symphysis; 4, incisive
fossa; 5, mental foramen; 6, attachment of
the digastric muscle , 7, depression at the
site of the facial artery ; 8, ansr'.e;. 9, attach-
ment of the superior constrictor of the
pharynx; 10, coronoid process; 11, condyle;
12, siprmoid notch ; 18, opening of the inferior
dental ranal ; 14, groove for the rnylo-hyoid
muscle; 15, alveolar border; i, incisor teeth:
c, canine teeth ; b, bicuspid teeth ; m, molars.

202 DIGESTION.

process, the anatomy of which will be considered farther on in treating of the temporo-
maxillary articulation. The anterior process, called the coronoid process, is for the at-
tachment of the temporal muscle, one of the most powerful of the muscles of mastication.
The greater portion of the external surface of the ramus, extending down to the angle, is
for the attachment of the masseter muscle. The internal surface of the ramus gives at-
tachment to several muscles ; viz., the external pterygoid, attached to the neck just be-
low the condyle, the temporal, the attachment to the coronoid process being much
more extensive on the internal than on the external surface, and the internal pterygoid,
which has its attachment at the angle.

Temporo- Maxillary Articulation. — The various classes of mammalia present great
differences in the temporo-maxillary articulation, differences which indicate, to a great
extent, their natural diet. In the carnivora, the long diameter of the condyle is trans-
verse, and it is so firmly embedded in the deep glenoid cavity of the temporal bone as
to admit of extended movements in but one direction. In these animals, lateral -and
antero-posterior sliding movements of the jaw are impossible, and there is very little
mastication of the food. In the rodentia, the long diameter of the condyle is antero-
posterior, the peculiar gnawing movements in these animals requiring a considerable
sliding movement of the lower jaw in this direction. In the herbivora, particularly the
ruminants, the condyle is small and slightly concave instead of convex as in most other
animals. It moves on a large projecting surface on the temporal bone, and the entire
jaw is capable of remarkably extensive lateral movements.

In man, the articulation of the lower jaw with the temporal bone is such as to allow,
to a considerable extent, of an antero-posterior sliding movement and a lateral move-
ment, in addition to the ordinary movements of elevation and depression. The condy-
loid process is convex, with an ovoid surface, the general direction of its long diameter
being transverse and slightly oblique from without inward and from before backward.
This process is received into a cavity of corresponding shape in the temporal bone, called
the glenoid fossa, which is bounded, anteriorly, by a rounded eminence (erninentia articu-
laris), the uses of which will be more fully described in connection with the movements
of the jaw.

Between the condyle of the lower jaw and the glenoid fossa, is an oblong, inter-ar-
ticular disk of fibro-cartilage. This disk is thicker at the edges than in the centre. It is
pliable and so situated that when the lower jaw is projected forward, making the lower
teeth project beyond the upper, it is applied to the convex surface of the eminentia ar-
ticularis and presents a concave surface for articulation with the condyle. One of the
uses of this cartilage is to constantly present a proper articulating surface upon the artic-
ular eminence and thus admit of the antero-posterior sliding movement of the lower jaw.
It is also important in the lateral movements of the jaw, in which one of the condyles
remains in the glenoid cavity and the other is projected, so that the bone undergoes a
slight rotation.

Muscles of Mastication. — To the lower jaw are attached certain muscles, by which it is
depressed, and others by which it is elevated, projected forward and drawn backward,
and moved from side to side. The following are the principal muscles concerned in the
production of these varied movements :

Muscles of Mastication.

Muscles which depress the lower jaw.
Mutcle. Attachments.

Digastric Mastoid process of the temporal bone — Lower

border of the inferior maxilla near the sym-
physis, with its central tendon held to the side
of the body of the hyoid bone.

MASTICATION. 203

Muscle. Attachments.

Mylo-hyoid Body of the hyoid bone — Mylo-hyoid ridge on the

internal surface of the inferior maxilla.

Genio-hyoid Body of the hyoid bone — Inferior genial tubercle

on the inner surface of the inferior maxilla near
the symphysis.

Platysma myoides Clavicle, acromion, and fascia — Anterior half of

the body of the inferior maxilla near the in-
ferior border.

Muscles ichich elevate the lower jaw and move it laterally and antero-posteriorly.

Temporal Temporal fossa — Coronoid process of the inferior

maxilla.

Masseter Malar process of the superior maxilla, lower border

and internal surface of the zygomatic arch —
Surface of the ramus of the inferior maxilla.

Internal pterygoid .Pterygoid fossa — Inner side of the ramus and angle

of the inferior maxilla.

External pterygoid Pterygoid ridge of the sphenoid, the surface be-
tween it and the pterygoid process, external
pterygoid plate, and the tuberosity of the palate
and the superior maxillary bone — Inner surface
of the neck of the condyle of the inferior
maxilla and the inter-articular fibro-cartilage.

Action of the Muscles which depress the Lower Jaw. — The most important of these
muscles have for their fixed point of action the hyoid bone, which, under these circum-
stances, is fixed by the muscles which extend from it to the upper part of the chest.
The central tendon of the digastric, as it perforates the stylo-hyoid, is connected with the
hyoid bone by a loop of fibrous tissue ; and, acting from this bone as the fixed point, the
anterior belly must of necessity tend to depress the jaw. The attachments of the mylo-
hyoid and the genio-hyoid render their action in depressing the jaw sufficiently evident,
which is also the case with the platysma myoides, acting from its attachments to the
upper part of the thorax.

It has been a disputed question whether the upper jaw does or does not participate
in the act of opening the mouth. That depression of the lower jaw is the main action
in ordinary mastication is sufficiently evident ; but it is possible, by fixing the lower jaw,
to perform the acts of mastication — laboriously and imperfectly it is true — by movements
of the upper jaw. In ordinary mastication, however, the upper jaw undergoes a slight
movement of elevation in opening the mouth ; and this becomes somewhat exaggerated
when the mouth is opened to the fullest possible extent.

Action of the Muscles which elevate the Lower Jaw and move it laterally and antero-
posteriorly. — The temporal, masseter, and internal pterygoid muscles are chiefly con-
cerned in the simple act of closing the jaws. As this is almost the only movement of
mastication in many of the carnivora, in this class of animals these muscles are most
largely developed. Their anatomy alone gives a sufficiently clear idea of their mode of
action ; and their immense power, even in the human subject, is explained by the number
of their fibres, by the attachments of many of these fibres to the strong aponeuroses by
which they are covered, and the fact that the distance from their origin to their insertion
is very short.

The attachments of the internal and external pterygoids are such that, by their alter-
nate action on either side, the jaw may be moved laterally, as their points of origin are
situated in front of and internal to the temporo-maxillary articulation. The articulation
of the lower jaw is of such a nature that, in its lateral movements, the condyles themselves

204 DIGESTION.

cannot be sufficiently displaced from side to side, but, with the condyle on one side fixed
or moved slightly backward, the other may be brought forward against the articular
eminence, producing a movement of rotation. The pterygoid muscles are largely de-
veloped in the herbivora, in which the lateral movements of mastication are so important.
The above explanation of the lateral movements of the jaw presupposes the possi-
bility of movements in an antero-posterior direction. Movements in a forward direction,
so as to make the lower teeth project beyond the upper, are effected by the pterygoids,
the oblique fibres of the masseter, and the anterior fibres of the temporal. By the
combined action of the posterior fibres of the temporal, the digastric, mylo-hyoid, and
genio-hyoid, the jaw is brought back to its position. By the same action it may also be
drawn back slightly from its normal position while at rest.

Action of the Tongue, Lips, and Cheeks, in Mastication. — Experiments on living
animals and phenomena observed in cases of lesions of the nervous system in the human
subject have fully demonstrated the importance of the tongue and cheeks in mastication.
The following observations of Panizza on the effects of section of both hypoglossal
nerves in dogs show the importance of the tongue, both in mastication and deglutition :
"After the section of the hypoglossal the movements of the tongue cease immediately,
but the general sensibility of that organ and the taste was not less marked. Indeed, if
milk, or bread moistened in the liquid, were presented to the dog, he made ineffectual
efforts to lap and to masticate, moving the head and the lower jaw ; the tongue, when
displaced, remaining in the same position, and even when a bolus of meat or bread was
put on its anterior surface, it was found for a long time after in the same place, which
proves that section of the hypoglossals destroys not only the movements necessary to
mastication, but also those of deglutition." We have lately had occasion to verify most
of these observations in a dog in which both sublingual nerves were divided. The experi-
ment, however, was made chiefly with reference to the action of the tongue in deglutition.

Section of the facial nerves is now a common physiological experiment. Opera-
tions of this kind and cases of facial palsy, which are not uncommon in the human
subject, show that when the cheek is paralyzed the food accumulates between it and the
teeth, producing great inconvenience. In animals, like the herbivora, which use the lips
and tongue extensively in the prehension of food, division of the facial and hypoglossal
nerves interferes materially with this function.

The tongue is a muscular organ which, by virtue of the complex arrangement of its
fibres, is capable of a great variety of important movements. By the action of what are
called the extrinsic muscles of the tongue, the organ is moved in various directions, while
the intrinsic muscles are capable at the same time of producing many changes in its form.
For example, by the action of those fibres of the genio-hyo-glossal muscles which aro
attached to the chin and the posterior part of the tongue, the whole organ is carried for-
ward and may be protruded to a considerable extent. At the same time the whole length
of the muscles may act upon the middle line of the tongue, to which they are attached,
and depress the centre so as to render it concave from side to side ; or the transverse
fibres of the tongue may act so as to make it longer and narrower. The tongue is drawn
into the mouth by the action of the anterior fibres of the genio-hyo-glossus on either side,
and may be still farther shortened by the contraction of the stylo-glossus and the interior
fibres of the hyo-glossus. The general action of the hyo-glossus, on either side, is to
draw down the sides of the tongue and make it convex from side to side. The stylo-
glossus and the palato-glossus draw the back of the tongue upward and backward toward
the pharnyx, and they are thus useful in the first processes of deglutition. By the com-
bined and varied actions of these and other muscles, the tongue is made to perform the
numerous movements which take place in connection with phonation, suction, mastica-
tion, deglutition, etc.

The varied and complicated movements of the tongue during mastication are not

SALIVA.

205

easily described. After solid food is taken into the mouth, the tongue prevents its escape
from between the teeth, and, by its constant movements, rolls the alimentary bolus over
and over and passes it at times from one side to the other, so that the food may undergo
thorough trituration. Aside from the functions of the tongue as an organ of taste, its sur-
face is endowed with peculiar sensibility as regards the consistence, size, and form of dif-
ferent articles ; and this property is undoubtedly important in determining when mastica-
tion is completed, although the thoroughness with which mastication is accomplished is
very much influenced by habit.

Tonic contraction of the orbicularis oris is necessary to keep the fluids within the mouth
during repose ; and this muscle is sometimes brought into action when the mouth is very
full, to assist in keeping the food between the teeth. This latter function, however, is
mainly performed by the buccinator; the action of which is to press the food between
the teeth and keep it in place during mastication, assisting, from time to time, in turning
the alimentary bolus so as to subject new portions to trituration.

The process of mastication is regulated to a very great extent by the exquisite sensi-
bility of the teeth to the impressions of hard and soft substances. It is only necessary
to call attention to the ease and certainty with which we recognize the presence and the
consistence of the smallest substance between the teeth, in order to appreciate the
advantages of this tactile sense in mastication. It is in this way, mainly, that we be-
come aware that the process of mastication is completed ; and it is this sense which ad-
monishes us instantly of the presence of bodies too hard for mastication, which, if allowed
to remain in the mouth, might seriously injure the teeth.

One of the most important of the digestive processes which take place in the mouth
is the incorporation of the saliva with the food, or insalivation. Not only has the saliva
a mechanical function, assisting to reduce the food to the proper form and consistence to
be easily swallowed, but it seems to be
necessary to the proper performance of
the subsequent processes of digestion
and is concerned to a certain extent in
the transformation of starch into sugar.
That the saliva is necessary to digestion
is proven by the grave effects upon the
general function of nutrition which fol-
low its loss in any considerable quan-
tity. This occasionally occurs from the
habit of excessive spitting or as the re-
sult of salivary fistula. It becomes im-
portant, therefore, to study the physical
and chemical properties of the saliva,
the sources from which it is derived,
and its mechanical and chemical func-
tions in digestion.

Saliva.

The fluid which is mixed with the
food in mastication, which moistens the
mucous membrane of the mouth, and
which may be collected at any time in
small quantity by the simple act of spu-
tation, is composed of the secretions of
a considerable number and variety of
glands. The most important of these
which are usually called the salivary

FIG. 51.— Salivary glands. (Le Bon.)
1, 2, parotid; 8, duct of Steno; 4, fnibmaarill(ir>/ ; 5.

gual; 6, mylo-hyoid muscle; 7, lingual branch of the fifth
nerve; 8, duct of Wharton; 9, digastric muede; 10?
Bterno-mastoid muscle; 11, external jnpular vein; 1'2. facial
vein; 13. temporal vein; 14, 15. internal juiriilar vein; 16,
branch of the cervical plexus ; 17, sublingual nerve.

are the parotid, submaxillary, and sublingual,
In addition, we have the labial and buccal

206 DIGESTION".

glands, the follicular glands of the tongue and general mucous surface, and certain
glandular structures in the mucous membrane of the pharynx. The liquid which be-
comes more or less incorporated with the food before it descends to the stomach, and
which must be considered as the digestive fluid of the mouth, is known as the mixed
saliva; but the study of the composition and properties of this fluid as a whole should be
prefaced by a consideration of the diiferent secretions of which it is composed.

The salivary glands belong to the variety of glands called racemose. They closely
resemble the other glands belonging to this class, and their structure will be considered
more particularly under the head of secretion.

Parotid Saliva. — The parotid is the largest of the three salivary glands. It is sit-
uated below and in front of the ear and opens by the duct of Steno into the mouth, at
about the middle of the cheek. The papilla which marks the orifice of the duct is
situated opposite the second large molar tooth of the upper jaw.

Numerous opportunities have presented themselves, in cases of salivary fistula, for the
study of the properties of the pure parotid saliva in the human subject ; and the situation
of the duct of Steno, in the herbivora especially, is such that this fluid can easily be ob-
tained by operations on the inferior animals. Prof. J. 0. Dalton has obtained the pure
parotid saliva from the human subject by simply introducing a silver tube, of from -fa
to -fa of an inch in diameter, into the duct by its opening into the mouth.

The following facts with regard to the properties of the parotid saliva observed by
Dalton are given in his own words, in a communication kindly made in answer to certain
inquiries :

" On the 28tb of July, 1863, I obtained, from a strong, healthy man, about two
drachms of the mixed saliva of the mouth, by causing him to hold in his mouth for a
short time a clean glass stopper, and collecting the secretion as it was discharged.

" One hour afterward I obtained, from the same man, four drachms of pure parotid
saliva, by introducing a long silver canula into the natural orifice of Steno's duct, on the
left side, and collecting the saliva as it flowed from the outer extremity of the canula.

"The two kinds of saliva compared as follows:

" Both were distinctly alkaline in reaction ; the parotid saliva rather the more so.

" The parotid saliva was rather clear and watery in appearance ; the saliva of the mouth
was quite opaline, with admixture of buccal epithelium, but became clear on filtration.

"The parotid saliva was rendered turbid by the action of heat, and by the addition of
nitric acid, as well as sulphate of soda in excess ; but not by sulphate of magnesia, nor by
ferro-cyanide of potassium with acetic acid.

" The saliva of the mouth, filtered clear, became turbid by heat and by nitric acid,
but showed no precipitate by either sulphate of soda or sulphate of magnesia in excess.
There was also a slight precipitate on the addition of pure acetic acid, which did not take
place in the parotid saliva,

" The parotid saliva showed no traces of sulpho-cyanogen on the addition of the per-
chloride of iron, but they were distinctly marked in the buccal saliva.

" On mixing the two kinds of saliva with boiled starch, and keeping the mixture at
the temperature of 100° Fahr., sugar was present in both specimens at the end of five
minutes. There was no marked difference between them in this respect.

" While making some similar experiments to the above on a previous patient, in April,
1863, I found that with the canula introduced into Steno's duct, not only was the dis-
charge of parotid saliva increased by the mastication of food, but that it ran from the
canula very much faster than in a state of rest, whenever the patient smiled, spoke, or
moved his lips or cheeks in any way."

The organic matter of the parotid saliva is coagulable by heat (212° Fahr.), alcohol,"
and the strong mineral acids. Dalton found, in the human saliva, that it was also coagu-
lated by an excess of sulphate of soda ; but Bernard states that, in the parotid saliva of

SALIVA. 207

the horse, the organic matter passed through a mixture of sulphate of soda but was
coagulated by sulphate of magnesia. Almost all physiologists agree that this organic
matter is not identical in its properties with albumen or with the peculiar principle
described by Miahle in the mixed saliva, under the name of animal diastase.

A compound of sulpho-cyanogen is now generally acknowledged to be a constant
constituent of the parotid saliva. This cannot be recognized by the ordinary tests in the
fresh saliva taken from the duct of Steno, but in the clear, filtered fluid which passes
after the precipitation of the organic matter, there is always a distinct red color on the
addition of the persulphate of iron. As this reaction is more marked in the mixed saliva,
the methods by which the presence of a sulpho-cyanide is to be demonstrated will be
considered in connection with that fluid.

In the human subject, the parotid secretion is more abundant than that of any other
of the salivary glands. The entire quantity in the twenty-four hours has not been
directly estimated ; but Prof. Dalton found that, during mastication, the quantity secreted
in twenty minutes on one side was 127*5 grains, and on the other side, 374-4 grains.

A curious fact with regard to the influence of mastication upon the flow from the
parotids was observed by Colin in the horse, ass, and ox. He found that, when mastica-
tion was performed on one side of the mouth, the flow from the gland on that side was
greatly increased, exceeding by several times the quantity produced upon the opposite
side. This fact was confirmed by Dalton, as already indicated, in the human subject.

The flow of saliva from the parotid takes place with greatly-increased activity during
the process of mastication. The orifice of the parotid duct is so situated that the fluid is
poured directly upon the mass of food as it is undergoing trituration by the teeth ; and,
as the secretion is more abundant on the side on which mastication is going on, and the
consistence of the fluid is such as to enable it to mix readily with the food, the function
of this gland is supposed to be particularly connected with mastication. This is undoubt-
edly the fact; although its flow is not absolutely confined to the period of mastication,
but continues, in small quantity, during the intervals. Its quantity is regulated some-
what by the character of the food, being much greater when the articles taken into the
mouth are dry than when they contain considerable moisture. There is a great difference
in different animals as regards the stimulation of the salivary glands by substances intro-
duced into the mouth. In the human subject, the stimulus produced by sapid sub-
stances will sometimes induce a great increase in the flow of the parotid saliva. Mits-
cherlich and Eberle observed this in persons suffering from salivary fistula and noted,
farthermore, that the mere sight or odor of food produced the same effect.

The supposition, which has been entertained by some authors, that the flow from the
parotid is dependent upon the mechanical pressure of the muscles or of the condyle of
the lower jaw during mastication has no foundation in fact. It is now well established
that one of the indispensable conditions in the production of a secretion is a great increase
in the quantity of blood circulating in the gland,, and that the vascular supply is regulated
through the nervous system. The fact that an alternation in the parotid secretion accom-
panies an alternation in the act of mastication is also an argument against this mechanical
theory ; for it is not to be supposed that during mastication there exists a difference in
the pressure of the muscles or of the condyles on the two sides, corresponding with the
differences which have been noted in the secretion from the glands on either side. In
the horse and in the dog, it has been observed that the secretion of the parotids is com-
pletely arrested during the deglutition of liquids, while the flow from the other salivary
glands is not affected.

To sum up the functions of the parotid saliva — aside from any chemical action which
it may have upon the food, which will be fully considered in connection with the mixed
saliva — it evidently has an important mechanical office. It is discharged in large quan-
tity during the entire process of mastication and is poured into the mouth in such a
manner as to become of necessity thoroughly incorporated with the food. Its function

208 DIGESTION.

is chiefly, although not exclusively, connected with mastication and indirectly, with deglu-
tition ; for it is only by becoming incorporated with this saliva, that the deglutition of
dry, pulverulent substances is rendered possible. Facts in comparative physiology, show-
ing a great development of the parotids in animals that masticate very thoroughly, par-
ticularly the ruminants, a slight development in those that masticate but slightly, and the
absence of these glands in animals that do not masticate at all, are additional arguments
in favor of these views.

Submaxillary Saliva. — In the human subject, the submaxillary is the second of the
salivary glands in point of size. Its minute structure is the same as that of the parotid.
As its name implies, it is situated below the inferior maxillary bone. It is in the anterior
part of what is known as the submaxillary triangle of the neck. Its excretory duct, called
sometimes the duct of Wharton, is about two inches in length and passes from the
gland, beneath the tongue, to open by a small papilla by the side of the frenum. This
gland is relatively very small in the herbivora but is largely developed in the carnivora,
in the latter being larger than the parotid.

The pure submaxillary saliva presents many important points of difference from the
secretion of the parotid. It was first studied as a distinct fluid by Bernard. It may be
obtained by exposing the duct and introducing a fine silver tube, when, on the introduc-
tion of any sapid substance into the mouth, the secretion will flow in large, pearly drops.
Bernard found this variety of saliva much more viscid than the parotid secretion. It is
perfectly clear, and, on cooling, frequently becomes of a gelatinous consistence. Its
organic matter is not coagulable by heat. In the dog, it is rather more strongly alkaline
than the parotid saliva. According to Bernard, it does not contain the sulpho-cyanide
of potassium.

The submaxillary gland pours out its secretion in greatest abundance when sapid sub-
stances are introduced into the mouth. In the solipeds and ruminants, Colin has ob-
served that the quantity of submaxillary saliva secreted is much increased during eating;
but, unlike the parotids, the secretion does not alternate on the two sides with the alter-
nation in mastication. He has found, in all the domestic animals, that the flow is greatly
influenced by the degree of sapidity of the food. Although sapid articles induce an
abundant secretion from the submaxillary glands, they also produce an increase in the
secretions from the parotids and sublinguals; and, on the other hand, movements of
mastication increase somewhat the flow from the submaxillaries, and these glands secrete
a certain amount of fluid during the intervals of digestion. The viscid consistence of the
submaxillary saliva renders it less capable of penetrating the alimentary mass during
mastication than the parotid secretion, so that it remains chiefly near the surface of the
alimentary mass.

Sublingual Saliva. — The sublinguals, the smallest of the salivary glands, are situated
beneath the tongue, on either side of the frenum. In minute structure they resemble the
parotid and the submaxillary glands. Each gland has a number of excretory ducts, from
eight to twenty, which open into the mouth by the side of the frenum; and one of the
ducts, larger than the others, joins the duct of the submaxillary gland near its termina-
tion in the mouth.

The secretion of the sublingual glands is more viscid even than the submaxillary sali-
va, but it differs in the fact that it does not gelatinize on cooling. It is so glutinous that
it adheres strongly to any vessel and flows with difficulty from a tube introduced into
the duct. Like the secretion from the other salivary glands, its reaction is distinctly al-
kaline. Its organic matter is not coagulable by heat, acids, or the metallic salts. Ac-
cording to Bernard, after desiccation it is redissolved by water and its viscid properties
are then restored.

In accordance with the view entertained by Bernard concerning the function of this

SALIVA. 209

variety of saliva and its special connection with deglutition, it is supposed to be secreted
immediately before and during the act of swallowing. The experiments which are ad-
vanced in support of this view are mostly those in which a tube was fixed in each of the
three salivary ducts in a dog, when the animal was caused to make movements of the
jaw, movements of deglutition, and at the same time the gustatory nerves were stimu-
lated by the introduction of vinegar into the mouth. In am experiment of this kind, it
was observed that fluid was secreted by all the glands, but in unequal proportions; "the
submaxillary saliva flowed very abundantly, the parotid saliva much less, and the sublin-
gual saliva flowed very feebly." Although the animal made movements of mastication,
experienced a gustatory impression, and made movements of deglutition, it is by no means
evident from this observation, or from others reported by Bernard, that the flow of the
sublingual saliva had any special connection with the act of deglutition. The observa-
tions of Colin on this subject show that, in the domestic ruminants, there is a constant
flow of the sublingual saliva during the time occupied in eating.

It has been experimentally demonstrated that the sublingual glands may be excited
to secretion by impressions made by sapid substances upon the nerves of taste, although
the flow is always less than from the submaxillary glands. The great viscidity of the
sublingual saliva renders it less easily mixed with the alimentary bolus than the secre-
tions from the parotid or the submaxillary glands.

Fluids from the Smaller Glands of the Mouth, Tongue, and Pharynx. — Beneath the
mucous membrane of the inner surface of the lips, are small, rounded, glandular bodies,
opening by numerous ducts into the buccal cavity, called the labial glands ; and, in the
submucous tissue of the cheeks, are similar bodies, called the buccal glands. The latter
are somewhat smaller than the labial glands. Two or three of the buccal glands are of
considerable size and have ducts opening opposite the last molar tooth. These are
sometimes distinguished as the molar glands. There are also a few small glands in the
mucous membrane of the posterior half of the hard palate ; but the glands on the under
surface of the soft palate are larger and more numerous and here form a continuous
layer. The glands of the tongue (lingual glands) are situated beneath the mucous mem-
brane, mainly on the posterior third of the dorsum ; but a few are found at the edges
and the tip. All of these are small, racemose glands, similar in structure to those which
have been called the true salivary glands. In addition to these structures, the mucous
membrane of the tongue is provided with a number of simple and compound follicular
glands, which extend over its entire surface but are most abundant at the posterior por-
tion, behind the circumvallate papillae.

In the pharynx and the posterior portion of the buccal cavity, are found the pharyn-
geal glands and the tonsils. In the pharynx, particularly the upper portion, racemose
glands, like those found in the mouth, exist in large numbers. The mucous membrane is
provided, also, with numerous simple and compound mucous follicles. The tonsils, situ-
ated on either side of the fauces between the pillars of the soft palate, consist of an ag-
gregation of compound follicular glands, held together by fibrous tissue. The number of
glands entering into the composition of each tonsil is from ten to twenty.

The secretion from the glands and follicles above enumerated cannot be obtained, ifi
the human subject, unmixed with the fluids from the true salivary glands. It has been
obtained, however, in small quantity, from the inferior animals, after ligature of all the
salivary ducts. This secretion is simply a grayish, viscid mucus, containing a number of
leucocytes and desquamated epithelial scales. It is this which gives the turbid and opa-
line character to the mixed saliva, as the secretions of the various salivary glands aiv nil
perfectly transparent. The fluid from these glands in the mouth is mixed with the sali-
vary secretions ; and that from the posterior part of the tongue, the tonsils, and the
pharyngeal glands passes down to the stomach with the alimentary bolus. This secretion,
consequently, forms a constant and essential part of the mixed saliva.
14

210 DIGESTION.

Mixed Saliva. — Although the study of the distinct secretions discharged into the
mouth possesses considerable physiological interest and importance, it is only the fluid
resulting from a union of them all, which can properly be considered in connection with
the general process of insalivation. In man it is necessary that the cavity of the mouth
should be continually moistened, if for nothing else, to keep the parts in a proper condi-
tion for phonation. A little reflection will make it apparent that the flow, from some of
the glands at least, is constant, and that, from time to time, a certain quantity of saliva
is swallowed. This is even more marked in some of the inferior animals, as the rumi-
nants. The discharge of fluid into the mouth, though diminished, is not arrested during
sleep. In the review of the different kinds of saliva, it has been seen that the flow from
none of the glands is absolutely intermittent ; unless it be so occasionally from the pa-
rotid, the secreting function of which is most powerfully influenced by the act of masti-
cation and the impression of sapid substances.

Upon the introduction of food, the quantity of saliva is enormously increased ; and
we have already noted the influence of the sight, odor, and occasionally even the thought
of agreeable articles. Many persons present a marked increase in the flow of saliva at
the sight of a lemon ; and we are all familiar, in a general way, with the impressions
which bring " water into the mouth." The experiments of Frerichs on dogs with gas-
tric fistulse, and the observations of Gardner on a patient with a wound in the oesopha-
gus, have demonstrated that the flow of saliva may be excited by the stimulus of food
introduced directly into the stomach without passing through the mouth.

Quantity of Saliva. — It is not easy to estimate, in the human subject, the entire
quantity of saliva secreted in the twenty-four hours ; and great variations in this regard
undoubtedly exist in different persons, and even in the same individual at different times.
An approximate estimate may be arrived at by noting, as nearly as possible, the average
quantity secreted during the intervals of digestion and adding to it the quantity ab-
sorbed by the various articles of food. Some of the earlier physiologists investigated
this subject with much patience. Be"rard quotes the experiments of Siebold, who col-
lected the saliva by holding the mouth open with the head inclined, receiving the
fluid in a vessel as fast as it was secreted. An estimate of this kind can only be ap-
proximative, and those made by Dalton are apparently the most satisfactory. This ob-
server found that he was able to collect from the mouth, without any artificial stimulus,
about five hundred and fifty-six grains of saliva per hour ; and he also found that wheaten
bread gained in mastication fifty-five per cent., and lean meat, forty-eight per cent, in
weight. Assuming the daily allowance of bread to be nineteen ounces and the allow-
ance of meat to be sixteen ounces, and estimating the quantity of saliva secreted during
twenty-two hours of interval, the entire quantity in twenty-four hours would amount to
20,164 grains, or a little less than three pounds avoirdupois, of which rather more than
one-half is secreted during the intervals of eating.

Eemembering that the quantity of saliva must necessarily be subject to great varia-
tions, this estimate may be taken as giving a sufficiently close approximation of the quan-
tity of saliva ordinarily secreted. It must be borne in mind, however, with reference
to this and the other digestive secretions, that this immense quantity of fluid is at no
one time removed from the blood, but is reabsorbed nearly as fast as secreted, and that,
normally, none of it is discharged from the organism.

General Properties and Composition of Saliva. — The mixed fluid taken from the
mouth is colorless, somewhat opaline, frothy, and slightly viscid. It generally has a faint
and somewhat disagreeable odor very soon after it is discharged. If it be allowed to
stand, it deposits a whitish sediment, composed mainly of desquamated epithelial scales,
with a few leucocytes, leaving the supernatant fluid tolerably clear. Its specific gravity
is variable, ranging from 1004 to 1006 or 1008. Its reaction is almost constantly alka-

COMPOSITION OF HUMAN SALIVA. 211

line ; although, under certain abnormal conditions of the system, it has occasionally been
observed to be neutral, and sometimes, though rarely, acid. We have occasionally ob-
served a distinctly acid taste in the saliva after very severe, prolonged, and exhausting
muscular exertion. The saliva becomes slightly opalescent by boiling or on the addition
of the strong acids. The addition of absolute alcohol produces an abundant whitish,
flocculent precipitate. Almost invariably the mixed saliva presents a more or less intense
blood -red tint on the addition of a per-salt of iron, which is due to the presence of a
sulpho-cyanide either of potassium or sodium.

A number of analyses of the human mixed saliva have been made by different chem-
ists, presenting, however, few differences, except in the relative proportions of water
and solid ingredients, which are probably quite variable. One of the most reliable of
these analyses is the following, by Bidder and Schmidt :

Composition of Human Saliva.

Water 995'16

Epithelium T62

Soluble organic matter 1'34

Sulpho cyanide of potassium 0'06

Phosphates of soda, lime, and magnesia 0'98

Chloride of potassium ) ~ _ .

Chloride of sodium

1,000-00

The organic principle of the mixed saliva, called by Berzelius ptyaline, is not affected
by heat or the acids, but, on the addition of an excess of absolute alcohol, is coagulated
in the form of whitish flakes, which may be readily separated by filtration. This sub-
stance has been closely studied by Mialhe and is described by him under the name of
animal diastase. This author regards it as the active principle of the saliva. It is ob-
tained from the human saliva by the following simple process :

The fluid from the mouth is first filtered, then treated with five or six times its weight
of absolute alcohol, by which a white or grayish-white precipitate is formed. This sub-
stance is collected on a filter and is dried in thin layers on a plate of glass in a current
of air at from 100° to 120° Fahr. It may then be preserved indefinitely in a well-stop-
pered bottle. The principle thus prepared may be dissolved in water, when it is insipid,
neutral, and becomes readily decomposed, giving rise to a substance resembling butyric
acid. It has no influence upon the nitrogenized alimentary principles, but, when brought
in contact with raw or hydrated starch, readily transforms it, first into dextrine, and
afterward into glucose. According to Mialhe, the energy of this action is such that one
part is sufficient to effect the transformation of more than two thousand parts of starch.

The presence of a certain quantity of sulpho-cyanide of potassium in the mixed saliva
can be demonstrated by the addition of a per-salt, especially the perchloride of iron.
That this is a constant and normal ingredient of the human saliva cannot be doubted.
We have frequently had occasion to apply this test to the saliva of different persons, and
the results have been invariably the same.

It has been a question whether the red color produced by the perchloride of iron be
really due to the presence of a sulpho-cyanide in the saliva; or, if it exist at all, whether
this salt be a normal constituent or be developed accidentally as a pathological condi-
tion, or produced, as has been suggested, by the action of reagents. The elaborate in-
vestigations of Longet seem to have settled these questions conclusively. He obtained
nearly three quarts of human saliva, which he collected in half an hour from forty sol-
diers, fasting, who, after having rinsed and cleaned the mouth, excited the secretion by
chewing pieces of India-rubber. The fluid was then concentrated so that all the sulpho-
cyanide was brought into a few drops, which showed, in an intense degree, the peculiar

212 DIGESTION.

reaction with the perchloride of iron. By suitable manipulations, the presence of sul-
phur was also established.

Longet states, farthermore, that he has examined the saliva from a great number of
persons, under all conditions, and has never failed to demonstrate the presence of the
sulpho-cyanide. Its proportion he found very variable, and in some cases it was so
slight that the reaction with the perchloride of iron did not immediately manifest itself;
but, by slowly evaporating the liquid to one-half or one-third of its original volume,
the reaction was observed in all cases.

It is probable that the sulpho-cyanide of potassium is a constant ingredient of each
of the three varieties of saliva. It has been found in the parotid, in cases of salivary
fistula, and was noted by Dalton in the saliva taken from the duct of Steno, although, in
this case, the saliva contained an organic principle which interfered with the test, but
which could be precipitated by alcohol and separated by filtration. Longet found the
sulpho-cyanide in the saliva from the submaxillary and sublingual glands, taken from the
floor of the mouth behind the inferior incisor and canine teeth.

Very little need be said concerning the remaining inorganic constituents of saliva,
except that they are of such a nature as almost invariably to render the fluid distinctly
alkaline. They exist in small proportion and do not appear to be connected in any way
with the functions of the saliva as a digestive fluid.

Functions of the /Saliva.

Physiologists are not entirely agreed concerning some of the most important questions
relating to the function of the mixed saliva in digestion. Bernard, from observations on
the lower animals, particularly on dogs, concludes that the operation of the saliva is simply
mechanical ; while others, in view of its property of rapidly transforming starch into
sugar, attribute to it an important chemical function. The experiments on which the
view of Bernard is based are conclusive, so far as they go. He has shown that none of
the distinct varieties of saliva from the dog affect starch ; that a mixture of the fluids
from the three salivary glands is likewise inoperative ; and that the mixed saliva from
the mouth of the dog, containing the secretion of the mucous glands of the mouth, con-
verts starch into sugar with difficulty. At the same time, however, he mentions the
well-known fact that the human mixed saliva changes starch into sugar with great
rapidity, and that the same effect is produced by the unmixed parotid or submaxillary
secretion. In the dog, amylaceous principles taken by the mouth are always found un-
altered in the stomach and are only transformed into sugar in the small intestines ; but
observations have shown that this is not the case in the human subject. These facts are
a sufficient argument against the direct application of experiments made on an exclusive-
ly carnivorous animal, like the dog, to the digestive process in man. "While there is no
reason to suppose that there is any material difference in the mammalia, as regards the
general operation of some of the functions, such as circulation or respiration, it is evident
that differences exist in the properties of the digestive fluids, as well as in the teeth and
jaws, corresponding with the great differences in the character and conditions of the
alimentary principles. In the study of digestion, therefore, the results of experiments
on the inferior animals cannot always be taken without reserve, anfl they should be con-
firmed by observations on the human subject; but, fortunately, the properties of nearly
all of the digestive fluids which have been studied minutely by vivisections have been
investigated more or less fully in man.

In 1831, Leuchs discovered that hydrated starch, mixed with fresh saliva and warmed,
became liquid in the space of several hours and was converted into sugar. This fact has
since been repeatedly confirmed ; and it is now a matter of common observation that
hydrated starch or unleavened bread, taken into the mouth, almost instantly loses the
property of striking a blue color with iodine and responds to the ordinary tests for sugar.
Of the rapidity of this action any one can easily convince himself by the simple experi-

FUNCTIONS OF THE SALIVA. 213

ment of taking a little cooked starch into the mouth, mixing it well with the saliva, and
testing in the ordinary way for sugar. This can hardly be done so rapidly that the reac-
tion is not manifested, and the presence of sugar is also indicated by the taste. Although
the human mixed saliva will finally exert the same action on uncooked starch, the trans-
formation takes place much more slowly. It has been shown by experiment that all the
varieties of human saliva have the same effect on starch as the mixed fluids of the mouth.
Dalton found no difference in the pure parotid saliva and the mixed saliva of the human
subject, as regards the power of transforming starch into sugar. Bernard obtained the
pure secretions from the parotid and from the submaxillary glands in the human subject,
by drawing it out of the ducts, as they open into the mouth, with a small syringe with
the nozzle arranged so as to fit over the papillae, and demonstrated their action on starch.
Longet showed that a mixture of the secretions of the submaxillary and the sublingual
glands had the same property.

It is unnecessary, in this connection, to recite the numerous experiments on the in-
fluence of the saliva of the inferior animals on starch; but it may be stated, as an estab-
lished and generally-accepted fact, that the mixed saliva and the secretion of the different
salivary glands, in the human subject, invariably transform cooked starch into sugar with
great rapidity in the mouth, and also, at the proper temperature, out of the body. It
has been also shown by Mialhe that the starch, although it is converted rapidly into sugar
in this process, is first transformed into dextrine. This point being settled, there arises
the important question whether the action of the saliva be important in the digestion of
starch, or whether this transformation be merely accidental; for it has been shown that
other fluids, among which may be mentioned the serum of the blood, the fluid found in
cysts, and mucus, have the same property, although none, except the intestinal juices, are
nearly so efficient as the saliva. And, again, the quantity of starch contained in the food
is so great that it would require, apparently, a longer contact with the saliva than usually
takes place in the mouth to make this action very efficient. These considerations make
it necessary to follow the amylaceous principles of food into the stomach and to ascer-
tain, if possible, whether the transformation into sugar be continued in this organ.

Bernard, after feeding a dog with starch, drew off the contents of the stomach by a
gastric fistula and found the starch unchanged, with no traces of sugar. This experi-
ment we have often repeated in public demonstrations, with the same results ; but the
differences already noted in the properties of the saliva of the human subject and of the
inferior animals destroy much of the value of such observations. Longet and others have
shown that the addition of gastric juice to the saliva does not interfere with the action
of the latter on starch, but it has been found that the reaction of the sugar thus resulting
from the transformation of the starch is masked by the presence of other principles con-
tained in the stomach. The question of the continuance, in the stomach, of the digestion
of starch by the saliva is settled by the following observation by Grtinewaldt and
Schroder, in 1853, on a woman with a gastric fistula:

"After a meal of raw starch, no sugar was found in the contents of the stomach, the
acid juice was drawn by the fistula, and was mixed with paste ; the transformation into
sugar commenced immediately. As Bidder has observed, the transforming property of
the saliva persists, even in the presence of free acids.

"A few ounces of starch swelled with boiling water were introduced in the stomach,
fasting, by the fistula; immediately after, a portion of the starch was expelled again;
already it contained sugar. A quarter of an hour after, a great deal of sugar was found
in the stomach, and the paste had become entirely fluid."

There can be no doubt that the saliva, in addition to its important mechanical func-
tions, transforms a considerable portion of the cooked starch, which is the common form
in which this principle is taken by the human subject, into sugar; but it is by no means
the only fluid engaged in its digestion, similar properties belonging, as we shall see here-
after, to the pancreatic and the intestinal juice. The last-named fluids are probably more

214 DIGESTION.

active, even, than the saliva. The saliva acts slowly and imperfectly on raw starch,
which becomes hydrated in the stomach and is digested mainly hy the fluids of the small
intestine. In all probability, the saliva does not digest all the hydrated starch taken as
food, the greater part passing unchanged from the stomach into the intestine. Those who
attribute merely a mechanical function to the saliva draw their conclusions entirely from
experiments on the lower animals, particularly the carnivora ; and it is evident that such
observations cannot be strictly applied to the human subject.

The principle which is specially active in the digestion of starch, in the human subject
at least, must exist in the pure secretion from the various glands as well as in the mixed
saliva. It has been isolated and studied by Mialhe, under the name of animal diastase.
Its properties and its action on starch have already been noted in treating of the com-
position of the mixed saliva.

In treating of the various fluids which are combined to form the mixed saliva, their
mechanical functions have necessarily been touched upon. To sum up this subject, how-
ever, it may be stated that the fluids of the mouth and pharnyx have quite as important an
office in preparing the food for deglutition and for the action of the juices in the stomach
as in the digestion of starch. Indeed, the former is probably the more important function
in man and the herbivora. It is a matter of common experience that the rapid degluti-
tion of very dry articles is impossible ; and the experiments of Bernard and others on
horses furnish very striking illustrations of the importance of the snliva as a purely me-
chanical agent. In the human subject, although mastication and insalivation are by no
means so complete as in some of the lower animals, the quantity of saliva absorbed by the
various articles of food is enormous. It seems impossible that the fluid thus incorporated
with the alimentary principles should not have an important influence on the changes
which take place in the stomach, although it must be confessed that our information on
this point is very meagre, except as regards the digestion of starch.

It is undoubtedly the abundant secretion of the parotid glands which becomes most
completely incorporated with the food during mastication and which serves to unite the dry
particles into a single coherent mass. In an experiment on a horse,. Bernard found that,
after the ducts of Steno had been divided, the portions of food, which were collected by
an opening into the oesophagus as they were swallowed, were not coherent and were
passed into the stomach with great difficulty. The time occupied in eating about three-
quarters of a pound of oats was twenty-five minutes; while, before the section of the
salivary ducts, a pound of oats was eaten in nine minutes.

The secretions from the submaxillary and sublingual glands and from the small glands
and follicles of the mouth, being more viscid and less in quantity than the parotid secre-
tion, penetrate the alimentary bolus less easily and have rather a tendency to form a glairy
coating on its exterior, agglutinating the particles on the surface with peculiar tenacity.

When the process of mastication and insalivation is completed and the food is passed
back into the pharynx, it meets with the secretion of the pharyngeal glands, which still
farther coats the surface with the viscid fluid which covers the mucous membrane in this
situation, thus facilitating the first processes of deglutition.

It has been observed that the saliva has a remarkable tendency to entangle bubbles of
air in the alimentary mass. In mastication, a considerable quantity of air is mixed with
the food, and this undoubtedly facilitates the penetration of the gastric juice. It is well
known that moist, heavy bread, and articles that cannot become impregnated in this way
with air, are not easily acted upon in the stomach.

Deglutition.

Deglutition is the act by which solid and liquid articles are forced from the mouth
into the stomach. The process involves first, the passage, by a voluntary movement, of
the alimentary mass through the isthmus of the fauces into the pharynx ; then a rapid
contraction of the constrictors of the pharynx, by which it is forced into the oesophagus ;

DEGLUTITION.

215

and, finally, a peristaltic action of the muscular walls of the oasophagus, extending from
its opening at the pharynx to the stomach.

Physiological Anatomy of the Parts concerned in Deglutition. — The parts concerned
in this function are the tongue, the muscular walls of the pharynx, and the O3sophagus.
In the passage of food and drink through the pharynx, it is necessary to completely pro-
tect from the entrance of foreign matters a number of openings which are exclusively for
the passage of air. These are above, the posterior nares and the Eustachian tubes, and
below, the opening of the larynx. • The mechanism by which these passages are closed
during the acts of deglutition is one of the most interesting subjects connected with this
function and has long engaged the attention of physiologists.

The tongue — a muscular organ capable of a great variety of movements, and en-
dowed, as we have seen, with highly important functions connected with mastication —
is the chief agent in the first processes of deglutition. Its physiological anatomy has
already been considered.

FIG. 52.— Cavities of the mouth and pharynx, etc. (Sappey.)

Section in the median line of the face and the superior portion of the neck, designed to show the moiith in its rela-
tions to the nasal fossae, the pharynx, and the larynx : 1, sphenoidal sinuses ; 2, internal orifice of the Eustachian
tube ; 8, palatine arch ; 4, velum pendulum palati ; 5, anterior pillar of the soft palate ; 6. posterior pillar of the
soft palate ; 7, tonsil ; 8. lingual portion of the cavity of the pharynx , 9, epiglottis ; 10, section of the hyoid
bone; 11, laryngeal portion of the cavity of the pharynx; 12, cavity of the larynx.

The pharynx, in which the most vigorous and complex of the movements of do.duti-
tion take place, is an irregular, funnel-shaped cavity, its longest diameter being trans-
verse and opposite the cornua of the hyoid bone, with its smallest portion at the opening
into the esophagus. Its length is about four and a half inches. It is connected superiorly
and posteriorly with the basilar process of the occipital bone and the upper cervical verte-

216

DIGESTION.

brse. It is imperfectly separated from the cavity of the mouth by the velum pendulum
palati, a movable musculo-membranous fold continuous with the roof the mouth and
marked by a line in the centre, which indicates its original development by two lateral
halves. This, which is called the soft palate, when relaxed, presents a concave surface
looking toward the mouth, a free, arched border, and a conical process hanging from the
centre, called the uvula. On either side of the soft palate, are two curved pillars or arches.

The anterior pillars of the fauces are formed by the palato-glossus muscle on either
side and run obliquely downward and forward, the mucous membrane which covers
them becoming continuous with the membrane over the base of the tongue. The posterior
pillars are more closely approximated to each other than the anterior. They run obliquely
downward and backward, their mucous membrane becoming continuous with the mem-
brane covering the sides of the pharynx. Between the lower portion of the anterior and
posterior pillars, are the tonsils; and in the substance of, and beneath the mucous mem-
brane of the palate and pharynx, are small glands, which have already been described.

In Fig. 52 are shown the cavities of the mouth and pharynx with their relations to
the nares and the larynx.

FIG. 53.— Muscles of fJie pharynx, etc. (Sappey.)

1, 2, 3, 4, 4, superior constrictor; 5, 6, 7, 8, middle constrictor; 9, 10, 11, 12, inferior constrictor; 18, 18. stylo-
pharynseus; 14, stylo-hyoid muscle; 15, stylo-glossus ; 16, hyo-glossus ; 17, mylo-hyoid muscle; 18, buccinator
muscle ; 19, tensor palati; 20, levator palati.

The isthmus of the fauces, or the strait through which the food passes from the mouth
to the pharynx, is bounded above, by the soft palate and the uvula ; laterally, by the pil-
lars of the palate and the tonsils ; and below, by the base of the tongue.

DEGLUTITION.

The openings into the pharynx above are the posterior nares and orifices of the Eusta-
chian tubes. Below, are the openings of the oesophagus and the larynx.

The muscles of the pharynx are the superior constrictor, the stylo-pharyngeus, the
middle constrictor, and the inferior constrictor ; and it is easy to see, from the situation of
these muscles, how, by their successive action from above downward, the food is passed
into the oesophagus.

The superior constrictors form the muscular wall of the upper part of the pharynx.
Their origin extends from the lower third of the margin of the internal pterygoid plate of
the sphenoid bone to the alveolar process of the last molar tooth, the intermediate line of
attachment being to tendons and ligaments. The fibres then pass backward and meet in
the median raphe, which is attached by aponeurotic fibres to a ridge on the basilar process
of the occipital bone, called the pharyngeal spine.

The stylo-pharyngeus muscle has a rounded portion above, by which it arises from the
inner surface of the base of the styloid process of the temporal bone. It passes between
the superior and middle constrictors of the pharynx, becomes thin, and spreading out, its
fibres mingle in part with the fibres of the constrictors and the palato-pharyngeus, and a
few pass to be inserted into the upper border of the thyroid cartilage.

Tho middle constrictor is a flattened muscle, arising from the cornua of the hyoid bone
and the stylo-hyoid ligament, its fibres passing backward, spreading into a fan-shape, and
meeting in the median raphe.

The inferior constrictor is the most powerful of the muscles of the pharynx. It arises
by thick, fleshy masses from the sides of the thyroid and cricoid cartilages of the larynx.
The inferior fibres curve backward, and the superior fibres, backward and upward, to
meet in the median raphe.

The muscles which form the fleshy portions of the soft palate are likewise important
in deglutition.

The levator palati, a long muscle of considerable thickness, arises from the apex of the
petrous portion of the temporal bone and the adjacent cartilaginous portion of the Eusta-
clrian tube ; and, spreading out in the posterior portion of the soft palate, as its name
implies, it raises the velum.

The tensor palati, sometimes called the circumflexus, is a broad, thin muscle, consist-
ing of a vertical portion, which is fleshy, and a horizontal portion, which is tendinous.
The fleshy fibres arise from the scaphoid fossa of the sphenoid bone, pass downward, be-
come tendinous, and wind around the hamular process ; after which the muscle spreads
out into a thin aponeurosis, which passes to the median line on the anterior portion of
the soft palate. Its action is to render the palate tense.

The palato-glossus forms the anterior pillar of the soft palate. It arises from the side
of the palate near the uvula and passes to be inserted into the side and dorsum of the
tongue. The action of this muscle is to constrict the isthmus of the fauces, by drawing
down the soft palate and elevating the base of the tongue.

The palato-pharyngeus forms the posterior pillar of the soft palate. It arises from the
soft palate by two fasciculi, and joins with the fibres of the stylo-pharyngeus, to be in-
serted into the posterior border of the thyroid cartilage. Its action is to approximate the
posterior pillars of the palate and depress the velum.

The azygos uvulse is the small muscle, consisting of two fasciculi, one on either side,
which forms the fleshy portion of the uvula. It has no very marked or important action
in deglutition.

The mucous membrane of the pharynx, aside from the various glands situated 1
it and in its substance, which have already been described, presents some peculiars
which are interesting more from an anatomical than a physiological point of view. In
the superior portion, which forms a cuboidal cavity just behind the posterior nares, the
membrane is darker and much richer in blood-vessels than in other parts. Its surface is
smooth and provided with ciliated, columnar epithelium, like that which covers the mem-

218 DIGESTION.

brane of the posterior nares. It is marked by a deep antero-posterior groove in the
median line ; and, on either side, parallel with the median line, are four smaller grooves.
In the horizontal portions, the mucous membrane in the central groove adheres to the
periosteum of the basilar process, particularly at its posterior extremity. Laterally, be-
low the level of the opening of the Eustachian tubes, and posteriorly, at the point where
it becomes vertical, the mucous membrane abruptly changes its character. The epithelial
covering is here composed of cells of the pavement-variety, similar to those which cover
the mucous membrane of the oesophagus. The membrane is also paler and is less rich
in blood-vessels. It is provided with papilla, some of which are simple, conical eleva-
tions, while others present from two to six conical processes with a single base. These
papilla} are rather thinly distributed over all of that portion of the mucous surface which
is covered with pavement-epithelium.

The contractions of the muscular walls of the pharynx force the alimentary bolus into
the oesophagus, a tube possessed of thick, muscular walls, extending to the stomach. The
oesophagus is about nine inches in length. It is cylindrical, and rather constricted at its
superior and inferior extremities. It commences in the median line behind the lower
border of the cricoid cartilage and opposite the fifth cervical vertebra. At first, as it de-
scends, it passes a little to the left of the cervical vertebra. It then passes from left to
right from the fourth or fifth to the ninth dorsal vertebra, to give place to the aorta. It
finally passes a little to the left again, and from behind forward, to its opening into the
stomach. In its passage through the diaphragm, it is surrounded by muscular fibres, so
that when this muscle is contracted in inspiration, its action has a tendency to close the
opening.

The coats of the oesophagus are two in number, unless we include, as a third coat, the
fibrous tissue which attaches the mucous membrane to the subjacent muscular tissue.

The external coat is composed of an external longitudinal, and an internal circular or
transverse layer of muscular fibres. In the superior portion, the longitudinal fibres are
arranged in three distinct fasciculi ; one in front, which passes downward from the pos-
terior surface of the cricoid cartilage, and one on either side, extending from the inferior
constrictors of the pharynx. As the fibres descend, the fasciculi become less distinct
and are finally blended into a uniform layer. The circular layer is somewhat thinner
than the external layer. Its fibres are transverse near the superior and inferior extrem-
ities of the tube and are somewhat oblique in the intermediate portion. The muscular
coat is from -^ to -^ of an inch in thickness.

In the upper third of the oesophagus, the muscular fibres are exclusively of the red or
striated variety, with some anastomosing bundles ; but, lower down, there is a mixture of
non-striated fibres, which appear first in the circular layer. These latter fibres become
gradually more numerous, until, in the lower fourth, they largely predominate. A few
striated fibres, however, are found as low down as the diaphragm.

The mucous membrane of the oesophagus is attached to the muscular tissue by a dense,
fibrous layer. It is quite vascular and reddish above, but becomes gradually paler in the
inferior portion. The mucous membrane is ordinarily thrown into longitudinal folds,
which are obliterated when the tube is distended. Its epithelium is thick, of the pave-
ment-variety, and is continuous with, and similar to the covering of the lower portion of
the pharynx. It is provided with papillae of the same structure as those found in the
pharynx, the conical variety predominating. Numerous small, racemose glands are found
throughout the tube, forming by their aggregation at the lower extremity, just before it
opens into the stomach, a glandular ring.

Mechanism of Deglutition. — For convenience of description, physiologists have gen-
erally divided the process of deglutition into three periods. The first period is occupied
by the passage of the alimentary bolus backward to the isthmus of the fauces. This may
appropriately be considered as a distinct period, because the movements are effected by

DEGLUTITIOK 219

the action of muscles under the control of the will. The second period is occupied by the
passage of the food from the isthmus of the fauces, through the pharynx, into the upper
part of the oesophagus. The third period is occupied by the passage of the food through
the oesophagus into the stomach.

In the first period, the tongue is the important agent. After mastication has been
completed, the mouth is closed and the tongue becomes slightly increased in width, and,
with the alimentary bolus behind it, is pressed from before backward against the roof of
the mouth. The act of swallowing is always performed with difficulty when the mouth
is not completely closed ; for the tongue, from its attachments, must follow, to a certain
extent, the movements of the lower jaw. The first part of the first period of deglutition,
therefore, is simple ; but, when the food has passed beyond the hard palate, it comes in
contact with the hanging velum, and the muscles are brought into action which render
this membrane tense and oppose it in a certain degree to the backward movement of the
base of the tongue. This is effected by the action of the tensor-palati and the palato-
glossus. The moderate tension of the soft palate admits of its being applied to the smaller
morsels, while the opening is dilated somewhat forcibly by masses of greater size.

It is easy to appreciate, in analyzing the first period of deglutition, that liquids and
the softer articles of food are assisted in their passage to the isthmus of the fauces by a
slight suction force. This is effected by the action of the muscles of the tongue, elevating
the sides and depressing the centre of the dorsum, while the soft palate is accurately
applied to the base.

The importance of the movements of the tongue during the first period of deglutition
is shown by experiments on the inferior animals and by cases of loss of this organ in
the human subject. In the experiments of Panizza, which have already been referred to
in connection with mastication, it was found that paralysis of the tongue by section of
the hypoglossal nerves in dogs deprived the animals of the power of swallowing, even
when a bolus of meat or bread was put upon its dorsal surface. In an observation on a
young dog, in which we divided both hypoglossal nerves, the effect upon deglutition was
very marked. The animal ate with difficulty, the pieces of meat which were given him
frequently dropping from the mouth. He was able to swallow only by jerking the head
suddenly upward, so as to throw the meat past the base of the tongue ; and, even when
deglutition commenced, the first steps took place slowly and with apparent difficulty.
The process of drinking was very curious. The animal made the usual noise in attempt-
ing to drink, but the tongue did not come out of the mouth, and the only way he seemed
to get any water was by jerking the head and moving the jaw so as to throw some of the
liquid into the mouth. On causing him to drink from a graduated glass, it was found
that he drank four fluid ounces in four minutes. In the case of a young girl, reported to
the Academy of Science, in 1718, by De Jussieu, in which there was congenital absence
of the tongue, deglutition was impossible until the food had been pushed with the finger
far back into the mouth. In cases of amputation of the tongue,, a portion of its base gen-
erally remains sufficient to press against the palate and thus act in the first period of deg-
lutition.

The movements in the first period of deglutition are under the control of the will but
are generally involuntary. When the food has been sufficiently masticated, it requires
an effort to prevent the act of swallowing. In this respect, the movements are like the
acts of respiration, except that the imperative necessity of air in the system must, in a
short time, overcome any voluntary effort by which respiration has been arrested.

The second period of deglutition involves more complex and important muscular
action than the first. By a rapid and almost convulsive series of movements, the food is
made to pass through the pharynx into the oesophagus. The movements are then entirely
beyond the control of the will, and belong to the kind usually called reflex. After the
alimentary mass has passed beyond the isthmus of the fauces, it is easy to observe a sud-
den and peculiar movement of elevation of the larynx by the action of muscles which

220 DIGESTION.

usually depress the lower jaw, but which are now acting from this bone as the fixed
point. The muscles which produce this movement act chiefly upon the hyoid bone.
They are the digastric (particularly the anterior belly), the mylo- hyoid, the genio-hyoid,
the stylo-hyoid, and some of the fibres of the genio-glossus. It is probable, also, that the
thyro-hyoid acts at this time to draw the larynx toward the hyoid bone. "With this ele-
vation of the larynx, there is necessarily an elevation of the anterior and inferior portions
of the pharynx, which are, as it were, slipped under the alimentary bolus as it is held by
the constrictors of the isthmus of the fauces.

Contraction of the constrictor muscles of the pharynx takes place almost simulta-
neously with the movement of elevation ; and the superior constrictor is so situated as to
grasp the morsel of food, and with it the soft palate. The muscles, the constrictors act-
ing from the median raphe, assist to elevate the anterior and inferior walls of the pharynx
and pass the food rapidly into the upper part of the oesophagus. All these complex
movements are accomplished with great rapidity, and the larynx and pharynx are then
immediately returned to their original position.

Protection of the Posterior Nares during the Second Period of Deglutition. — When
the act of deglutition is performed with regularity, no portion of the liquids and solids
swallowed ever finds its way into the air-passages. The entrance of foreign substances
into the posterior nares is prevented in part by the action of the superior constrictors of
the pharynx, which, as we have seen, embrace, during their contraction, not only the ali-
mentary mass, but the velum pendulum palati itself, and in part, also, by contraction of
the muscles which form the posterior pillars of the soft palate.

During the first part of the second period of deglutition, the soft palate is slightly
raised, being pressed upward by the morsel of food. This fact has been observed in cases
in which the parts have been exposed by surgical operations, and its mechanism has also
been observed in the human subject, by Bidder and Kobelt. In one case — that of a young
man who had lost the superior maxillary bone, as well as the zygoma — the soft palate
could be observed from its superior surface ; and, at each movement of deglutition, the
palate, which is naturally inclined downward, became more horizontal, and the posterior
wall of the pharynx came forward to meet it. The same movement of the pharynx was
observed by Kobelt in the case of a soldier who received a severe sabre-cut in the neck.

"While the food is passing through the pharynx, the palato-pharyngeal muscles, which
form the posterior pillars of the soft palate, are in a state of contraction by which the
edges of the pillars are nearly approximated, forming, with the uvula between them,
almost a complete diaphragm between the postero-superior and the antero-inferior parts
of the pharynx. This, with the application of the posterior wall of the pharynx to the
superior face of the soft palate, completes the protection of the posterior openings of
the nasal fossse. The fact that the posterior pillars are thus contracted and approximated
during deglutition may be easily verified by simply watching these parts with a mirror
during an effort at swallowing. In a case, observed by Berard, it was shown that the
muscular action of the soft palate was absolutely necessary to the protection of the nares,
particularly in swallowing liquids. In this instance, a young lady was affected with
complete paralysis of the velum, which allowed liquids to return so freely by the nose in
swallowing that she was obliged to retire from observation whenever she drank.

Protection of the Opening of the Larynx, and Uses of the Epiglottis in Deglutition. —
The entrance of the smallest quantity of solid or liquid foreign matter into the larynx
produces violent and distressing cough. This accident is of not infrequent occurrence,
especially when an act of inspiration is inadvertently performed while solids or liquids
are in the pharynx. During inspiration, the glottis is opened, and at that time only can
a substance of any considerable size find its way into the respiratory passages. Respira-
tion is interrupted, however, during each and every act of deglutition ; and there can,

DEGLUTITION. 221

therefore, be hardly any tendency at that time to the entrance of foreign substances into
the larynx. During a regular act of swallowing, nothing can find its way into the respir-
atory passages, so complete is the protection of the larynx during the period when the
food passes through the pharynx into the oesophagus.

The situation of the epiglottis has naturally led physiologists to attribute to it great
importance in preventing the entrance of particles of food and liquids into the larynx. It
will be remembered that this cartilaginous, leaf-like process is attached to the anterior
portion of the larynx, and is usually erect, lying against the base of the tongue. In the
movements of the tongue and larynx incident to deglutition, the epiglottis is necessarily
applied to the superior face of the larynx so as to close the opening. Although, during
deglutition, the glottis is covered in this way, it is necessary to study closely all the con-
ditions which are involved and to ascertain what is the actual value of each of the various
means by which entrance of foreign bodies into the air-passages is prevented, for this
protection is accomplished by several distinct provisions.

It is evident, from the anatomy of the parts and the necessary results of the contrac-
tions of the muscles of deglutition, that, while the food is passing through the pharynx,
the larynx, by its elevation, passes under the tongue as it moves backward, and the soft
base of this organ is, as it were, moulded over the glottis. With the parts removed from
the human subject or from one of the inferior animals, we can imitate the natural move-
ments of the tongue and larynx, and it is evident that this provision alone must be suffi-
cient to protect the larynx from the entrance of solid or semisolid particles of food,
particularly when we remember how the alimentary particles are agglutinated by the
saliva and how easy their passage becomes over the membrane coated with a slimy
mucus. Experiments on the inferior animals and observations upon the human subject
have conclusively settled the question that the deglutition of all articles, except liquids, is
generally effected without difficulty when the epiglottis has been removed or lost by
accident or disease. The same is true when, in addition, the intrinsic muscles of the
larynx have been paralyzed by the section of nerves, or even when closure of the rima
glottidis is forcibly prevented. It has been shown, however, by the experiments of
Longet, that, when the larynx is in part prevented from performing its movement of
ascension, the deglutition of a moist mass of alimentary matter is effected with difficulty
and is followed by a sharp cough, indicating the entrance of a certain quantity of foreign
matter into the air-passages.

It is impossible for the muscles of the pharynx to contract without drawing together
the sides of the larynx, to which they are attached, and assisting to close the glottis. At
the same time, as the movements of respiration are arrested during deglutition, the lips
of the glottis fall together, as they always do except in inspiration. This fact we have
repeatedly observed in demonstrating the respiratory movements of the glottis; for,
when the larynx is thus exposed, the animal makes frequent efforts at deglutition. In
addition to this passive and incomplete approximation of the vocal chords, it has repeat-
edly been observed that the lips of the glottis are accurately and firmly closed during
each act of deglutition.

Longet justly attaches great importance to the exquisite sensibility of the top of the
larynx in preventing the entrance of foreign substances. His experiments of dividing all
the nervous filaments distributed to the intrinsic muscles show that their action is not
essential. But, on division of the superior laryngeal, the nerve which gives sensibility
to the parts, he found that liquids occasionally passed in small quantity into the trachea.
This is attributed to the want of sensibility in the mucous membrane above the glottis:
"for the animal is not aware in time of the presence of liquid which may accidentally
get into the supra-laryngeal cavity, the occlusion of the glottis is sometimes too tardy
and does not take place until after the passage of the liquid ; or, again, the animal, in-
stead of then making a sudden expiration, makes an unseasonable inspiration which
facilitates the introduction of the foreign substance into the air-passages, and the cough

222 DIGESTION.

does not take place until this is already in contact with the tracheal or bronchial mucous
membrane.'" These experiments strikingly illustrate the conservative function of the
acute sensibility of the mucous membrane above the glottis. JSTo foreign substance can
find its way into the air-passages by simply dropping into the cavity situated above the
vocal cords when respiration is interrupted, but can only enter by being drawn in forcibly
and suddenly with an act of inspiration, when the glottis is widely opened. It is now
well known to the practical physician that direct applications cannot be made to the in-
terior of the larynx, unless an instrument be suddenly introduced with the inspiratory act ;
and, at this time, a little dexterity will enable an operator to introduce bodies of consider-
able size below the vocal chords.

Before the experiments of Magendie, in 1813, physiologists were generally of the
opinion, judging from anatomical relations, that the epiglottis had the function of pro-
tecting the larynx from the entrance of particles of food during the second period of deg-
lutition. Magendie extirpated the entire epiglottis in dogs and found that the animals
swallowed liquids and solids without difficulty, the act being very seldom followed by
cough. The observations on deglutition were made an hour after the removal of the
epiglottis. In other animals, the superior and inferior laryngeal nerves were divided,
thus paralyzing the muscles of the glottis. The deglutition of liquids especially be-
came difficult and was followed generally by cough. As the result of these observations,
Magendie came to the conclusion that the larynx is protected during deglutition by clos-
ure of the glottis itself.

Although the experiments on animals were apparently conclusive, observations on
the human subject have been cited, in which, after destruction of the epiglottis by dis-
ease, there existed persistent difficulty in swallowing liquids. As numerous pathological
observations of this character have been reported, the question could not be regarded as
entirely settled by the researches of Magendie. It was with the view of determining
this more rigorously, that farther experiments were instituted in 1841, by Longet.

In investigating this question, Longet removed the epiglottis from six dogs. He found
that, in the animals kept until the parts were perfectly cicatrized, more or less cough
followed the deglutition of liquids. One of these he kept for six months and found that
when he drank milk or water cough never failed to follow. The same fact was noted in
three of the animals that were killed on the nineteenth day and in one that was killed
on the thirtieth day. In all, the complete excision of the epiglottis was verified by post-
mortem examination. In one of the animals, killed two days after the operation, that
generally swallowred liquids without coughing, there was found a swelling at the base of
the tongue which projected over the larynx.

Several cases of loss of the epiglottis in the human subject are quoted by Longet in
support of his view that this part is necessary to the complete protection of the air-pas-
sages, particularly in the deglutition of liquids. Two of the most striking of these cases
were observed by Larrey, in Egypt. One of these was the case of General Murat, who
was wounded by a ball passing through the neck from one angle of the jaw to the other,
cutting off the epiglottis, which was expelled by the mouth. In this instance, the diffi-
culty in the deglutition of 'liquids was so great, that it became necessary to introduce
them through a tube passed into the oesophagus. In the other case, the epiglottis was
entirely removed by a wound and was preserved and presented to the surgeon. In
this instance, the difficulty in the deglutition of liquids was even greater than in the
former; each effort at swallowing being followed by convulsive and suffocating cough.
This difficulty persisted after the parts had become completely cicatrized. In these cases,
it is possible that the injury to muscles and other parts from such severe wounds might
interfere with the movements of the larynx or the closure of the glottis and thus disturb
deglutition. In a case in which the epiglottis had entirely sloughed away as a conse-
quence of syphilitic disease, observed by Dr. Austin Flint, the difficulty in swallowing
liquids, although sufficiently well marked, was by no means so great as in the cases men-

DEGLUTITION. 223

tioned above. The difficulty in swallowing was noted as not great, but the patient swal-
lowed liquids more easily than solids. The difficulty consisted of cough and loss of breath,
as the patient described it. It was less when articles were swallowed while the patient
was in the recumbent posture, and food and drink were habitually taken in that position.
At the time that this patient, a female, was in the Belle vue Hospital under the observa-
tion of Dr. Flint, the deglutition was improving. Dr. Flint noted that, after she had been
in the hospital a few days, on causing her to swallow in his presence, the act of degluti-
tion was performed with a certain deliberation but without difficulty. An examination
of the parts with the laryngoscope was made by Dr. Church, in the presence of Dr. Flint
and Dr. Dalton : " The absence .of the epiglottis was determined by sight. The vocal
chords were distinctly seen. The little excrescences described as apparent to the touch
were visible."

In the case just described, there was not a constant and considerable difficulty in
deglutition ; but it is stated that difficulty had existed, undoubtedly from the passage of
articles into the larynx, and when no such accident took place the act was performed
with a " certain deliberation." It is a curious fact, also, that, when the difficulty in swal-
lowing was considerable, deglutition was accomplished most easily in the recumbent
posture, in which the tendency of particles of food to pass into the larynx must have been
much lessened.

While, with attention on the part of the subject, the larynx may frequently, and per-
haps generally/ be protected from the entrance of foreign substances during deglutition,
after loss of the epiglottis when other parts are not atfected, a study of the numerous
cases of this lesion as the result of disease or injury shows that the epiglottis is by no
means so inefficient in the protection of the larynx as was supposed by Magendie. Still,
it is but one of the means which have been provided for this end.

Since the air-passages have been so fully explored by means of the laryngoscope, this
instrument has been used to a certain extent in the study of the phenomena of degluti-
tion. In July, 1865, a note was presented to the French Academy of Sciences, giving
the results of experiments by Dr. Krishaber on the mechanism of deglutition as studied
by autolaryngoscopy, followed by a note on the same subject by M. H. Guinier. Dr.
Krishaber, as the result of his observations, gave the following conclusions :

" 1st. In the act of deglutition the alimentary bolus passes in one of the pharyngeal
grooves, over one of the sides of the epiglottis tilted by the elevation of the larynx ; the
bolus thus arrives at the oesophagus at the moment when, by the contraction of the con-
strictor muscles, the pharynx is shortened and brought in front of the mass.

" 2d. The deglutition of liquids is effected in the same manner ; these passing, how-
ever, quite frequently upon the epiglottis itself, which happens very rarely with solid ali-
ments.

" 3d. A quantity — extremely small, it is true — of liquid engages itself during normal
deglutition around the border of the epiglottis and moistens the mucous membrane of
the larynx and even of the vocal chords.

" 4th. In gargling, the larynx being widely opened, a larger quantity finds its way
into the vocal organ.

" 5th. An alimentary bolus may be easily tolerated in the respiratory passages ; that
is to say, in the larynx, as far as the vocal chords and even in the interior of the trachea.

a 6th. The sensibility of the trachea to the impression of foreign bodies is infinitely
less than that of the larynx.

" Yth. Hard and cold bodies, as, for example, a sound, are not tolerated in the respir-
atory passages ; while any soft body, which can adhere to the mucous membrane and
has a temperature like that of the parts touched, is easily tolerated in the respiratory
passages and kept in the trachea many minutes without producing the slightest cough."

These observations confirm the views of Longet and others concerning the passage of
alimentary substances down the pharynx by the sides of the epiglottis ; nnd, in that case,

224 DIGEST;

liquids would almost certainly pass aronnd the borders in quantity sufficient to moisten
the mucous membrane below. It must be remembered, however, that the sensibility of
the air-passages is very unequal in different persons, and that it may be considerably
modified by education of the parts. This should make us hesitate to accept the \ie\\
that, in gargling, the larynx receives a quantity of liquid, and that an alimentary bolus
may be tolerated in the trachea for many minutes without coughing.

To sum up the mechanism by which the opening of the larynx is protected during the
deglutition of solids and liquids, we hare only to carefully follow the articles as they
over the inclined plane formed by the back of the tongue and the anterior and inferior
part of the pharynx. As the food is making this passage in obedience to the contraction
of the muscles which carry the tongue backward, draw up the larynx, and constrict the
pharynx, the soft base of the tongue and the upper part of the larynx are applied to each
other, with the epiglottis, which is now inclined backward, between them ; at the same
time the glottis is closed, in part by the action of the constrictor muscles attached to the
sides of the thyroid cartilages, and in part by the action of its intrinsic muscles. If the
food be tolerably consistent and united into a single bolus, it slips easily from the back
of the tongue along the membrane covering the anterior and inferior part of the phar-
ynx; but if it be liquid or of little consistence, a portion takes this course, while another
portion passes over the epiglottis, being directed by it into the two grooves or gutters by
the side of the larynx. It is by these means, together with those by which the posterior
nares are protected, that all solids and liquids are passed into the oesophagus, and the
second period of deglutition is safely accomplished.

The third period of deglutition is the most simple of afl. It involves merely contrac-
tions of the muscular walls of the oesophagus, by which the food is forced into the stom-
ach. The longitudinal fibres shorten the tube and slip the mucous membrane, lubricated
by its glairy secretion, above the bolus ; while the circular fibres, by a progressive peri-
staltic contraction from above downward, propel the food into the stomach. The pas-
sage of food down the oesophagus was for the first time closely studied by Magendie,
who noted, in this connection, many curious and important facts. In numerous experi-
ments on the lower animals, he observed that> while the peristaltic contractions of the
upper two-thirds of the tube were immediately followed by a relaxation, which contin-
ued till the next act of deglutition, the lower third remained contracted generally for
about thirty seconds after the passage of the food into the stomach. During its contrac-
tion, this part of the oesophagus was hard, like a cord firmly stretched. This was fol-
lowed by relaxation ; and this alternate contraction and relaxation continued constantly,
even when the stomach was empty, although, during digestion, the contractions were fre-
quent in proportion to the quantity of food in the stomach. The contraction was always
increased by pressing the stomach and attempting to pass some of its contents into the
oesophagus. This provision is undoubtedly important in preventing regurgitation of the
contents of the stomach, especially when the organ is exposed to pressure, as in urina-
tion or defalcation. We have already noted the action of the crura of the diaphragm,
which has a tendency to close the oesophageal opening during inspiration.

The length of time occupied in the third period of deglutition was noted by Magendie
in the inferior animals, but we have been unable to find any definite observations on this
point in the human subject, although this would have been easy in the cases of gastric
fistula which, from time to time, have come under the observation of physiologist-. Ma-
gendie found that the alimentary bolus sometimes occupied two or three minutes in its
passage, and that it was often momentarily arrested in its course. It frequent!
though we were onrselves conscious of a very slow passage of food down the cesophagn?,
and not infrequently a piece of bread or a mouthful of liquid is taken to hasten it ; but
it is not probable that every alimentary bolus remains for two or three minutes in the
oesophagus, and liquids undoubtedly are swallowed with considerable rapidity, as they

DEGLUTITION. 225

can soon be recognized in the stomach by their temperature. As the lower part of the
oesophagus is composed chiefly of unstriped muscular fibres, it is probable that here the
contractions are more gradual than in the upper portions.

I we have already had occasion to remark, the muscular movement* which take place
during all the periods of deglutition are peculiar. The first act is generally involuntary from
inattention, but it is under the control of the will. The second act is involuntary, when
once commenced, but may be excited by the voluntary passage of solids or liquids beyond
the velum pendulum palati. It is impossible to perform the second act of deglutition un-
:ue article, either solid or liquid, in the pharynx. It is easy to make three
or four successful efforts consecutively, in which there is elevation of the larynx with all
the other characteristic movements ; but a little attention will show that with each act
a small quantity of saliva is swallowed. When the efforts have been frequently repeat-
ed, the movements become impossible, until time enough has elapsed between them for
the saliva to collect. This fact we personally verified before writing this paragraph,
and it was demonstrated to be due to the absence of liquid ; for, immediately after, an
ounce of water was swallowed without difficulty by sixteen successive movements of
deglutition. This experiment also shows the small quantity of liquid (only half a drachm)
.ry to excite the contraction of the muscles concerned in the second act.

All the movements of deglutition, except those of the first period, must be regarded as
::ally reflex, depending upon an impression made upon the afferent nerves distrib-
uted to the mucous membrane of the pharynx and oesophagus.

The position of the body has little to do with the facility with which deglutition is
effected. Liquids or solids may be swallowed indifferently in all postures. Berard states
that a juggler, in his presence, passed an entire bottle of wine from the month to the
stomach, while standing on his head. The same feat we have lately seen accomplished
with apparent ease, by a juggler who drank three glasses of beer while standing on his
hands in the inverted posture.

Deglutition of Air. — In the celebrated essay of Magendie on the mechanism of vom-
iting, it is stated that as soon as nausea commenced the stomach began to fill with air, so
that, before vomiting occurred, the organ became tripled in size. Magendie showed, far-
therraore, that the air entered the stomach by the oesophagus, for the distention occurred
when the pylorus was ligated. In * subsequent memoir, the question of the deglutition
of air. aside from the small quantity which is incorporated with the food during mastica-
tion and insalivation, was farther investigated. It was found that some persons had the
faculty of swallowing air, and, by practice, Magendie himself was able to acquire it,
although it occasioned such distress that it was discontinued. Out of a hundred students
of medicine, eight or ten were found able to swallow air.

It is not very uncommon to find persons who have gradually acquired this habit in
order to relieve uncomfortable sensations in the stomach ; and, when confirmed, it occa-
sions persistent disorder in the process of digestion. Quite a number of cases of this
kind are reported by Magendie, and in several it was carried to such an extent as to pro-
duce great distention of the abdomen. A curious case of habitual air-swallowing is re-
I by Dr. Austin Flint in his work on the Practice of Medicine.

Although the subject of air-swallowing properly belongs to pathology, the feet that
the muscles of deglutition are capable, in some individuals, of forcing air into the stom-
ach, is not without physiological interest.

15

DIGESTION.

CHAP TEE VIII.

STOMA CH-DIGESTION.

Physiological anatomy of the stomach — Peritoneal coat — Muscular coat — Mucous coat— Glandular apparatus in the
stomach — Gastric, or peptic glands — Mucous glands — Closed follicles — Gastric juice — Mode of obtaining the gas-
tric juice — Gastric fistula in the human subject in the case of St. Martin — Secretion of the gastric juice— Composi-
tion of the gastric juice — Source of the acidity of the gastric juice — Ordinary saline constituents of the gastric juice
—Action of the gastric juice in digestion— Constituents upon which the activity of the gastric juice depends— Ac-
tion of the gastric juice upon meats — Action upon albumen, fibrin, caseine, and gelatine — Action upon vegetable
nitrogenized principles— Albuminose, or peptones — Action of the gastric juice upon fats — Action upon saccharine
and amylaceous principles— Duration of stomach-digestion — Digestibility of different aliments in the stomach —
Circumstances which influence stomach-digestion — Character of the contractions of the muscular coat of the
stomach — Movements in the cardiac and in the pyloric portion — Mechanism of the movements of the stomach—
Eumination, and rcgurgitation from the stomach — Summation in the human subject — Eructation.

Physiological Anatomy of the Stomach.

THE most dilated portion of the alimentary canal, in man, is the stomach. It serves
the double purpose of a receptacle for the food and an organ in which certain important
digestive processes take place. It is situated in the upper part of the abdominal cavity
and is held in place by folds of the peritoneum and by the oesophagus. Its form is not
easily described. It has been compared to a bagpipe, which it resembles somewhat,
when moderately distended. As we should naturally suppose from the fact that the
stomach periodically receives considerable quantities of solids and liquids, its form and
position are subject to great variations. "When empty, it is flattened, and in many parts
its opposite walls are in contact. When moderately distended, its length is from thirteen
to fifteen inches, its widest diameter, about five inches, and its capacity, one hundred and
seventy-five cubic inches, or about five pints. The parts usually noted in anatomical de-
scriptions are : a greater and a lesser curvature ; a greater and a lesser pouch ; a cardiac,
or oasophageal opening ; and a pyloric opening, which leads to the intestinal canal. The
great pouch is sometimes called the fundus.

The coats of the stomach are three in number; the peritoneal, muscular, and mucous.
By some, the fibrous tissue which unites the mucous to the muscular coat is regarded as
a distinct covering and is called the fibrous coat.

Peritoneal Coat. — This is simply a process of the peritoneum, similar in structure to
the membrane which covers the other abdominal viscera. It is a reflection of the mem-
brane which lines the general abdominal cavity, which, on the viscera, is somewhat thin-
ner than it is on the walls of the cavity. Over the stomach, the peritoneum is from -$±-3
to Fro °f an incn m thickness. It belongs to the class of serous membranes and con-
sists of fibres of the white inelastic tissue, mingled with a considerable number of elastic
fibres. It is closely adherent to the subjacent muscular coat and is not very abundantly
supplied with blood-vessels and nerves. Lymphatics have been demonstrated only in the
subserous structure. The surface of the peritoneum is everywhere covered with regu-
larly-polygonal, flattened cells of pavement or tessellated epithelium, closely adherent to
each other and presenting a perfectly smooth surface which is continually moistened
with a small quantity of watery secretion. An important function of this membrane is
to present a smooth surface covering the abdominal parietes and viscera, so as to allow
of free movements of the organs over each other and against the walls of the abdomen.

Muscular Coat. — Throughout the whole of the alimentary canal, from the cardiac
opening of the stomach to the anus, the muscular fibres forming the middle coat are of

PHYSIOLOGICAL ANATOMY OF THE STOMACH. 227

the involuntary, pale, or unstriped variety. These fibres, called sometimes muscular
fibre-cells, are very pale, with faint outlines, fusiform or spindle-shaped, and contain each
an oval, longitudinal nucleus. They are very closely adherent by their sides, and are so
arranged as to dovetail into each other, forming sheets of greater or less thickness,
depending upon the number of their layers. The muscular coat of the stomach varies in
thickness in different animals. In the human subject, it is thickest in the region of the
pylorus and is thinnest at the fundus. Its average thickness is about ^ of an inch. In
the pylorus, it is from T^ to TV of an inch thick, and in the fundus, from 5V to A °f an mcn-
The muscular fibres exist in the stomach in two principal layers ; an external, longi-
tudinal layer and an internal, circular layer, with a third layer of oblique fibres extending
over the great pouch only, which is internal to the circular layer. The direction of the
fibres in these layers can generally be seen in a stomach which has been dried and inflated.
The longitudinal fibres are continued from the oesophagus and are most marked over the
lesser curvature. They are not continued very distinctly over the rest of the stomach.
The circular and oblique fibres are best seen when the organ has been everted and the
mucous membrane carefully removed. The circular layer is not very distinct to the left
of the cardiac opening, over the great pouch, but in other parts it is tolerably regular.
Toward the pylorus, the fibres become more numerous, and, at the opening into the
duodenum, they form a powerful muscular ring, which is sometimes called the sphincter
of the pylorus, or the pyloric muscle. At this point they project considerably into the
interior of tbe organ and cease abruptly at the opening into the duodenum, so as to form
a sort of valve, presenting, when contracted, a flat surface looking toward the intestine.
The oblique layer takes the place, in great part, of the circular fibres over the great
pouch. It extends obliquely over the fundus from left to right and ceases at a distinct
line extending from the left margin of the oesophagus to about the junction of the middle
with the last third of the great curvature. This anatomical fact is interesting, for it
is at about the point where the oblique layer of fibres ceases that the stomach becomes
constricted during the movements which are incident to digestion, dividing the organ into
two tolerably distinct compartments.

FIG. 54.— Longitudinal fibres of the stomach. (Sappey.)

1, lesser curvature; 2, 2. greater curvature ; 3, greater pouch; 4, lesser pouch ; 5, C, 6, lower end of the oesophagus ; 7,7,
pylorus; 8, 8, longitudinal fibres at the lesser curvature; 9, fibres extending over the greater curvature; 10, 10,
a very thin layer of loneritndinal fibres over the anterior surface of the stomach; 11, circular fibres seen through
the thin layer of longitudinal fibres.

228

DIGESTION.

The blood-vessels of the muscular coat are quite numerous and are arranged in a
peculiar, rectangular net-work, which they always present in the non- striated muscular
tissue. The nerves belong chiefly to the sympathetic system and are demonstrated with
difficulty.

FIG. 55. — Fibres seen with the stomach everted. (Sappey.)

1, 1, oesophagus ; 2, circular fibres at the cesophageal opening ; 8. 3. circular fibres at the lesser curvature ; 4, 4, circu-
lar fibres at the pylorus ; 5, 5. 6, 7, 8, oblique fibres ; i», 10, fibres of this layer covering the greater pouch ; 11, por-
tion of the stomach from which these fibres have been removed to show the subjacent circular fibres.

Mucous Coat. — Passing from the oesophagus to the stomach, a very marked change
takes place in the character of the mucous membrane. The white, hard appearance of
the oesophageal lining, due to its covering of pavement-epithelium, abruptly ceases, pre-
senting a sharply-defined, dentated border; and the membrane of the stomach is soft,

velvety in appearance, and of a reddish-gray
color. In some of the inferior animals, as the
horse, the characteristic membrane of the oesoph-
agus is prolonged into the stomach and forms
a large, white zone around the cardiac opening,
with abruptly-defined edges, contrasting strong-
ly with the rest of the lining membrane of the
stomach.

The mucous lining of the stomach is loosely
attached to the submucous muscular tissue and
is thrown into large, longitudinal folds, which
become effaced as the organ is distended. When
the muscular coat of the stomach is in a condi-
tion of cadaveric rigidity, the longitudinal fold-
ing of the mucous membrane is very marked.
If the mucous membrane be stretched or if the
stomach be everted and distended, and the
mucus, which always exists in greater or less
abundance over the surface, be gently removed
under a stream of water, the membrane will be found marked with innumerable po-
lygonal pits or depressions, enclosed by ridges, which, in some parts of the organ, are
quite regular. These are best seen with the aid of a simple lens, as many of them are

%ff?yff3£Sft*J£

nified 20 diameters. (Sappey.)

PHYSIOLOGICAL ANATOMY OF THE STOMACH. 229

quite small. The size of the pits is very variable, but the average is about ^TJ of an
inch. This appearance is not distinct toward the pylorus; the membrane here present-
ing irregular, conical projections and well-marked villi resembling those found in the
small intestine. The surface of the mucous membrane is covered with columnar or pris-
moidal epithelium, the cells being tolerably regular in shape, each with a clear nucleus
and a distinct nucleolus.

The thickness of the mucous membrane of the stomach varies in different parts. It
is usually thinnest near the oesophagus and thickest near the pylorus. Its thinnest portion
measures from 7^ to ^ of an inch ; its thickest portion, from T\ to ^ of an inch ; and
the intermediate portion, about ^ of an inch.

Glandular Apparatus of the Stomach. — Extending from the bottoms of the pits in the
mucous membrane of the stomach to the submucous connective tissue, are immense num-
bers of racemose glands. These are generally arranged in tolerably distinct groups, sur-
rounded by fibrous tissue, each group belonging to one of the polygonal depressions.
The tissue which connects the tubes is dense but not abundant. There are marked dif-
ferences in the anatomy of the glands of the stomach in different parts of the organ,
which are particularly interesting, as they are supposed to correspond with differences in
the function of various parts of the mucous membrane. There are, indeed, two distinct
varieties of glands; the gastric glands, found throughout the organ, except in the pyloric
portion, and the mucous glands found chiefly in the pyloric portion, with a few scattered
irregularly through the other portions of the mucous membrane. These demand special
consideration, as the former are supposed to secrete the gastric juice and are active only
during digestion, while the latter secrete a glairy mucus, which is not produced specially
during digestion and which has no distinct digestive function with which we are ac-
quainted.

Gastric, or Peptic Glands.— These glands are found throughout the entire extent of
the mucous membrane of the stomach, except around the pyloric orifice and in the lesser
pouch. In the human subject, their distribution, as compared with that of the mucous
glands, is much wider than in most of the inferior animals. They vary in their length
with the variations in the thickness of the mucous membrane. Recent researches have
shown that all of these glands are racemose. They present, in the upper fourth or fifth of
their length, a single tube, lined by a continuation of the columnar epithelium covering the
surface of the mucous membrane. Below this, they divide into several branches, pri-
mary and secondary, and are lined with rounded cells of glandular epithelium, having the
appearance of simple racemose glands. The cells lining the branching tubes are some-
times called peptic cells. They each have a nucleus and a nucleolus, contain numerous
granules, and are about T^Vir of an inch in diameter. This is the general character of the
glands in the greater part of that portion of the mucous membrane which secretes the
gastric juice. They readily undergo post-mortem alteration, and, in the human subject,
are only to be seen satisfactorily in the fresh stomachs of subjects who have died sud-
denly, having previously been in a condition of perfect health.

Mucous Glands.— Near the pyloric extremity of the stomach and in the lesser pouch,
where the mucous membrane is decidedly paler than over the rest of the organ, the
character of the glands is peculiar. As a rule, the glands in these situations are com-
pound ; but they do not present more than two or three divisions until they have passed
through about one-half of the thickness of the mucous membrane, when they break up
into numerous small secondary tubes. The important peculiarity of these glands is
that they are lined throughout with columnar epithelium and are everywhere deprived
of the cells found in the true peptic glands. The structure of the glands from different
portions of the stomach is shown in Fig. 57.

Closed Follicles. — In the substance of the mucous membrane, between the tubes and
near their c&cal extremities, are occasionally found closed follicles, like the solitary glands

230

DIGESTION.

and patches of Peyer of the intestines. These are not always present in the adult, but
are generally found in children. They are usually most abundant over the greater curva-
ture, though they may be found in other situations. In their anatomy they are identical
with the closed follicles of the intestines and do not demand special consideration in this
connection.

Fio. 57.— Peptic and mucous glands ; magnified 100 diameters. (Sappey.)

A. Peptic gbnd from the middle portion of the stomach : 1, excretory canal; 2, 2, 2, the three principal branches of

the gland ; 3, 8, 3, secondary branches filled with rounded cells.

B. Peptic gland from the pyloric portion: 1, excretory canal; 2, 2, the two principal branches; 8, 3, terminal culs-

de-sac.

C. Mucous gland from the pyloric portion : 1, excretory canal; 2, 2, the two branches; 3, 3, 3, 3, 3, secondary branches ;

4, 4, 4, small, terminal, racemose glands.

Gastric Juice.

At the present day it seems profitless to argue the question of the existence of a
digestive fluid in the stomach ; and the discussions of the earlier physiologists as regards
the possibility of the existence of a fluid capable of dissolving the articles of food have
only an historical interest. Our definite knowledge of the most important physiological
properties of this fluid dates from the celebrated observations of Dr. Beaumont on Alexis
St. Martin, the Canadian, who had a large fistulous opening into the stomach. These
observations were commenced in May, 1825, and were continued for a number of years.
The first publication of them was in the Philadelphia Medical Recorder, in 1826.

Mode of obtaining the Gastric Juice. — The ingenious experiments of Dr. Beaumont
upon the case of St. Martin gave an impulse to the study of digestion and pointed out
the way in which the action of the gastric juice could be investigated. The fact that Dr.
Beaumont noted the action of human gastric juice upon all the ordinary articles of food
enabled physiologists to compare with it the properties of the secretion obtained from the

GASTBIC JUICE.

231

inferior animals, an indispensable condition in the study of the digestive fluids. In 1843,
Blondlot published a treatise on digestion, in which he gave the results of experiments
on dogs with fistulous openings into the stomach. This observer is generally spoken of
as the first to obtain the gastric juice by the establishment of a fistula into the stomach
in the inferior animals ; but Longet states that, in December, 1842, Dr. Bassow read a
paper before the Imperial Society of Naturalists of Moscow, which was published in the
Bulletin for that year, in which he gave an account of a number of successful attempts
to establish gastric fistulas in dogs. In the animals operated upon by Bassow, the
fistula was not kept open by a canula, and he was much annoyed by its tendency to
close. There is no reason to suppose that Blondlot was aware of the experiments of
Bassow, which, as Longet remarks, were little known to physiologists and, as far as we
are aware, were not quoted in works on physiology before the publication of Longet's
treatise, in 1861. With some slight modifications in the operative procedure, the method
of Blondlot is the one now in common use.

The establishment of a permanent gastric fistula is now one of the simplest and most
common of the physiological experiments. The dog is the animal generally used; and,
from the fact that he is not very subject to peritonitis, the operation almost always ends
in recovery, and the animal can be trained so that the juice may be obtained in quantity
and with great facility. The operative procedure which we have found most convenient
is the following :

It is best to choose a dog of medium size, young, but nearly, if not entirely full grown,
in perfect health, and of good disposition. Bringing the animal under the influence of
ether, he is to be held firmly on the back, and an incision
about two inches in length is made in the median line into the
abdominal cavity. This incision should be commenced from
half an inch to an inch below the ensiforrn cartilage. Intro-
ducing the finger into the abdominal cavity, the stomach can
readily be felt, especially if it be moderately distended ; and,
with a pair of hooked, or bull-dog forceps, that portion of the
stomach nearest the wound may be seized and drawn out of
the abdomen. It is important to make the fistula into that
portion of the anterior wall of the stomach which is nearest
the wound, in order to avoid disturbance in the position of the
viscera; and the organ is in the most favorable position for
the operation if it be moderately distended with food.

A portion of the stomach being drawn out of the abdomen,
a slit is made parallel to the longitudinal fibres, just large
enough to admit the canula.

A silver canula, about an inch and a quarter in length, half
an inch in diameter, and provided with a straight rim or flange
at each end about half an inch in width, is now introduced into
the stomach and firmly secured in place by a ligature sur-
rounding it and passed in and out through the coats of the
stomach near the lips of the wound, like the string of a purse.
This canula may be single or, as suggested by Bernard, double,
one half screwing into the other so that it may be elongated to
twice the length it has when closed. This is somewhat con-
venient, as the tube may be introduced elongated, and, when
the swelling of the parts has subsided, it may be shortened by a
key, so as not to project beyond the abdominal walls.

After the canula has been firmly fixed in the stomach, the
tube, with one of its flanged ends projecting, should be drawn to the upper part of the
opening in the abdomen, and the wound closed by sutures passed through the integument,
muscles, and peritoneum.

FIG. 58. — Tube for gastric fis-
tula. (Bernard.)

A, B, section of the silver tube
psrtlv uiiMTewed; 0, projec-
tion 'to receive the key used
in turning the screw : I>. head
of the key; E, extremity of
the tube.

232

DIGESTION".

59.— Gastric fistula. (Bernard.)
E, stomach; D, duodenum; M, muscles of the abdomen, di-
vided ; O, opening of the fistula.

The dog will generally eat on the second or third day after the operation ; and perito-
nitis— aside from the inflammatory action which agglutinates the stomach at the site of
the operation to the walls of the abdomen — rarely follows. It is best to feed the animal
sparingly a short time before operating, as there is some difficulty in seizing the stomach
when it is entirely empty.

Having established a permanent fistula into the stomach, after the wound has cica-
trized around the canula, the animal suffers no inconvenience and may serve indefi-
nitely for experiments on the gastric
juice. Many physiologists have been in
the habit of exciting the flow of this
fluid by the introduction into the stom-
ach of pieces of tendon or hard, indi-
gestible articles, on the ground that the
fluid taken from the fistula, under these
circumstances, is unmixed with the pro-
ducts of stomach-digestion ; but it has
been shown that the quantity and char-
acter of the juice are influenced by the
nature of the stimulus which causes its
secretion, and it is proper, therefore, to
excite the action of the stomach by ar-
ticles which are relished by the animal.
For this purpose, lean meat may be
given, cut into pieces so small that they
will be swallowed entire, and first
thrown into boiling water so that their exterior may become somewhat hardened. The
cork is then removed from the tube, which is freed from mucus and debris, when

the gastric juice will begin to flow, sometimes immediately
and sometimes in from three to five minutes after the food
has been taken. It flows in clear drops or in a small stream
for about fifteen minutes, nearly free from the products of
digestion. At the end of this time it is generally accom-
panied with grumous matter, and the experiment should
be concluded if it be desired simply to obtain the pure se-
cretion. In fifteen minutes, from two to three ounces of
fluid may be obtained from a good-sized dog, which, when
filtered, is perfectly clear; and this operation may be re-
peated three or four times a week without interfering with
the quality of the secretion or injuring the health of the
animal.

Although instances of gastric fistula in the human sub-
ject had been reported before the case of St. Martin and
have been observed since that time, the remarkably healthy
condition of the subject and the extended experiments of
so competent and conscientious an observer as Dr. Beau-
mont have rendered this case memorable in the history of
physiology. It is undoubtedly the fact that this is the only
instance on record in which pure, normal gastric juice has
been obtained from the human subject; and it served a
most important purpose as the standard for comparison of
subsequent experiments on the inferior animals. The de-
tails of this case, condensed from the monograph of Beau-
mont, are briefly the following:
Alexis St. Martin, a Canadian voyageur in the service of the American Fur Company,

FIG. 69. — Dog irWi a f/astric fistula.
(Beclard.)

GASTRIC JUICE.

233

eighteen years of age, of good constitution and perfectly healthy, was wounded in the
left side by the accidental discharge of a gun loaded with duck-shot. The wound was
received on the 6th of June, 1822, and the muzzle of the gun was not more than a yard
distant from the body. The contents of the gun entered posteriorly, carrying away
integument and muscles from a space the size of the hand, with the anterior half of the
sixth rib, fracturing the fifth rib, lacerating the lower portion of the left lobe of the
lung and the diaphragm, and perforating the stomach. The patient was seen by Dr.
Beaumont twenty-five or thirty minutes after the accident, when the above facts were
noted, and an opening into the stomach was discovered large enough to admit the fore-
finger. Extensive sloughing took place, and for seventeen days every thing that was
swallowed passed out at the wound, and nourishment was administered by the rectum.
In the spring of 1824, the wound had cicatrized, and the patient had perfectly recovered
his health ; but, in the process of cure, seven pieces of cartilage had come away, and three
or four inches of the sixth rib, with about half of the lower edge of the fifth rib, had been
removed by an operation. The perforation into the stomach was irregularly-circular in
form and about two and a half inches in circumference. This opening was closed by a
protrusion of the mucous membrane of the stomach in the form of a. valve, which could
readily be depressed by the finger so as to expose the interior of the organ. This valve
effectually prevented the discharge of the contents of the stomach, which had annoyed
the patient previous to the winter of 1823-'24.

FIG. 61.— Gastric fistula in the case of St. Martin. (Beaumont.)

A, A, A, B, borders of the opening into the stomach ; C, left nipple ; D, chest ; E, cicatrices from the wound made
for the removal of a piece of cartilage; F, F, F, cicatrices of the original wound.

From May, 1825 until August of the same year, St. Martin was under the observation
of Dr. Beaumont and submitted to numerous experiments. At the end of that time, he
returned to Canada and was lost sight of for four years, during which time he married
nnd became the father of two children, " worked hard to support his family, and enjoyed
robust health and strength." He then came again under the observation of Dr. Beau-
mont and continued in his service, doing the work of a common servant, until March,
1831. After this he was under observation from time to time until 1836 ; all this time
enjoying perfect health, with good digestion, and having become the father of several
more children. The last published observations made upon this case were in 1856.

The following was the method employed by Dr. Beaumont in extracting the juice:

234 DIGESTION.

The subject was placed on the right side in the recumbent posture, the valve was de-
pressed within the aperture, and a gum-elastic tube, of the size of a large quill, was
passed into the stomach to the extent of five or six inches. On turning him upon the left
side until the opening became dependent, the stimulation of the tube caused the secretion
to flow, sometimes in drops and sometimes in a small stream. The quantity of fluid or-
dinarily obtained was from four drachms to an ounce and a half. The usual time for
collecting the juice was early in the morning, before he had eaten. It was remarked
that under these circumstances there was never an accumulation of gastric juice in the
stomach, and its flow was only excited by the stimulus of the tube. It was also repeat-
edly observed that the introduction of alimentary principles, while the tube was in the
stomach, produced an almost instantaneous increase in the flow.

Thanks to these opportunities for observing the action of the human stomach, followed
by the experiments of Blondlot and others on the inferior animals, now so common,
physiologists have become pretty well acquainted with the phenomena which attend the
secretion of the gastric juice.

Secretion of the Gastric Juice. — As the earlier observers were unacquainted with the
laws which regulate the production of secreted fluids as distinguished from those which
contain only excrementitious principles, their ideas concerning the secretion of the gastric
juice were necessarily indefinite. One of the most important facts developed by Beau-
mont was that the normal solvent fluid of the stomach is only produced in obedience to
the stimulus of food, during the natural process of digestion. Recent advances in physio-
logical chemistry have enabled experimenters to correct many errors in the observations
of Beaumont concerning the properties and action of the gastric juice, but his descrip-
tions of the phenomena which accompany its secretion have been repeatedly verified.

During the intervals of digestion, the mucous membrane is comparatively pale, " and
is constantly covered with a very thin, transparent, viscid mucus, lining the whole inte-
rior of the organ." On the application of any irritation, or, better, on the introduction
of food, the membrane changes its appearance. It now becomes red and turgid with
blood ; small pellucid points begin to appear in various parts, which are, in reality, drops
of gastric juice ; and these gradually increase in size until the fluid trickles down the
sides in small streams. The membrane is now invariably of a strongly acid reaction,
while at other times it is either neutral or faintly alkaline. The thin, watery fluid thus
produced is the true gastric juice. Although the stomach may contain a clear fluid at
other times, this is generally abnormal, is but slightly acid, and does not possess the
marked solvent properties characteristic of the natural secretion. It has been shown by
Beaumont, and his observations have been repeatedly confirmed by experiments on the
inferior animals, that the gastric juice is secreted in greatest quantity and possesses the
most powerful solvent properties, when food has been introduced into the stomach by
the natural process of deglutition. Under these circumstances the stimulation of the
mucous membrane is general, and secretion takes place from the entire surface capable
of producing the fluid. When any foreign substance, as the gum-elastic tube used in
collecting the juice, is introduced, the stimulation is local, and the flow of fluid is com-
paratively slight. It has been also observed that the quantity immediately secreted on
the introduction of food, after a long fast, is always much greater than when food has
been taken after the ordinary interval.

While natural food is undoubtedly the proper stimulus for the stomach, and while, in
normal digestion, the quantity of gastric juice is perfectly adapted to the work it has to
perform, it has been noted that savory and highly-seasoned articles generally produce a
more abundant secretion than those which are comparatively insipid. An abundant
secretion is likewise excited by some of the vegetable bitters.

Impressions made on the nerves of gustation have a marked influence in exciting the
action of the mucous membrane of the stomach. Blondlot found that sugar, introduced

GASTRIC JUICE. 235

into the stomach of a dog by a fistula, produced a flow of juice much less abundant than
when the same quantity was taken by the mouth. To convince himself that this did not
depend upon the want of admixture with the alkaline saliva, he mixed the sugar with saliva
and passed it in by the fistula, when the same difference was observed. It is a curious
fact that, in some animals, particularly when they are very hungry, the sight and odor
of food will induce secretion of gastric juice.

The gastric juice is probably one of. the most sensitive of the secreted fluids to dis-
turbing influences. It was remarked by Beaumont that a febrile condition of the system,
the depression resulting from an excess in eating and drinking, or even purely mental
conditions, such as anger or fear, vitiated, diminished, and sometimes entirely suppressed
secretion by the stomach. At some times the mucous membrane became red and
dry, and at others it was pale and moist. In such morbid conditions, it is stated that
drinks were immediately absorbed, but that food remained in the stomach undigested for
twenty-four or forty-eight hours.

The influence of the nervous system on the secretion of gastric juice, exerted particu-
larly through the pneumogastric nerves, is very marked and important, but its considera-
tion belongs properly to the section on the nervous system.

After the food has been in part liquefied and absorbed and in part reduced to a pulta-
ceous consistence, the secretion of gastric juice ceases; the movements of the stomach
having gradually forced that portion of the food which is but partially acted upon in this
organ or is digested only in the small intestines, out at the pylorus. The stomach is thus
entirely emptied, the mucous membrane becomes pale, its reaction loses its marked acid
character and becomes neutral or faintly alkaline.

Secretion in Different Parts of the Stomach. — The differences already noted in the
anatomy of the mucous membrane of the stomach in different parts of the organ point
to the important question of a possible difference in the physiological action of the secre-
tions of different parts, particularly the pyloric portion and the rest of the general surface.
We can learn but little that is definite with regard to this point from observations on
the inferior animals, unless they be confirmed in the human subject. The observations,
however, of Kolliker, Goll, and Donders, on the pig, are very satisfactory, and subse-
quently they were fully confirmed as regards the human subject. It is well known that an
acidulated infusion of the mucous membrane of the stomach possesses, if properly pre-
pared, all the digestive properties of the true gastric juice, and that this is not the case
with similar infusions of the mucous membrane from any other parts. Kolliker, in ex-
periments on artificial digestion made in conjunction with Dr. Goll, " on the gastric mu-
cous membrane of the pig, clearly showed that the two kinds of glands entirely differ in
respect of their solvent power ; inasmuch as those with the round cells dissolved acidu-
lated coagulated protein-compounds in a very short time ; those with cylindrical epithe-
lium, on the contrary, either did not operate at all, or produced a slight effect only after
a longer period." The same author farther states that these observations were confirmed
by Donders and himself in the human stomach.

Although the character of the secretion in different parts of the stomach is not the
same in all animals, it must be admitted that, in man, the mucous membrane of the stom-
ach, in what is called the pyloric zone, does not secrete the true, acid, solvent, gas-
tric juice. In other words, this fluid is produced only in those portions of the stomach
in which the mucous membrane is provided with tubes lined with cells of glandular epi-
thelium, or what have been called the stomach-cells.

In most of the modern works on physiology, allusion is made to the probable quantity
of gastric juice secreted in the twenty-four hours. The estimates on this point can be
only approximative, even in the inferior animals, and they give no definite information
concerning the normal quantity in the human subject. Bidder and Schmidt, Lehmann,
Corvisart, and others, have made calculations of the probable quantity, either by collect-
ing the juice for a certain time and multiplying the quantity thus obtained by a number

236 . DIGESTION.

to represent the whole twenty-four hours, or by ascertaining the amount of fluid required
to digest a certain weight of food and estimating from this the quantity necessary to dis-
pose of all the food taken during the day. Both of these methods are manifestly incor-
rect. In the first, the intermittency of the secretion is not taken into account ; and, in
the second, it is incorrectly assumed that digestion out of the hody is accomplished pre-
cisely as it takes place in the stomach.

Dr. Beaumont was sometimes able to collect, in from ten to fifteen minutes, two
ounces of pure gastric juice, simply by the stimulation produced by the gum-elastic
catheter used in the operation ; but he expressly states that, in this case, only a part of the
mucous membrane is excited to secretion, while the flow is very much increased by the
introduction of food by the mouth, which produces a general excitation of the secreting
membrane. Estimates like those of Bidder and Schmidt, which put the quantity of gas-
tric juice secreted in twenty-four hours by a healthy man of ordinary size at six thou-
sand four hundred grammes, or about fourteen pounds, are probably not exaggerated,
although they are of necessity merely approximative.

The enormous quantity of fluid daily secreted by the mucous membrane of the stom-
ach would excite surprise were it not considered that, after this fluid has performed its
office in digestion, it is immediately reabsorbed, and but a small quantity of the secretion
exists in the stomach at any one time. During digestion, a circulation of material is
going on, in which the stomach is continually producing, out of materials furnished by
the blood, a fluid which liquefies certain elements of the food and, as fast as this is ac-
complished, is absorbed again by the blood, together with the principles that have been
thus digested.

Composition of the Gastric Juice.

The gastric juice is mixed in the stomach with more or less mucus secreted by the
lining membrane. When drawn by a fistula, it generally contains particles of food, which
have become triturated and partially disintegrated in the mouth, and is always mixed
with a certain quantity of saliva, which is swallowed during the intervals of digestion as
well as when the stomach is in a state of functional activity. By adopting certain pre-
cautions, however, the fluid may be obtained nearly free from impurities, except the ad-
mixture of saliva. The juice taken from the stomach during the first moments of its
secretion and separated from mucus and foreign matters by filtration is a clear fluid, of
a faint yellowish or amber tint, and possessing little or no viscidity. Its reaction is
always strongly acid ; and it is now a well-established fact that any fluid, secreted by
the mucous membrane of the stomach, which is either alkaline or neutral, is not the nor-
mal gastric juice.

The specific gravity of the gastric juice in the case of St. Martin, according to the
observations of Beaumont and Silliman, was 1005 ; but later, Dr. F. G. Smith found it
in one instance, 1008, and in another, 1009. There is every reason to suppose that the
fluid, in the case of St. Martin, was perfectly normal, and from 1005 to 1009 may be
taken as the range of the specific gravity of the gastric juice in the human subject.
There is undoubtedly considerable variation, as regards specific gravity, in the inferior
animals.

The gastric juice is described by Beaumont as inodorous, when taken directly from
the stomach ; but it has rather an aromatic and a not disagreeable odor when it has been
kept for some time. It is a little saltish, and its taste is similar to that of "thin, mu-
cilaginous water slightly acidulated with muriatic acid." The gastric juice from the dog
has something of the odor peculiar to this animal.

It has been found by Beaumont, in the human subject, and by those who have experi-
mented on the gastric juice of the lower animals, that this fluid, if kept in a well-
stoppered bottle, will retain its chemical and physiological properties for an indefinite pe-
riod. The only change which it undergoes is the formation of a pellicle, consisting of a

COMPOSITION OF THE GASTRIC JUICE. 237

vegetable, confervoid growth, upon the surface, some of which breaks up and falls to the
bottom of the vessel, forming a whitish, tlocculent sediment. We have now (1875) a
specimen of gastric juice which was taken from a dog witli a gastric fistula in January,
1862. It has no putrefactive odor and is apparently in the same condition as when it
was first drawn. In addition to this remarkable faculty of resisting putrefaction, this
process is arrested in decomposing animal substances, both when taken into the stomach
and when exposed to the action of the gastric juice out of the body.

There are on record no minute quantitative analyses of the human gastric juice,
except those by Schmidt, of the fluid from the stomach of a woman with gastric fistula;
and in this case there is reason to suppose that the secretion was not normal. The analysis
of the gastric juice of St. Martin by Berzelius was not minute. The analyses of Schmidt
give less than six parts per thousand of solid matter, while Berzelius found over
twelve parts per thousand. In all the comparatively recent analyses, there have been
found a free acid or acids ; a peculiar organic matter, generally called pepsin ; and various
inorganic salts, among which may be mentioned as most important, the chlorides of
sodium, potassium, and calcium, with the phosphates of lime, magnesia, and iron. Of
these constituents, the salts possess little physiological importance as compared with the
organic matter and the acid principles.

The following analysis by Bidder and Schmidt gives the mean of nine observations
upon dogs:

Table of Solid Constituents of the Gastric Juice of the Dog.
(Bidder and Schmidt.)

Ferment (pepsin.) , 17*127

Free hydrochloric acid (?) 3'050

Chloride of potassium 1*125

Chloride of sodium 2*507

Chloride of calcium 0'624

Chloride of ammonium 0'468

Phosphate of lime 1*729

Phosphate of magnesia 0*226

Phosphate of iron 0*082

26-938

In another series of three experiments, in which the saliva was allowed to pass into
the stomach, the proportion of free acid was 2*337, and the proportion of organic matter
was somewhat increased.

Organic Principle of the Gastric Juice. — This principle, called pepsin or gasterase, is
an organic nitrogenized body, peculiar to the gastric juice, and, as we shall see farther on,
is essential to its digestive properties. When the gastric fluid was first obtained, even by
the imperfect methods employed anterior to the observations of Beaumont and of Blond-
lot, an organic matter was spoken of as one of its constituents.

Experiments on artificial digestive fluids, by Eberle, Schwann and Miiller, Wasmann,
and others, have demonstrated that acidulated infusions of the mucous membrane of the
stomach, possessing all the physiological properties of the gastric juice, contain an organic
matter, first isolated by Wasmann, on which the solvent powers of these acid fluids seem
to depend. Mialhe, who has obtained this substance in great purity by the process recom-
mended by Vogel, describes the following properties as characteristic of the organic
matter in artificial gastric juice : Dried in thin slices on a plate of glass, it is in the form
of small, grayish, translucent scales, with a faint and peculiar odor and a feebly bitter
and nauseous taste. It is soluble in water and in a weak alcoholic mixture, but is in-
soluble in absolute alcohol. A solution of it is rendered somewhat turbid by a tempera-

238 DIGESTION.

ture of 212° Fahr., but it is not coagulated, although it loses its specific properties. It is
not affected by acids but is precipitated by tannin, creosote, and a great number of the
metallic salts. This substance dissolved in water slightly acidulated possesses, in a very
marked degree, the peculiar solvent properties of the gastric juice; but, it has been found
by Payen and Mialhe not to be so active as the principle extracted from the gastric juice
itself, which is described by Payen under the name of gasterase. In the abattoirs of
Paris, Mialhe collected from the secreting stomachs of calves as they were killed, from
six to ten pints of gastric juice ; and from this he extracted the pure pepsin by the pro-
cess recommended by Payen, which consists merely in one or two precipitations by
alcohol. This substance he found to be identical with the principle obtained by Payen
from the gastric juice of the dog. Its action upon albuminoid matters was precisely the
same as that of pepsin extracted from artificial gastric juice, except that it was more
powerful.

Source of the Acidity of the Gastric Juice. — Reaumur and Spallanzani recognized
that the fluid from the stomach has, at certain times, an acid reaction ; and subsequent
observations have confirmed this fact and have shown that this reaction is invariable
during digestion. But, although the most distinguished and skilful chemists of the day
have attempted to ascertain the source of this acidity, from Prout, in 1823, to Blondlot,
in 1858, embracing Leuret and Lassaigne, Tiedemann and Gmelin, Berzelius, Chevreul,
Bidder and Schmidt, Dumas, Lehmann, Bernard and Barreswil, with a host of others,
the question has not yet received a solution which is generally accepted.

The method made use of by some of those who profess to have found free hydrochloric
acid in the gastric juice has been to subject the fluid to distillation, testing the acid fluid
which passes over with nitrate of silver ; but the experiments of Bernard and Barreswil
on the gastric juice from dogs, and the more recent observations of Dr. F. G. Smith on
the gastric juice from St. Martin, have shown that this process is really of little value.
The following observations by Bernard and Barreswil seem to show that, although
hydrochloric acid may be obtained from gastric juice by distillation, it does not neces-
sarily exist in the fluid in a free state ; which is a very important consideration in a ques-
tion in which every thing depends upon the absolute accuracy of modes of analyses :

In subjecting the gastric juice of the dog to distillation at a low temperature, with all
the necessary precautions, it was found that the first products did not present an acid re-
action. It was at first thought that this would be a ground for the exclusion of hydrochloric
acid, which is considered to be volatile ; but it was found that, in the distillation of water
which had been slightly acidulated with hydrochloric acid, the first products were neu-
tral, and the acid was disengaged only in the fluid which passed over toward the last
periods of the process. On again distilling the gastric juice, it was found that the prod-
uct was neutral, presenting no precipitate with the nitrate of silver, until about four-
fifths of the fluid had passed over; that afterward, the fluid which passed over was distinct-
ly acid, but did not precipitate with the salts of silver ; and " finally, only toward the last
instants, when there remained only a few drops of gastric juice to evaporate, the acid
liquid which was produced gave a marked precipitate with the salts of silver, which was
not dissolved by concentrated nitric acid." It was found that the addition to the gastric
juice of a small quantity of oxalic acid produced a marked opacity due to the formation
of the insoluble oxalate of lime, while an equal quantity of the same reagent produced no
opacity in water containing a proportion of two thousandths of hydrochloric acid, to
which chloride of calcium had been added. From this experiment, Bernard concluded
that the hydrochloric acid in the gastric juioe exists in the condition of a chloride and
not in a free state.

Prof. F. G. Smith, who had an opportunity of examining the gastric juice from St.
Martin, in 1856, took the fluid from the stomach after two ounces of dry bread had been
chewed and swallowed, and subjected it to distillation. The first fluid which passed over

COMPOSITION OF THE GASTRIC JUICE. 239

was neutral, and the residue, after the temperature had been somewhat raised, produced
a slight precipitate with the nitrate of silver, which was soluhle in ammonia. In an-
other experiment, a mixture of lactic acid and chloride of sodium in solution was sub-
jected to distillation, and the product formed a slight precipitate with the nitrate of sil-
ver, which was soluble in ammonia. In another experiment, a mixture of lactic acid
and chloride of sodium in solution was subjected to distillation, and the product formed
a slight precipitate with the nitrate of silver. The precipitation, in this instance, was
attributed to the passage of a small quantity of chloride of sodium with the vapors, and
it is to this, also, that he attributes the opalescence of the products of distillation of the
gastric juice, when treated with the nitrate of silver. These experiments are of great
interest in so far as they confirm the observations of Bernard, Villefranche, and Bar-
reswil, on the gastric juice of the dog.

The experiments of Lehmann are even more conclusive. He found that pure gastric
juice, when evaporated in vacua, develops hydrochloric acid ; but he also found that
chloride of calcium is decomposed during evaporation with lactic acid in vacuo and
attributes the generation of hydrochloric acid in the gastric juice to the decomposition
with this salt, and not the chloride of sodium, as was thought by Bernard, Villefranche,
and Barreswil.

The addition of a small quantity of oxalic acid to gastric juice produces a precipitate
of the insoluble oxalate of lime, which does not take place in the presence of free hydro-
chloric acid, even when it exists in very minute quantity. No one has denied that this
reaction always takes place in the gastric juice ; but, in this fluid, is it inconsistent with
the presence of a small quantity of hydrochloric acid ? We have found that the addition
of two drops of ordinary hydrochloric acid to half a fluidounce of gastric juice does not
prevent the precipitation of the oxalate of lime, which, in the single observation referred
to, was prevented only when the quantity of acid was increased to five drops. On adding
oxalic acid to fresh urine, the precipitate of oxalate of lime was marked ; but, after the
addition of two drops of ordinary hydrochloric acid, this reaction did not take place.
Taken in connection with the fact that many of the ordinary chemical reactions are pre-
vented or modified in fluids containing organic substances, this would lead us to inquire
whether free hydrochloric acid may not exist in small quantity in the gastric juice, and,
as an exceptional phenomenon, the reaction between the oxalic acid and the soluble salts
of lime still take place, or whether the acid may not unite with the organic principle,
forming, as was suggested by Schiff, chlorohydropeptic acid. In support of this latter
view, it is to be remembered that Mulder has formed combinations of organic principles
with various of the mineral acids, such as the sulphuric and the hydrochloric. In these
compounds, the acid character remains, but the ordinary reactions of the acid are lost.

With the abundant opportunities which have been presented for the chemical study
of the gastric juice, not only in the inferior animals but in man, and in view of the nu-
merous elaborate researches into the nature of this fluid by the most skilful physiological
chemists of the day, it is a matter of surprise that the question of the existence of free
hydrochloric acid, or its condition as regards combination with the organic matter, is
not settled. It certainly cannot now be regarded as determined beyond question. If,
as is supposed by Bidder and Schmidt, there be a proportion of chlorine which cannot be
accounted for by the quantity of ordinary bases in the gastric juice, it probably does not
exist as free hydrochloric acid, but it is in some way united with organic matter.

In 1786, Macquart indicated the presence of lactic acid in the gastric juice of the calf,
attributing the acidity of the gastric juice of the ox and the sheep to free phosphoric
acid. Since then there have been numerous analyses in which this princ-ipU' has been
said to be found. Among those who early adopted this view, may be mentioned Che-
vreul, Graves, and Leuret and Lassaigne. After the analyses by Prout, in 1823, and the
observations of Beaumont on the fluid obtained from St. Martin, and until the publication
of the experiments of Bernard, Villefranche, and Barreswil, in 1844, hydrochloric acid

240 DIGESTION.

was generally supposed to be the free acid of the gastric juice. It is chiefly on the last-
named observations— which have been supported by Bernard in his later publications and
by the confirmatory experiments of Lehmann and others — that those who admit the
presence of free lactic acid in quantity in the gastric juice rest their belief.

We have already referred to the experiments of Bernard, which show that an artificial
fluid containing chloride of sodium and lactic acid in solution behaves, during distillation,
in every way like the normal gastric juice. These show, also, how hydrochloric acid
may be produced during the last period of the distillation by decomposition of the
chlorides. We have seen that this observation was confirmed by Lehmann, who noted
the same reaction during evaporation at the ordinary temperature, in vacuo, although he
supposed the action in the gastric juice to be upon the chloride of calcium instead of the
chloride of sodium. Lehmann found in the acid residue, free lactic acid, lactate of lime,
and alkaline chlorides. Bernard and Lehmann have brought forward other experimental
facts to show that the gastric juice contains lactic acid. If starch be boiled in a solution
containing hydrochloric acid, it soon loses its property of forming a blue compound with
iodine ; while if it be boiled with lactic acid, no such change is observed. If starch be
boiled with a solution containing hydrochloric acid, to which has been added a soluble
lactate in excess, it remains unaltered ; which shows, according to Bernard, that hydro-
chloric acid in a free state cannot exist in the presence of an excess of a salt of lactic
acid. By similar experiments, the same observer assumes to prove that the existence of
hydrochloric acid is inadmissible in the presence of a phosphate or an acetate in excess.
Lehmann has found that starch boiled with gastric juice retains the property of being
colored blue by iodine. These experiments are considered by Bernard as positive proof
that the acid of the gastric juice is the lactic; and the fact "seems to him to be at the
present day beyond contestation." The facts adduced by Lehmann, however, are even
stronger. By operating upon a large quantity of gastric juice, he formed the lactates in
such a quantity that he was enabled to subject them to ultimate analysis and determine
positively the nature of the acid. He found that the acid had the composition of lactic
acid formed from sugar, and not that of the acid formed from the juice of the muscular
tissue.

In view of the facts above mentioned and the somewhat uncertain basis on which
the supposition of the presence of free hydrochloric acid is founded, it seems almost cer-
tain that the principal free acid of the gastric juice is the lactic. It is important to re-
member that, while the experiments of Bernard and Lehmann were made on gastric
juice from the dog, they have been confirmed, in their essential particulars, by the more
recent observations of Prof. F. G. Smith on the normal gastric juice from the human
subject.

It now only remains to discuss the question of the existence in the gastric juice of the
acid phosphate of lime, to the exclusion altogether of free acids ; a theory first proposed
by Blondlot in 1843, and entertained and defended by him, as late as 1858, notwithstand-
ing the fact that this view has met with no favor among physiologists.

To Blondlot belongs the rare merit of having been one of the first, if not the very
first, to propose and execute an experiment by which the normal gastric juice could be
obtained in quantity from a living animal. In his first analysis of the fluid thus obtained,
he denied the existence of any acid principles except the biphosphate of lime. This
view he holds at the present day ; and, notwithstanding the elaborate researches of the
most distinguished physiological chemists, in all of which a free acid of some kind has
been recognized, he still ardently defends his original position. The question of the exist-
ence in the gastric juice of the acid phosphate of lime, to the exclusion of free acids, may
be discussed in a few words.

Assuming that the gastric juice contains a free acid, a view which the arguments of
Blondlot fail to disprove, the question arises whether the biphosphate of lime may not
also exist in this fluid. On this point there can be no doubt. All the modern analyses

COMPOSITION OF THE GASTRIC JUICE. 241

of the gastric juice give the phosphate of lime as one of its constituents; and Blondlot
justly remarks that it is strange to see, in certain analyses, the neutral phosphate of lime
and hydrochloric or lactic acid put down as existing together, as though the phosphoric
acid were able to retain the two equivalents of the base in the presence of either of these
two acids. The fact is, that basic phosphate of lime, a salt insoluble in pure water but
soluble in acid solutions, is invariably decomposed in the presence of acids as powerful as
the hydrochloric or the lactic. It then loses two equivalents of the base and is trans-
formed into an acid phosphate.

There can be no doubt of the constant presence of the acid phosphate of lime in the
gastric juice, at least in the dog, and its quantity is undoubtedly increased in this animal
during the digestion of bones, by the action of the acid fluid upon their phosphatic con-
stituents; but the arguments of Blondlot against the existence of a free acid have little
or no weight. One of those on which most stress is laid is that the gastric juice does not
act upon the carbonates, which would undoubtedly be the case if it contained a free
acid. The simple reply to this is that there is sufficient evidence to show that it is
not the fact. Melsens, using a specimen of fluid obtained by Blondlot from the dog and
given to Dumas, found that seventy-three grammes of juice dissolved, in twenty-four
hours, 0-108 of a gramme of calcareous spar (crystallized carbonate of lime). He con-
firmed this observation by several experiments, so that there can be no doubt as to its
accuracy.

It is plain, therefore, that, while the acid phosphate of lime has been shown to be a
constant constituent of the pure gastric juice, contributing, in a certain degree, to its
acidity, it is not by any means to be regarded as the sole acid principle ; the phosphate
probably existing in this form by virtue of the presence in this fluid of a free acid.

On what does the acidity of the gastric juice depend? This is the simple question to
which the foregoing discussion naturally leads; and it is one which can be answered
almost with positiveness, although it is not settled to the satisfaction of all physiologists
and there are some conflicting observations which can be harmonized only by new re-
searches.

Aside from the conditions under which acids, such as butyric, acetic, or lactic, are
developed from articles of food taken into the stomach, the evidence is strongly in
favor of free lactic acid as the principle on which the gastric juice mainly and constantly
depends for its acidity. There also exists a certain quantity of biphosphate of lime ; and
this is the only condition in which a phosphate of lime can exist in the presence of free
lactic acid.

The observations of Bidder and Schmidt indicate, apparently, a quantity of chlorine
in the gastric juice not to be accounted for by the proportion of bases obtained by ulti-
mate analysis. There is evidence sufficiently positive to show that there is no hydro-
chloric acid in the gastric juice, in a condition which allows the fluid to present the re-
actions which are observed when this acid exists in a free state. If there be any hydro-
chloric acid not in combination with metallic bases, it is united with organic matter in
such a way as to prevent the manifestations of its ordinary properties, except that of
acidity. The fact that some of the mineral acids can be made to unite in this way with
albuminoid substances lends color to this supposition ; although farther investigations
are necessary to demonstrate that this takes place in the gastric juice.

Ordinary Saline Constituents of the Gastric Juice. — It has been experimentally de-
monstrated that artificial fluids, containing the organic principle of the gastric juice and
the proper proportion of free acid, are endowed with all the digestive properties of the
normal secretion from the stomach, and that these properties are rather impaired when
an excess of its normal saline constituents is added or when the relation of the salts to
the water is disturbed by concentration. Boudault and Corvisart evaporated two hun-
dred grammes of the gastric juice of the dog to dryness and added to the residue fifty
16

242 DIGESTION.

grammes of water. They found that the fluid thus prepared, containing four times the
normal proportion of saline principles, did not possess by any means the energy of action
on alimentary substances of the normal secretion. These facts have led physiologists to
attach little importance to the ordinary saline principles found in the gastric juice.

In the various analyses of the pure juice from the human subject and the inferior
animals, particularly dogs, chemists have discovered the chlorides of sodium, calcium,
potassium, and ammonium, the phosphate of lime (necessarily in the form of the
biphosphate), magnesia, and a small proportion of phosphate of iron. Of these princi-
ples, the chloride of sodium has always been found to exist in greatest abundance.

Action of the Gastric Juice in Digestion.

In treating of the composition of the gastric juice, frequent allusion has been made to
its solvent action in digestion and to the constituents on which this property depends.
Certain of the principles most readily attacked by this fluid are acted upon by weak acid
solutions containing no organic matter ; but, although some physiologists have been dis-
posed to regard the processes of solution which take place in the stomach as dependent
merely on the presence of a free acid, it is now well established that the presence of a
peculiar organic principle is an indispensable condition to the performance of real diges-
tion by the gastric fluid. It has also been fully established that fluids containing the or-
ganic principle of the gastric juice have no digestive properties unless they also possess
the proper degree of acidity ; and it is as well settled that fluids containing acids alone
have no action on albuminoids similar to that which takes place in digestion, and that
when these principles are dissolved by them it is simply accidental.

It is a curious fact that the presence of any one particular acid does not seem essen-
tial to the digestive properties of the gastric juice, so long as the proper degree of acidity
is preserved. In the experiments of Bernard, Villefranche, and Barreswil, after saturating
the gastric juice with neutral phosphate of lime and adding acetic, phosphoric, or hydro-
chloric acid in such quantity that it certainly existed in a free state, the digestive proper-
ties of the fluid were retained. These authors regard it as essential that the normal acid
of the gastric juice should be thus capable of being replaced indifferently by other acids ;
for, they say, in case any salt were introduced into the stomach which would be decom-
posed by the lactic acid of the gastric juice, digestion would be interfered with, unless the
liberated acid could take its place. It can readily be appreciated that transient disturb-
ances might occur from this cause, were the existence of any one acid principle indispen-
sable to the digestive properties of the gastric juice ; while, if only a certain degree of
acidity were required, this condition might be produced by any acid, either derived from
the food or secreted by the stomach.

Enough has already been said, under the head of the organic principle of the gastric
juice, to show that the presence of this substance is likewise a condition indispensable to
digestion.

As far as has been ascertained by experiments upon artificial digestion, the mucus,
which always exists in greater or less quantity in the stomach, does not seem to be im-
portant. It is usual in these experiments to separate mucus and extraneous matters from
gastric juice by filtration before it is used; and the digestive properties of the fluid thug
treated are not sensibly affected when the mucus is allowed to remain.

In studying the physiological action of the gastric juice, it must always be borne in
mind that the general process of digestion is accomplished by the combined, as well as
the successive action of the different digestive fluids. The act should be viewed in its en-
semble, rather than as a process consisting of several successive and distinct operations, in
which different classes of principles are dissolved by distinct fluids. The food meets with
the gastric juice, after having become impregnated with a large quantity of saliva ; and it
passes from the stomach to be acted upon by the intestinal fluids, having imbibed both
saliva and gastric juice. By studying the different digestive fluids in too exclusive a

ACTION OF THE GASTRIC JUICE IN DIGESTION. 243

manner, many physiologists, while professing to assign definite and distinct properties to
each, thus investing the function of digestion with the attraction of simplicity, have
necessarily ignored or distorted facts and have assumed a completeness for the sum of
our information on this subject, which does not exist.

When the acts which take place in the mouth are properly performed, the following
alimentary substances, comminuted by the action of the teeth and thoroughly insalivated,
are taken into the stomach : muscular tissue, containing the muscular substance envel-
oped in its sarcolemma, blood-vessels, nerves, white fibrous tissue holding the muscular
fibres together, interstitial fat, and a small quantity of albumen, fibrin, and corpuscles
from the blood, all combined with a considerable quantity of inorganic saline matters;
albumen, sometimes unchanged, but generally in a more or less perfectly coagulated con-
dition; fatty matter, sometimes in the form of oil and sometimes enclosed in vesicles,
constituting adipose tissue ; gelatine and animal matters in a liquid form extracted from
meats, as in soups ; caseine, in its liquid form united with butter and salts in milk, and
coagulated in connection with various other principles in cheese ; vegetable nitrogenized
principles, of which gluten may be taken as the type ; vegetable fats and oils ; saccharine
principles, both from the animal and the vegetable kingdom, but chiefly from vegeta-
bles ; the different varieties of amylaceous principles ; and, finally, organic acids and salts,
derived chiefly from vegetables. These principles, particularly those from the vegetable
kingdom, are united with more or less innutritions matter, such as cellulose. They are
also seasoned with aromatic principles, condiments, etc., which are not directly used in
nutrition.

The various articles coming under the head of drinks are taken without any consider-
able admixture with the saliva. They embrace water, the various nutritious or stimulant
infusions (including alcoholic beverages), with a small proportion of inorganic salts in
solution.

All the articles enumerated above are more or less modified in the stomach ; and the
action of the gastric juice upon them will now be taken up in detail.

Action of the Gastric Juice upon Meats. — There are three ways in which the action
of the gastric juice upon the various articles of food may be studied. One is to subject
them to the action of the pure fluid taken from the stomach, as was done by Beaumont, in
the human subject, and by Blondlot and others, in experiments upon the inferior animals ;
another is to make use of properly-prepared acidulated infusions of the mucous membrane
of the stomach, which have been shown to have sensibly the same properties as the gastric
juice, differing only in activity ; and another is to examine from time to time the contents
of the stomach after food has been taken. By all of these methods of study, it has been
shown that the digestion of meat in the stomach is far from being complete. The parts of
the muscular structure most easily attacked are the fibrous tissue which holds the muscular
fibres together, with the sarcolemma, or sheath of the fibres themselves. If the gastric
juice of the dog be placed in a vessel with finely-chopped lean meat and be kept in contact
with it for a number of hours at from 80° to 100° Fahr., agitating the vessel occasionally
so as to subject, as far as possible, every particle of the meat to its action, the filtered fluid
will be found increased in density, its acidity diminished, and presenting all the evidences
of having dissolved a considerable portion of the tissue. There always, however, will
remain a certain portion which has not been dissolved. Its constitution is nevertheless
materially changed ; for it no longer possesses the ordinary character of muscular tissue,
but easily breaks down between the fingers into a pultaceous mass. On subjecting this
residue to microscopical examination, it is found not to contain any of the white inelastic
fibres; and the fibres of muscular tissue, although presenting the well-marked and char-
acteristic striae, are broken into short pieces and possess very little tenacity. It is evi-
dently only the muscular substance which remains; the connective tissue and the sarco-
lemma having been dissolved. These facts we have repeatedly noted, and, even on adding

244

DIGESTION.

fresh juice to the undigested matter, we have been unable to dissolve it to any considerable
extent, the residue not being sensibly diminished in quantity, and the muscular substance
always presenting its characteristic striae, on microscopical examination.

Although it is stated by many, in a general way, that the nitrogenized alimentary
principles are digested by the gastric juice, a review of actual experiments will show that
the digestion of meat in the stomach is substantially such as we have just indicated.
Beaumont, in his experiments on artificial digestion, while he frequently states that the
meat is completely digested, describes the mixture, after a digestion of eight or nine hours,
as about the color of whey and depositing a fine sediment of a reddish color after standing
for a few minutes. In no case does he distinctly state that meat is ever completely dis-
solved. Pappenheim examined animal matters, especially muscular tissue, in various
stages of digestion by the gastric juice, and noted the disintegration of the tissue and
division of the muscular fibres into fragments, but not the solution of the true muscular
substance. Burdach describes the digestion of meat as consisting in the solution of its
cellular tissue, which is dissolved, first separating the muscular fibres, and finally being
converted into a pultaceous mass, more or less brown. The same facts, essentially, have
been noted by Bernard in experiments with the gastric juice of different animals. This
observer has found that the fluid from the stomach of the rabbit or the horse is much
inferior, as regards the activity of its action upon meat, to the gastric juice of the dog.
He compares the disintegrating process which takes place in the stomach to the action
of boiling water in cooking.

I

I

FIG. 62. — Matters taken from the pyloric portion of tlie stomach of a dog during digestion of mixed food.

(Bernard.)

a, disintegrated muscular fibres, the striae having disappeared ; &, c, muscular fibres, in which the striae have partly
disappeared ; cZ, cZ, d, globules of fat ; e, e, e, starch ; g, molecular granules.

Whether the gastric juice be entirely incapable of acting upon the muscular substance
or not, the above-mentioned facts clearly show that muscular tissue is usually not com-
pletely digested in the stomach. The action in this organ is to dissolve out the inter-
muscular fibrous tissue and the sarcolemma, or sheath of the muscular fibres, setting the
true muscular substance free and breaking it up into small particles. The mass of tissue
is thus reduced to the condition of a thin, pultaceous fluid, which passes into the small
intestine, where the process of digestion is completed. As far as a great part of the true
muscular substance is concerned, the action in the stomach is preparatory and not final.

ACTION OF THE GASTRIC JUICE IN DIGESTION. 245

The constituents of the blood (albumen, corpuscles, etc.), which may be introduced
in small quantity in connection with muscular tissue, are probably completely dissolved
in the stomach.

Action upon Albumen, Fibrin, Caseine, and Gelatine. — Dr. Beaumont thought that
raw albumen, or white of egg, became first coagulated in the stomach and was afterward
dissolved ; but this has been disproved by numerous other observers, who, however, have
experimented chiefly on dogs. Reference to the experiments of Beaumont will show that
the phenomena which he described as taking place in a mixture of equal parts of white
of egg and gastric juice, kept at the temperature of the body for three hours, do not really
indicate coagulation. He states that " in ten or fifteen minutes, small, white flocculi began
to appear, floating about ; and the mixture became of an opaque and whitish appearance.
This continued slowly and uniformly to increase for three hours, at which time the fluid
had become of a milky appearance ; the small flocculi, or loose coagula, had mostly dis-
appeared, and a light-colored sediment subsided to the bottom." If white of egg be mixed
with equal parts of pure water and be gently stirred with a glass rod, the same small,
white flocculi will make their appearance, and the mixture will become opaque and
whitish. This is due to the disengagement of shreds of the membranes in which the
clear albumen is contained ; these being invisible in pure white of egg, from the fact that
the two substances have the same refractive power. A very different appearance is
presented when water containing even a small quantity of nitric acid is added to a liquid
containing albumen. True coagulation then takes place, and the mixture becomes imme-
diately filled with large, dense clots ; or the mass may become nearly solidified, if the acid
be added in sufficient quantity. Longet and Schiff injected a filtered watery mixture of
albumen into the stomach of a dog through a fistulous opening and found that no coagu-
lation took place.

The action of the gastric juice upon uncooked white of egg is to disintegrate its
structure, separating and finally dissolving the membranous sacs in which the pure
albumen is contained. It also acts upon the albumen itself, forming a new fluid substance,
called albuminose, or albumen-peptone, which, unlike albumen, is not coagulated by heat
or acids, but is precipitated by alcohol, tannin, and many of the metallic salts.

The digestion of raw or imperfectly-coagulated albumen takes place with considerable
rapidity in the stomach. Beaumont gave St. Martin the white of two eggs when the
stomach was empty and found that it had been completely disposed of in an hour and a
half. The digestion of albumen in this form is more rapid than when it has been com-
pletely coagulated by heat.

Coagulated white of egg is almost if not entirely dissolved by the gastric juice. If a
cube of albumen in this condition be subjected to the action of the gastric juice at the
temperature of the body, taking care to agitate it occasionally, the edges and corners
gradually become rounded, and nearly the whole mass finally breaks down and is dissolved,
having previously become softened so that it may be easily crushed between the fingers.
Usually, one or two points appear in the mass, which are acted upon with difficulty or
may resist solution entirely. It is a matter of common as well as scientific observation,
that eggs when hard-boiled are less easily digested than when they are soft-boiled or raw.

The products of the digestion of raw or of coagulated albumen (albumen-peptone)
are essentially the same. It is probable that the entire process of digestion and absorp-
tion of albumen takes place in the stomach, and, if any pass out of the pylorus, the
quantity is exceedingly small.

Fibrin, as distinguished from the so-called fibrin of the muscular tissue, or musculino,
is not a very important article of diet. The action of the gastric juice upon it is more
rapid and complete than upon albumen. The well-known action upon fibrin of water
slightly acidulated with hydrochloric acid has led some physiologists to assume that the
acid is the only constituent in the gastric juice necessary to the digestion of this principle ;

246 DIGESTION.

but careful observations on the comparative action of acidulated water and of artificial
or natural gastric juice show that the presence of the organic matter is necessary to
the digestion of this as well as of other nitrogenized alimentary principles. The action of
water containing a small proportion of acid is to render fibrin soft and transparent, fre-
quently giving to the entire mass a jelly-like consistence. The result of the digestion of
fibrin in the gastric juice, or in an acidulated fluid to which pepsin has been added, is
its complete solution and transformation into a substance which is not affected by heat,
acids, or by rennet.

The substance resulting from the action of gastric juice upon fibrin, called by Leh-
mann, fibrin-peptone, presents many points of similarity with the albumen-peptone, but
nevertheless has certain distinctive characters. Lehrnann, indeed, supposes that there are
differences between the products of the digestion of all the various nitrogenized aliment-
ary principles, sufficiently well marked to distinguish them from each other.

Liquid caseine is immediately coagulated by the gastric juice, by virtue both of the
free acid and the organic matter. Once coagulated, caseine is acted upon in the same
way as coagulated albumen. The caseine which is taken as an ingredient of cheese is
digested in the same way. According to Lehmann, coagulated caseine requires a longer
time for its solution in the stomach than most other nitrogenized substances ; and it is
stated by the same author, on the authority of Elsasser, that the caseine of human milk,
which coagulates only into a sort of jelly, is more easily digested than caseine from cow's
milk. The product of the digestion of caseine is a soluble substance, not coagulable by
heat or the acids, called by Lehmann, caseine-peptone.

Gelatine is rapidly dissolved in the gastric juice, when it loses the characters by
which it is ordinarily recognized, and no longer forms a jelly on cooling. This substance
is much more rapidly disposed of than the tissues from which it is formed, and the prod-
ucts of its digestion in the gastric juice resemble the substances resulting from the di-
gestion of the albuminoids generally.

Action on Vegetable Nitrogenized Principles. — These principles, of which gluten may
be taken as the type, undoubtedly are chiefly, if not entirely digested in the stomach.
Raw gluten is acted upon very much in the same way as fibrin, and cooked gluten be-
haves like coagulated albumen. Vegetable articles of food generally contain gluten in
greater or less quantity, or principles resembling it, as well as various non-nitrogenized
principles, and cellulose. The fact that these articles are not easily attacked in any por-
tion of the alimentary canal, unless they have been well comminuted in the mouth, is
shown by the passage of grains of corn, beans, etc., in the fa3ces. When properly pre-
pared by mastication and insalivation, the action of the gastric juice is to disintegrate
them, dissolving out the nitrogenized principles, freeing the starch and other matters so
that they may be more easily acted upon in the intestines, and leaving the hard, indi-
gestible matters, such as cellulose, to pass away in the faeces. The nitrogenized portions
of bread are probably acted upon in the stomach in the same way and to the same ex-
tent as albumen, fibrin, and caseine.

Albuminose, or Peptones.

The product or the sum of the products of the digestion of nitrogenized alimentary
principles in the stomach was first closely studied by Mialhe, who regarded the action
of the gastric juice on all principles of this class as resulting in their transformation into
a new substance which he called albuminose. Lehmann has since investigated the prin-
ciples resulting from the action of the gastric juice on various nitrogenized matters and
describes them under the name of peptones. It has been conclusively shown that stom-
ach-digestion is not merely a solution of certain alimentary principles, but that these
substances undergo very marked changes and lose the properties by which they are gen-
erally recognized. That the different principles resulting from this transformation re-

ALBUMINOSE, OR PEPTONES. 247

semble each other very closely is also undoubted ; but there are differences in .the chemi-
cal composition of the products of digestion of different principles, as well as differences,
which have lately been noted, as regards their behavior with reagents.

Albuminose is a colorless liquid, with a feeble odor resembling that of meat. It is
not coagulable by heat, acids, or by pepsin ; a property which distinguishes it from almost
all of the nitrogenized principles of food. It is coagulated, however, by many of the
metallic salts, by chlorine, and by a solution of tannin, after it has been acidulated by
nitric acid. On evaporating albuminose to dryness, the residue consists of a yellowish-
white substance, resembling desiccated white of egg. This is soluble in water, when it
regains its characteristic properties ; but it is entirely insoluble in alcohol.

Lehmann found a great similarity between the substances resulting from the digestion
of the various albuminoid bodies, and even those produced by the digestion of gluten,
chondrine, and gelatinous tissues. He was unable to obtain the peptones free from min-
eral substances. In the condition of greatest purity in which they have been obtained,
they have been found to be white, amorphous, odorless, with a mucous taste, very solu-
ble in water, and insoluble in alcohol. Their watery solutions redden litmus. They
combine readily with bases, forming neutral salts soluble in water. The differences be-
tween the various peptones are not as yet very well defined. Lehmann states that they
always contain the same proportion of sulphur that existed in the albuminoid substances
from which they are formed. According to this observer, the gastric juice transforms the
various nitrogenized alimentary principles into these liquid substances, which are not easily
coagulable and which present slight differences in chemical composition and general prop-
erties, varying with the principles from which they are formed. Those which have been
most particularly described are fibrin-peptone, albumen-peptone, and caseine-peptone.

With even the imperfect knowledge which we have of the properties of albuminose,
it is evident that stomach-digestion, aside from its function in preparing certain articles
for the action of the intestinal fluids, does not simply liquefy certain of the alimentary
principles, but changes them in such a way as to render them endosmotic and provides
against the coagulation which is so readily induced in ordinary nitrogenized bodies.
Albuminose passes through membranes with great facility, and, as we have seen, is not
coagulable by heat or the acids.

Another, the most important and the essential change which is exerted by the gastric
juice upon the albuminoids, is that by which they are rendered capable of assimilation
by the system after their absorption. The important fact that pure albumen and gela-
tine, when injected into the blood, are not assimilable, but are rejected by the kidneys,
was first demonstrated by Bernard and Barreswil. These observers found, also, that albu-
men and gelatine which had previously been digested in gastric juice were assimilated in
the same way as though they had penetrated by the natural process of absorption "from
the alimentary canal. The same is true of caseine and fibrin. These facts, showing that
something more is necessary in stomach-digestion than mere solution, point to pepsin as
the important active principle in producing the peculiar modifications so necessary to
proper assimilation of nitrogenized alimentary substances. The action by which the
albuminoids are thus modified in certain of their chemical and physical properties, as
well as dissolved, was formerly called catalytic; bat the signification of this term as
applied to the functions of digestion, assimilation, and nutrition, is so indefinite, that it
seems to be hardly more than a word used to express an absence of positive knowledge.
Certain it is, however, that the action of pepsin is essential to the changes which occur
in the albuminoid alimentary principles, resulting in the formation of what is known as
albuminose, or peptones; and the change into albuminose takes place in all nitrogenized
principles that are liquified in the stomach. This may occur even when the albuminoid
matters are somewhat advanced in putrefaction, and the gastric juice undoubtedly pos-
sesses antiseptic properties, which fact accounts for the frequent innocuousness of animal
substances in various stages of decomposition when taken into the stomach.

248 DIGESTION.

Action of the Gastric Juice on Fats, Sugars, and Amylaceous Substances. — Beaumont
does not say much with regard to the changes which fatty substances undergo in the stom-
ach, except that they are '* digested with great difficulty." All the recent observations
on this subject show that these principles, when taken in the condition of oil, pass out
at the pylorus unchanged. Most of the fatty constituents of the food are liquefied at the
temperature of the body ; and, when taken in the form of adipose tissue, the little vesi-
cles in which the oleaginous matter is contained are dissolved, the fat is set free and
melted, and floats in the form of great drops of oil on the alimentary mass. The action
of the stomach, then, seems to be to prepare the fats for digestion, chiefly by dissolving
the adipose vesicles, for the complete digestion which takes place in the small in-
testine.

The varieties of sugar of which glucose is the type undergo little if any change in
digestion and are probably for the most part directly absorbed by the mucous membrane
of the stomach. This is not the case, however, with the varieties of sugar classed with
cane-sugar. It has been shown that cane-sugar injected into the veins of a living animal
is not assimilated by the system but is immediately rejected by the kidneys. When,
however, it has been changed into glucose by the action of a dilute acid or by digestion
in the gastric juice, it no longer behaves as a foreign substance and does not appear in the
urine. This leads to a consideration of the changes which cane-sugar undergoes in the
stomach. Experiments have shown that this variety of sugar, after being digested for
several hours in the gastric juice, is slowly converted into glucose. This action does not
depend upon any constituent of the gastric juice except the free acid ; and an exceedingly
dilute mixture of hydrochloric acid had an equally marked efiect. Experiments in arti-
ficial digestion have shown that cane-sugar is transformed into glucose by the gastric
juice very slowly, the action of this fluid in no way differing from that of very dilute
acids. In the natural process of digestion, this action may take place to a certain ex-
tent ; but it is not shown to be constant or important, and we must look to intestinal di-
gestion for the rapid and efficient transformation of cane-sugar.

The action of gastric juice, unmixed with saliva, upon starch is entirely negative, as
far as any transformation into sugar is concerned. When the starch is enclosed in vege-
table cells, it is set free by the action of the gastric juice upon the nitrogenized parts.
Raw starch, in the form of granules, becomes hydrated in the stomach, on account of
the elevated temperature and the acidity of the contents of the organ. This is not the
form, however, in which starch is generally taken by the human subject ; but when it is
so taken, the stomach evidently assists in preparing it for the more complete processes
of digestion which are to take place in the small intestine.

Gooked or hydrated starch, the form in which it exists in bread, farinaceous prepara-
tions generally, and ordinary vegetables, is not affected by the pure gastric juice and
passes out at the pylorus unchanged. It must be remembered, however, that the gastric
juice does not prevent a continuance of the action induced by the saliva ; and experi-
ments have shown that gastric juice taken from the stomach, when it contains a notable
quantity of saliva, has, to a certain extent, the power of transforming starch into sugar.
It has already been remarked that, with regard to this question, experiments on dogs, as
these animals do not naturally take starch as food, do not correspond with observations
on the human subject.

The changes which vegetable acids and salts, the various inorganic constituents of
food, and the liquids which come under the head of drinks undergo in the stomach are
very slight. Most of these principles can hardly be said to be digested; for they are
either liquid or in solution in water and are capable of direct absorption and assimila-
tion. With regard to most of the inorganic salts, they either exist in small quantity in
the ordinary water taken as drink or are united with organic nitrogenized principles.
In the latter case, they become intimately combined with the organic principles result-
ing from stomach-digestion. We have already seen that the various peptones have been

DURATION OF STOMACH-DIGESTION". 249

found to contain the same inorganic constituents which existed in the nitrogenized prin-
ciples from which they are formed.

Some discussion has arisen with regard to the action of the fluids of the stomach upon
the phosphate and the carbonate of lime, salts which are considered nearly if not en-
tirely insoluble. The action upon these principles is interesting, as they are essential
constituents of the osseous tissues. Observations in both natural and artificial digestion
have shown that the calcareous constituents of bone are, to a certain extent, dissolved
in the gastric juice. Bones are digested to a considerable extent in the stomach, although
the greater part passes through the alimentary canal and is discharged unchanged in the
fasces. Beaumont has shown this to be true in the human subject by experiments which
he performed, out of the body, with gastric juice taken from St. Martin. In these ob-
servations, after a certain portion of the bone had been dissolved, the action was in-
creased by the addition of fresh gastric juice. In the natural process of digestion, the
solution of the calcareous elements of bone is more rapid than in artificial digestion,
from the fact that the juice is being continually absorbed and secreted anew by the mu-
cous membrane of the stomach.

Duration of Stomach-Digestion.

Now that the relative importance of the stomach and the small intestines in digestion
is more fully understood, less interest is attached to the length of time required for the
action of the gastric juice upon different articles of food than formerly, when the stom-
ach was regarded as the principal, if not the sole digestive organ. It was thought at
one time that the food was converted in the stomach into a pultaceous mass called chyme,
which passed into the intestine, where the assimilable portion, the chyle, was separated
and absorbed by the lucteals. Beaumont, in preparing the elaborate table which has
been so much quoted, conceived that the simple action of the gastric juice represented
the chief part of the digestive process ; and that it was possible, from experiments with
this fluid, to ascertain the digestibility of different articles. From this point of view, he
regarded fatty substances, which are now known to be digested exclusively in the small
intestines, as requiring a very long time for their digestion.

Understanding, as we do, that comparatively few articles, and these belonging exclu-
sively to the class of organic nitrogenized principles, are completely dissolved in the
stomach, it is evident that the length of time during which food remains in this organ, or
the time occupied in the solution of food by gastric juice, out of the body, does not rep-
resent the absolute digestibility of different articles. It is, nevertheless, an interesting and
an important question to ascertain, as nearly as possible, the duration of stomach-digestion.

There has certainly never been presented so favorable an opportunity for determining
the duration of stomach-digestion as in the case of St. Martin. From a great number
of observations made on digestion in the stomach itself, Beaumont came to the con-
clusion that " the time ordinarily required for the disposal of a moderate meal of the
fibrous parts of meat, with bread, etc., is three to three and a half hours." The obser-
vations of Prof. F. G. Smith, made upon St. Martin many years later, give two hours as
the longest time that aliments remained in the stomach. In a remarkable case of intes-
tinal fistula, reported by Prof. Busch, of Bonn, it was noted that food began to pass out
of the stomach into the intestines fifteen minutes after its ingestion and continued to
pass for three or four hours, until the stomach was emptied.

Undoubtedly, the duration of stomach-digestion varies in different individuals and is
greatly dependent upon the kind and quantity of food taken, conditions of the nervous
system, exercise, etc. As a mere approximation, the average time that food remains in
the stomach after an ordinary meal may be stated to be from two to four hours.

Digestibility of Different Aliments in the Stomach.— We are indebted to Beaumont
for nearly all that is positively known regarding the facility with which different articles

250

DIGESTION.

are disposed of in the stomach. While it is fully understood that most of the substances
experimented upon by him are not completely digested by the gastric juice, and although
he was often wrong in assuming that articles of food were digested when they had not
become completely liquefied and consequently endosmotic, the table which he prepared
with so much care was the result of such conscientious and extended research, that it
must always be recognized as of great value. Nearly all of the results given in the table
are derived from experiments frequently repeated and " performed under the naturally
healthy condition of the stomach and ordinary exercise." They show the mean time
employed in the digestion, in the stomach, of most of the ordinary articles of food, in the
person of a healthy young man of good digestive powers. Of course it must be under-
stood that there are important peculiarities in different individuals, which could not be
considered. As many of the alimentary substances experimented upon are but slightly
acted on by the gastric juice, it has been thought proper, in making the selections from
the table, to discard all articles which are mainly digested in the small intestine.
With these modifications, therefore, the following table may be taken as representing
the comparative rapidity with which most of the ordinary nitrogenized articles are acted
upon in the stomach ; they being either completely dissolved, and probably directly ab-
sorbed by its mucous membrane, or prepared for the action of the intestinal fluids, passing
gradually out at the pylorus. It must be remembered, however, that slow digestion does
not always indicate that the process is difficult, and the action of the gastric fluids upon
many articles which apparently give no. trouble in digestion is by no means rapid.

Table showing the Digestibility of various Alimentary Substances in the

Stomach. (Beaumont.)

Articles of Diet.

Mode of Prepara-
tion.

§ *
z *

Articles of Diet.

Mode of Prepara-
tion.

S a

1 s

2-45
4-00
4-00
4-00
4-30
1-30
3-00
3-00
3-30
3-30

4-00
4-15

i-oo

1-00
1-45
2-40
2-00
3-00
4-00
4-15
5-30
2-30
3-20
2-30
3-30
3-45
2-30
2-30
2-30
2-30
3-30
2-30
2-00
4-30
3-13
3-30
3-45
3-15
3-30
1-30
2-00
2-50

Milk...

Boiled
Raw
do.
Whipped
Roasted
Soft-boiled
Hard-boiled
Fried
Baked
Boiled
do.
Fried
Broiled
Fried
do.
Boiled
Raw
Roasted
Stewed
Broiled
Roasted
Broiled
Roasted
Broiled
Roasted
Boiled
do.
Fried
Broiled
Boiled
Roasted
Broiled
Fried
Broiled
Roasted
Raw
Stewed
Broiled
Fried
Boiled
Roasted
Boiled
Roasted
do.

2-00
2-15
2-00
1-30
2-15
3-00
3-30
3-30
2-45
2-00
1-30
1-30
3-00
3-30
3-30
4-00
2-55
3-15
8-30
1-35
2-30
2-30
3-00
3-00
3-30
3-10
3-36
4-00
3-00
3-00
3-15
4-00
4-30
3-15
5-15
3-00
3-00
3-15
4-15
4-30
2-18
2-25
2-30
2 30

Fricasseed
Boiled
Roasted
do.
do.
Boiled
do.
do.
do.
do.

do.

do.
do.
do.
do.
do.
Broiled
Boiled
Fried
Boiled
do.
Warmed
Broiled
Boiled
Raw
Boiled
do.
do.
Roasted
Baked
Boiled
Raw
do.
Boiled
do.
do.
do.
Baked
do.
Raw
do.
do.

do

Fowls domestic

E^fS, fresh .

do. do

Ducks, domesticated
do wild

do. do
do. do.

do. do

do. bean

do. do
Custard ...

do. chicken

Codfish, cured dry
Trout, salmon, ftvsh
do. do. do . .

do. oyster

do. beef, vegetables, |
and bread f
do. marrow-bones
Pitas' feet, soused
Tripe, do

Bass, striped, do
Flounder, do
Catfish, do
Salmon, salted

Oysters, fresh
do. do

Spinal marrow, animal

do do

Venison steak
Pig, sucking

Heart, animal..

Cartilage

Lamb fresh

Tendon
Hash, meat and vegetables.

Beef, fresh, lean, rare
Beef-steak

Beef, fresh, lean, dry
do. with mustard, etc
do. with salt only
do

Gelatine

Cheese, old, strong
Green corn and beans

Mutton, fresh
do. do
do. do

Parsnips

Potatoes, Irish.

Veal, fresh
do do

do. do
Cabbage, head
do. do. with vinegar
do. do

Pork Bleak

do. fat and lean
do. recently salted
do. do.

Carrot, orange
Turnips, flat. . .

do. do.
do. do.
do. do.
Turkey wild

Beets ..

Bread, corn
do. wheat, fresh
Apples, sweet, mellow
do. 8oii r, do
do. do. hard

do. domesticated
do. do.
Goose, wild

CIRCUMSTANCES WHICH INFLUENCE STOMACH-DIGESTION. 251

Most of the facts recorded in the ahove table are in accordance with the popular ideas
regarding the digestibility of various articles, based upon general experience. With these
as a guide, the following may be taken as a summary of what is known regarding the
facility with which different articles are disposed of in the stomach :

Milk is one of the articles digested in the stomach with greatest ease. Its highly-nu-
tritive properties and the variety of principles which it contains render it extremely valu-
able as an article of diet, particularly when the digestive powers are impaired and when
it is important to supply the system with considerable nutriment. Eggs are likewise
highly nutritious and are easily digested. Raw and soft-boiled eggs are more easily
digested than hard-boiled. Whipped eggs are apparently disposed of with great facility.
As a rule, the flesh of fish is more easily digested than that of the warm-blooded animals.
Oysters, especially when raw, are quite easy of digestion. The flesh of mammals seems
to be more easily digested than the flesh of birds. Of the different kinds of meat, veni-
son, lamb, beef, and mutton are easily digested, while veal and fat roast-pork are digested
with difficulty. Soups are generally very easily digested. The animal substances which
were found to be digested most rapidly, however, were tripe, pigs' feet, and brains.
Vegetable articles are represented in the table as being digested in about the same time
as ordinary animal food ; but a great part of the digestion of these substances takes place
in the small intestine. Bread is digested in about the time required for the digestion of
the ordinary meats.

Circumstances which influence Stomach-Digestion.

The various conditions which influence stomach-digestion, except those which relate
exclusively to the character or the quantity of food, operate mainly by influencing the
quantity and quality of the gastric juice. It is seldom, if ever, that temperature has any
influence ; for the temperature of the stomach in health does not present variations suffi-
cient to have any marked effect upon digestion. Experiments in artificial digestion have
shown that alimentary substances are most vigorously acted upon when maintained in
contact with gastric juice at or near 100° Fahr.

As a rule, gentle exercise, conjoined with repose or agreeable and tranquil occupation
of the mind, is more favorable to digestion than absolute rest. Violent exercise or severe
mental or physical exertion is always undesirable immediately after the ingestion of a
large quantity of food, and, as a matter of common experience, has been found to retard
digestion. Sleep, if light and taken in the sitting posture, seems almost necessary to easy
digestion in many persons ; but it should be continued for only a few minutes. A pro-
longed and deep sleep immediately after a full meal is almost always injurious, and ex-
traordinary heaviness at that time is generally an indication that too much food has been
taken.

The effects of sudden and considerable loss of blood upon stomach-digestion are very
marked. After a full meal, the whole alimentary tract is deeply congested, and this con-
dition is undoubtedly necessary to the secretion, in proper quantity, of the various diges-
tive fluids. When the entire quantity of blood in the economy is greatly diminished from
any cause, there is a difficulty in supplying the amount of gastric juice necessary for a
very full meal, and disorders of digestion are apt to occur, especially if a large quantity
of food have been taken. This is also true in inanition, when the quantity of blood is
greatly diminished. In this condition, although the system constantly craves nourish-
ment and the appetite is frequently enormous, food should be taken in small quantities at
a time.

As a rule, children and young persons digest food which is adapted to them more
easily and in larger relative quantity than those in adult life or in old age ; but, ordina-
rily, in old age, the digestive processes are carried on with more vigor and regularity
than the other vegetative functions, such as general assimilation, circulation, or respiration.

252 DIGESTION.

Influence of the Nervous System on the Stomach. — It is well known that mental
emotions frequently have a marked influence on digestion, and this, of course, can take
place only through the nervous system. Of the two nerves which are distributed to the
stomach, the pnetimogastric has been the more carefully studied, experiments upon the
sympathetic being difficult and unsatisfactory. Although the complete history of the
influence of the pueumogastric nerves upon digestion belongs to the section on the nervous
system, it will be interesting in this connection to consider briefly some of the facts
which have been ascertained with regard to the influence which these nerves exert upon
the stomach.

After section of the pneumogastric nerves in the neck, acts of deglutition are apparent-
ly performed, but the food usually collects in and distends the paralyzed oesophagus and
does not pass to the stomach. It is not surprising, therefore, that the first experiments
upon the influence of the pneumogastrics on digestion should have been contradictory, some
contending that section of the nerves arrested stomach-digestion, while others maintained
that the nerves had little or no influence upon the stomach. It is evident that, without
an appreciation of the effects of section of the pneumogastrics upon deglutition, observa-
tions on the influence of their section upon stomach-digestion would be of little value.

The experiments of Longet seem to show that, while section of the pneumogastrics in
the neck undoubtedly diminishes the secretion of gastric juice, the production of this fluid
is not entirely arrested. He states that in dogs, one or two days after section of the
nerves, he found the lacteals filled with chyle after milk had been passed into the stom-
ach ; but it is now well known that chyle is in great part, if not entirely formed in the
intestinal canal, without the intervention of the stomach. Another experiment, however,
is more interesting. After section of the pneumogastrics, having exposed the mucous
membrane of the stomach, he found that an acid fluid appeared in parts which were sub-
jected to mechanical or galvanic irritation. The general results of his experiments on
this subject were that, after the division of both pneumogastric nerves, small quantities of
food could be digested in the stomach, but that a considerable mass was only chymitied
on the surface, the centre not undergoing any alteration. This he attributes, not so much
to arrest of secretion of the gastric juice, as to paralysis of the movements of the stomach,
which, when the mass of food is considerable, are necessary in order to expose all parts
to the action of the gastric juice.

The experiments of Bernard on this subject are very clear and satisfactory. When
the mucous membrane of the stomach was turgid with blood, the animal (a dog) being in
full digestion and provided with a large gastric fistula so that the changes which might
take place in the stomach could be readily observed, the pneumogastrics were divided in
the neck. At once the mucous membrane became pale and flaccid, and the secretion of
gastric juice was arrested. When the animal died after section of the pneumogastrics
during digestion, it was remarked that the absorption of chyle seemed to have been ar-
rested, the lacteals being found to contain coagulated chyle even as far as the villi of the
intestines. According to these experiments, the action of gastric juice which might exist
in the stomach at the time of section of the pneumogastrics would continue, but no new
fluid is secreted ; and, if the fluid thus remaining in the stomach be neutralized, digestion
is immediately arrested. In one experiment in which the pneumogastrics had been
divided, having previously emptied the stomach, Bernard introduced meat finely divided.
The next day, the meat had a distinctly-ammoniacal odor and an alkaline reaction, the
result of spontaneous decomposition. These experiments show only an immediate arrest
of the secretion of the gastric juice. In certain exceptional instances, in which animals
survive the section of both nerves for a number of days or sometimes even recover, it
has been noted that, after a few days, an acid secretion again takes place in the stomach.

Although much confusion exists in the earlier observations on the effects of section of
the pneumogastrics upon the stomach, the conclusions to be drawn from recent experi-
ments are tolerably definite.

MOVEMENTS OF TPIE STOMACH. 253

There can be no doubt that division of both these nerves produces immediate and
grave disorder in the process of stomach-digestion, amounting, it is more than probable,
to complete arrest of the secretion of the gastric juice. Its secretion may be induced
again by local stimulation, but the quantity is always greatly diminished. Under these
circumstances, it is possible that very small quantities of food may be digested in the
stomach a day or two after the operation ; and, if the animal survive for a considerable
time the secretion may be to a certain extent reestablished. Serious trouble in stomach-
digestion is produced by the paralysis of the muscular coats of the stomach consequent
upon section of both pneumogastrics.

Movements of the Stomach.— As the articles of food are passed into the stomach by
the acts of deglutition, the organ gradually changes its form, size, and position. When
the stomach is empty, the opposite surfaces of its lining membrane are in contact in
many parts and are thrown into numerous longitudinal folds. As the organ is distended,
these folds are effaced, the stomach itself becoming more rounded; and, as the two ends
with the lesser curvature are comparatively immovable, the whole organ undergoes a
movement of rotation, by which the anterior face becomes superior and is applied to the
diaphragm. At this time the great pouch has nearly filled the left hypochondriac region,
the greater curvature looks anteriorly, and comes in contact with the abdominal walls.
Aside from these changes, which are merely due to the distention, the stomach under-
goes important movements, which continue until its contents have been dissolved and
absorbed or have passed out at the pylorus. But while these movements are taking
place, the two orifices are guarded, so that the food shall remain for the proper time
exposed to the action of the gastric juice. We have already noted the rhythmical con-
tractions of the lower extremity of the oesophagus, by which regurgitation of food is
prevented ; and the circular fibres, which form a thick ring at the pylorus, are constantly
contracted, so that, at least during the first periods of digestion, only liquids and that
portion of food which has been reduced to a pultaceous consistence can pass into the
small intestine. It is well known that this resistance at the pylorus does not endure in-
definitely, for indigestible articles of considerable size, such as stones, have been passed
by the anus after having been introduced into the stomach ; but observation has shown
that masses of digestible matter are passed by the movements of the stomach to the
pylorus, over and over again, and that they do not find their way into the intestine until
they have become softened and broken down.

The contractions of the walls of the stomach are of the kind characteristic of the
non-striated muscular fibres. If the finger be introduced into the stomach of a living
animal during digestion, it is gently but rather firmly grasped by a contraction, which is
slow and gradual, enduring for a few seconds, and as slowly and gradually relaxing and
extending to another part. The movements during digestion undoubtedly present certain
differences in different animals ; but there can be no doubt that the phenomenon is univer-
sal. In dogs, when the abdomen is opened soon after the ingestion of food, the stomach
appears pretty firmly contracted on its contents. In a case reported by Todd and Bow-
man, in the human subject, in which the stomach was very much hypertrophied and the
walls of the abdomen were very thin, the vermicular movements could be distinctly
seen. These movements were active, resembling the peristaltic movements of the intes-
tines, for which, indeed, they were mistaken, as the nature of the case was not recog-
nized during life. No argument, therefore, seems necessary to show that, during diges-
tion, the stomach is the seat of tolerably active movements.

A peculiarity in the movements of the stomach, which has been repeatedly observed
in the lower animals, particularly dogs and cats, and in certain cases has been confirmed
in the human subject, is that, at about the junction of the cardiac two-thirds with the
pyloric third, there is frequently a transverse band of fibres so firmly contracted as to
divide the cavity into two almost distinct compartments. It has also been noted that tho

254 DIGESTION.

contractions in the cardiac division are much less vigorous than near the pylorus ; the
stomach seeming simply to adapt itself to the food by a gentle pressure as it remains in
the great pouch, while, in the pyloric portion, divided off as it is by the hour-glass con-
traction above-mentioned, the movements are more frequent, vigorous, and expulsive.
We must again refer, however, to the observations of Beaumont for the only accurate
description of the movements of the stomach, as they take place during digestion in the
human subject.

The experiments of Beaumont were generally made with the subject lying on the
right side, and the movements of the stomach were observed by following with the eye a
particular morsel of food as it passed along, or by introducing the bulb of a thermometer
into the organ and allowing it to move with the alimentary mass. It was invariably
found that the movements of the thermometer-bulb were the same as those observed by
identifying and following a particular portion of food. As the alimentary bolus enters
by the cardiac opening, it turns to the left, descends into the greater pouch, and follows
the greater curvature to the pyloric end. It then returns to the cardiac orifice by the
lesser curvature and takes again the same course as before. While these revolutions, so
to speak, of the alimentary mass are going on, the food is turned over and over, so that
it becomes intimately mixed with the digestive fluids and subjected to a certain amount
of trituration. This action is undoubtedly of great importance, as fresh portions of food
are thereby successively exposed to the action of the gastric juice, and the boluses, with
their particles agglutinated to a certain extent in the mouth, are disintegrated and pene-
trated with the gastric fluid in every part.

A marked difference was observed between the movements in the cardiac and in the
pyloric portion. When the thermometer-bulb arrived at the contracted septum, which
was three or four inches from the pyloric end, it was at first stopped by the forcible con-
traction ; but, in a short time, there was a gentle relaxation which allowed it to pass,
when it was drawn quite forcibly for three or four inches toward the pyloric opening.
When in this portion of the stomach, the bulb was firmly grasped and made to undergo
a spiral motion ; and, if drawn forcibly out, it gave to the fingers the sensation of being
held by a strong suction force. As soon as relaxation occurs, the bulb is passed back to
the seat of stricture, and, when pulled through this, it moves freely in the great cavity.
Each one of these revolutions was found to occupy from one to three minutes. They
were slower at first than after digestion had been somewhat advanced.

The mechanism of the movements of the stomach is easily appreciated when we con-
sider the number and varied direction of the fibres which form the muscular coat of the
stomach, and the fact that the stomach, when distended, is more or less displaced with
every movement of the diaphragm. It is easy to understand, also, how, in the pyloric
portion, where the muscular fibres are thickest and the cavity is elongated and compara-
tively small, the movements should be more vigorous and expulsive than in the rest of the
organ. We have already alluded to the fact that the movements of the stomach are
animated by the pneumogastric nerves and become arrested when both these nerves are
divided.

As the result chiefly of the observations of Beaumont, the following may be taken as
a s nnmary of the physiological movements of the stomach in digestion:

The stomach normally undergoes no movements until food is passed into its cavity.
When food is received, at the same time that the mucous membrane becomes congested
and the secretion of gastric juice commences, contractions of the muscular coat begin,
which are slow and irregular during the commencement of stomach-digestion, but become
more vigorous and regular as the process advances. After digestion has become fully
established, the stomach is generally divided, by the firm and almost constant contraction
of an oblique band of fibres, into a cardiac and a pyloric portion ; the former occupying
about two-thirds, and the latter, one-third of the length of the organ. The contractions
of the cardiac division of the stomach are uniform and rather gentle ; while, in the

REGURGITATION OF FOOD, AND ERUCTATION. 255

pyloric division, they are intermittent and more expulsive. The effect of the contractions
of the stomach upon the food contained in its cavity is to subject it to a tolerably uniform
pressure, with a certain amount of trituration and agitation, in the cardiac portion, the
general tendency of the movement being toward the pylorus along the greater curvature,
and back from the pylorus toward the great pouch along the lesser curvature. At the
constricted part, which separates the cardiac from the pyloric portion, there is an ob-
struction to the passage of the food until it has been sufficiently acted upon by the secre-
tions in the cardiac division to have become reduced to a pultaceous consistence. The ali-
mentary mass then passes into the pyloric division, and, by a more powerful contraction
than occurs in other parts of the stomach, it is passed into the small intestine. This
completes the distinction between the two portions of the stomach, the cardiac division
only, as we have already seen, possessing a mucous membrane capable of secreting the
true solvent gastric juice.

The revolutions of the alimentary mass, thus accomplished, take place slowly, by gen-
tle and persistent contractions of the muscular coat ; the food occupying from one to
three minutes in its passage entirely around the stomach. Every time that a revolution
is accomplished, the contents of the stomach are somewhat diminished in quantity ;
probably, in a slight degree, from absorption of digested mater by the stomach itself, but
chiefly by the gradual passage of the softened and disintegrated mass into the small intes-
tine. This process continues until the stomach is emptied, occupying a period of from
two to four hours ; after which, the movements of the stomach cease until food is again
introduced.

Regurgitation of Food, and Eructation.

Regurgitation of part of the contents of the stomach, in the human subject, although
of frequent occurrence, particularly in early life, is not strictly a physiological act ; and
this is always due either to overloading of the stomach or to some pathological condition.
Hut in some of the inferior animals this is habitual ; a certain class, called ruminants,
regularly passing the food, after the first deglutition, in small quantities from the paunch
into the mouth, where it undergoes a second mastication and is only then permitted to
pass to the secreting stomach and the rest of the alimentary canal. Animals of this
class, examples of which are the ox, sheep, goat, camel, and the deer tribe, are invari-
ably herbivorous and take into the stomach a large bulk of matter from which is elabo-
rated a comparatively small quantity of nutriment. During the period when they are
nourished by milk, rumination does not take place.

Considerable interest is attached to the function of rumination in the inferior ani-
mals, in connection with human physiology, from the fact that an analogous process has
sometimes been observed in the human subject ; though this is rare and is generally con-
nected with a pathological condition. Such cases have been often quoted, and, in the
earlier works on physiology, were frequently exaggerated ; but, a few instances, well au-
thenticated, are on record in which rumination had become habitual. A very remark'
able case of this kind is reported by Home. The subject was an idiot-boy, aged nineteen
years, who had an appetite so ravenous that it became necessary to restrict the quantity
of food. At dinner he ordinarily ate about a pound and a half of meat and vegetables,
swallowing the whole in two minutes. He began to chew the cud at the end of a quar-
ter of an hour. The muscles of the throat could be seen to contract when the bolus was
passed back to the mouth. He chewed the food by two or three movements of the jaws
and then swallowed it again. This was repeated at intervals for half an hour, during
which time he was always more quiet than usual. The intellect was so feeble that it was
impossible to ascertain whether the rumination were voluntary or involuntary. One of
the cases of rumination most frequently referred to is that of M. Cambay, who studied
the phenomena in his own person and made it the subject of an inaugural thesis ; and
another is the case of the brother of M. P. Berard. In these instances, as far as could

256 DIGESTION.

be ascertained from tlie sensations during the act, the regurgitation of food was effected
by persistent contractions of the muscular walls of the stomach, assisted by a slight and
almost involuntary contraction of the abdominal muscles and diaphragm. It is stated by
Cambay that, in his case, the taste of the articles of food was not modified, " but that it
is with something of a sense of pleasure that the ruminator thus causes to return to the
mouth the aliments that he has taken into the stomach, which makes them undergo a
new trituration."

Rumination in the human subject is not a physiological act. It is evident that the sub-
stances returned to the mouth are not usually impregnated with the gastric juice, for they
have not the disagreeable acid taste of ordinary vomited matters. The acts are generally
preceded by a sense of fulness in the stomach, and their mechanism is probably nearly
the same as that of the regurgitation of small quantities of milk from the distended
stomachs of young children, which is so common. In the person of Cambay, the first
act was said to be voluntary, but succeeding ones were not under the control of the will.
Undoubtedly, the faculty of regurgitating the food may be improved by practice, and
we have known of an instance in which it was apparently cultivated as an accom-
plishment.

The mechanism of regurgitation of portions of the contents of the stomach, aside
from instances simulating rumination, has been so often alluded to that it demands in this
connection but a passing mention. In some persons, this act may be accomplished by a
voluntary muscular effort, especially when the stomach is overloaded. It occasionally
happens, when the stomach is somewhat distended, that a small portion of its contents
suddenly finds its way to the mouth without even the consciousness of the individual.
The muscular contraction which produces this slight regurgitation is so insignificant that
there must necessarily have been some relaxation at the cardiac opening of the stomach,
which under ordinary conditions is, as we know, firmly closed. The act is then produced,
in part by a slight contraction of the abdominal muscles and diaphragm, and in part by
contractions of the stomach itself and anti-peristaltic movements of the oesophagus. It
has nothing of the violent, expulsive character of true vomiting, which is produced by
the spasmodic and involuntary contraction of the abdominal muscles and diaphragm, the
stomach being passive.

The discharge of gases from the oesophagus by the mouth, accompanied with a pe-
culiar and characteristic sound, is very common. This is usually accomplished without
any marked contraction of the muscles concerned in vomiting and evidently requires very
little force. Usually, the cardia is so effectually closed as to prevent the passage even of
gases ; and, in eructation, there must be a temporary relaxation of this opening. When
thus relaxed, the act is accomplished chiefly by contractions of the stomach and oesopha-
gus. It is generally accompanied or preceded by sensible convulsive movements of the
oesophagus, involving, possibly, contractions of its longitudinal fibres, which would favor
relaxation of the cardiac opening. Although it is usually involuntary, this act is some-
times under the control of the will. When it occurs, while it is difficult or impossible to
prevent the discharge of the gas, the accompanying sound may be readily suppressed.
Eructation is frequently a matter of habit, which in many persons becomes so developed
by practice that the act may be performed voluntarily at any time.

INTESTINAL DIGESTION. 257

CHAPTER IX.

INTESTINAL DIGESTION.— DEF^ECA TION.

Physiological anatomy of the small intestine— Glands of Brunner— Intestinal tubules, or follicles of Lieberkuhn—
Solitary glands, or follicles, and the patches of Peyer — Intestinal juice — General properties of the intestinal
juice — Action of the intestinal juice in digestion — Pancreatic juice — Action of the pancreatic juice in digestion —
Destruction of the pancreas— Cases of fatty diarrhoea— Action of the pancreatic juice upon starchy, saccharine,
and nitrogenized principles— Action of the bile in digestion— Biliary fistula— General constitution of the bile-
Variations in the flow of bile — Movements of the small intestine — Peristaltic and antiperistaltic movements —
Function of the gases in the small intestine — Influence of the nervous system upon the peristaltic movements —
Physiological anatomy of the large intestine— Digestion hi the large intestine— Contents of the large intestine-
Composition of the faeces — Excretine and excretoleic acid — Stercorine — Movements of the large intestine — Defae-
cation— Gases found in the alimentary canal.

Physiological Anatomy of the Small Intestine.

THE small intestine, so called on account of its small size as compared with the rest
of the intestinal tract, is the long, cylindrical tube which occupies the greatest part of
the abdominal cavity. This must now be regarded as the most important division.of the
digestive system ; and its physiological anatomy, together with that of the great glands
which discharge their secretions into its cavity, is indispensable as an introduction to
the study of intestinal digestion. As it is in the small intestine that the final elaboration
of most of the alimentary principles takes place, and here, also, that these principles are
taken into the circulating fluid, we shall find, in our study of its anatomy, certain parts
which are concerned in digestion, and others which, as far as we know, are connected
only with the function of absorption. It will be most convenient, however, to consider,
in this connection, all the structures found in the small intestine which possess physio-
logical interest.

The small intestine, extending from the pyloric extremity of the stomach to the ileo-
ca3cal valve, is held to the spinal column by a double fold of serous membrane, called the
me^ehTeryT As the peritoneum which lines the cavity of the abdomen passes from
either side to the spinal column it comes together in a double fold just in front of the
great vessels along the spine, and, passing forward, splits again into two layers, which
become continuous with each other and enclose the intestine, forming its external coat.
The width of the mesentery is usually from three to four inches; but, at the commence-
ment and the termination of the small intestine, it suddenly becomes shorter, binding the
duodenum and that portion of the intestine which opens into the caput coli closely to the
subjacent parts. The mesentery thus keeps the intestine in place but allows of a certain
amount of motion, so that the tube may become convoluted, accommodating itself to the
size and form of the abdominal cavity. The form of these convolutions is irregular and
is continually changing.

The length of the small intestine, in situ, is probably from fifteen to eighteen feet
(Sappey) ; but the canal is very distensible, and its dimensions are subject to constant
variations. When separated from the mesentery and measured without stretching, its
length has been found to be, on an average, about twenty feet. Its diameter is about
•one and a quarter inch.

The small intestine has been divided into three portions, which present anatomical
and physiological peculiarities, more or less marked. These are the duodenum^ the jeju^
num, and the ileum.

The duodenum has received its name from the fact that it is about the length of the
breadth of twelve fingers, or from eight to ten inches. This portion of the intestine is
considerably wider than the constricted, pyloric end of the stomach, with which it is con-
17

258

DIGESTION.

tinuous, and is also much wider than its continuation, the jejunum. It presents a curve,
which is ordinarily described by anatomists as consisting of three portions. The first,
called the hepatic or ascending portion, is about two inches in length. This is much less
firmly fixed by its peritoneal attachment than the other portions and is nearly covered
by the serous membrane. Its direction is outward, backward, and slightly upward.
Turning downward, and a little inward, it merges into the second, called the descending

FIG. 63.— Stomach, liver, small intestine, etc. (Sappey.)

1, inferior surface of the lirer; 2, round ligament of tlie liver; 8, gall-bladder; 4, superior surface of the
right lobe of the liver ; 5, diaphragm; 6, lower portion of the oesophagus; 7, stomach; 8, gastro-liepatic omen-
turn; 9, spleen; 10, gastro-spJenic omentum ; 11, duodenum; 12, 12, small intestine; 13, cacum; 14,
appendix vermiformis ; 15, 15, transverse colon ; 16, sigmoid flexure of the colon ; 17, urinary bladder.

or vertical portion, the length of which is about three inches. This is covered with
peritoneum only on its anterior surface and is somewhat more firmly attached than the
ascending portion. The intestine then makes a second bend, and the third or the trans-
verse portion is horizontal in its course, passing across the spine to the left hypochon-
drium. This portion is about five inches in length. It is narrower than the others, is
but partially covered by peritoneum, and is more firmly bound down than any other part
of the small intestine.

The coats of the duodenum, like those of the other divisions of the intestinal tube, are
three in number. Commencing externally, we have the serous, or-pfiritoneal coat, which
has already been described. The middle, or muscular coat is composed of the involuntary,
or unstriped muscular fibres, such as exist in the stomach, arranged in two layers. The
external, longitudinal layer is not very thick, and the direction of its fibres can be made

PHYSIOLOGICAL ANATOMY OF THE SMALL INTESTINE. 259

out easily only at the outer portions of the tube opposite the attachment of the mesen-
tery. Near the mesenteric border, the fibres are very faint. This is true throughout the
whole of the small intestine; although the fibres are most numerous in the duodenum.
The internal, circular, or transverse layer of fibres is considerably thicker than the longi-
tudinal layer. These fibres encircle the tube, running, for the most part, at right angles
to the external layer, but some of them having rather an oblique direction. The circu-
lar layer is thickest in the duodenum, diminishing gradually in thickness to the middle
of the jejunum, but after that maintaining a nearly uniform thickness throughout the
canal to the ileo-cjgcjd val VQ.

The jejunum, the second division of the small intestine, is continuous with the duo-
denum. It presents no well-marked line of separation from the third division, but is
generally considered to include the upper two-fifths of the small intestine, the lower
three-fifths being called the ileum. It has received the name jejunum from the fact
that it is almost always found empty after death. This portion of the intestine presents
no important peculiarities as regards its peritoneal and muscular coat.

The ileum is somewhat narrower and thinner than the jejunum, otherwise possessing
no marked peculiarities except in the structure of its mucous membrane. This opens
into the commencement of the colon and is the termination of the small intestine.

Mucous Membrane of the Small Intestine. — The mucous coat of the small intestine is
somewhat thinner than the lining membrane of the stomach. It is thickest in the duo-
denum and gradually becomes thinner until we reach the ileum. It is highly vascular,
presenting, like the mucous membrane of the stomach, a great increase in the quantity
of blood during the process of digestion. It has a peculiar soft and velvety appearance,
and, during digestion, it is of a vivid-red color, being pale-pink during the intervals. It
presents for anatomical description the following parts: ], folds of the membrane, called
valvula3 conniventes; 2, duodenal racemose glands, or the glands of Brunner ; 3, intesti-
nal tubules, or follicles of Liebarkuhn ; 4, intestinal villi ; 5, solitary glands, or follicles ;
6, agminated glands, or patches of Peyer.

The valvuhe conniventes, simple transverse duplicatures of the mucous membrane
of the intestine, are particularly well marked in man, although they are found in some
of the inferior animals belonging to the class of mamma-Is, as the elephant and the camel.
They render the extent of the mucous membrane much greater than that of the other
coats of the intestine. Commencing at about the middle of the duodenum, they extend,
with no diminution in number, throughout the jejunum. In the ileum they become pro-
gressively more and more scanty, until they are lost at about its lower third. Sappey
found about six hundred of these folds in the first half of the small intestine and from two
hundred to two hundred and fifty in the lower half. He estimates that, in those portions
of intestine where they are most abundant, they increase the length of the mucous mem-
brane to about double that of the tube itself; but in the ileum they do not increase the
length more than one-sixth. The folds are always transverse and occupy usually from
one-third to one-half of the circumference of the tube, although a few may extend entirely
around it. The greatest width of each fold is in the centre, where it measures from a
quarter to half an inch. From this the width gradually diminishes until the folds are
lost in the membrane as it is attached to the muscular coat. Between the folds are
found fibres of connective tissue similar to those which attach the membrane throughout
the whole of the alimentary tract. This, though loose, is constant, and it prevents the
folds from being effaced, even when the intestine is distended to its utmost. Between
the folds are also found blood-vessels, nerves, and lymphatics.

The position and arrangement of the valvula3 conniventes is such that they move freely
in both directions and may be applied to the inner surface of the intestine either above
or below their line of attachment. It is evident that the food, as it passes along in obe-
dience to the peristaltic movements, must, by insinuating itself beneath the folds and

260 DIGESTION.

passing over them, be exposed to a greater extent of mucous membrane than if these
valves did not exist. This is about the only definite use that can be assigned to them.
They cannot, as has been supposed by some, have any considerable influence upon the
rapidity of the passage of the alimentary mass along the intestinal canal.

Thickly set beneath the mucous membrane in the first half of the duodenum, and
scattered here and there throughout the rest of its extent, are the duodenal racemose
glands, or the glands of Brunner. These are not found in other parts of the intestinal

canal. In their structure, they closely
resemble the racemose glands of the
oesophagus. On dissecting the muscu-
lar coat from the mucous membrane,
they may be seen with the naked eye,
in the areolar tissue, in the form of lit-
tle, rounded bodies, about one-tenth of
an inch in diameter. Examined micro-
scopically, these bodies are found to
consist of a large number of short, blind
tubes branching in every direction and
held together by a few fibres of con-
nective tissue. The tubes have blood-
vessels ramifying on their exterior and
are lined with glandular epithelium.

They collect together to terminate in
FIG. 64.— Gland of Bmnner, from the human subject. (Frey.) -, ,. -.

an excretory duct which penetrates the

mucous membrane and opens into the intestinal cavity. When these structures are ex-
amined in a perfectly fresh preparation, the excretory duct is frequently found to contain
a clear, viscid mucus, of an alkaline reaction. This secretion has never been obtained in
quantity sufficient to admit of the determination of its chemical or physiological proper-
ties. Its quantity must be infinitely small as compared with the secretion produced
by the glandular tubes found in such immense numbers throughout the intestinal tract,
and it cannot be regarded as constituting an important part of the fluid known as the
intestinal juice.

The intestinal tubules, or the follicles of Lieberkiihn, the most important glandular
structures in the intestinal mucous membrane, are found throughout the whole of the
small and large intestine. In examining a thin section of the mucous membrane, these
little tubes are seen closely packed together, occupying nearly the whole of its structure.
From the great extent of the membrane, it can readily be conceived that their number
must be immense. Between the tubules, are blood-vessels, embedded in a dense stroma
of fibrous tissues with numerous unstriped muscular fibres. In a vertical section of
the mucous membrane, the only situations where the tubules are not seen are in that
portion of the duodenum where the space is occupied by the ducts of the glands of Brun-
ner and immediately over the centre of the larger solitary glands and some of the closed
follicles which are collected to form the patches of Peyer. The tubes are not entirely
absent in the patches of Peyer, but are here collected in rings, twenty or thirty tubes deep,
which surround each of the closed follicles. A microscopical examination of the surface
of the mucous membrane by reflected light shows that the openings of the tubules are
between the villi.

The tubules are usually simple, though sometimes bifurcated, are composed externally
of a structureless basement-membrane, and are lined with a single layer of columnar epi'
thelium like the cells which cover the villi, the only difference being that, in the tubes,
the cells are a little shorter. These cells never contain fatty granules, even during the di-
gestion of fat. The central cavity which the cells enclose, which is about one-fourth of
the diameter of the tube, is filled with a clear, viscid fluid, which is the most important

PHYSIOLOGICAL ANATOMY OF THE SMALL INTESTINE.

261

constituent of the intestinal juice. The length of the tubules is equal to the thickness ot
the mucous membrane and is about 7*7 of an inch. Their diameter is about ^^ of an
inch. In man, they are cylindrical, terminating in a single, rounded, blind extremity,
which is frequently a little larger than the rest of the tube. These tubules are the chief
agents concerned in the production of the fluid known as the intestinal juice.

FIG. 65. — Intestinal tubules; magnified 100 diameters. (Sappey.)

A. From the dog. 1, excretory canal ; 2, 2, primary branches ; 3. 8, secondary branches; 4, 4, terminal culs-de-sac.

B. From the ox. 1, excretory canal ; 2, principal branch, dividing into two ; 8, branch undivided ; 4, 4, terminal

culs-de-sac,

C. From the sheep. 1, trunk; 2, 2, branches.

D. Single tube, from the pi?.

E. From the rabbit and hare. 1, simple gland ; 2, 8, 4, bifid glands ; 5, compound gland from the duodenum.

The intestinal villi, though chiefly concerned in absorption, are most conveniently
considered in this connection. These exist throughout the whole of the small intestine
but are not found beyond the ileo-cascal valve, although they cover that portion of the
valve which looks toward the ileum. Their number is very great, and they give to the
membrane its peculiar and characteristic velvety appearance. They are found on the
valvulse conniventes as well as on the attached portions of the mucous membrane. In
the duodenum and jejunum, they are most numerous. In these parts, there are from
7,200 to 13,000 villi to a square inch, and, in the ileum, from 5,YOO to 10,000 to a square
inch. Sappey estimates, on an average, about V,200 to the square inch and more than ten
millions (10,125,000) throughout the whole of the small intestine. The villi vary some-
what in form in different animals. In the human subject, they are flattened cylinders
or cones. In the duodenum, where they resemble somewhat the elevations found in the
pyloric portion of the stomach, they are shorter and broader than in other situations
and are more like flattened, conical folds. In the jejunum and ileum, they are in the
form of long, flattened cones and cylinders. As a rule, the cylindrical form predominates
in the lower portion of the intestine. In the jejunum they attain their greatest length,

262

DIGESTION.

measuring here from ^ to ^ of an inch in length by TV to -^ of an inch in breadth at
their base.

The structure of the villi shows them to be simple elevations of the mucous mem-
brane, provided with blood-vessels, and probably also with lacteals, or intestinal lym-
phatics. Externally is found a single layer of long, columnar epithelial cells, resting on

FIG. 66. — Intestinal mllus. (Leydig.) FIG. 67. — Capillary net-work of an intestinal villus. (Frey.)

a, a, a, epithelial covering- ; 6, 6, capillary net-work ; a, venous trunk ; &, arterial trunk,

c, c, longitudinal muscular fibres ; d, lacteal.

a structureless basement-membrane. These cells, though closely adherent to the sub-
jacent parts during life, are easily detached after death and are almost always destroyed
and removed in injected preparations. They adhere firmly to each other and are isolated
with difficulty in microscopical preparations. Kolliker has shown that the membranes on
the free surfaces of these cells are thickened and finely striated, forming, as it were, a

special membrane covering the villus and exter-
nal to the cells. This membrane may be raised
up from the cells and exhibited by the action
of water.

The substance of the villus is composed of a
strom a of amorphous matter, in which are em-
bedded nuclei and a few fibres, fibro-plastic
cells, and numerous non- striated muscular
fibres. The blood-vessels are very numerous;
four or five, and sometimes as many as twelve
or fifteen arterioles entering at the base, ram-
ifying through the substance of the villus,
but not branching or anastomosing, or even
diminishing in caliber until, by a slightly wavy
turn or loop, they communicate with the ven-
ous radicles, each of which is somewhat larger
than the arterioles. The veins all converge
to two or three branches, finally emptying into a large trunk situated nearly in the
axis of the villus.

FIG. S&.—Epithdi-wm of the small intestine of the
rabbit. (Funke.)

PHYSIOLOGICAL ANATOMY OF THE SMALL INTESTINE. 263

The nuclei of the muscular fibres of the villi may be shown by treating them with
acetic acid after the epithelium has been removed. These fibres appear to be longi-
tudinal, forming a thin layer surrounding the villus, about half-way between the pe-
riphery and the centre and continuous with the muscular coat of the intestine. The mus-
cular fibres, from their arrangement, would seem to be capable of shortening the villus;
and this has actually been observed in specimens taken from the intestine shortly after
deatli.

The anatomy of the lacteals as they originate in the villi has been the subject of much
controversy ; but almost all anatomists are now agreed that these vessels commence by
blind extremities, which are either single or present a few short, rounded diverticula
leading to a single tube.

Owing to the excessive tenuity of the walls of the lacteals in the villi, it has been
found impossible to fill them with an artificial injection, although the lymphatics sub-
jacent to them may be easily distended and studied in this way. Those who profess to
have seen the single lacteal in the villus have done so by examining the parts when the
lacteal system has been engorged with chyle.

We must still regard the question of the origin of the lacteals in the intestinal villi as
one of great obscurity. They may originate by a delicate, anastomosing plexus, just be-
neath the epithelium, as is thought probable by Sappey, or the chyle may pass through
the epithelial layer and a part of the substance of the villus, according to the view pre-
sented by Recklingliausen, without the intervention of distinct vessels, until the particles
reach the central tube.

No satisfactory account has ever been given of nerves in the intestinal villi. If any
exist in these structures, they probably are derived from the sympathetic system, which
is largely distributed to the intestinal canal.

The solitary glands or follicles and the patches of Peyer, or agminated glands, have
one and the same structure, the only difference being that those called solitary are scat-
tered singly in very variable numbers throughout the small and large intestine, while the
agminated glands consist of numbers of these follicles collected into patches of different
sizes. These patches are generally found in the ileum. The number of the solitary
glands is so variable that it is impossible to give any general estimate of it. They are
sometimes absent. The patches of Peyer are always situated in that portion of the intes-
tine opposite the attachment of the mesentery. They are likewise variable in number
and are irregular in size. They usually are irregularly-oval in form, and measure from
half an inch to an inch and a half in length by three-fourths of an inch in breadth.
Sometimes they are three or four inches long, but the largest are always found in
the lower part of the ileum. Their number is about twenty, and they are generally
confined to the ileum; but when they are very numerous— for they sometimes exist
to the number of sixty or eighty— they may be found in the jejunum or even in the
duodenum.

Two varieties of the patches of Peyer have been lately described by anatomists. In
one of these varieties, the patch is quite prominent, its surface being slightly raised
above the general mucous surface, while, in the other, the surface is smooth, and the
patch is distinguished at first with some difficulty. The more prominent patches are cov-
ered with mucous membrane arranged in folds something like the convolutions on the
surface of the brain. The valvulae conniventes are arrested at or very near their borders.
These are the only patches which are generally described as the glands of Peyer, the
others, which may be called the smooth patches, being generally overlooked. The latter
are covered with a smooth, thin, and closely-adherent mucous membrane. Their follicles
are small and numerous. The borders of these patches are much less strongly marked than
those of the first variety. As they are evident only upon close examination and as they
are the only patches present in certain individuals, it is said that sometimes the patches
of Peyer are entirely, wanting. They are generally less numerous than the first variety

264

DIGESTION.

and according to Sappey, are most abundant in persons of feeble constitution. The
villi are very large and prominent on the mucous membrane covering the first variety

of Peyer's patches, especially at the summit of the folds.
In the second variety, the villi are the same as over other
parts of the mucous membrane, except that they are
placed more irregularly and are not so numerous.

The intimate structure of the patches of Peyer has not
been definitely settled in all its particulars. It is well deter-
mined, however, that the follicles which compose them are
completely closed, the openings which have been said to
exist being undoubtedly accidental ruptures made in pre-
paring specimens for microscopical examination. These
follicles are somewhat pear-shaped, with their pointed
projections directed toward the cavity of the intestine.
Just above .the follicle, there is generally a small opening
in the mucous membrane, surrounded by a ring of intes-
tinal tubules, and leading to a cavity, the base of which
is convex and formed by the conical projection of the
follicle. The diameter of the follicles is from T^ to
-fa or even T^ of an inch. The small-sized follicles are
generally covered by mucous membrane and have no
opening leading to them. Each follicle consists of a rather

tary glands upon the valvulse con-
niventes.

FIG. 69.— Patch of Peyer. (Sappey.)

1, 1, 1, patch of Peyer ; 2, 2, folds seen
on the surface; 3, 3, grooves be-
tween the folds ; 4, 4, fossettes be-
tween some of the folds ; 5, 5, 5,
5, 5, 5, 5, 5, valvulae conniventes;

smaller 'son tary7 «fands!' 8, 's,' soli- strong capsule composed of an almost homogeneous or
very slightly fibrous membrane, enclosing a semifluid,
grayish substance, cells, blood-vessels, and probably lym-
phatics. The semifluid matter is of an albuminoid character. The cells are very small,
rounded, and mingled with numerous small, free nuclei. The blood-vessels have rather a
peculiar arrangement. In the first place they are distributed between the follicles, so as
to form a rich net-work surrounding each one. Numerous capillary branches are sent
from these vessels into the interior of the follicle, returning in the form of loops.
The obscurity in the anatomy of the follicles is chiefly with regard to the arrangement

of their lymphatic vessels. These have not been dis-
tinctly traced within the investing membrane. They
have been demonstrated surrounding the follicles, but it
is still doubtful whether they exist in their interior.
This question is so unsettled that it is impossible to
make a definite statement on the subject. All that is
known is that, during digestion, the number of lacteals
coming from the Peyerian patches is greater than in
other parts of the mucous membrane ; but vessels con-
taining a milky fluid are never seen within the follicles.
The mucous membrane covering the prominent
patches is generally so thick and folded that the closed
follicles cannot be seen from above and are only dis-
cernible from the under surface. In the smooth patch-
es, the follicles are generally well brought out by macer-
ation in acetic acid.

The description of the follicles which compose the

FIG. 10.— Patch of Peyer, seen from its

attached surface,. (Sappey.)

1,1, serous coat of the intestine; 2, 2,2.2, patches of Peyer answers, in general terms, for the soli-
serous coat removed to show the * J

patch ; 3, s, fibrous coat of the intes- tary glands, except that the latter are iound in botn

vaTvuli c'onSvenies5' 5' &' 5' * 5' 5' * the small and the large intestine.

INTESTINAL JUICE. 265

Intestinal Juice.

Of the three fluids with which the food is brought in contact in the intestinal canal,
namely, the bile, the pancreatic juice, and the intestinal juice, the last, the secretion of
the mucous membrane of the small intestine, presents the greatest difficulties in the in-
vestigation of its properties and function. If it be admissible to reason from the known
mechanism of secretion in other parts, it is fair to suppose that the normal secretion
from the mucous membrane of the small intestine can only take place in obedience to
the stimulus of food. The same cause induces the secretion of the pancreatic juice and
increases the flow of bile. As we have already seen, the food, as it passes from the
stomach into the duodenum, is to a great extent disintegrated and is mingled with the
secretions from both the mouth and the stomach. Under these circumstances, it is evi-
dently impossible to collect the intestinal juice under perfectly physiological conditions,
in a state of purity sufficient to allow of extended experiments regarding its composition,
properties, and action in digestion.

Bidder and Schmidt experimented upon dogs and cats, shutting off from the intestine
the bile and pancreatic juice, and found that starch introduced into the canal became
transformed into sugar. They also observed that fat was emulsified to a considerable
degree, and that albumen and meat were partially disintegrated and digested. These
observers were unable to collect the intestinal juice in quantity sufficient for analysis.
That which they obtained was found to be colorless, very viscid, and strongly alkaline
in its reaction.

As far as the composition and general properties of the intestinal juice are concerned,
the observations of Colin upon horses are the most definite, although it is questionable
whether he succeeded in obtaining the fluid in a normal state. To collect the fluid, an
incision was made into the abdominal cavity, and from four and a half to six feet of the
small intestine were drawn out.
This portion was emptied by gen-
tly pressing with the finger from
above downward, while, with the

other hand, the upper portion was <,---, x *- ™

kept closed. Without removing £gaJ> XE=J^= -^ * <~3

the fingers, two soft clamps were r

. r FIG. 71.— Clamp for isolating a portion of the ^ntest^ne. (Colin.)

then applied, thus shutting off the ^ iower plate; *, upper plate; C, fixed screw; D, movable screw in

exposed part of the intestine from Place' ^ screw turned so as to allow the clamp to be passed

1 around the intestine.

the rest of the canal. The gut was

then returned and the wound in the abdomen closed. At the end of half an hour, the
animal was killed by bleeding, and the contents of the isolated portion of the intestine
were examined. The quantity of juice obtained was considerable, being from 1,235 to
1,852 grains for about six and a half feet of intestine. It was always found to be much
less when intestinal digestion had been suspended, and its quantity could be increased by
the injection into the loop of a little solution of manna, sulphate of soda, or aloes. The
fluid thus obtained was clear, slightly yellowish, with a saline taste and an alkaline re-
action. It was mixed with mucus, which formed a sediment when the fluid was allowed
to stand, and could be separated by filtration. Notwithstanding the care with which
these observations were conducted, it is not probable that the fluid thus obtained by
Colin was the normal intestinal juice ; and it certainly does not correspond in its gen-
eral characters with the fluids which have been studied by other experimenters.

It becomes an interesting question, in this connection, to determine whether the soli-
tary and the agminated glands produce any secretion which is discharged into the intes-
tinal cavity. Although these follicles are closed, the observations of Colin have shown
pretty conclusively that they are capable of producing a secretion ; but the precise mode
of its formation is not so apparent. The experiment by which this was demonstrated

266 DIGESTION.

was made on a pig, an animal in which there is an enormous agminate gland, ribbon-
shaped and over six feet in length. That portion of the ileum in which the gland is
situated was emptied, and about four and a half feet of it were isolated by two ligatures
from the rest of the canal. At the end of an hour the animal was killed and the intestine
examined. The surface of the gland was found covered with a layer of mucus, thicker
and more consistent than over other portions of the membrane. The only way in which
it could reasonably be supposed that this secretion was produced is by exhalation through
the membranes of the follicles, as there is no evidence that their contents are discharged
by rupture.

FIG. 72.— Isolated portion of the intestine. (Colin.)

Taking only into consideration experiments upon the inferior animals, little definite
information has been obtained concerning the composition and properties of the intestinal
juice. We can readily see that this must be the case, since it has thus far been impossi-
ble, in observations of this kind, to fulfil the necessary. physiological conditions. Farther
facts are evidently needed to harmonize the opposite results arrived at by different ex-
perimenters. It was the same in the progress of the physiology of stomach-digestion,
which was unsettled and obscure until the normal gastric juice was obtained by Beau-
mont. The following case of intestinal fistula, reported by Busch, has done much to elu-
cidate this subject :

The case referred to was that of a woman, thirty-one years of age, who, in the sixth
month of her fourth pregnancy, was injured in the abdomen by being tossed by a bull.
The wound was between the umbilicus and the pubes, presenting two contiguous open-
ings connected with the intestinal canal. It was supposed that the openings were into
the upper third of the small intestine. At the time the patient first came under observa-
tion, every thing that was taken into the stomach was discharged by the upper opening,
and all attempts to establish a communication between the two by a surgical operation
had failed. At this time, the patient was extremely emaciated, had a voracious appetite,
and was evidently suffering from defective nutrition resulting from the constant dis-
charge of alimentary matter from the fistula. Having been treated, however, by the
introduction of cooked alimentary substances into the opening connected with the lower

ACTION OF THE INTESTINAL JUICE IN DIGESTION. 267

end of the intestine, she soon improved in her nutrition and was then made the subject
of extended and interesting observations upon intestinal digestion.

With regard to the general properties of the intestinal juice, the observations of Busch
upon his case of intestinal fistula agree with those of Bidder and Schmidt upon the lower
animals. He never, in the natural condition, found a large quantity of secretion in the in-
testine. The fluid was white or of a pale rose-color, consistent, and always strongly alka-
line. The maximum proportion of solid matter which it contained was 7'4 and the mini-
mum, 3-87 per cent. The secretion apparently could not be obtained in sufficient quantity
for ultimate analysis. No better opportunity than this could be presented for studying
the intestinal juice in its pure state. The nature of the case made it impossible that there
should be any admixture of food, pancreatic juice, bile, or the secretion of the duodenal
glands ; and, during the process of digestion, the lower part of the intestine undoubtedly
produced a fluid of perfectly normal character. When we come to consider the action
of the intestinal juice upon the various articles of food, our most reliable facts will be
drawn from the observations made upon this case.

From what has been ascertained by experiments upon the lower animals and observa-
tions on the human subject, the intestinal juice has been shown to possess the following
characters :

Its quantity in any portion of the mucous membrane which can be examined is small ;
but, when the extent of the canal is considered, it is evident that the entire quantity of
intestinal juice must be great, although, beyond this, no reliable estimate can be made.

The intestinal juice is viscid and has a tendency to adhere to the mucous membrane.
It is generally either colorless or of a faint rose^tinjt, and its reaction is invariably alkaline.

With regard to the composition of the intestinal juice, little of a definite character has
been learned. All that can be said is that its solid constituents exist in the proportion
of about 5 '47 parts per hundred. In most analyses of fluids from the intestine, there is
reason to believe that the normal intestinal juice was not obtained.

The organs which secrete the fluid known as the intestinal juice are the follicles of
Lieberktihn, the glands of Brunner, and possibly the solitary follicles and patches of Peyer.
The fluid, however, is chiefly secreted by the follicles of Lieberktihn, which, as we have
seen, exist in the mucous membrane of the intestine in immense numbers. Although the
other organs mentioned do not contribute much to the secretion, they produce a certain
quantity of fluid ; and the intestinal juice must be regarded as a compound fluid, like the
saliva, and not the product of a single variety of glands, like the gastric juice.

Action of the Intestinal Juice in Digestion.

The physiological action of the 'intestinal juice has been closely studied in the inferior
animals by Frerichs and by Bidder and Schmidt, but their experiments have been some-
what contradictory. All observers, however, are agreed that this fluid is more or less
active in transforming starch into sugar. We must turn finally to the observations of
Busch, on the case of intestinal fistula in the human subject, for the most satisfactory and
definite information on this subject. In many points, it is true, these observations sim-
ply confirm those which have been made upon the inferior animals, but they are of great
value, as they establish conclusively many important facts regarding the physiological
action of the intestinal juice in the human subject.

In the case reported by Busch, starch, both raw and hydrated, when introduced into
the lower opening, where it came in contact only with the intestinal juice, was invariably
changed into glucose. Cane-sugar was not transformed into glucose but appeared in
the faeces as cane-sugar. This is important, with reference both to the want of action
of the intestinal juice upon cane-sugar and the fact that cane-sugar, as such, is not ab-
sorbed in quantity by the intestinal mucous membrane.

Coagulated albumen and cooked meat were always more or less digested by the intes-
tinal juice. This fact coincides with the observations of Bidder and Schmidt.

268 DIGESTION.

The observations which were made on fats, melted butter, and cod-liver oil, showed
that the pure intestinal juice had little or no action upon them. These substances always
appeared in the fseces unchanged. AY hen, however, fatter matters were taken into the
stomach, they were discharged from the upper opening in the intestine, in the form of a
very fine emulsion, and could not be recognized as fat.

It is evident, from these facts, that the intestinal juice is important in digestion, more
as a fluid which aids the general process as it takes place in the small intestine than as
one which has a peculiar action upon any distinct class or classes of alimentary princi-
ples. It undoubtedly assists in completing the digestion of albuminoid substances and in
transforming starch into sugar. Although, in the latter process, its action is very
marked, the same property belongs to the saliva and the pancreatic juice. Intimately
mingled — as it always is during digestion — with the bile and the pancreatic juice as well
as with various alimentary substances, the intestinal juice should be studied as it operates
upon the food, in connection with the other fluids found in the small intestine, the diges-
tive action of all being most intimately associated.

Pancreatic Juice.

The physiological anatomy of the pancreas does not^ demand a very extended consid-
eration, as most of the points of its descriptive anatomy have no direct relation to its
physiology, and its minute anatomy belongs properly to the subject of secretion. The
pancreas is a glandular organ, situated transversely in the upper part of the abdominal
cavity, and closely applied to its posterior wall. Its form is elongated, with an enlarged,
thick portion, called the head (which is attached to the duodenum), a body, and a pointed
extremity, which is in close relation to the hilum of the spleen. Its average weight is
from four to five ounces ; its length is about seven inches ; its greatest breadth, about an
inch and a half; and its thickness, three-quarters of an inch. It lies behind the perito-
neum, which covers only its anterior surface.

FIG. 73. — Gall-bladder, ductus cJioledocJius, and pancreas. (Le Bon.) •

a, gall-bladder: &, hepatic duct; c, opening of the second duct of the pancreas; d, opening of the pancreatic and
the bile-duct; e, e, duodenum ; / ductus choledochus; p, pancreas.

According to Bernard, who has made numerous investigations into the anatomy of
this gland, there are nearly always, in the human subject, two ducts opening into the
duodenum; one which opens in common with the ductus communis choledochus, and
one which opens about an inch above the main duct, called by Bernard the recurrent or

PANCREATIC JUICE.

269

accessory duct. The main duct is about an eighth of an inch in diameter and extends
along the body of the gland, becoming larger as it approaches the opening. The sec-
ond duct is smaller and becomes diminished in caliber as it nears the duodenum. Many
anatomists describe but a single duct, regarding the other as anomalous. The dissections
of Bernard, however, were very numerous and show the almost constant occurrence of
two ducts.

In general appearance and minute structure, the pancreas is like the parotid and sub-
maxillary glands. By the older anatomists it was known as the u abdominal salivary
gland," on account of this resemblance in structure and an
assumed similarity in the nature of their secretions. Eecent
developments in the physiology of the pancreatic juice have
caused this name to be discarded.

Bernard was the first to obtain normal pancreatic juice
from a living animal and to give a definite idea of its properties
and functions ; a point which it is proper to particularly insist
upon, inasmuch as, since his discovery, some have pretended
that the facts which he established had been demonstrated
before. The following method for collecting the pancreatic
juice from a living animal, one which we have repeatedly em-
ployed with success, is essentially that recommended by Ber-
nard:

The animal generally employed by Bernard in these ex-
periments is the dog. Selecting one of tolerably large size,
he is secured to the operating-table and placed upon his left
side. An incision from three to four inches in length is then
made in the right hypochondrium, just below and parallel
with the border of the last rib. The parts are first divided
down to the fascia transversalis and the peritoneum. An
opening is then made into the abdominal cavity about half
the length of the incision through the skin and muscles,
which brings to view the duodenum and a portion of the pan-
creas. The duodenum, with the pancreas attached to it, is
then carefully drawn out of the abdomen. The next step is
to introduce a small canula into the principal pancreatic duct.
In the dog, there are always two pancreatic ducts ; a small
duct, which opens into the intestine at or near the opening of
the bile-duct, and a principal duct, which is situated about an
inch below. To collect the juice, the tube should be intro-
duced into the principal duct. This is found by turning the
duodenum and pancreas so as to expose the posterior surface
of the gland, when the duct, which is very short and almost
concealed by the tissue of the pancreas, may be seen oblique-
ly penetrating the intestinal wall. In the dog, the pancreas
is composed of two portions ; one, called the horizontal por-
tion, which is attached to the duodenum, and a vertical por-
tion, which passes away from the intestine between the folds
of the mesentery. The duct is generally situated near the
point where the pancreas ceases to be attached to the intes-
tine. The tissue of the pancreas is to be carefully pushed
away from the duct with the end of the canula or the point
of a knife, a small longitudinal slit is made in it with the
scissors, and a silver canula, about one-twelfth of an inch in diameter and four inches in
length, is introduced and firmly secured in place by a ligature wJiich has previously been

FIG. 74. — Canula for a pancre-
atic fistula. (Bernard.)

A, stylet, the extremity of which
should pass a little beyond
the end of the canula J5. to
facilitate its introduction into
the pancreatic duct ; B, ean-
nla, provided with little
grooves c, c, to hold the
threads for Attachment into
the duct and into the bladder
used to collect the pancreatic
juice.

270 DIGESTION.

thrown around the duct. The canula should be provided with a well-fitting stylet, with
the point rounded so that it may he introduced into the duct with ease ; and the end of
the canula should be somewhat roughened, so that the ligature may secure it well in
place. The canula will enter the duct for a short distance only, and it should not be in-
troduced forcibly. After this has been accomplished, the canula may be steadied by at-
taching it with a single stitch to the wall of the intestine. The stylet is now to be with-
drawn and the parts carefully returned to the abdomen, leaving the end of the canula
projecting at the anterior portion of the wound, which should be carefully closed. Ber-
nard recommends to first raise up the fascia and peritoneum with hooks and carefully
attach their edges with sutures, and then to close, in the same way, the incision in the
muscles and integument. The animal may now be kept upon the table, and the fluid
which is discharged from the tube collected in a test-tube, or a thin gum-elastic-bag may
be attached. This may be provided with a stopcock, so that the fluid may be drawn off

at will.

I

I

FIG. 75.— Canula fixed in the pancreatic duct. (Bernard.)

A, principal pancreatic duct of the dog ; B, smaller pancreatic duct ; C, ligature securing a canula in the principal duct ;
D, D, ligature attaching the canula to the intestine, for security; E, canula; F, bladder, provided with a stop-
cock G, to collect the pancreatic juice ; P, P, pancreas ; I, I, intestine.

Like the other digestive fluids, the pancreatic juice is secreted in abundance only
during the process of digestion. It is therefore necessary to feed the animal moderately
about an hour before the operation, so that the pancreas may be in full activity. When
it is exposed at that time, it is filled with blood and has a rosy tint, contrasting strongly
with its pale appearance during the intervals of digestion.

In performing the above experiment, it is generally better not to employ an anes-
thetic agent, as this very frequently produces vomiting, arrests digestion for a time, and
consequently interferes with the secretion of the pancreatic juice. This, however, is not
always the case. We have sometimes performed the operation with the aid of ether and
have obtained a fair amount of fluid. It is also necessary to avoid traction upon the duo-
denum as much as possible, for this is almost sure to produce vomiting. To obtain the
best results, the operation should be performed rapidly and with very little exposure of
the pancreas. In some very successful experiments, Bernard has obtained from sixty
to one hundred grains of juice in an hour, from a dog of medium size.

Some of the most interesting facts developed by Bernard concerning the pancreatic
juice relate to phenomena connected with its secretion. It is important to remember

PANCREATIC JUICE.

271

that the secretion of the pancreas is entirely suspended during the intervals of digestion.
This fact has been definitely settled by Bernard and can easily be observed by opening
animals in digestion and while fasting. In the first instance, the pancreatic duct will be
found full of normal secretion, and, in the other, it will be almost, if not entirely, empty.
Bernard has also found that the pancreatic juice begins to flow into the duodenum during
the first periods of stomach-digestion, before alimentary matters have begun to pass in
quantity into the intestine.

FIG. 76.— Pancreatic fistula. (Bernard.)

Fall-grown shepherd-do? (female), in which a pancreatic fistula has been established A, silver tube to which ?
bladder has been attached; B, bladder; C, stopcock for the purpose of collecting the juice which accumulates
in the bladder.

Another important fact determined by Bernard is that the secretion of the pancreas
is readily modified by irritation and inflammation following the operation. When we
come to treat of the general properties of the normal pancreatic fluid, it will be seen that
its characteristics are, decided alkalinity, viscid consistence, and coagulability by heat.
It is almost always the case that, a few hours after the canula is fixed in the duct, the
juice loses some of these characters and flows in abnormal quantity. With respect to
susceptibility to irritation, the pancreas is peculiar ; and its secretion is sometimes ab-
normal from the first moments of the experiment, especially if the operative procedure
have been prolonged and difficult. That the properties above described are characteristic
of the normal pancreatic secretion, there can be no doubt ; as, in all instances, fluid taken
from the pancreatic duct of an animal suddenly killed while in full digestion is strongly
alkaline, viscid, and coagnlable by heat. This excessive sensitiveness of the pancreas has
rendered fruitless all the attempts of Bernard to establish a permanent pancreatic fistula
from which the normal juice could be collected ; and we are not disposed to admit that
the fluid collected by recent German observers, from permanent fistula}, represents phys-
iological conditions.

General Properties and Composition of the Pancreatic Juice. — In all the inferior ani-
mals from which the pancreatic secretion has been obtained in a normal condition, the
fluid has been found to present pretty uniform characters. It is viscid, slightly opaline,

272 DIGESTION.

and has a distinctly alkaline reaction. Bernard found the specific gravity of the fluid
from the dog to be 1040. The quantity of organic matters which the normal secretion
contains is very great, so that the fluid is completely solidified on the application of heat.
This great coagulability is one of the properties by which the normal fluid may be distin-
guished from that which has undergone alteration.

Composition of the Pancreatic Juice of the Dog. (Bernard.)

Water , 900 to 920

Organic matters, precipitable by alcohol and containing )
always a little lime (pancreatinc, trypsine, etc.) \ ' '

Carbonate of soda, 1

Chloride of sodium, € 10 to 6'40

Chloride of potassium, I

Phosphate of lime, J 1,000 1,000

f

Most of the analyses which have been made of the pancreatic fluid are not to be relied
upon, as the manner in which the juice was obtained shows generally that it was not
normal. There is no doubt, however, that the fluid which was obtained from the dog
and analyzed by Bernard possessed all of its characteristic physiological properties.

The chemical properties of the organic principles of the pancreatic juice are distinctive.
Although, like albumen, they are coagulated by heat, the strong mineral acids, and abso-
lute alcohol, they differ from albumen in the fact that their dried alcoholic precipitate can
be redissolved in water, giving to the solution all the physiological properties of the nor-
mal pancreatic secretion. Bernard has also found that they are coagulated by an excess
of sulphate of magnesia, which will coagulate caseine but has no effect upon albumen.
It is important to recognize this distinction between the organic matters of the pancreatic
juice and other nitrogenized principles, especially albumen, from the fact that the last-
named substance has the property of forming an emulsion with fats, though not so readily
and completely as the pancreatic juice ; and it is essential to decide whether the organic
principles be peculiar and distinct substances, or albumen transuded pathologically, per-
haps, from the blood. There can be no doubt, in view of the marked chemical and physi-
ological peculiarities of pancreatine and trypsine, that they are distinct proximate princi-
ples, characteristic of the pancreatic secretion and found in no other fluid.

Researches have shown that pancreatine and trypsine are essential physiological
constituents of the pancreatic juice, giving to this fluid its peculiar digestive properties.
The contents of the duodenum, as the partly digested matters pass from the stomach, are
generally acid; but this does not at all interfere with the action of the pancreatic juice.
Although the secretion itself is alkaline, it retains its physiological properties when it
has been rendered acid by admixture with gastric juice.

The inorganic constituents of the pancreatic juice do not possess any great physiologi-
cal interest, inasmuch as they do not seem to be essential to its peculiar digestive proper-
ties. It has been shown, indeed, by Bernard, that the organic principles alone, extracted
from the pancreatic juice and dissolved in water, are capable of imparting to the fluid all
the physiological characters of the normal secretion.

The entire quantity of pancreatic juice secreted in the twenty-four hours has been
variously estimated by different authors. After what has been said concerning the varia-
tions to which the secretion is subject, it is not surprising that these estimates should
present great differences. Bernard was able to collect from a dog of medium size from
eighty to one hundred grains in an hour ; but it must be remembered that only one of the
ducts was operated upon, and that the gland is always very susceptible to irritation.
There is no accurate basis for an estimate of the quantity of pancreatic fluid secreted in
the twenty-four hours in the human subject, or of the quantity necessary for the digestion
of a definite amount of food.

ACTION OF THE PANCREATIC JUICE IN DIGESTION. 273

Unlike the gastric juice, the secretion of the pancreas, under ordinary conditions of
heat and moisture, rapidly undergoes decomposition. In warm and stormy weather, the
alteration is marked in a few hours; but, at a temperature of from 50° to 70° Fahr., it
decomposes gradually in from two to three days. The changes which the fluid thus
undergoes are interesting, from the fact that some physiologists, having experimented
with an altered or an abnormal secretion, have failed to recognize certain of the charac-
teristic properties of the normal fluid. As it thus undergoes decomposition, the fluid
acquires a very offensive, putrefactive odor, and its coagulability diminishes, until finally
it is not affected by heat. The alkalinity, however, increases in intensity ; and, when
neutralized with an acid, there is a considerable evolution of carbonic acid, which does
not occur in fresh pancreatic juice.

Action of the Pancreatic Juice in Digestion.

It is only since the observations of Bernard, in 1848, that the pancreatic juice has been
regarded as a fluid of any great importance in digestion. It has now been demonstrated,
both by cases of disorganization of the pancreas in man and by experiments on animals
in which the tissue of the organ has been destroyed, that the pancreatic juice is essential
to digestion and to life, animals dying of inanition when its function has been abolished.

The most striking feature in the discovery made by Bernard was the action of the
pancreatic juice in the digestion of fats; it being shown that these principles are acted
upon almost exclusively by the pancreas, and that they pass through the alimentary canal
undigested when this organ has been destroyed. For this reason, probably, the action
of the pancreas in the digestion of fatty substances has received an undue prominence ;
and its action upon other articles of food, though not at the present day overlooked, does
not always receive proper consideration. We shall find that the pancreatic juice has an
important action in the digestion of nearly all the alimentary principles as they pass out
from the stomach.

Action upon Fats. — Even before the publication of Bernard's researches, it was pretty
generally admitted that the digestion of fat consisted in its minute subdivision and sus-
pension in the form of an emulsion. This view was adopted from the fact that, during
the absorption of fats from the intestinal canal, the lacteals and thoracic duct always
contain innumerable small, fatty globules ; but the ideas of physiologists as to the par-
ticular fluid by which the emulsification of fats is accomplished were not very well
settled. The most generally-received opinion, however, was that this was effected by
the bile ; but experiments on this subject were very contradictory.

One of the most remarkable facts observed by Bernard was that, in the rabbit, after
the ingestion of fatty matters, vessels filled with white chyle do not make their appearance
at the commencement of the small intestine, as in other animals, but are first seen from
twelve to twenty inches below the pylorus. The anatomical peculiarity in these animals
is that the pancreatic duct, instead of opening into the intestine with the bile-duct at the
upper part of the small intestine, has its opening from twelve or twenty inches below,
just at the point where the chyliferous vessels are observed. This fact, which we have
frequently confirmed, points directly to the pancreatic juice as the agent principally, if
not exclusively, concerned in emulsifying the fats; while it shows that the bile possesses
little or no immediate efficiency in this regard. Following out this line of inquiry, and
operating with fresh, coagulable pancreatic juice and the liquid fats or those capable of
being liquefied by gentle heat, it was found that slight agitation of this fluid with the fats
produced a very fine and permanent emulsion, similar in every respect to the milky fluid
found in the lactenls during digestion. In fact, comparative analyses of the lymph and
chyle have shown that the latter liquid is nothing more than lymph with the addition of
fatty emulsion. As soon as the absorption of fat is completed, the lacteal vessels lose
their opaque, white contents and carry nothing but colorless lymph. This is one of the
18

274 DIGESTION.

great experimental facts upon which is based the view that the pancreatic juice has the
property of digesting the fats. Concerning the accuracy of this observation there can be
no doubt. The fact has been so frequently confirmed, that it must now be considered as
established beyond question, and we can add our testimony to its accuracy from personal
observation. It is true that some of the German physiologists have been unable to con-
firm these experiments ; but, by carefully following out the process indicated by Ber-
nard, which is detailed with great care, we have invariably found his observations to be
correct. It is well known that many of the German experimenters operated with pan-
creatic juice which was not coagulable and which Bernard regards as abnormal and in-
capable of digesting fat.

The pancreatic juice is the only one of the digestive fluids which is capable of forming
a complete and permanent emulsion with fats. The fact that the other digestive fluids
will not accomplish this is easily demonstrated as regards the saliva, gastric juice, and bile.
The intestinal juice is then the only one which might be supposed to have this property.
The observations of Busch on this point, in his case of intestinal fistula, are conclusive.
He found that fatty matters taken into the stomach were discharged from the upper
opening in the intestine in the form of a fine emulsion and were never recognizable as
oil ; but that fat introduced into the lower intestinal opening was not acted upon and
was discharged unchanged in the faeces.

Another peculiarity noted by Bernard in the emulsion resulting from the action of
pancreatic juice upon fats is that it persists when diluted with water and will pass
through a moistened filter like milk. This does not take place in the imperfect emulsion
formed by a mixture of oil with any other of the digestive fluids.

Although the normal pancreatic juice is constantly alkaline, this is not an indispensa-
ble condition as regards its peculiar action upon fats ; for the emulsion is none the less
complete when the fluid has been previously neutralized with gastric juice.

Bernard has shown that the pancreatic juice and the tissue of the pancreas have the
property of saponifying fats, or decomposing them into a fatty acid and glycerine, and that
this property is not possessed by any other tissue or liquid of the economy. The question
naturally arises, then, whether this be an accidental property of the tissue and the secre-
tion of the pancreas or whether partial saponification of fat take place in digestion. Con-
cerning this point there is no difference of opinion among physiological chemists. The
fat which is contained in the lacteal vessels is always neutral ; and the absence of any
fatty acid has been recognized by Bernard as well as by others. The inevitable conclu-
sion to be drawn from this fact is, that, while fat may be in part decomposed into an acid
and glycerine by the pancreatic juice, out of the body, in the natural process of digestion,
either this does not take place or the acid is not absorbed by the lacteals. The greatest
part, if not the whole, of the fat which is digested in the small intestine is simply formed
into an emulsion by the pancreatic juice and undergoes no chemical alteration.

To complete the experimental evidence of the action of the pancreatic juice in the
digestion of fats, Bernard attempted to extirpate or destroy the pancreas in a living ani-
mal. This he found very difficult. All attempts to extirpate the organ with the knife
being unsuccessful, the injection of foreign matters into the duct was resorted to. After
a great number of unsuccessful experiments, in two instances, the functions of the gland
were suspended for a time and its tissue was partly destroyed by the injection of melted
tallow. In both of these observations, the effects upon digestion were very marked.
Although the appetite was voracious, the animals became gradually emaciated, and the
faeces contained a large quantity of rancid, undigested fat. At the same time, other ali-
mentary principles, incompletely digested, were recognized in the discharges. In two
dogs operated upon by Bernard, in which the experiments were successful, the nutrition
and the alvine discharges became normal at the thirteenth and the seventeenth day.
After the animals had completely recovered, they were killed, and the pancreas in both
instances was found partially destroyed.

ACTION OF THE PANCREATIC JUICE IN DIGESTION. 275

Now that the action of the pancreatic juice upon fats is so well understood, it is a
matter of surprise that the cases of fatty diarrhoea connected with disorganization of the
pancreas, which were reported by Dr. Richard Bright, in 1832, did not direct the atten-
tion of physiologists to the function of this organ. These cases, with others of a similar
character which have been reported from time to time, are now brought forward as
strong evidence of the action of the pancreas in the digestion of fats. Many of them pre-
sented a train of symptoms analogous to those observed in animals after partial destruc-
tion of the gland. The presence of fat in the alvine dejections was most marked ; and,
as is now well known, this could be nothing but the undigested fatty principles of the
food. In the three cases observed by Bright, the pancreas was found so disorganized
that its secreting function must have been almost, if not entirely, abolished. In the case
reported by Mr. Lloyd, the condition was the same ; and, in the case reported by Dr.
Elliotson, " the pancreatic duct and the larger lateral branches were filled with white
calculi." Another interesting case of disease of the pancreas is described in the catalogue
of the Anatomical Museum of the Boston Society for Medical Improvement, in 1847. In
this case, it was observed by the patient that fatty discharges from the bowels did not
take place unless fatty articles of food had been taken. After death, a large tumor was
found in the situation of the pancreas, but all trace of the normal structure of the organ
had been destroyed. Many more cases of this character are quoted by Bernard and
others, and they fully confirm the observations and experiments which have been made
upon the lower animals. They all seem to show that the function of the pancreas in
digestion is essential to life, but that one of the chief disorders in digestion incident to the
destruction of this gland relates to the digestion of fa^s.

Taking into consideration all the facts bearing upon this subject, the conclusion is in-
evitable that the chief agent in the digestion of fats is the pancreatic juice; and that this
fluid acts by forming with the fat a very fine emulsion, thus reducing it to a form in
which it can be absorbed. How far the bile may assist in this process is a question which
will come up for consideration hereafter; but the facts with regard to the pancreatic
juice are conclusive.

Action upon Starchy and Saccharine Principles. — The action of the pancreatic juice
in transforming starch into sugar was first observed, in 1844, by Valentin, who experi-
mented with an artificial fluid made by infusing pieces of the pancreas in water. Bou-
chardat and Sandras first noted this property in the normal pancreatic secretion. Pan-
creatine is undoubtedly the principle concerned in the action of this fluid upon starch.

The property of converting starch into sugar is possessed by several of the digestive
fluids. We have seen that the starchy elements of food are acted upon by the saliva,
that this action is not necessarily arrested as these principles, mixed with the saliva,
pass into the stomach, and that the intestinal juice of itself is capable of effecting the
transformation of starch into sugar to a considerable extent. It therefore becomes an
important question to determine precisely how far the pancreas is actually concerned in
the digestion of this class of principles.

Bernard places the pancreatic juice at the head of the list of the digestive fluids which
act upon starch. This view is undoubtedly correct ; although he goes a little too far
in claiming that starch is almost exclusively digested by the pancreas. Bernard's ex-
periments, however, were made chiefly on dogs, and these animals do not naturally take
starch as food. In man, some of the starchy principles of the food are acted upon by
the saliva, but, undoubtedly, most of the starch taken as food is digested in the small in-
testine. Although the intestinal juice is capable of effecting the transformation of starch
into sugar, the experimental evidence is conclusive that in this it is subordinate to the
pancreatic juice, which latter effects this transformation, at the temperature of the body,
with extraordinary activity. There is no positive evidence that the bile has any thing to
do with this action.

276 DIGESTION".

To sum up the whole process of the digestion of starch, it may be stated, in general
terms, that this principle, when hydrated, which is the usual condition in which it is
taken into the stomach of the human subject, is slightly acted upon by the saliva, both
in the mouth and after it has passed into the stomach ; when it is taken raw, it is hy-
drated in the stomach and usually undergoes no transformation into sugar until it has
passed into the small intestine ; and, when it passes out at the pylorus, mainly by the ac-
tion of the pancreatic juice but with the assistance of the intestinal juice, it is transformed
into glucose and in this form is absorbed.

We have already followed out the digestion of sugar as far as the small intestine.
Glucose undergoes no change in the stomach and is taken directly into the circulation.
It is probable, also, that a small quantity of cane-sugar may in like manner be taken up
by the blood-vessels of the intestinal mucous membrane. It has been shown that a small
quantity of cane-sugar is transformed into glucose in the stomach, but, as we noted in
treating of stomach-digestion, the quantity is inconsiderable, and the transformation de-
pends simply upon the presence of a free acid in the gastric juice.

As most of the saccharine principles of food exist in the form of cane-sugar, it is the
action of the digestive fluids upon this variety of sugar which possesses the greatest phys-
iological interest. As cane-sugar passes from the stomach into the duodenum it is al-
most instantly transformed into glucose. This fact has lately received additional con-
firmation in the case of intestinal fistula observed by Busch. In this case, when cane-
sugar was introduced in quantity into the stomach, fasting, the fluid which escaped from
the upper end of the intestine contained a small quantity of glucose but never any cane-
sugar.

It now becomes a question whether the transformation of cane-sugar into glucose be
effected by the bile, the intestinal juice, or the pancreatic juice. The pancreatic juice
and the intestinal juice are the two fluids which might be supposed to have this effect;
for it has been repeatedly demonstrated that the bile hac of itself no direct action upon
any of the alimentary principles. This point is settled by the experiments of Busch npon
the lower end of the intestine, in his case of fistula. Matters introduced into this lower
opening came in contact with the intestinal juice only. He found that cane-sugar, ex-
posed thus to the action of the intestinal juice, was not converted into glucose, but a
large portion of it was found in the faeces. His observations also indicate that cane-
sugar is not readily absorbed by the intestinal mucous membrane until it has been trans-
formed into glucose.

Out of the body, the pancreatic juice is capable, if kept but for a short time in con-
tact with any of the saccharine principles, of transforming them into lactic acid. The
contents of the small intestine are sometimes alkaline or neutral and are sometimes acid.
When a very large quantity of sugar has been taken, a part of it may be converted in the
intestine into lactic acid, and this may happen with the sugar which results from the
digestion of starch ; but, under ordinary conditions, starch and cane-sngar are readily
changed into glucose and are absorbed without undergoing farther transformation. All
the varieties of sugar, after they have been absorbed by the portal vein and carried to
the liver, are here transformed into glucose, the only form, apparently, under which they
can be used in nutrition.

Action of the Pancreatic Juice upon Nitrogenized Principles. — We have frequently had
occasion to insist upon the great relative importance of intestinal digestion, and it has
been apparent that, in the stomach, the process of disintegration of food is not final,
even as regards many of the nitrogenized principles, but is rather preparatory to the
complete liquefaction of these principles, which takes place in the small intestine. The
experiments, already referred to, of Bernard, in which the pancreas has been partially
destroyed in dogs, show rapid emaciation, with great voracity, and the passage, not only
of unchanged fats and starch, but of undigested nitrogenized matter in the dejections.

ACTION OF THE BILE IN DIGESTION. 277

In some instances, pieces of tripe which had been fed to the animal were recognizable in
the fa)ces "by their aspect, because of their slight alteration." The voracious appetite,
progressive emaciation, and the passage of all classes of alimentary substances in the
fasces, after this operation, demonstrate conclusively the great importance of the pancre-
atic juice in digestion. But, when we inquire into the precise mode of action of this
fluid upon the albuminoids, the question becomes one of great difficulty. If the bile be
shut off from the intestine and discharged externally by a fistulous opening, the same
voracity and emaciation are observed ; and yet there is no single alimentary substance
upon which the bile, of itself, can be shown to exert a decided digestive action. Farther-
more, the pancreatic juice is evidently calculated to act upon alimentary principles after
they have been subjected to the action of the stomach, a preparation which is absolutely
essential to proper intestinal digestion; and, once passed into the intestine, the food
comes in contact with a mixture of pancreatic juice, intestinal juice, and bile. We have
to study, therefore, the special action of the pancreatic secretion upon the albuminoids,
as far as it can be isolated, and its action in conjunction with the other intestinal fluids
and in the presence of other alimentary principles in process of digestion. The first
definite observations upon these points were made by Bernard. He found that the albu-
minoid substances generally, exposed to the action of the pancreatic juice out of the
body, became rapidly softened and dissolved in some of their parts, but soon passed into a
condition of putrefaction. An analogous change, it will be remembered, also takes place
in starchy and fatty matters when exposed to the action of the pancreatic juice out of
the body, and they pass through the various stages of transformation respectively into
lactic acid and the fatty acids. This putrefactive action does not take place in albuminoids
which have been precipitated after having been cooked, or in raw gluten or caseine. The
presence of fat also interferes with putrefaction ; so that Bernard concludes that the fats
have an important influence in the intestinal digestion of nitrogenized principles. Ex-
periments made since the observations of Bernard have shown that the active principle
of the pancreatic juice concerned in the digestion of albuminoids is trypsine, the trans-
formation of starch into sugar being effected by pancreatine.

Taking into consideration what has been positively ascertained concerning the action of
the pancreatic juice upon the albuminoids, there can be no doubt with regard to the impor-
tance of its function in the digestion of these principles after they have been exposed to
the action of the gastric juice. Experiments upon the digestion of these substances after
they have passed out of the stomach show that they undergo important and essential
changes as they pass down the intestinal canal. While the bile and the intestinal juice are
by no means inert, they seem to be only auxiliary in their action to the pancreatic juice.

The preparation which the albuminoids undergo in the stomach is undoubtedly neces-
sary to the easy digestion, in the small intestine, of that portion which is not dissolved by
the gastric juice. This fact has been conclusively demonstrated by experiments on in-
testinal digestion in the inferior animals and by the observations of Busch in the case of
intestinal fistula in the human subject.

Action of the J3ile in Digestion.

A great deal of diversity of opinion has existed among physiologists concerning the
functions of the bile. It is now pretty generally acknowledged that this fluid has, of
itself, no marked influence upon any of the different classes of alimentary principles,
such as we have observed in the other secretions discharged into the alimentary canal.
This being the case, it is important to decide whether the bile be essential in assisting or
modifying the action of other secretions or whether it be entirely inert in the digestive
process. From the fact that it is poured into the upper part of the small intestine, it
would seem that it must have some office, either in modifying the digestion and absorp-
tion of food or in the passage of alimentary substances or their residue down the intes-
tinal tract. It is difficult to suppose that a fluid which is brought in contact with the ali-

278 DIGESTION.

mentary mass in that portion of the intestine where the most important digestive pro-
cesses commence should be simply excrementitious ; yet this is the view entertained by
some experimentalists. In this position of the subject, naturally the first question to
decide relates to the excrementitious or recrementitious character of the bile ; or whether,
in other words, the bile be separated from the blood simply to be discharged from the
body or have some important function to perform as a secretion. An apparently simple
method of settling this question has been employed by many experimenters, but with re-
sults which are not satisfactory, unless they can be in some way harmonized. Schwann,
Nasse, Bidder and Schmidt, and Bernard, whose observations will be more fully consid-
ered hereafter, have performed experiments upon animals in which the bile was entirely
shut off from the intestine and discharged from the body by a fistula. If the bile be sim-
ply excrementitious, it should follow that animals operated upon in this way would not
suffer from the discharge of the bile by a fistula and its diversion from the intestine ; but,
in all of them, death occurred with symptoms pointing to defective nutrition consequent
upon grave disorder of digestion. The same result followed our own experiments on this
subject. On the other hand, Blondlot attempts to show that the bile is simply an excre-
tion, and that animals thrive and will live for an indefinite period, when the bile is
diverted from its natural course and is discharged from the body.

In the experiments of those who simply closed the ductus communis choledochus, the
effects of shutting off the bile from the intestine were modified by the consequent undue
accumulation of this fluid in the biliary passages. The only way to obviate this difficulty
was to discharge the bile by a fistula, as was first done by Schwann. The first experi-
ments reported by Schwann were made upon sixteen dogs and one rabbit. Of these,
only six can be regarded as successful ; and, in the others, the animals either died of
peritonitis resulting from the operation, or recovered, the fistulous opening into the gall-
bladder becoming closed and the communication between the liver and the intestine re-
establishing itself. These six animals died, apparently of inanition, respectively, after
seven, thirteen, seventeen, twenty-five, sixty-four, and eighty days. In all, except the
two animals that lived for sixty-four and eighty days respectively, there was gradual
diminution in weight from the date of the operation, notwithstanding that a large quan-
tity of food was taken. In the two exceptions, there was first diminution in weight, then
the flesh was partially regained, but it subsequently diminished until death occurred. In
these six animals, there was every reason to believe that death occurred from the aboli-
tion of the digestive function of the bile, and the disturbances in nutrition were very much
like those produced by Bernard by destruction of the pancreas. These experiments
were confirmed in their essential particulars by Bidder and Schmidt, Nasse, and Bernard.
These facts seem to show that the bile is not simply an excrementitious fluid, and that
its function, after it is discharged into the intestine, is not only important but absolutely
essential to life. The only experiment which is opposed to this view is one reported by
Blondlot.

The experiment by Blondlot was made upon a dog. The fistula was established in
the fundus of the gall-bladder, the ductus communis having been tied and a portion ex-
sected. Fifteen days after the operation, the animal had become extremely thin, but ate
well, and, according to the report of the experimenter, was in perfect health. During all
this time, however, he habitually licked the bile, but he was finally prevented from doing
this by a muzzle. From the moment when the dog ceased to swallow the bile, the nutri-
tion began to improve, and in three months he had recovered the natural amount of
flesh. A farther account of this experiment is given by Blondlot in another memoir.
The animal, while in perfect health aside from the existence of the fistula, was claimed
by the owner, from whom it had been stolen before it passed into the hands of the ex-
perimenter. "With the fistula still open, the dog was used by its owner for hunting and
lived for five years. At the end of this time it was returned to M. Blondlot, but died
while in his possession, two months after.

ACTION OF THE BILE IN DIGESTION. 279

The important question then to determine was that the bile had been completely shut
off from the intestinal canal. An examination of the parts was consequently made in
the presence of a number of physicians and students. On the most minute dissection, it
was impossible to find any communication between the bile-duct and the duodenum ;
and the conclusion arrived at was that the animal had lived for five years without a drop
of bile passing into the intestine, and, consequently, that this fluid was useless in digestion.

The facts obtained by all other observers are in direct opposition to the above experi-
ment. After a number of trials, we succeeded in establishing a biliary fistula in a dog,
the operation being followed by no inflammation of the peritoneum, and, notwithstanding
that the animal was voracious and consumed daily large quantities of food, it died in
thirty-eight days, of inanition. If our own observation and those of other experimenters
be correct, it is impossible that an animal should live in perfect health for years with all
the bile discharged by a fistula.

There is reason to believe that the experiment of Blondlot was inaccurate, and that a
communication existed between the bile-duct and the duodenum, which was not discov-
ered at the dissection after death. The following observation strengthens us in this
opinion :

We made an attempt on one occasion to ascertain the total amount of bile secreted in
twenty-four hours; and, with this view, the ductus communis choledochus was exposed
in a dog, the bile contained in the gall-bladder was pressed out, a canula, with an elastic
bag attached, was fixed in the duct, and the external wound was closed, leaving the end
of the canula, with the bag attached, protruding from the abdomen. The bag ruptured
twenty-three hours after, and the experiment was consequently unsuccessful in the end
for which it was undertaken. The tube dropped out at the end of forty-eight hours, and
the external wound quickly healed. Thirty days after the operation the animal was
killed. He had then entirely recovered, and no bile had been discharged externally for
a long time. The alvine dejections were perfectly normal, and there could be no doubt
that the bile was regularly discharged into the duodenum. On dissection after death,
the liver was found normal, and the papilla which marks the opening of the bile-duct
into the duodenum was natural in appearance. It was with the greatest difficulty, how-
ever, that the communication between the bile-duct and the duodenum could be found ;
yet, after patient searching for more than an hour, a small, tortuous tract was discovered.
Had it not been certain that bile had been constantly discharged into the intestine, it
might have been assumed, even after careful examination, that no such communication
existed.. This examination convinced us that it was possible that the communication
between the duct and the intestine had been reestablished in Blondlot's case, and that it
had escaped observation in the dissection after death.

The isolated experiment of Blondlot does not therefore invalidate the results obtained
by Schwann and confirmed by so many eminent physiologists. The bile is not simply an
excretion but has an important and essential office to perform in the process of intestinal
digestion. We have, however, conclusively shown that, in addition to its recrementitious
function, it separates from the blood an important excrementitious principle, cholesterine,
which, under a modified form, is discharged in the faeces. This function of the liver will
be fully considered under the head of excretion. It is sufficient for our present purposes
to show that the bile, unlike any other fluid in the organism, has two distinct functions,
dependent upon two distinct classes of constituents. The peculiar principles known as
the biliary salts, which are produced in the liver, give to it its digestive properties; and
the cholesterine, which is simply separated from the blood by the liver, gives it its ex-
crementitious character.

As we are much better acquainted with the excrementitious than with the digestive
function of the bile, we shall consider, in this connection, only a few of the points con-
cerning the chemistry of this fluid, deferring a full account of its composition until we
come to treat of it as an excretion.

280

DIGESTION.

The bile varies in color and consistence in different animals. It usually has a greenish,
yellowish, or brownish hue. In the human subject, it has a dark, golden-brown color
and is somewhat viscid in consistence, chiefly from admixture with the mucus of the gall-
bladder. The specific gravity of human bile has been found to be about 1018. Its reac-
tion is faintly alkaline.

Physiological chemists have long since recognized in the bile peculiar principles,
which are found in no other part of the organism ; but the exact nature of these con-
stituents was first described by Strecker, in 1848, who obtained from the bile of the ox
two principles, cholic and choleic acid, which he found to exist in this fluid in combina-
tion with soda. The cholic acid of Strecker, which may be decomposed into a new acid
and a principle called glycine, and the choleic acid, from which may be formed a new
acid and taurine, are called by Lehmann, respectively, glycocholic and taurocholic acid.
In the bile of the ox, these are found combined with soda, and the peculiar proximate
principles of this fluid are now recognized as the glycocholate of soda, a crystalline sub-
stance, and the taurocholate of soda, which is of a resinous consistence and is stated to
be uncrystallizable. In the human bile, Dalton has found a resinous substance, which,
from its behavior with various reagents, is undoubtedly analogous to the taurocholate
of soda of ox-bile, but which he could not obtain in a crystalline form.

FIG. 11.— Crystals oj glycocholate of soda. (Eobin.)

In addition to the biliary salts, the bile contains the ordinary inorganic salts, found
in nearly all the animal fluids, a small quantity of fat, the oleates, margarates, and stea-
rates of soda and potassa, mucus from the gall-bladder, and cholesterine ; the last being
an excrementitious product. The action of the bile in digestion, whatever its nature may

ACTION OF THE BILE IN DIGESTION. 281

be, undoubtedly depends chiefly upon the biliary salts, and perhaps to some extent upon
its saponaceous constituents.

Experiments with regard to the action of the bile upon different alimentary substances
out of the body have not led to any definite results. It is only in connection with the other
digestive fluids that the bile seems to be efficient ; and the only observations which have
thrown any light upon the subject are those made upon digestion in the living organism.
Simple ligation of the bile-duct has taught us very little regarding the effects of shutting off
the bile from the intestine ; for the immediate effects of the operation generally interfered
with the process of digestion, and subsequently the experiment was necessarily disturbed
by the effects of the retention of bile in the excretory passages. As would naturally be
expected, these observations have been quite contradictory. The most satisfactory ex-
periments upon the digestive function of the bile have followed the establishment of a
fistulous opening into the gall-bladder, the flow of bile at the same time being completely
shut off from the intestine. In all experiments of this kind in which fatal inflammation
did not follow the operation, death has taken place from inanition, notwithstanding an
increase in the quantity of food taken. This result is not due simply to the loss of the
solid matter discharged in the bile, which is small in proportion to the total daily loss of
weight ; but it undoubtedly proceeds from disordered nutrition, which has its starting-
point in disordered digestion.

Observations on a Dog with a Biliary Fistula. — We have now to study the modifica-
tions in digestion and nutrition which are the result of simply diverting the bile from the
intestine. With that view, we followed carefully these changes in an animal with a
biliary fistula that was under our own observation. This experiment confirmed, in all
important particulars, those of Schwann and of Bidder and Schmidt. It is given here
somewhat in detail, for, inasmuch as no inflammation followed the operation and nothing
occurred to complicate the effects of the diversion of the bile from the intestine, we re-
garded the experiment as remarkably successful.

November 15, 1861, a biliary fistula was established in a young cur-dog weighing
twelve pounds. The abdominal organs were very little exposed, and the experiment,
from the first, promised to be very satisfactory. The bile-duct was first ligated next the
intestine and at its junction with the cystic duct, and the intermediate portion was ex-
sected. The incision in the abdomen was in the median line just below the ensiform
cartilage, and was about three inches long. The funclus of the gall-bladder was then
drawn to the upper portion of the wound, and the bile was evacuated by a small opening,
the edges of which were attached to the abdominal parietes. The wound in the abdo-
men was then closed, except the opening into the gall-bladder, into which a few shreds
of lamp-wicking were introduced.

The animal appeared to do perfectly well after the operation and ate the usual quan-
tity the next day. He was kept in a warm room, although the weather was mild ; and
a careful record was made of his condition every day. The fistula occasionally showed a
tendency to close, but it was kept open by the occasional introduction of a glass rod.
From time to time, while the animal was under observation, he licked the bile as it
flowed from the fistula. This was afterward prevented by a long wire-muzzle, the sides
of which were covered with oil-silk.

The abdomen was somewhat tumid, with some rumbling in the bowels, for five days
after the operation. The first alvine discharge took place on the evening of the second
day. The faeces seemed in all regards normal. After that time, they became very infre-
quent, although the animal ate well every day. The faeces that were passed after the
third day were of a grayish color and moderately soft. They had an exceedingly offensive
and penetrating odor. At about the fifteenth day, the faeces became more frequent, and,
from that time, were passed three or four times a day. Generally, they were clay-col-
ored ; but on one or two occasions they were quite dark. They always had a peculiarly
offensive odor.

282

DIGESTION.

The weight of the animal remained stationary for about four days. On the sixth day
(November 20th), the weight began to diminish. He weighed on that day, before feed-
ing, eleven and one-quarter pounds. November 22d, he weighed but little over eleven
pounds. November 24th, he weighed ten pounds. He maintained this weight until
December 1st, when the weight again began to diminish. On December 6th, the weight
was nine pounds. On December 7th, the weight was reduced to eight and a half pounds,
and the strength began to fail manifestly. December 10th and llth, he gained a little,
on those days weighing nine pounds; but, after that, he progressively diminished in
strength and in weight until death occurred, thirty-eight days after the operation. The
weight was then seven and a half pounds, showing a total loss of four and a half pounds,
or 37|- per cent.

During the first nine days of the observation, the animal ate well but not ravenously,
taking about three-quarters of a pound of beef-heart daily. On the tenth day, the appe-
tite increased. He ate on that day, at one time a pound, and at another, half a pound of
meat. He ate on an average about a pound and a half of beef-heart daily, until the day
before his death. During the last five or six days, he seemed very ravenous and was not
allowed to eat all that he would at one time. At this time he was ordinarily fed twice a
day. He would not eat fat, even when very hungry. During the last day, when too

FIG. IB.— Dog with a Hilary fistula.

From a rough sketch made the fourteenth day after the operation. A small glass A'essel is tied aroitnd the body
to collect the bile, and a wire muzzle, the lower part of which is covered with oil-silk, is placed over the mouth to
prevent the animal from licking the bile. The dog is considerably emaciated.

weak to stand, he attempted to eat while lying down. During the last twelve days of
the observation, he attempted constantly to eat the fa3ces. During the last days of the
experiment, when the dog had become much reduced in weight, he became very cross
and snapped at every animal that came near him. There was never any icterus, fetor
of the breath, or falling off of the hair.

A careful examination of the animal was made after death. The gall-bladder was
somewhat contracted but not obliterated, and the fistula would admit a large-sized
male catheter. Both ends of the divided bile-duct were found impervious, and there was
no passage of bile into the intestine. The abdominal organs were normal, with the
exception of evidences of slight peritoneal inflammation around the wound and over the
convex surface of the liver. There was no fat in the omentum or anywhere in the body,
except a very small quantity at the bottom of the orbit.

The above observation is a type of the instances — which are not very numerous — in

ACTION OF THE BILE IX DIGESTION. 283

which the bile has been completely shut off from the intestine and discharged externally
by a fistula into the gall-bladder. As far as could be ascertained, this animal, from the
first, presented no disturbances which were not due solely to the absence of the bile from
the intestine and its discharge externally. Although the phenomena here presented do
not teach us much that is definite concerning the digestive action of the bile, taken in
connection with what has been ascertained concerning the general properties of this se-
cretion, they throw some light upon its functions.

One of the functions which has been ascribed to the bile is that of regulating the peris-
taltic movements of the small intestine and of preventing putrefactive changes in the
intestinal contents and the abnormal development of gas. Experiments on this point are
somewhat conflicting. Our own observations would lead us to doubt the constant influ-
ence of the bile upon the peristaltic movements. During the first few days of our experi-
ment, the dejections were very rare ; but they afterward became regular, and, at one
time, even, there was a tendency to diarrhoea. There can be no doubt, however, that
the bile retards the putrefaction of the contents of the intestinal canal, particularly when
animal food has been taken. The faeces in the dog were always extremely offensive.
Bidder and Schmidt found this to be the case in dogs fed entirely on meat ; but the faeces
were nearly odorless when the animals were fed on bread alone. In the case of intes-
tinal fistula in the human subject, the evacuations which took place after the intro-
duction of alimentary substances into the lower portion of the intestine had an unnaturally
offensive and putrid odor. In this case, as it was impossible for matters to pass from the
portions of the intestine above the fistula to those below, the food introduced into the
lower opening was completely removed from the action of the bile.

As far as the digestion of the different alimentary principles is concerned, it has been
shown that the bile, of itself, has no particular action upon any of them. In the faeces
of animals with biliary fistula, the only peculiarity which has been observed, aside from
the putrefactive odor and the absence of the coloring matter of the bile, has been the
presence of an abnormal proportion of fat. "We have observed this in the faeces of a pa-
tient suffering under jaundice apparently due to temporary obstruction of the bile-duct.
This fact was noted in the dogs experimented upon by Bidder and Schmidt.

The various experiments which have been performed upon animals render it almost
certain that the bile has an important influence, either upon the digestion or upon the ab-
sorption of fats. Bidder and Schmidt noted in animals with biliary fistula that the chyle
contained very much less fat than in health. In an animal with a fistula and the bile-duct
obliterated, the proportion of fat was 1'90 parts to 1,000 parts of chyle ; while, in an ani-
mal with the biliary passages intact, the proportion was 32*79 parts per 1,000. In ani-
mals operated upon in this way, there is frequently a great distaste for fatty articles of
food. In our own observation, the dog refused fat meat, even when very hungry and
when lean meat was taken with great avidity.

Experiments concerning the influence of the bile upon the absorption of fats have re-
sulted in hardly any thing definite. We know only the fact that, when the bile is diverted
from the intestine, the proportion of fat in the chyle is greatly reduced, and a large pro-
portion of the fat taken with the food passes through the intestine and is found in the
faeces.

The action of the bile in exciting muscular contraction, particularly in the smooth
muscular fibres, is pretty well established. It has been shown by Schiff that this fluid
acts upon the muscular fibres situated in the substance of the intestinal villi, causing
them to contract, and, according to his view, assisting in the absorption of chyle by emp-
tying the lacteals of the villi. The whole subject, however, of the absorption of fats is
exceedingly difficult of investigation ; and our knowledge of it has not been sensibly ad-
vanced by the experiments upon the influence exerted by the bile. Notwithstanding the
obscurity in which this subject is involved, it is certain that the progressive emaciation,
loss of strength, and final death of animals deprived of the action of the bile in the intes-

284

DIGESTION.

tine, are due to defective digestion and assimilation. In spite of the great quantities of food
taken by these animals, the phenomena which precede the fatal result are simply those
of starvation. It may be that the biliary salts are absorbed by the blood 'and are neces-
sary to proper assimilation ; but there is no experimental basis for this supposition, and
it is impossible to discover these salts in the blood of the portal system by the ordinary
tests. It is more probable that the biliary salts influence in some way the digestive pro-
cess and are modified and absorbed with the food.

The observations of Bidder and Schmidt show conclusively that the characteristic
constituents of the bile are absorbed in their passage down the alimentary canal. Hav-
ing arrived at a pretty close estimate of the quantity of bile daily produced in dogs, they
collected and analyzed all the fascal matter passed by a dog in five days. Of the dry
residue of the faeces, the proportion which could by any possibility represent the biliary
matters did not amount to one-fourth of the dry residue of the bile which must have been
secreted during that time. They also estimated the total quantity of sulphur contained
in the faeces and found that the entire quantity was hardly one-eighth of that which
was discharged into the intestine in the bile ; and, inasmuch as nearly one-half of that
found in the faeces came from hairs which had been swallowed by the animal, the experi-
ment showed that nearly all the sulphur contained in the non-crystallizable element of
the bile (the taurocholate of soda) had been taken up again by the blood. These obser-
vations show conclusively that the greater part of the bile, with the biliary salts, is ab-
sorbed by the intestinal mucous membrane. Prof. Dalton has attempted to follow these
principles into the blood of the portal system, but has never been able to detect the bili-
ary salts, by the most careful analysis. Like the peculiar principles of other secretions
which are reabsorbed in the alimentary canal, these substances become changed and are
not to be recognized by the ordinary tests, after they are taken into the blood.

Although it is the digestion and absorption of fatty substances which seem to be
most seriously interfered with in cases of biliary fistula in the inferior animals, the rapid
loss of weight and strength indicates great disturbance in the digestion and absorp-
tion of other articles of food. A fact which indicates a connection between the bile and
the process of digestion is that the flow of this secretion, although constant, is greatly
increased when food passes into the intestinal canal. This has been noted by all who
have experimented on the subject. The following observations on the dog, showing the
variations in the flow of bile from the fistula, were made twelve days after the fistula had
been established, when the weight of the animal had been reduced from twelve to ten
pounds.

Table of Variations in the Flow of JBile with JDigestion.

(At each observation, the bile was drawn for precisely thirty minutes.)

Time after Feeding.

Fresh Bile.

Dried Bile.

Percentage of
Dry Kesidue.

Immediately

Grains.

8'103

Grains.

0-370

4-566

One hour

20*527

0-1:86

2-854

Two hours

35-760

1-080

3-023

Four hours

38-939

1-404

3-605

Six hours

22-209

0987

4-450

Eight hours

86-577

1-327

3-628

Ten hours

24-447

0-833

3'407

Twelve hours

5-710

0-247

4-325

Fourteen hours

5-000

0-170

3-400

Sixteen hours

8-643

0-309

B-5h5

Fjiffhteen hours .

9-970

0-277

2-778

Twenty hours

4*769

0-170

3-565

Twenty-two hours

7*578

0-293

3-866

MOVEMENTS OF THE SMALL INTESTINE. 285

Disregarding slight variations in this table, which might be accidental, it may be
stated, in general terms, that the bile commences to increase in quantity immediately
after eating ; that its flow is at its maximum from the second to the eighth hour, during
which time the quantity does not vary to any great extent ; after the eighth hour it
begins to diminish, and, from the twelfth hour to the time of feeding, it is at is minimum.

Although it has been pretty satisfactorily demonstrated that the presence of the bile
in the small intestine is necessary to proper digestion and even essential to life, and
although the variations in the flow of bile with digestion are now well established, it
must be confessed that we have scarcely any definite information concerning the mode
of action of the bile in intestinal digestion and absorption. Nearly all that we can say on
this point is that its action seems to be auxiliary to that of the other digestive fluids.

Movements of the Small Intestine.

By the contractions of the muscular coat of the small intestine, the alimentary mass
is made to pass along the canal, sometimes in one direction and sometimes in another ;
the general tendency, however, being toward the ca3cum. The partially-digested matters
which pass out at the pylorus are prevented from returning to the stomach by the pecul-
iar arrangement of the fibres which constitute the pyloric muscle. The passage from
the stomach to the intestine, as we have seen, becomes constricted gradually, so that
food of the proper consistence finds its way easily into the duodenum ; but, viewed
from the duodenal side, the constriction is abrupt, so that regurgitation is generally
difficult.

Once in the intestine, the food is propelled along the canal by peculiar move-
ments, which have been called peristaltic, when its direction is toward the large
intestine, and antiperistaltic, when the direction is reversed. These movements are
of the character peculiar to the unstriped muscular fibres; viz., slow, gradual, the
contraction enduring for a certain time and being followed by a correspondingly slow
and gradual relaxation. Both the circular and the longitudinal muscular layers par-
ticipate in these movements. If we carefully watch this action in the intestines of
an animal after the abdomen has been opened, we can sometimes see a gradual constric-
tion produced by the action of the circular fibres at. a certain point, which is slowly
propagated along the tube, while, at the same time, the longitudinal fibres are alternate-
ly contracted and relaxed in the same gradual manner, shortening and elongating the
tube and facilitating the onward passage of its contents. It can readily be appreciated
how movements of this kind are capable of propelling the alimentary mass slowly but
certainly along the intestinal tract, even when the direction is in opposition to the force
of gravity ; and we can see how admirably these movements are calculated to thorough-
ly incorporate the food with the digestive fluids and to expose those parts which have
been completely liquefied to the absorbent action of the mucous membrane.

Although the mechanism of the propulsive movements of the intestine maybe studied
in living animals after opening the abdomen, or, better still, in animals just killed, the
movements thus observed do not entirely correspond with those which take place under
natural conditions. In vivisections, no movements are observed at first; but, soon after
exposure of the parts, nearly the whole intestine moves like a mass of worms. In the
normal process of digestion, the movements are never so general or so active ; they take
place more regularly and consecutively in those portions in which the contents are most
abundant, and the movements are generally intermittent, being interrupted by long inter-
vals of repose. In Prof. Busch's case of intestinal fistula, there existed a large ventral
hernia, the coverings of which were so thin that the peristaltic movements could be readily
observed. In this case, the general character of the movements corresponded with what
has been observed in the inferior animals. It was noted that the movements were not
continuous, and that there were often intervals of rest for more than a quarter of an hour.

286 DIGESTION.

It was also observed that the movements, as indicated by flow of chymous matter from
the upper end of the intestine, were intermitted with considerable regularity during part
of the night. Antiperistaltic movements, producing discharge of matters which had been
introduced into the lower end of the intestine, were frequently observed.

As far as has been ascertained by observations upon the human subject and warm-
blooded animals, the regular intestinal movements are excited by the passage of alimen-
tary matter from the stomach through the tube during the natural process of digestion.
By a very slow and gradual action of the muscular coat of the intestine, its contents are
passed along, occasionally the action being reversed for a time, until the indigestible
residue, mixed with a certain quantity of intestinal secretion, more or less modified, is
discharged gradually into the caput coli. These movements are apparently not continu-
ous, and they depend somewhat upon the quantity of matter contained in different parts of
the intestinal tract. If we are to judge from the movements in the inferior animals after
the abdomen has been opened, the intestines are constantly changing their position, prin-
cipally by the action of their longitudinal muscular fibres, so that the force of gravity does
not oppose the on \vard passage of their contents as much as if the relative position of the
parts were constant. There are no definite observations concerning the relative activity
of the peristaltic movements in different portions of the intestine ; but, from the fact that
the jejunum is constantly found empty, while the ileum contains a considerable quantity
of pultaceous matter, it would seem that the movements must be more vigorous and
efficient in the upper portions of the canal.

The gases which are constantly found in the intestine "have an important mechanical
function. They are useful, in the first place, in keeping the canal constantly distended
to the proper extent, thus avoiding the liability to disturbances in the circulation and
facilitating the passage of the alimentary mass in obedience to the peristaltic contrac-
tions. They also support the walls of the intestine and protect these parts against con-
cussions in walking, leaping, etc. The gases are useful, likewise, in offering an elastic
but resisting mass upon which the compressing action of the abdominal muscles may bs
exerted in the acts of straining and expiration. If we could suppose the intestinal tube
to be entirely free from gaseous contents, it is evident that the functions above mentioned
would be performed imperfectly and with difficulty.

There can be hardly any question that the normal movements of the intestine are
due principally to the impression made upon the mucous membrane by the alimentary
matters, to which is added, perhaps, the stimulating action of the bile. It is difficult to
determine with accuracy what part the bile plays in the production of these movements,
from the fact that the normal action of the intestine is not easily observed. In the case
of intestinal fistula so often referred to, when food was introduced into the lower end of
the canal, there was at first an abundant evacuation every twenty-four hours ; but sub-
sequently it became necessary to use enemeta. As there was no communication between
the lower and the upper end of the intestine, this fact is an evidence that the peristaltic
movements can take place without the action of the bile. Experiments upon the inferior
animals concerning the influence of the bile upon the peristaltic movements are somewhat
contradictory. When the abdomen is opened during life, vigorous movements may some-
times be excited by pressing bile into the intestine from the gall-bladder; and the same
result is occasionally observed when the bile is applied to the peritoneal surface in an
animal recently killed. But the various experiments in which the bile has been diverted
from the intestine and discharged by a fistula, taking the frequency of the alvine dejec-
tions as a test, show that regular peristaltic movements may take place without the in-
tervention of the bile.

The vigorous peristaltic movements which occur soon after death have been explained
in various ways. It has been shown that these movements are not due to a lower-
ing of the temperature or to exposure of the intestines to the air. The latter fact
may be easily verified by killing a rabbit, when vigorous movements may be seen through

PHYSIOLOGICAL ANATOMY OF THE LARGE INTESTINE. 287

the thin abdominal walls, even while the cavity is unopened. According to Schiff, the
only cause of these exaggerated movements is diminution or arrest of the circulation.
This physiologist, by compressing the abdominal aorta in a living animal, was able to ex-
cite peristaltic movements in the intestine as vigorous as those which take place after
death ; and, on ceasing the compression, the movements were arrested.

The nerves distributed to the small intestine are derived from the sympathetic, and
from branches of the pneumogastric, which latter come from the nerve of the right side
and are distributed to the whole of the tract, from the pylorus to the ileo-caecal valve.
The intestine receives no filaments from the left pneumogastric. The experiments of
Brachet, by which he attempted to prove that the movements of the intestines were
under the control of the pneumogastric and nerves emanating from the spinal cord, have
not been verified by other observers. Recent experiments render it probable that an
influence, derived from the cerebro-spinal system, is essential to the functions of the
sympathetic ganglia, which may account for some of the results obtained by Brachet
after dividing the spinal cord. The experiments of Miiller, however, render it certain
that the peristaltic movements are to some extent under the influence of the sympathetic
system. In these experiments, movements of the intestine were produced by galvaniza-
tion of filaments of the sympathetic distributed to its muscular coat, after the ordinary
post-mortem movements had ceased. The same results followed the application of caustic
potash to the semilunar ganglia, the movements reappearing when the potash was applied,
44 with extraordinary vivacity " in the rabbit, after the abdomen had been opened and the
movements had entirely ceased. These experiments have been confirmed by Longet,
who found, however, that the movements did not take place unless alimentary matters
were contained in the intestine.

It must be acknowledged that very little is known concerning the reflex actions which
take place through the sympathetic system ; but there is certainly good ground for sup-
posing that certain reflex functions are performed by this system of nerves, one of the
most important of which is the production of peristaltic movements in obedience to the
impression made by alimentary substances upon the mucous membrane. This impression
is probably conveyed to the semilunar ganglia and reflected back through the motor nerves
to the muscular coat of the intestine.

Physiological Anatomy of the Large Intestine.

The large intestine, so called because its diameter is greater than that of the rest of
the intestinal tract, receives for the most part only the indigestible residue of the food,
mingled with certain of the secretions which are discharged into the small intestine. In
the human subject, the processes of digestion which take place in this part of the ali-
mentary canal are unimportant ; and it is probable that, under physiological conditions,
hardly any thing but water is absorbed by its lining membrane. Matters are, however,
stored up in the large intestine for a number of hours, and a certain amount of secretion
takes place from its follicular glands.

The entire length of the large intestine is from four to six feet. Its diameter is great-
est at its commencement, where it measures, when moderately distended, from two and a
half to three and a half inches. According to the observations of Brinton, the average
diameter of the tube beyond the ca3cum is from one and two-thirds to two and two-
thirds inches. Passing from the ceBcum, the canal diminishes in caliber, gradually and
very slightly, to where the sigmoid flexure opens into the rectum, This is the narrowest
portion of the canal. Beyond this, the rectum gradually increases in diameter, forming
a kind of pouch, which abruptly diminishes in size near the external opening, to form the
anus.

The general direction of the large intestine is from the caecum in the right iliac fossa
to the left iliac fossa, thus encircling the convoluted mass formed by the Email in-

288

DIGESTION.

testine, in the form of a horseshoe. From the csecum to the rectum, the canal is
known as the colon. The first division of the colon, called the ascending colon,

passes almost directly upward
to the under surface of the liver ;
the canal here turns at nearly
a right angle, passes across the
upper part of the ahdomen, and
is called the transverse colon ;
it then passes downward at
nearly a right angle, forming
the descending colon. The
last division of the colon, called
the sigmoid flexure, is situated
in the left iliac fossa and is in
the form of the italic letter S.
This terminates in the rectum,
which is not straight, as its
name would imply, but presents
at least three distinct curva-
tures, as follows : it passes first
in an oblique direction from the
left sacro-iliac symphysis to the
median line opposite the third
piece of the sacrum; it then
passes downward, in the me-
dian line, following the con-
cavity of the sacrum and coc-
cyx ; and the lower portion,
which is about an inch in length,
turns backward to terminate in
the anus.

The form of the large intes-
tine is peculiar. The ca3cum,'
or caput coli, presents a round-
ed, dilated cavity, continuous
with the colon above and com-
municating by a transverse slit
with the ileum. At its lower
portion, is a small, cylindrical
tube, from one to five inches in
length, opening below and a little posterior to the opening of the ileum, called the ver-
miform appendix. This is covered with peritoneum and is possessed of a muscular and
a mucous coat. It is sometimes entirely free and is sometimes provided with a short
fold of mesentery for a part of its length. The coats of the appendix are very thick.
The muscular coat consists of longitudinal fibres only. The mucous membrane is pro-
vided with tubules and closed follicles, the latter frequently being very numerous. This
little tube, which is only about one-third of an inch in diameter, generally contains a
quantity of clear, viscid mucus. The uses of the vermiform appendix are unknown.

Ileo-cmcal Valve. — The most interesting anatomical peculiarity of the caBCUin is the
opening by which it receives the contents of the small intestine. This opening is ar-
ranged in the form of a valve, known as the ileo-csecal valve, situated at the inner and
posterior portion of the caecum. The small intestine, at its termination, presents a

FIG. 79.— Stomach, pancreas, large intestine, etc. (Sappey.)
1, anterior surface of the liver; 2, pall-bladder; 3, 3, section of the dia-
phragm ; 4, posterior surface of the stomach ; 5, lobus Spigelii of the
liver; 6, cceliac axis; 7, coronary artery of the stomach; 8, splenic
artery; 9, spleen; 10, pancreas; 11. superior mesenteric vessels; 12,
duodenum ; 13, upper extremity of the small intestine ; 14, lower end
of the ileum; 15, 15, mesentery; 16. ccfcum; 17, appendix vermi-
formis; 18, ascending colon; 19, 19. transverse colon; 20, de-
scending colon ; 21, sigmoid flexure, of the colon ; 22, rectum ; 23,
urinary bladder.

PHYSIOLOGICAL ANATOMY OF THE LARGE INTESTINE. 289

shallow concavity, which is provided with a horizontal, button-hole slit opening into
the caecum. The surface of the valve which looks toward the small intestine is cov-
ered with a mucous membrane provided with villi and in all respects resembling the
general mucous lining of the small intestine. Viewed
from the ca3cum, a convexity is observed corresponding
to the concavity upon the other side. The caecal surface
of the valve is covered with a mucous membrane identi-
cal with the general mucous lining of the large intestine.
It is evident, from an examination of these parts, that
pressure from the ileum would open the slit and allow
the easy passage of the semifluid contents of the intes-
tine; but pressure from the ca3cal side approximates
the lips of the valve, and the greater the pressure the
more firmly is the opening closed. The valve itself is
composed of folds formed of the white fibrous tissue of
the intestine (the cellular tunic of some anatomists), and
circular muscular fibres from both the small and the
large intestine, the whole being covered with mucous
membrane. The lips of the valve unite at either extrem-
ity of the slit and are prolonged on the inner surface of
the cascum, forming two raised bands or bridles; and
these become gradually effaced and are thus continuous FIG. 80.— Opening of the small intes-
with the general lining of the canal. The posterior bridle , t™™t° the ccecum (Le Bon.)

1, small intestine; 2, ileo-ca?cal valve;

is a little longer and more prominent than the anterior. 3, caecum; 4, opening of the appen-
These assist somewhat in enabling the valve to resist gj^^JSi j^TS! ?2r£
.pressure from the csecal side. The longitudinal layer of SofcjJ' ?' f°ld8 °f th° mU°OU3
muscular fibres and the peritoneum pass directly over the

attached edge of the valve and are not involved in its folds. These give strength to the
part, and, if they be divided over the valve, gentle traction will suffice to draw out and
obliterate the folds, leaving a simple and unprotected communication between the large
and the small intestine.

• Peritoneal Coat. — Like most of the other abdominal viscera, the large intestine is
covered by peritoneum. The ca3cum is covered by this membrane only anteriorly and
laterally. It is usually bound down closely to the subjacent parts, and its posterior sur-
face is without a serous investment; although sometimes it is completely covered, and
there may be even a short mesocoecum. The ascending colon is likewise covered with
peritoneum only in front and is closely attached to the subjacent parts. The same ar-
rangement is found in the descending colon. The transverse colon is almost completely
invested with peritoneum ; and the two folds forming the transverse mesocolon separate
to pass over the tube above and below, uniting again in front to form the great omentum.
The transverse colon is consequently quite movable. In the course of the colon and the
upper part of the rectum, particularly on the transverse colon, are found a number of
little sacculated pouches filled with fat, called the appendices epiploi'csB. The sigmoid
flexure of the colon is invested with peritoneum, except at the attachment of the iliac
mesocolon. This division of the intestine is capable of considerable motion. The upper
portion of the rectum is almost completely covered by peritoneum and is but loosely IK-!U
in place. The middle portion is closely bound down, and is covered with peritoneum only
anteriorly and laterally. The lowest portion of the rectum has no peritoneal covering.

Muscular CWf.— The muscular fibres of the large intestine have an arrangement quite
different from that which exists in the small intestine. The external, longitudinal layer,
instead of extending over the whole tube, is arranged in three distinct bands, which com-
19

290 DIGESTION".

mence in the caecum at the vermiform appendix. Passing along the ascending colon,
one of the bands is situated anteriorly, and the others, latero-posteriorly. In the trans-
verse colon, the anterior hand becomes inferior and the two latero-posterior bands be-
come respectively postero-superior and postero-inferior. In the descending colon and
the sigmoid flexure, the muscular bands resume the relative position which they had in
the ascending colon. As these longitudinal fibres pass to the rectum, the anterior and
the external bands unite to pass down on the anterior surface of the canal, while the
posterior band passes down on its posterior uurface. Thus the three bands are here
formed into two. These two bands as they pass downward, though remaining distinct,
become much wider; and longitudinal muscular fibres commencing at the rectum are
situated between them, so that this part of the canal, especially in its lower portion, is
covered with longitudinal fibres in a pretty uniform layer.

The arrangement of the muscular fibres of the rectum has been closely studied by Sap-
pey. He has found that, as far as their terminations are concerned, the fibres may be
divided into an external, a middle, and an internal layer. The posterior fibres of the ex-
ternal layer pass away from the lower portion of the rectum, are reflected backward
along the concavity of the sacrum, and are attached to the promontory. These fibres,
which are generally pale, Sappey proposes to designate as retractors of the anus. A few
of the posterior fibres are attached to the aponeurosis and the parts between the coccyx
and the promontory. In front, the external fibres are attached to the aponeurosis which
covers the vesiculaa seminales, and laterally they are inserted into the deep pelvic fascia.
The termination of the middle layer of the fibres is less clearly made out. Those situated at
the sides of the rectum are inserted into "a very dense cellulo-fibrous band, which, by its
opposite surface, gives insertion to a great number of fibres of the levator ani." The
others are many of them continuous with the fibres of the levator ani as they pass along
the floor of the pelvis. Some of the fibres of the deep layer are attached by little tendons,
which pass between the external and the internal sphincter, to the deep portions of the
skin encircling the anus. The importance of closely studying the attachments of these
fibres will be appreciated when we come to treat of defalcation.

Over the ca3cum and the colon, the anterior band of muscular fibres is from one-third
to one-half an inch in width. The postero-external band is not more than half so wide,
and the postero-internal band is even narrower. The muscular bands are much shorter
than the canal itself, and their attachment to the walls gives the intestine a peculiar sac-
culated appearance. That this is produced by the arrangement of the muscular fibres,
may be demonstrated by dividing them in various places or by removing them entirely,
when the canal may be extended to double its original length. Between the bands there
are no longitudinal muscular fibres; but circular or transverse muscular fibres exist
throughout the whole length of the large intestine. In the caecum and the colon, the cir-
cular fibres are so pale and the layers are so thin that their presence is demonstrated with
great difficulty. In the rectum they are somewhat more numerous. About an inch
above the anus, the circular fibres are collected into a pretty well-marked muscular ring,
which has been called the internal sphincter.

Mucous Coat. — The mucous lining of the large intestine presents several important
points of difference from that which is found in the small intestine. It is paler, somewhat
thicker and firmer, and is more closely adherent to the subjacent parts. In no part of this
membrane are there any folds, like those which form the valvulae conniventes of the small
intestine ; and the surface is perfectly smooth and free from villosities.

Throughout the entire mucous membrane, from the ileo-caecal valve to the anus, are
innumerable orifices which lead to simple follicular glands. These structures resemble in
all respects the follicles of the small intestine, except that they are a little longer, owing
to the greater thickness of the membrane, are wider, and are rather more numerous.
Among these small follicular openings are found, scattered irregularly throughout the

PHYSIOLOGICAL ANATOMY OF THE LARGE INTESTINE. 291

membrane, larger openings which lead to utricular glands, resembling the closed follicles,
in general structure, except that they have an orifice opening into the cavity of the in-
testine, which is sometimes so large as to be visible to the naked eye. The number of
these glands is very variable, and they are irregularly disseminated throughout the intes-
tine, in company with the closed follicles, except in the rectum, where they are absent.
In the caecum and colon, numerous isolated, closed follicles are generally found, which
are identical in structure with the solitary glands of the small intestine. These are ex-
ceedingly variable, both in number and size.

The mucous membrane of the rectum, in the upper three-fourths of its extent, does
not differ materially from that of the colon. In the lower fourth, the fibrous tissue by
which the lining membrane is united to the subjacent muscular coat is loose, and the
membrane, when the canal is empty, is thrown into a great number of irregular folds.
At the site of the internal sphincter, five or six little semilunar valves have been observed,
with their concavities directed toward the colon. These form an irregular, festooned
line, which surrounds the canal ; their folds, however, are small and have no tendency
to obstruct the passage of faecal matters. The simple follicles are particularly abundant
in the rectum, and the membrane is constantly covered with a thin coating of mucus.
Another peculiarity to be noted in the mucous membrane of the lower portion of the
rectum, is its great vascularity, the veins, especially, being very numerous.

Finally, the rectum terminates in the anus, a button-hole orifice, situated a little in
front of the coccyx, which is kept closed and somewhat retracted, except during the pas-
sage of the faeces, by the powerful external sphincter. This muscle is composed entirely
of red, or striated fibres, which are arranged in the form of an ellipse, its long diameter
being antero-posterior.

It is now almost universally admitted that the digestion of all classes of alimentary sub-
stances is completed either in the stomach or in the small intestine, and that the mucous
membrane of the large intestine does not secrete a fluid endowed with any well-marked
digestive properties. The simple follicles, the closed follicles, and the utricular glands,
produce a glairy mucus, which, as far as we know, serves merely to lubricate the canal.
This has never been obtained in sufficient quantity to admit of any accurate investigation
into its properties.

In studying the changes which the alimentary mass undergoes in its passage through
the small intestine, we have seen that, in this portion of the canal, the greatest part of all
the nutritive material is not only liquefied but is absorbed. Sometimes fragments of mus-
cular fibre, oil-globules, and other matters in a state of partial disintegration, are to be
detected in the faeces by the microscope ; but generally this is either the result of taking
an excessive quantity of these substances or it depends upon some derangement of the
digestive apparatus. When intestinal digestion takes place with regularity, the trans-
formation of the alimentary mass into faecal matter is slow and gradual. As the con-
tents of the stomach are passed little by little into the duodenum, the chymous mass be-
comes of a bright-yellow color, and its fluidity is increased, from the admixture of bile
and pancreatic fluid. In passing along the canal, the consistence of the mass gradually
diminishes, from the absorption of its liquid portions, and the color becomes darker;
and, by the time that the contents of the ileum are ready to pass into the crccum, the
greatest part of those substances which we have recognized as alimentary principles
have become changed and absorbed. The various forms of starchy and saccharine prin-
ciples, unless they have been taken in excessive quantity, soon disappear from the in-
testine ; and the glucose, which is the result of their digestion, may be recognized in the
blood of the portal system. As a rule, fatty matters are not found in the lower part of
the ileum, having passed into the lacteals in the form of an emulsion. Neither fibrin,
albumen, nor caseine, can be detected in the ileum; and, as we have seen, the muscular
substance, as recognized by its microscopical characters, becomes gradually disintegrated

292 DIGESTION.

and is lost — except a few isolated fragments deeply colored with bile — some time before
the indigestible residue passes into the large intestine.

In the human subject, those portions of the food which resist the successive and com-
bined action of the different digestive secretions are derived chiefly from the vegetable
kingdom. Hard, vegetable seeds, the cortex of the cereals, spiral vessels, and, in fine,
all parts which are composed largely of cellulose, pass through the intestinal canal with-
out much change. These substances form, in the faeces, the greatest part of what can be
recognized as the residue of matters taken as food. It is well known that an exclusively
animal diet, particularly if the nutritious principles be taken in a concentrated and read-
ily-assimilable form, leaves very little undigested matter to pass into the large intestine,
and gives to the fseces a character quite different from that which is observed in herbiv-
orous animals or in man when subjected to an exclusively vegetable diet. The charac-
ters of the residue of the digestion of albuminoid substances are not very distinct. As a
rule, none of the albuminoids are to be recognized in the healthy faeces by the ordinary
tests.

Many insoluble inorganic substances are taken with the food and appear unchanged
in the fasces. The fseces of dogs fed exclusively on bones, which were formerly adminis-
tered internally as a remedy for epilepsy, under the name of album Grcecum, are composed
almost entirely of calcareous matter. "With regard to the ordinary inorganic constituents
of the faaces, however, it is difficult to say how much is derived from the ingesta and
how much from the different intestinal secretions.

Contents of the Large Intestine.

"When the contents of the small intestine have passed the ileo-caecal valve, they be-
come changed in their general character, partly from admixture with the secretions of
this portion of the canal, and are then known as the faeces. The most palpable of these
changes relate to consistence, color, and odor.

Faecal matter has a much firmer consistence than the contents of the ileum, which is
due to a constant absorption of the liquid portions. As a rule, the consistence is great in
proportion to the length of time that the fseces remain in the large intestine ; and this is
variable in different persons and in the same person, in health, depending somewhat upon
the character of the food. The color changes from the yellow, more or less bright,
which is observed in the ileum, to the dark yellowigh-brown, characteristic of the faeces.
Although the bile-pigment cannot usually be recognized by the ordinary tests, it is this
which gives to the contents of the large intestine their peculiar color, which is lost when
the bile is not discharged into the duodenum. In a specimen of healthy human fasces,
which had been dried, extracted with alcohol, the alcoholic solution precipitated with
ether, and the precipitate dissolved in distilled water, we failed to detect the slightest
trace of the biliary salts by Pettenkofer's test. In a watery extract of the same faeces,
the addition of nitric acid also failed to show the reaction of the coloring matter of the
bile. The color of the faeces, however, has been found to vary considerably with the diet.

The odor of the fseces, which is characteristic and quite different from that of the
contents of the ileum, is somewhat variable and is due in part to the peculiar decompo-
sition of the residue of the food, in part to the decomposition of the bile, and in part to
matters secreted by the mucous membrane of the colon and of the glands near the anus.

The entire quantity of fasces in the twenty-four hours was found by Wehsarg to be
about 4'6 ounces. This was the mean of seventeen observations ; the largest quantity
being 10'8 ounces, and the smallest, 2*4 ounces.

The reaction of the faeces is undoubtedly very variable, depending chiefly upon the
character of the food. Marcet found the human excrements always alkaline. "Wehsarg,
on the other hand, found the reaction generally acid, but very frequently, alkaline or
neutral.

CONTENTS OF THE LARGE INTESTINE. 293

The first accurate analyses of the faeces were made by Berzelius ; but the great ad-
vances which have been made in physiological chemistry since that time have enabled
later observers to arrive at results much more definite and satisfactory. Marcet has lately
discovered a crystallizable substance peculiar to the human fasces ; and we have recently
shown that probably the most important excrementitious principle discharged by the
rectum is derived from the bile and is a peculiar modification of cholesterine. Most of
our statements concerning the composition of the faeces in health will be derived from
the researches of Wehsarg and of Marcet and from our own observations.

The proportions of water and solid matter in the faeces is variable. Berzelius found,
in the healthy human fasces, 73'3 parts of water and 26*7 parts of solid residue. The
average of seventeen observations by Wehsarg was precisely the same. In the observa-
tions of Wehsarg, the mean quantity of solid matter discharged in the faaces in the twenty-
four hours was 463 grains, the extremes being 882*8 grains and 251'6 grains. The pro-
portion of undigested matters in the solid residue was very small, averaging but little
more than ten per cent., the mean quantity in the twenty-four hours in ten observations
being but 52'5 grains. This was found, however, to be exceedingly variable ; the largest
quantity being 126'5 grains, and the smallest, 12'5 grains.

Microscopical examination of the fasces reveals the various vegetable and animal struct-
ures which we have referred to as escaping the action of the digestive fluids. Wehsarg
also found a " finely divided faecal matter " of indefinite structure, but containing partly
disintegrated intestinal epithelium. Crystals of cholesterine were never observed. When-
ever the matter is neutral or alkaline, crystals of the ammonio-magnesian phosphate are
found. Mucus is also found in variable quantity in the faeces, with desquamated epithe-
lium, and a few leucocytes.

The quantity of inorganic salts in the faeces is not great. In addition to the ammonio-
magnesian phosphate, phosphate of magnesia, phosphate of lime, and a small quantity of
iron have been found. The chlorides are either absent or are present only in small
quantity.

Marcet has pretty generally found in the human faeces a substance possessing the
characters of margaric acid, and volatile fatty acids; the latter free, however, from
butyric acid. Cystine is mentioned as an occasional constituent of the fasces. He also
found a coloring matter, which is probably a modification of biliverdine.

In 1854, Marcet described a new substance in the human faeces, which he called excre-
tine, and an acid called excretoleic acid, which he supposed to be a compound of excre-
tine. These substances and the one which we described in 1862, under the name of ster-
corine, are, as far as we know, the only principles that have been recognized as charac-
teristic of the normal faeces ; and the stercorine we have found to be one of the most dis-
tinct and important of the excrementitious principles in the body. The relations of
excretine to the process of disassimilation of the tissues have not been so clearly indicated.

Excretine and Excretoleic Acid.— Excretine was obtained by Marcet from the healthy
human fa?ces in the following way : The faeces were first treated with boiling alcohol
until nothing more could be extracted. This alcoholic solution was acid and deposited
a sediment on cooling. Milk of lime was then added to the solution, producing a yel-
lowish-brown precipitate and leaving the fluid of a clear straw-color. The precipitate
was then collected on a filter, dried, afterward agitated with ether and filtered, forming
a clear, yellow solution. In from one to three days, beautiful, long, silky crystals of ex-
cretine were formed, generally collected into tufts adhering to the sides of the vessel.
Examined by the microscope, these were found to consist of acictilar, four-sided prisms
of variable size. This substance is insoluble in water, slightly soluble in cold alcohol, but
is very soluble in ether and in hot alcohol. Its alcoholic solutions are faintly though dis-
tinctly alkaline. Its fusing-point is from 203° to 205° Fahr. It may be boiled with
potash for hours without undergoing saponification. Apparently, the quantity of excre-

294 DIGESTION.

tine contained in the fasces is not very great, as only 12'6 grains were obtained by Marcet
from nine evacuations.

We have very little definite information concerning the production of excretine.
Marcet examined, on one occasion, the contents of the small intestine of a man that had
died of disease of the heart, without finding any excretine. It is probable that this
principle is formed in the large intestine, although farther observations are wanting on
this point.

The substance called excretoleic acid is very indefinite in its composition and proper-
ties. It is described as an olive-colored fatty acid, insoluble in water, non-saponifiable,
and very soluble in ether and in hot alcohol. It fuses at from 77° to 79° Fahr.

Stercorine. — This principle, which we discovered in the fasces in 1862, was described
by Boudet in 1833, as existing in excessively minute quantity in the serum of the blood,
and was called by him seroline. As we found it to be the most abundant and character-
istic constituent of the stercoraceous matter, we proposed to call it stercorine; particu-
larly as our researches led us to the opinion that it really does not exist in the serum, but
is formed from cholesterine by the processes employed for its extraction.

Stercorine may be extracted in the following way : The faeces are first evaporated to
dryness, pulverized, and treated with ether. The ether-extract is then passed through
animal charcoal, fresh ether being added until the original quantity of the ether-extract
has passed through. It is impossible to decolorize entirely the solution by this process ;
but it should pass through perfectly clear and of a pale-amber color. The ether is then
evaporated, and the residue is extracted with boiling alcohol. This alcoholic solution is
evaporated, and the residue is treated with a solution of caustic potash for one or two
hours at a temperature a little below the boiling-point, by which all the saponifiable fats
are dissolved. The mixture is then largely diluted with water, thrown upon a filter, and
is washed until the fluid which passes through is neutral and perfectly clear. The filter is
then carefully dried, and the residue is washed out with ether. The ether solution is then
evaporated, extracted with boiling alcohol, and the alcoholic solution is evaporated. The
residue of this last evaporation is composed of pure stercorine.

When first obtained, stercorine is a clear, slightly amber, oily substance, about the
consistence of Canada balsam used in microscopical preparations. In four or five days
it begins to show the characteristic crystals. These are few in number at first, but soon
the entire mass assumes a crystalline form. In one analysis, we obtained, from seven
and a half ounces of normal human faeces (the entire quantity for the twenty -four hours),
10-417 grains of stercorine, the extract consisting of nothing but crystals. This was all
the stercorine to be extracted from the regular, daily evacuation of a healthy male
twenty-six years of age and weighing about one hundred and sixty pounds. In the ab-
sence of other investigations, the daily quantity of this substance excreted may be as-
sumed to be not far from ten grains.

In many regards, stercorine bears a close resemblance to cholesterine. It is neutral,
inodorous, and insoluble in water and in a solution of potash. It is soluble in ether and in
hot alcohol, but is almost insoluble in cold alcohol. A red color is produced when it is
treated with strong sulphuric acid. It may be easily distinguished from cholesterine,
however, by the form of its crystals. It fuses at a low temperature, 96'8° Fahr., while
cholesterine fuses at 293° Fahr.

Stercorine crystallizes in the form of thin, delicate needles, frequently mixed with
clear, rounded globules, which are probably composed of the same substance in a non-
crystalline form. When the crystals are of considerable size, the borders near their ex-
tremities are split longitudinally for a short distance. The crystals are frequently ar-
ranged in bundles, as in Fig. 81, in which they are represented as seen under a -^-inch
objective. In Fig. 82, the crystals are represented as seen under a |-inch objective.
These crystals cannot be confounded with excretine, which crystallizes in the form of

CONTENTS OF THE LARGE INTESTINE.

295

regular, four-sided prisms, or with the thin rhomboidal or rectangular tablets of
cholesterine. They are identical with the crystals of seroline figured by Robin and
Vendiel.

There can be no doubt with regard to the origin of the stercorine which exists in the
fasces. We have found that, whenever the bile is not discharged into the duodenum, as
is probably the case, for a time, in icterus accompanied with clay-colored evacuations,
stercorine is not to be discovered in the dejections. In one case of this kind, in which
the faeces were subjected to examination, the matters extracted with hot alcohol were
entirely dissolved by boiling for fifteen minutes with a solution of potash, showing the

FIG. 81.— Stercorine from the human faces.

FIG. 82. — Stercorine from the same specimen after it had
been melted, placed upon a glasx slide, covered with
thin glass, and allowed to crystallize.

The crystallization was very slow, occupying several weeks.

absence of cholesterine and stercorine. In another examination of the faeces from this
patient, made nineteen days after, when the icterus had almost entirely disappeared and
the evacuations had become normal, stercorine was discovered. These facts show that
the cholesterine of the bile, in its passage through the intestine, is changed into ster-
corine. Both of these principles are crystalline, hon-saponifiable, are extracted by the
same chemical manipulations, and behave in the same way when treated with sulphuric
acid. The stercorine must be regarded as a slight modification of cholesterine, which
is the excrementitious principle of the bile.1

We have found that the change of cholesterine into stercorine is directly connected
with the process of intestinal digestion. If an animal be kept for some days without
food, cholesterine will be found in the faeces, although, for a few days, stercorine is also
present. It is a fact generally recognized by those who have analyzed the faeces, that
cholesterine does not exist in the normal evacuations ; but, whenever digestion is arrested,
the bile being constantly discharged into the duodenum, cholesterine is found in large quan-
tity. For example, in hibernating animals, cholesterine is always present in the faeces.
The same is true of the contents of the intestines during foetal life ; the meconium always

* Our researches into the functions of cholesterine have left no doubt that this is an excrementitious principle
hardly second in importance to urea. We have found that cholesterine is always more abundant in the blood com-
ing from the brain than in the blood of the general arterial system or in the venous blood from other parts ;
that its quantity is hardly appreciable in venous blood from the paralyzed side in hemiplegia; and that it is sep-
arated from the blood bv the liver. We have also shown that, in cases of serious structural disease of the liver
accompanied by symptoms pointing to blood-poisoning, cholesterine accumulates in the blood, constituting a con-
dition which we have called cholesteramia. This subject will be fully discussed under the head of excretion.
a full account of our observations upon the functions of cholcsterine, see The American Journal of the Medical
Sciences, October, 1862.

296 DIGESTION".

containing a large quantity of cholesterine, which disappears from the evacuations when
the digestive function becomes established.

Movements of the Large Intestine.

Movements of the general character which we have noted in the small intestine occur
in the large intestine, although the peculiarities in the arrangement of the muscular fibres
and the more solid consistence of the contents render these movements in the large in-
testine somewhat distinctive. In all instances where the movements have been observed
in the human subject or in the lower animals, they have been found to be less vigorous and
rapid than the contractions of the small intestine. Indeed, when the abdominal organs
are exposed, either in a living animal or immediately after death, movements of the large
intestine are generally not observed, except on the application of mechanical or galvanic
irritation ; and they are then more circumscribed and are much less marked than in any
other part of the alimentary canal. In the rabbit, in which the colon is very large, the
few spontaneous movements which are sometimes seen on opening the abdomen immedi-
ately after death are feeble and irregular, particularly in the cascum. That the fasces re-
main for a considerable time in some of the sacculated pouches of the colon, is evident
from the appearance which they sometimes present of having been moulded to the shape
of the canal. This appearance is frequently observed in the dejections, which are then
said to be " figured."

In the ca3cum, the pressure of matters received from the ilemn forces the mass onward
into the ascending colon, and the contractions of its muscular fibres are undoubtedly
slight and inefficient. Once in the colon, it is easy to see how the contractions of the
muscular structure (the longitudinal bands shortening the canal, and the transverse fibres
contracting below and relaxing above) are capable of passing the faecal mass slowly
onward. Although the transverse fibres are thin and seemingly of little power, their con-
traction is undoubtedly sufficient to empty the sacculi, when assisted by the movements of
the longitudinal fibres, especially as the canal is never completely filled and the faeces are
frequently in the form of small, moulded lumps. By these slow and gradual movements,
the contents of the large intestine are passed toward the sigmoid flexure of the colon,
where they are arrested until the period arrives for their final discharge. The time
occupied in the passage of the faeces through the ascending, transverse, and descending
colon is undoubtedly variable in different persons, as we find great variations in the inter-
vals between the acts of defaecation. During their passage along the colon, the contents
of the canal assume more and more of the normal faecal consistence and odor and become
slightly coated with the mucous secretion of the parts.

It has been pretty conclusively shown that the accumulation of fseces generally takes
place in the sigmoid flexure of the colon ; for, under normal conditions, the rectum is found
empty and contracted. This part of the colon is much more movable than other por-
tions and is better calculated as a receptacle for fasces. At certain tolerably regular in-
tervals, the faecal matter is passed into the rectum and is then almost immediately dis-
charged from the body.

Defalcation.

In health, expulsion of faecal matters takes place with regularity generally once in
the twenty-four hours. This rule, however, is by no means invariable, and dejections
may habitually occur twice in the day or every second or third day, within the limits of
perfect health. It is well known that habit has a great influence upon the regularity of
defsecation ; and sometimes, in cases of irregularity, physicians have recommended pa-
tients to make an effort to void the faeces at a certain time every day, this practice being
frequently followed by the best results. At the time when defalcation ordinarily takes
place, a peculiar sensation is experienced calling for an evacuation of the bowels ; and,
if this be disregarded, the desire may pass away, after a little time, the act becoming

DEFECATION. 297

impossible. Under these circumstances, it is probable that the faeces are passed out of
the rectum by antiperistaltic action.

The condition which immediately precedes the desire for defecation is probably the
descent of the contents of the sigmoid flexure of the colon into the rectum. It was for-
merly thought that the faeces constantly accumulated in the dilated portion of the rec-
tum, where they remained until an evacuation took place ; but the arguments of O'Beirne
against such a view are conclusive. He has demonstrated, by numerous explorations in
the human subject, that, under ordinary conditions, the rectum is contracted and con-
tains neither faeces nor gas. It is, indeed, a fact familiar to every surgeon, that the rec-
tum usually contains nothing which can be reached by the finger in physical examina-
tions, and that paralysis or section of the muscles which close the anus by no means in-
volves, necessarily, a constant passage of faecal matter. O'Beirne not only found the rectum
empty and presenting a certain amount of resistance to the passage of injected fluids, but,
on passing a stomach-tube into the bowel, after penetrating from six to eight inches it
passed into a space in which its extremity could be moved with great freedom, and there
was instantly a rush of flatus, of fluid faeces, or of both, through the tube. In some in-
stances in which nothing escaped through the tube, the instrument conveyed to the hand
an impression of having entered a solid mass ; and on being withdrawn it contained solid
faeces in its upper portion. According to this observer, the sensation which leads to an
effort to discharge the faeces is due to the accumulation of matters in the sigmoid
flexure, which finally present at the contracted portion of the rectum just at its com-
mencement. This constriction, situated at the most superior portion of the rectum, is
sometimes spoken of as the sphincter of O'Beirne.

The above is undoubtedly the mechanism of the descent of faecal matter into the
rectum in defaecation, as the act is usually performed ; but, under certain circumstances,
faeces must accumulate in the dilated portion of the rectum. Ordinarily, the discharge
of faeces only takes place after the efforts have been continued for a certain time ; and
when the evacuation is " figured," the whole length discharged frequently exceeds so
much the length of the rectum, that it is evident that a portion of it must have come
from the colon. O'Beirne states, indeed, that he has frequently examined the rectum at
the moment when a moderate inclination to go to stool is felt, and found it empty and con-
tracted. But, in cases in which the faeces are very fluid, or when the call for an evacua-
tion has not been regarded and has become imperative, the immediate discharge of mat-
ters when the sphincter is relaxed shows that the rectum has been more or less distended.
In many persons of constipated habit, and particularly in old subjects, the rectum may
become the seat of large accumulations of hardened and impacted fa3ces ; but this is a
pathological condition.

The sensation which ordinarily precedes and gives rise to the evacuation of faecal mat-
ter is peculiar and very variable in intensity. When this sensation is well marked but not
excessive, it is probably due to the presence of faecal matter in the rectum, not in suffi-
cient quantity, however, to press forcibly upon the sphincter. Pressure upon the rectum
from any cause, or irritation of its mucous membrane, is apt to give rise to this peculiar
sensation to a very marked degree. In some diseases, the exaggeration of this sensation,
then called tenesmus, is very distressing.

In the process of defaecation, the first act is the passage, by peristaltic contractions,
of the contents of the sigmoid flexure of the colon through the slightly-constricted open-
ing of the rectum into its dilated portion below. The faecal matter, however, is not al-
lowed to remain in this situation, but it passes into the lower portion of the rectum, in
obedience to the contractions of its muscular coat, assisted by the action of the abdomi-
nal muscles and the diaphragm. The circular fibres of the rectum undergo the ordinary
peristaltic contraction ; and the action of the longitudinal fibres is to render the rectum
shorter and more nearly straight. The internal and the external sphincter present a cer-
tain amount of resistance to the discharge of the faeces, more particularly the external

298 DIGESTION.

sphincter, which is a striated muscle of considerable power. There is always, however,
a voluntary relaxation of this muscle, or rather a cessation of its semi-voluntary con-
traction, which immediately precedes the expulsive act. The dilatation of the anus is
also facilitated by the action of the levator ani, which arises from the posterior surface
of the body and rarnus of the pubis, the inner surface of the spine of the ischium, and a
line of fascia between these two points, passes downward, and is inserted into the me-
dian raphe of the perineum and the sides of the rectum, the fibres uniting with those of
the sphincter. While this muscle forms a support for the pelvic organs during the act
of straining, it steadies the end of the rectum, and, by its contractions, favors the relaxa-
tion of the sphincter and draws the anus forward.

The action of the diaphragm and the abdominal muscles is very simple. They merely
compress the abdominal organs, and consequently those contained in the pelvis, and as-
sist in the expulsion of the contents of the rectum. The diaphragm is the most impor-
tant of the voluntary muscles concerned in this process ; and, during the act of straining,
the lungs are moderately filled and respiration is interrupted. The vigor of these efforts
depends greatly upon the consistence of the faecal mass, very violent contractions being
frequently required for the expulsion of hardened faeces after long constipation. Al-
though more or less straining generally takes place, the contractions of the muscular
coats of the rectum are frequently competent of themselves to expel the faeces, espe-
cially when they are soft. This can be shown by arresting all voluntary muscular action
during an easy act of defsecation, when the faeces may be passed by contractions of the
rectum alone.

By a combination of the movements above described, the floor of the perineum is
pressed outward, the anus is dilated, the sharp bend in the lower part of the rectum is
brought more into line with the rest of the canal, and a portion of the contents of the
rectum is expelled. Very soon, however, the passage of faeces is interrupted by a con-
traction of the levator ani and the sphincter, "by which the anus is suddenly and rather
forcibly retracted. This muscular action may be effected voluntarily; but, after the
sphincter has been dilated for a time, the evacuation is interrupted in this way, notwith-
standing all efforts to oppose it. After a time, another portion of faeces is discharged,
until the matters have ceased to pass out of the sigmoid flexure and the rectum has
been emptied. The mucous membrane of the rectum, which is rather loosely held to
the subjacent tissue, is slightly prolapsed during an evacuation, but it returns shortly after
the act has been completed.

Very little need be said concerning the influence of the nervous system on the move-
ments concerned in defaecation. The non-striated muscular fibres which form the mus-
cular coat of the rectum are supplied with nerves from the sympathetic system ; and to
the external sphincter are distributed filaments from the last sacral pair of the spinal
nerves. These nerves bring the sphincter to a certain degree under the control of the
will and impart likewise the property of tonic contraction, by which the anus is kept
constantly closed.

Gases found in the Alimentary Canal.

In the human subject, a certain quantity of gas is generally found in the stomach and
in the small and large intestine. The most accurate analyses of these gases, as they may
be supposed to exist in the human subject in health, are those of Magendie and Chev-
reul, who had the opportunity of examining the bodies of several criminals immediately
after execution.

The gases in the stomach appear to have no definite function. They generally exist
in very small quantity, and they are sometimes absent. The oxygen and nitrogen are de-
rived from the little bubbles of air which are incorporated with the alimentary bolus dur-
ing mastication and insalivation. The other gases are probably evolved from the food
during digestion ; at least, there is no satisfactory evidence that they are produced in any

GASES CONTAINED IN THE STOMACH, SMALL INTESTINE, ETC. 299

other way. Magendie and Chevreul collected and analyzed a small quantity of gas from
the stomach of an executed criminal a short time after death and ascertained that it had
the following composition :

Gases contained in the Stomach.

Oxygen 11-00

Carbonic acid 14*00

Pure hydrogen 3'55

Nitrogen 7145

100-00

Magendie and Chevreul found three different gases in the small intestine. Their ex-
aminations were made upon three criminals soon after execution. The first was twenty-
four years of age, and, two hours before execution, had eaten bread and Gruyere cheese
and had drunk red wine and water. The second, who was executed at the same time, was
twenty-three years of age, and the conditions as regards digestion were the same. The
third was twenty-eight years of age, and, four hours before death, he ate bread, beef, and
lentils, and drank red wine and water. The following was the result of the analyses :

Gases contained in the Small Intestine.

First Criminal Second Criminal. Third Criminal.

Carbonic acid 24-39 40'00 25-00

Pure hydrogen 55'53 51-15 8'40

Nitrogen 20'08 8'85 66'60

100-00

100-00

100-00

No oxygen was found in either of the examinations, and the quantities of the other
gases were so variable as to lead to the supposition that their proportion is not at all defi-
nite. We have already alluded to the mechanical function of these gases in intestinal
digestion.

In the large intestine, the constitution of the gases presented the same variability as
in the small intestine. Carburetted hydrogen was found in all of the analyses. In the
large intestine of the first criminal and in the rectum of the third, were found traces of
sulphuretted hydrogen. The following is the result of the analyses in the cases just
cited. In the third, the gaseous contents of the caecum and the rectum were analyzed
separately :

Gases contained in the Large Intestine.

First Criminal.

Second Criminal.

Third Criminal.

Third Criminal.

Carbonic acid..

43-50

70'00

Caecum.

12-50

Rectum.
42-86

Carburetted hydrogen and traces of sul-
phuretted hydrogen

5-47

Pure hydrogen and Carburetted hydro-

11-60

11-18

Pure hydrogen.

7'50

Carburetted hydrogen

12-50

Nitrogen. . .

51*03

18-40

67-50

45-96

100-00

100-00

100-00

100-00

Origin of the Intestinal Gases. — With our present information on this subject, the
most reasonable view to take of the origin of the gases normally found in the intestines
is that they are given off from the articles of food in their various stages of digestion and

300 ABSORPTION.

decomposition. That this is the principal source of the intestinal gases, there can be no
doubt; and it is well known that certain articles of food, particularly vegetables, gen-
erate much more gas than others. The principal gases found in the intestinal canal may
all be obtained from the food. Some of them, as hydrogen and carburetted hydrogen,
do not exist in the blood ; and it is difficult to conceive how they can be generated in the
intestine except by decomposition of some of the articles of food. Hydrogen and its
compounds are always found in quantity in the small and the large intestine.

It is said that gas is sometimes found in the intestines of the foetus, and that it may
be generated in a loop of intestine in a living animal, after a portion of the canal has been
drawn out, isolated by ligatures, freed from its liquid and gaseous contents, and returned
to the abdomen. In some diseased conditions, also, it is very common for the abdomen
to become rapidly tympanitic, the gas being generated so quickly that its presence is not
easily explained by supposing it to be evolved by decomposition of the ingesta. It has,
indeed, been supposed that the intestinal mucous membrane is capable of secreting gases
as well as liquids ; but there do not appear to be any positive facts in support of this
view. No doubt some of the gases which may be formed in the intestine are capable
of absorption. It is impossible to say, however, that even the gases normally held in
solution in the blood, namely, oxygen, nitrogen, and carbonic acid, are exhaled from the
blood into the intestinal cavity. Oxygen is never given off in this way. for this gas has
been found only in the stomach and is there derived from air which has been swallowed.
With regard to the origin of the other gases found in the intestine under the peculiar
circumstances just mentioned, in which they are apparently generated with much rapidity,
there are not sufficient data to enable us to form an intelligent opinion.

CHAPTER X.

ABSORPTION-LYMPH AND CHYLE.

General considerations of absorption — Absorption by blood-vessels — Absorption by lacteal and lymphatic vessels —
Physiological anatomy of the lacteal and lymphatic system— Absorption by the lacteals— Absorption from parts
not connected with the digestive system— Absorption of fats and insoluble substances— Variations and modifica-
tions of absorption— Imbibition and endosmosis — Imbibition by animal tissues — Mechanism of the passage of
liquids through membranes— Capillary attraction — Endosmosis through porous septa — Endosmosis through ani-
mal membranes— Endosmosis through liquid septa — Diffusion of liquids — Endosmotic equivalents— Modifications
of endosmosis— Application of physical laws to the function of absorption— Transudation— Lymph and chyle-
Mode of obtaining lymph -Quantity of lymph— Properties and composition of lymph— Alterations of the lymph
— Corpuscular elements of the lymph — Leucocytes — Development of leucocytes in the lymph and chyle — Glob-
ulins— Origin and function of the lymph — General properties of the chyle — Composition of the chyle— Compara-
tive analyses of the lymph and the chyle— Microscopical characters of the chyle — Movement of the lymph and
chyle.

DIGESTION has two great objects : one is to liquefy the different alimentary princi-
ples ; and the other, to commence the series of transformations by which these principles
are rendered capable of nourishing the organism. The principles thus acted upon are
taken into the blood as fast as the requisite changes in their constitution are effected ;
and, once received into the circulation, they become part of the great nutritive fluid, sup-
plying the waste which the constant regeneration of the tissues from materials furnished
by the blood necessarily involves. The only group of principles which possibly does not
obey this general law is the fats. Although a small portion of the fat taken as food
passes directly into the blood-vessels of the intestinal canal, by far the greatest part finds
its way into the circulation by means of special absorbent vessels which empty into large
veins. In whatever way fat enters the blood, it is never dissolved, but is reduced to the
condition of a fine emulsion.

ABSORPTION" BY BLOOD-VESSELS. 301

The process by which digested materials are taken into the blood is called absorption.
It is now recognized that two sets of vessels are concerned in the performance of this
function; namely, the blood-vessels and the lacteals. Those parts of the food which
have been rendered fluid and are capable of forming a homogeneous mixture with the
blood-plasma are absorbed chiefly by the blood-vessels, although a small portion finds its
way into the lacteals. The emulsified fats are taken up in greatest part by the lacteals,
although a small quantity is taken directly into the blood. In treating of this subject, it
will be convenient to consider separately the action of these two kinds of vessels.

Absorption by JBlood- Vessels.

That soluble substances can pass through the delicate walls of the capillaries and
small veins and that absorption actually takes place in great part by blood-vessels, are
facts which hardly demand discussion at the present day. Soluble principles which
have disappeared from the alimentary canal have been repeatedly found in the blood
coming from this part, even when the lymphatics have been divided and communication
existed only through the blood-vessels. The old theoretical view which was entertained
before the lymphatics and lacteals were discovered was that absorption took place by
blood-vessels ; but, after special absorbent vessels had been described, it was generally
supposed that they furnished the only avenue for the entrance of new matters into the
economy, although the doctrine of vascular absorption was retained by a few. It was
only after the conclusive experiments of Magendie, in 1809, that positive proof was given
of the absorbing power of the blood-vessels. These experiments settled the question of
vascular absorption, although they led some to take too exclusive a view of the impor-
tance of the venous radicles in this function and to deny that absorption took place to any
considerable extent through the lymphatic and the lacteal system. At the present day,
there is no difference of opinion among physiologists concerning the direct absorption of
nutritive matters by the blood-vessels of the alimentary canal. It has been repeatedly
shown, indeed, that, during absorption, the blood of the portal vein is rich in albumi-
noids, sugar, and in other principles resulting from digestion.

In the mouth and oesophagus, the sojourn of alimentary principles is so brief and
the changes which they undergo so slight, that no absorption of any moment can take
place. It is evident, however, that the mucous membrane of the mouth is capable of
absorbing certain soluble matters, from the effects which are constantly observed when
the smoke or the juice of tobacco is retained in the mouth, even for a short time. In
the stomach, however, the absorption of certain materials takes place with great activity.
A large proportion of the ingested liquids and of those principles of food which are dis-
solved by the gastric juice and converted into albuminose is taken up directly by the
blood-vessels of the stomach. It may, indeed, be assumed, as a general law, that di-
gested matters are in great part absorbed as soon as their transformations in the alimen-
tary canal have been completed.

In the passage of the food down the intestinal canal, as we have already seen, there
is a constant loss of material. As the digestion of the albuminoids is completed, these
principles are absorbed, and their passage into the mass of blood is indicated chiefly by
an increase in its proportion of albuminoid constituents. Many of the other products of
digestion, such as glucose and fatty emulsion, have also been demonstrated in quantity
in the blood of the portal vein during absorption. The fats, though taken up in greatest
part by the lacteals, are always found in greater or less quantity in the portal blood. It
has frequently been observed that, after a full meal consisting largely of fat, the blood
from the portal vein, as it cools and coagulates, leaves a white scum of fat upon the sur-
face. On one occasion, we observed, in the portal blood of an animal killed in full diges-
tion, a layer of fat on cooling so thick that a quantity of blood, which was spilled upon
a table and the floor, was white, like milk. We have since frequently attempted to

302 ABSORPTION.

demonstrate this excessively chylous condition of the blood during the absorption of fats,
but have found that it is not generally so well marked.

The greatest part of the food is absorbed by the intestinal mucous membrane, and,
with the alimentary substances proper, a large quantity of secreted fluid is reabsorbed.
This fact is particularly striking as regards the bile. The biliary salts disappear as the
alimentary mass passes down the intestine and are undoubtedly absorbed, although they
are so changed that they cannot be detected in the blood by the ordinary tests. In this
portion of the alimentary canal, it will be remembered that an immense absorbing sur-
face is provided, by the arrangement of the mucous membrane in folds, forming the val-
vulae conniventes, and by the presence of the innumerable villi which are found through-
out the small intestine. A certain portion of the gaseous contents of the intestines is also
absorbed, although it is not easily ascertained what particular gases are thus taken up.

Absorption by Lacteal and Lymphatic Vessels.

The history of the discovery of what is ordinarily termed the absorbent system of
vessels, from the vague allusions of Hippocrates, Galen, Aristotle, and others, to the de-
scription of the thoracic duct in the middle of the sixteenth century, by Eustachius, and
finally to the discovery of the lacteals by Asellius, in 1622, is more interesting in an ana-
tomical than in a physiological point of view. Our knowledge of the anatomy of the
absorbent system dates from the discovery of the thoracic duct ; but, from the discovery
of the lacteals by Asellius, dates the history of these vessels as the carriers of nutritive
matters from the intestinal canal to the general system.

In 1649, Pecquet discovered the receptaculum chyli and demonstrated that the lacteals
did not pass to the liver, but emptied the chyle into the commencement of the thoracic
duct, by which it was finally conveyed into the venous system. In 1650-'51, the ana-
tomical history of the absorbect vessels was completed by the discovery, by Rudbeck,
of vessels carrying a colorless fluid, in the liver and finally in almost all parts of the
body. Eudbeck demonstrated the anatomical identity of these vessels with the lacteals.
They were afterward carefully studied by Bartholinus, who gave them the name of lym-
phatics. It is unnecessary to follow out the various researches made into the structure
of the lymphatics in man and the inferior animals by the Hunters, Hewson, Monro,
Cruikshank, and other of the older anatomists and physiologists.

The old idea, which dates from the discoveries of Asellius and Pecquet, that the lac-
teals absorb all the products of digestion, was overthrown by the experiments of Magen-
die and of those who experimented after him upon vascular absorption. It is now known
that the fatty portions of the food, reduced to a very fine emulsion by the pancreatio
juice, are absorbed by this system of vessels, and that these are the only principles which
are taken up in great quantity. The arguments which we have already mentioned are
sufficient to establish this fact. If the abdomen of a living animal be opened during full
digestion, then, and then only, will the lacteals and the thoracic duct be found dis-
tended with fatty emulsion. If the organ which digests fat be rendered incapable of
performing its function, the lacteals cease to carry chyle. These vessels do not appear
in the mesentery until the food has passed the orifice of the pancreatic duct. Finally,
the observations of Bouchardat and Sandras remove all doubt as to the absorption of the
products of the digestion of fatty matters by the lacteals ; for these observers found not
only that in dogs the proportion of fat in the chyle was increased pari passu with an in-
crease in the quantity of fat taken as food, but that the particular kinds of fat adminis-
tered to the animals could be recognized in the chyle. We have seen that a certain quan-
tity of fat escapes the lacteals and is absorbed directly by the blood-vessels ; and it be-
comes an important question to determine whether the lacteals, in addition to their more
prominent function, be not concerned in the absorption of drinks, the albuminoids, saline
and saccharine matters, etc. This question will be taken up after a consideration of
certain points in the anatomy of the lymphatic system.

ABSORPTION BY LACTEAL AND LYMPHATIC VESSELS. 303

Physiological Anatomy of the Lacteal and Lymphatic System. — One of the most diffi-
cult problems in anatomy is to determine the situation and mode of origin of the lym-
phatics in different parts of the body. The tenuity of the walls of these vessels, even in
their course, and the presence of innumerable valves, render it impossible to study them
by the ordinary methods of injection. Since it has been ascertained, however, that they
originate in many parts by a rich, anastomosing plexus, their anatomy has been well
made out in certain situations by simply puncturing with a fine-pointed canula the parts
in which the plexus is supposed to exist, and allowing a fluid, generally mercury, to
gently diffuse itself in the vessels of origin. Following the course of the vessels, the
fluid passes into the larger trunks and thence to the lymphatic glands. The regularity
of the plexus through which the fluid is first diffused and the passage of the injection
through the larger vessels to the glands are positive proof that the lymphatics have been
penetrated and that the appearances observed are not the result of mere infiltration.

By the method of investigation above indicated, we may recognize the superficial
vessels of the skin, deeper vessels situated just beneath the skin, and vessels in the serous
membranes, glandular organs, lungs, tendons, etc., in addition to the larger trunks, such
as the thoracic duct. The lacteal system presents essentially the same characters as the
general lymphatics, and the vessels are filled with colorless lymph during the intervals
of digestion. In many situations, the lymphatics present in their course little, solid
structures called lymphatic glands.

The mode of origin of the finest vessels, in the lymphatic radicles, is exceedingly ob-
scure, notwithstanding the numerous investigations which have been made within the
last few years, particularly by German anatomists. We shall first describe, however,
the mode of origin of what may be called the true vessels, in those parts in which
the results of anatomical study seem positive and definite, before we discuss the va-
rious theories which have been proposed to account for certain of the phenomena of
absorption.

Lymphatics have not been actually injected and demonstrated in all the tissues of the
body ; but, in some parts in which it has been thus far impossible to inject them, we are
not justified in assuming positively that they do not exist. For example, in the intestinal
villi, according to Sappey, these vessels have never been seen, although their existence is
almost certain. The most generally received view with regard to the ordinary mode of
origin of the lymphatic vessels is that they commence by a capillary plexus, which does
not communicate with either the small arteries, veins, or the capillary blood-vessels, and
is generally situated external to the blood-vessels. It does not appear that the vessels
composing this plexus vary much in size. They are very elastic, and, after distention
by injection, they return to a very small diameter when the fluid is allowed to escape.
It is probable, therefore, that the capacity of the vessels is much exaggerated by the
means which are taken to render them apparent. In the elaborate observations by Dr.
Belaieff, of St. Petersburg, into the origin of the lymphatics of the penis, the walls of the
vessels were rendered apparent by the action of nitrate of silver in solution in pure water,
and it is probable that they were very little distended. The smallest of these vessels had
a diameter of about ^$ of an inch. This may be taken as their average diameter in the
primitive plexus. This plexus, when the vessels are abundant, as they are in certain
parts of the cutaneous surface, resembles an ordinary plexus of capillary blood-vessels,
except that the walls of the vessels are thinner and their diameter is greater.

The smallest lymphatic vessels are by far the most numerous. They are arranged in
the form of a fine plexus, very superficially situated in the skin. A second plexus exists
just beneath the skin, composed of vessels of much greater diameter. The skin is thus
enclosed, as it were, between two plexuses of capillary lymphatics. A plexus analogous
to the most superficial plexus of the skin is found just beneath the surface of the mucous
membranes. These may, indeed, be classed with the superficial lymphatics. The deep
lymphatics are much larger and less numerous, and their origin is less easily made out.

304

ABSORPTION.

These accompany the deeper veins in their course. They receive the lymph from the
superficial vessels.

No valvular arrangement is found in the smallest lymphatics ; but the vessels coming
from the primitive plexuses, as well as the large vessels, contain valves in immense num-
bers. These valves, being so closely set in the vessels, give to them, when filled with
injection, a peculiar and characteristic beaded appearance.

FIG. 83. — Superficial lym-
phatics of the skin of the
palmar surface of the
finger. (Sappey.)

FIG. 84.— Deep lymphatics of the skin
of the finger. (Sappey.)

1, 1, deep net- work of cutaneous lymphat-
ics; 2, 2, 2, 2, lymphatic trunks con-
nected with this net-work.

FIG. 85 — Same finger, lat-
eral view, si i owing lym-
phatic trunks connected
with the superficial net-
work. (Sappey.)

The course of the lymphatics is generally tolerably direct. As they pass toward the
great trunks by which they communicate with the venous system, they present a peculiar
anastomosis with the adjacent vessels, called anastomosis by bifurcation ; that is, as a
vessel passes along with other vessels nearly parallel with it, it bifurcates, and the two
branches pass into the nearest vessels on either side. These anastomoses are quite fre-
quent, and they generally occur between vessels of equal size. In their course, the ves-
sels pass through the lymphatic glands, which will be described farther on.

A notable peculiarity in the lymphatic vessels is that they vary very little in size,
being nearly as large at the extremities as they are near the trunk. In their course, they
are always much smaller than the veins and do not progressively enlarge as they pass on
to the great lymphatic trunks. The largest-sized vessels as they pass from the skin are
from -fa to T^ of an inch in diameter, and the larger vessels, in their course, have a diameter
of from T^ to -|- of an inch. As in the case of the smallest lymphatics in the primitive plexus,
the elasticity of the walls of the vessels renders their caliber greatly dependent upon the
pressure of fluid in their interior. Many anatomists have noticed that vessels, which are

ABSORPTION BY LACTEAL AND LYMPHATIC VESSELS.

305

hardly perceptible while empty, are capable of being dilated to the diameter of half a line
or more, returning to their original size as soon as the distending fluid is removed.

The peculiarities which the lymphatics present in the different tissues and organs do
not possess much physiological interest, except the arrangement of the vessels of origin
in the substance of the brain and spinal cord. In the skin, the only interesting peculiarity
which we have not already noticed is that the vessels appear to be very unequally dis-
tributed in different parts of the surface. According to Sappey, they are particularly

FIG. 86.— Superficial lympJiatics of the arm.
(Sappey.)

FIG. 87. — Superficial lymphatics of the leg.
(Sappey.)

abundant in the scalp over the biparietal suture, the soles of the feet and the palms of the
hand, the fingers at the lateral portion of the last phalanges, and the scrotum. In the
median portion of the scrotum, they attain their highest degree of development. They
are also found, though in less number, originating from around the median line on the
anterior and posterior surface of the trunk, the posterior median portion of the extremi-
ties, the skin over the mammaa, and around the orifices of the mucous passages. Sappey
has injected lymphatic vessels in the anterior portion of the forearm, the thigh, and the
leg, and the middle portion of the face, although they are demonstrated with difficulty in
these situations. If they exist at all in other portions of the cutaneous surface, they are
not numerous and are rudimentary
20

306 ABSORPTION.

In the mucous system the lymphatics are very abundant. Here are found, as in the
skin, two distinct layers which enclose between them the whole thickness of the mucous
membrane. The more superficial of these layers is composed of a rich plexus of small
vessels, and, beneath the mucous membrane, is a plexus consisting of vessels of larger size
and less numerous. The superficial plexus is exceedingly rich in the mixed structure
which forms the lips and the glans penis, and around the orifices of the mouth, the nares,
the vagina, and the anus. There are certain mucous membranes in which the lymphatics
have never been injected. In the serous membranes, the lymphatics have been demon-
strated in great abundance. Lymphatics have been demonstrated taking their origin in
the voluntary muscles, the diaphragm, the heart, and the non-striated muscular coats of
the hollow viscera, although their investigation in these situations is exceedingly difficult.

Lymphatics are found coming from the lungs in immense numbers. These arise in
the walls of the air-cells and surround each pulmonary lobule with a close plexus. The
deep vessels follow the course of the bronchial tubes, passing through the bronchial glands
and the glands of the bifurcation of the trachea, to empty into the thoracic duct and the
great lymphatic duct of the right side.

In the glandular system, including the ductless glands, and in the ovaries, the lym-
phatic vessels are, as a rule, more abundant than in any other parts of the body. They
are especially numerous in the testicle, the ovary, the liver, and the kidney.

In the substance of the brain and spinal cord, Robin and His have demonstrated a
curious system of vessels which entirely surround the capillary blood-vessels and are
connected with the lymphatic trunks or reservoirs described by Fohmann under the pia
mater. The capillary blood-vessels thus float in a fluid contained in these cylindrical
sheaths, which exceed them in diameter by from YIHTO ^° TTJF °f an incn- These investing
vessels follow the blood-vessels in their ramifications, and contain a clear fluid, with bodies
resembling the lymph-corpuscles. When Robin first described these vessels minutely, he
did not state definitely their physiological relations ; but he has since published a memoir
in which he describes them as true lymphatic vessels, analogous to the lymphatics which
partly surround the small blood-vessels in fishes, reptiles, and batrachians. In these ani-
mals, the lymphatics in many parts nearly surround the blood-vessels, to the walls of
which the edges of their proper coat are adherent ; and that portion of the wall of the
blood-vessel which is thus enclosed forms at the same time the wall of the lymphatic.
This disposition of the lymphatics in the brain and spinal cord would allow of free inter-
change, by endosmosis and exosmosis, of the liquid portions of the blood and the lymph.

The lymphatic vessels from the superficial and deep portions of the head and face on
the right side, and those from the superficial and deep portions of the right arm, the right
half of the chest, and the mammary gland, with a few vessels from the lungs, pass into
the great lymphatic duct (ductus lymphaticus dexter), which empties into the venous
system at the junction of the right subclavian with the internal jugular. This vessel is
about an inch in length and from one-twelfth to one-eighth of an inch in diameter. It is
provided with a pair of semilunar valves at its opening into the veins, which effectually
prevent the ingress of blood.

The vessels from the inferior extremities, and those from the lower portions of the
trunk, the pelvic viscera, and the abdominal organs, generally pass into the thoracic duct.
In their course, all of the lymphatics pass through the small, flattened, oval bodies, called
the lymphatic glands, which are so abundant in the groin, the axilla, the pelvis, and in some
other parts. From two to six vessels, called the vasa afferentia, enter these bodies, having
first broken up into a number of smaller vessels just before they pass in. They pass out
by a number of small vessels which- unite to form one, two, or three trunks, generally of
larger size than the vasa afferent] a. The vessels which thus emerge from the glands are
called vasa efferentia.

The lymphatics of the small intestine, called lacteals, pass from the intestine between
the folds of the mesentery to empty, sometimes by one, and sometimes by four or five

ABSORPTION BY LACTEAL AND LYMPHATIC VESSELS.

307

trunks, into the receptaculum chyli. In their course, the lacteals pass through several
sets of lymphatic glands, which are here called mesenteric glands.

The thoracic duct, into which the great majority of the lymphatic vessels empty, is

FIG. 88. — Stomach, intestine, and mesentery, with the mesenteric bloorf -vessel* and lacteal!}. (Copied and slightly

reduced from a figure in the original work of Asellius. published in 1 (>•_'•>.)
A, A. A. A. A, mesenteric arteries and veins; B. B, B, B. B, B. B. B, B. B, lacteals; C. 0. C, C, mesentery; T), 1),

stomach; K, pyloric portion of the stomach; F, duodenum; G. G, G, jejunum; H, H, H, H, H, ileiiui ; I, artery

and vein on the fundus of the stomach ; K, portion of the omentuin.

a vessel with exceedingly delicate walls and about the size of a goose-quill. It com-
mences by a dilatation, more or less marked, called the receptaculum chyli. This is
situated upon the second lumbar vertebra. The canal passes upward in the median

308

ABSORPTION.

line for the inferior half of its length. It then inclines to the left side, forms a
semicircular curve something like the arch of the aorta, and empties at the junction of

the left subclavian with the internal
jugular vein. It diminishes in size
from the receptaculum to its middle
portion and becomes larger again
near its termination. It occasionally
bifurcates near the middle of the
thorax, but the branches become re-
united a short distance above. At
its opening into the venous system,
there is generally a valvular fold,
but, according to Sappey, this is not
constant. There is always, however,
a pair of semilunar valves in the
duct, from three-quarters of an inch
to an inch from its termination, which
effectually prevent the entrance of
blood from the venous system.

It is probable that the lymphatic
and lacteal vessels have no direct con-
nection with the blood-vessels, except
by the two openings by which they
discharge their contents into the ven-
ous system. The foregoing sketch of
the descriptive anatomy of what has
been called the absorbent system of
vessels shows that they may collect
fluids, not only from the intestinal ca-
nal during digestion, but from nearly

FIG. 89.— Thoracic duct. (Mascagni.)

1, thoracic duct; 2, great lymphatic duct; 3, receptaculum chyli;
4, curve of the thoracic duct just before it empties into the
venous system.

every tissue and organ in the body,
and that these fluids are received into
the venous circulation.
Structure of the Lacteal and Lymphatic Vessels. — The lymphatic vessels, even those
of largest size, are remarkable for the delicacy and transparency of their walls. This is
well illustrated in the case of the lacteals, which are hardly visible in the transparent
mesentery, unless they be filled with opaque chyle.

From the difficulty in studying the lymphatics at their origin, except by means of
injections or by reagents which stain the vessels, investigations into the structure of the
smallest vessels have been very few and are not very satisfactory. It is supposed, how-
ever, that the vessels here consist of a single amorphous coat, resembling, in this regard,
the capillary blood-vessels. Dr. Belaieff describes, in the capillary lymphatics of the
penis, a lining of epithelial cells arranged in a single layer. These cells are oval, polygo-
nal, fusiform or dentated, with their long diameter in the direction of the axis of the
vessels.

In all but the capillary lymphatics, although the walls are excessively thin, three dis-
tinct coats can be distinguished. The internal coat consists of an elastic membrane lined
with oblong epithelial cells. This coat readily gives way when the vessels are forcibly
distended. The middle coat is composed of longitudinal fibres of the white fibrous tissue,
with delicate elastic fibres and unstriped muscular fibres arranged transversely. The
external coat is composed of the same structures as the middle coat ; but the fibres are
arranged, for the most part, longitudinally. In this coat, the muscular fibres do not form
a continuous sheet, but are collected into separate fasciculi, which have a direction either

ABSORPTION BY LACTEAL AND LYMPHATIC VESSELS. 309

longitudinal or oblique. The fibres of connective tissue are very abundant and loosely
unite the vessels to the surrounding parts. The internal and the middle coat are closely
adherent to each other; but the external coat may readily be separated from the others.
Blood-vessels have been found in the walls of the lymphatics, but, as yet, the presence
of nerves has not been demonstrated.

The walls of the lymphatic vessels are very closely adherent to the surrounding tis-
sues ; so closely, indeed, that even a small portion of a vessel is detached with great dif-
ficulty, and the vessels, even those of large size, cannot be followed out and isolated for
any considerable distance.

In all the lymphatic vessels, beginning a short distance from their
plexu.s of origin, are found numerous semilunar valves, generally ar-
ranged in pairs, with their concavities looking toward the larger trunks.
These folds are formed of the inner two coats ; but the fold formed of
the lining membrane is by far the wider, so that the free edges of the
valves are considerably thinner than that portion which is attached di-
rectly to the vessel. In some of the vessels, at the point where one lym-
phatic communicates with another, there is a valve formed of two folds,
one of which is much wider than the other ; but, in the valves situated in
the course of the vessels, the curtains are of about equal size. The valves
are very numerous in all of the lymphatics, but they are most abundant
in the superficial vessels. The distance between the valves is from one-
twelfth to one-eighth of an inch, near the origin of the vessels, and from
one-quarter to one-third of an inch, in their course. In the lymphatics
situated between the muscles, the valves are less numerous. They are
always relatively few in the vessels of the head and neck and in all that
have a direction from above downward. Although there are a number
of valves in the thoracic duct, they are not so numerous here as in the
smaller vessels.

In their anatomy and general properties, the lymphatics bear a close
resemblance to the veins. Although much thinner and more transparent,
their coats have nearly the same arrangement. The arrangement of
valves is entirely the same ; and, in both systems, the folds prevent the FIG. 90.— Valves of
reflux of fluids when the vessels are subjected to pressure. A number
of forces (which will be considered hereafter) combine to produce the
flow of lymph and chyle in the absorbent system. Among these is intermittent pressure
from surrounding parts, which could only operate favorably in vessels provided with nu-
merous valves.

We have already referred to the great elasticity of the lymphatics. It is now pretty
generally admitted that the larger vessels and those of medium size are endowed also
with contractility, although the action of their muscular fibres, like that of all fibres of
the involuntary or non-striated variety, is slow and gradual. Todd and Bowman have
demonstrated this property by mechanically irritating the thoracic duct in an animal re-
cently killed, but they observed that the contraction was very slow. Milne-Edwards,
quoting from a manuscript presented by Colin to the Academy of Sciences, in 1858, states
that this observer noted alternate filling and emptying of some of the lacteal vessels in
the mesentery of the ox ; portions of the vessels becoming alternately enlarged in the
form of pouches, and contracted so that they almost disappeared. There can be no
doubt that the lymphatic vessels possess a certain degree of contractility, which is fully
as marked, perhaps, as in the venous system.

One of the most important points in connection with the physiological anatomy of
the lymphatic vessels, and one, indeed, upon which rest our ideas of the mechanism of
absorption by these vessels, is the question of the existence of orifices in their walls, which
might allow the passage of solid particles or emulsions. The most recent observations

310

ABSORPTION.

have indicated the probable existence of stomata, of variable size and irregular shape, in
the smallest vessels; but it must be acknowledged that one of the strongest arguments
in favor of the existence of these orifices is, not their anatomical demonstration, but the
fact of the actual passage, through the walls of the vessels, of fatty particles, the en-
trance of which cannot be explained by the well-known laws of endosmosis- The ana-

B

FIG. 91. — Lymphatic plexus, showing the epithelial lining of the vessels, (Belaieff.)

tomical evidence of the existence of openings is derived mainly from preparations stained
with nitrate of silver. It is assumed that nitrate of silver stains the solid parts of tis-
sues and the borders of the epithelial cells, and that areas which do not present any
staining are necessarily open, If this be true, and this view is now very generally ac-
cepted, we may consider the existence of openings in the lymphatic vessels as demon-
strated. In preparations of the lymphatics, the solution of silver is seen staining the
tissues and the borders of the epithelial cells lining the vessels ; but there are areas be-
tween these cells where no staining is observed and in which no nuclei are brought on
by staining with carmine. It is not impossible, however, that the solutions used may
fail to attack all parts of the tissue, and that these colorless areas may be closed by an
amorphous membrane.

With regard to the origin of the lymphatics in the tissues, it does not seem that our
actual knowledge extends beyond the small vessels, such as are observed in the superfi-
cial net-work of the skin. Within the last few years, Recklinghausen and others have
assumed the existence, in the connective tissue (which is so widely distributed in the
organism), of minute tubes or canaliculi, which open into the lymphatic vessels, and that
these are the true vessels of origin of a great part of the lymphatic system. These lit-
tle vessels are called serous canaliculi. This view, however, is not sustained by positive
demonstration and must be regarded as purely hypothetical ; and the same may be said
of the opinion advanced by some that the lymphatics originate in lacunae or spaces in the
connective tissue or in a system of canals formed by connective-tissue corpuscles and
fibres. Sappey asserts very emphatically that not one lymphatic vessel has ever been
demonstrated as arising from the substance of connective tissue ; and a careful study of
recent observations in Germany shows this to be the fact.

Lymphatic Glands. — In the course of the lymphatic vessels, are found numerous small,

ABSORPTION BY LACTEAL AND LYMPHATIC VESSELS. 311

lenticular bodies, called lymphatic glands. The number of these glands is very great, al-

though it is estimated with difficulty, from the fact that many of them are very small and

are consequently liable to escape obser-

vation. It may be stated as an approxi-

mation that there are from six hundred

to seven hundred lymphatic glands in

the body. Their size and form are also

very variable within the limits of health.

They are generally flattened and len-

ticular, some as large as a bean, and

others as small as a small pea or even

a pin's-head. They are arranged in

two sets; one superficial, correspond-

ing with the superficial lymphatic ves-

sels, and a deep set, corresponding with

the deep vessels. The superficial glands

are most numerous in the folds at the

flexures of the great joints and about

the great vessels of the head and neck.

The deep-seated glands are most numer-

ous around the vessels coming from the

great glandular viscera. A distinct set

of large glands is found connected with

the lymphatic vessels between the

folds of the mesentery. These are

known as the mesenteric glands. All

of the lymphatic vessels pass through

glands before they arrive at the great

lymphatic trunks, and most of them

pass through several glands in their

r»nnr«A

There is some difference of opinion

, , . , .

among anatomists concerning the inti-
mate structure of the lymphatic glands. Some regard them as composed simply of a
plexus of lymphatic vessels, held together by a delicate stroma of fibrous tissue ; while
others deny that there is any direct communication between the afferent and the efferent
vessels, assuming that the vessels which penetrate the glands break up into small branches
which open into a parenchyma filled with closed follicles, and that the fluids are collected
from the glands by a second set of capillaries connected with the efferent lymphatics.
According to the latter view, the mesenteric glands are little more than collections of
follicles like the solitary glands of the intestines, held together by a delicate fibrous
structure. This difference of opinion seems to be due to the different methods which
have been employed in studying the structure of the glands. Taking, for example, the
results arrived at by two prominent investigators, Sappey, who has studied these organs
with great success by injections, seems to have clearly demonstrated a lymphatic plexus
in their interior, while Kolliker, whose investigations have been confined chiefly to ex-
aminations of the organs in a recent state, has not been able to follow out the lymphatic
vessels, but has accurately described the contents of the alveoli, or what are regarded by
others as closed follicles. In attempting to represent what has been actually demon-
strated concerning the structure of these bodies, we shall first take up the appearances
which are observed in the fresh structures, and afterward, those points which have been
demonstrated by minute injections.

The perfect, healthy glands are of a grayish-white or reddish color, of about the con-

FIG. 92.— Lymphatics and lymphatic glands. (Sappey.)
uPPer extremity of the thoracic duct, passing behind the
internal jugular vein ; 2, opening of the thoracic duct into
the internal jugular and left subclavian vein. The lym-
phatic glands aie seen in the course of the vessels.

312 ABSORPTION.

sistence of the liver, presenting a hilum where the larger blood-vessels enter and the
efferent vessels emerge, and covered, except at the hilum, with rather a delicate mem-
brane, composed of inelastic, with a few elastic fibres. Their exterior is somewhat tu-
berculated, from the projections of the follicles just beneath the investing membrane.
The interior of the glands is soft and pulpy. It presents a coarsely-granular cortical
substance, of a reddish- white or gray color, which is from one-sixth to one-fourth of an
inch in thickness in the largest glands. The medullary portion, which comes to the sur-
face at the hilum, is lighter colored and coarser than the cortical substance. Through-
out the gland, are found delicate fasciculi of fibrous tissue connected with the investing
membrane, which serve as a fibrous skeleton for the gland and divide its substance into
little alveoli. The structure is far more delicate in the cortical than in the medullary
portion.

Within the alveoli, are irregularly-oval, closed follicles, about ^^ of- an inch in di-
ameter, filled with a fluid and with cells like those contained in the solitary glands of the
intestines and the patches of Peyer. These follicles do not seem to occupy the medul-
lary portion of the glands, which, according to Kolliker, is composed chiefly of a net-
work of lymphatic capillaries, mixed with rather coarse bands of fibrous tissue. The
follicular structures in the lymphatic glands resemble the closed follicles in the mucous
membrane of the intestinal canal and the Malpighian bodies of the spleen.

The elaborate researches of Sappey leave scarcely any doubt as to the course and ar-
rangement of the lymphatic vessels in the interior of the lymphatic glands, although the
view advanced by him that these bodies consist mainly of lymphatics with a little
fibrous tissue cannot be sustained. By pricking a perfectly healthy gland with the deli-
cate point of his apparatus for injecting the lymphatics, he has seen the mercury succes-
sively fill the different capillary vessels and pass into the vasa efferentla. Sappey does
not appear, however, to have caused the injection to pass from the afferent to the effer-
ent vessels, entirely through this plexus ; and, while the fact of the continuity of these
vessels through a capillary plexus is extremely probable, it has not, as yet, been posi-
tively proven.

As far as has been ascertained, the following is the course of the lymphatic vessels
through the glands : From two to six vasa afferentia approach the gland, and, when
within about a quarter of an inch of it, they break up into numerous small branches which
penetrate its investing membrane. In the substance of the gland, these vessels are dis-
tributed in the capillary plexus just described and emerge by the vasa efferentia, which
are always larger than the afferent vessels and are from one to three in number. In
attempting to pass injections entirely through the glands, the fluid has frequently been
observed to pass into the small veins ; so that some anatomists have assumed that there
is a connection in the substance of the glands between the lymphatics and the blood-
vessels. It is altogether probable that the passage of fluids into the veins under these
circumstances is due to rupture of the vessels ; and, at all events, the direct connection
between them and the lymphatics has never been satisfactorily demonstrated.

The lymphatic glands are supplied with blood by sometimes one, but generally by sev-
eral small arteries, which penetrate at the hilum. These vessels pass directly to the medul-
lary portion and there break up into several coarse branches, to be distributed to the
cortical substance, where they ramify in an exceedingly delicate capillary net-work, witli
rather wide meshes, in the closed follicles found in this portion of the gland. This capil-
lary plexus also receives branches from small arterial twigs which penetrate the capsule
of the gland at different points. Returning on themselves in loops, the vessels unite to
form one or more large veins, which generally emerge at the hilum.

Very little is known regarding the distribution of nerves in the lymphatic glands.
A few filaments from the sympathetic system enter with the arteries, but they have
never been traced to their final distribution. The entrance of filaments from the cerebro-
spinal system has never been demonstrated.

ABSORPTION BY LACTEAL AND LYMPHATIC VESSELS.

313

FIG. 93.— Different varieties of lymphatic glands. (Sappey.)

It is evident, from the structure of the lymphatic glands, that they must materially
retard the passage of the lymph toward the great trunks; and it is well known in
pathology that morbid matters taken
up by the absorbents are frequently
arrested and retained in the nearest
glands.

The function of the lymphatic
glands is very obscure. By some
they are supposed to have an im-
portant office in the elaboration of
the corpuscular elements of the
lymph and chyle; and it has been
observed that the lymph contained
in vessels which have passed through
no glands is relatively poor in cor-
puscles, while the large trunks and
the efferent vessels contain them in
large numbers. This single fact is
indefinite enough, as regards the
mode of formation of the lymph-
corpuscles, but it represents about
all that is actually known concern-
ing the function of the lymphatic
glands.

In endeavoring to estimate the
share which the lacteal s and lym-
phatics have in the function of ab-
sorption, it becomes an important question to determine what principles these vessels
are capable of taking up, beside the fatty elements of the food, and how far, if at all,
they assist the blood-vessels in the absorption of the general products of digestion.

Absorption of Albuminoids l)y the Lacteals. — Comparative analyses of the lymph and
chyle always show in the latter fluid an excess of albuminoid matters. As we may rea-
sonably suppose that, during the intervals of digestion, the lacteals carry ordinary lymph —
for, at this time, these vessels are filled with a colorless, transparent fluid, having the gen-
eral physical characters of lymph — it is natural to infer* that the excess of nitrogenized
matters in the white chyle is due to absorption of albuminoids from the intestinal canal.
Mr. Lane collected the chyle from the lacteals of a donkey, seven and a half hours after
a full meal of oats and beans, and compared its composition with that of the lymph. The
analyses were made by Dr. Rees, who found that the chyle contained about three times
as much albumen and fibrin as the lymph. While by far the greater part of the products
of digestion of the albuminoids is absorbed by the blood-vessels, there can be no doubt
that a small portion is also taken up by the lacteals.

Absorption of Glucose and Salts by the Lacteals. — What has just been stated regard-
ing the absorption of albuminoids applies with equal force to saccharine matters and
the inorganic salts. Small quantities of sugar and sometimes lactic acid have been
detected in the chyle from the thoracic duct in the herbivora ; and the presence of sugar
in both the lymph and the chyle has been accurately determined by Colin.

It is true that the products of the digestion of saccharine and amylaceous matters are
taken up mainly by the blood-vessels, but a small quantity is also absorbed by the lac-
teals. In the comparative analyses of the chyle and lymph by Dr. Rees, the proportion
of inorganic salts was found to be considerably greater in the chyle. The great excess

314 ABSORPTION.

in the quantity of blood coming from the intestine and the rapidity of its circulation, as
compared with the chyle, will explain the more rapid penetration by endosmosis of the
soluble products of digestion.

Absorption of Water ~by the Lacteals. — There can be no doubt that a small portion of
the liquids taken as drink finds its way into the circulation by the lacteals, although the
greatest part passes directly into the blood-vessels. This has been proven by experi-
ments of a most positive character. Leuret and Lassaigne state that, when an animal is
fed with an aliment which is very substantial and is killed during digestion, the thoracic
duct contains a very small quantity of chyle ; but, when the animal has taken liquids with
the food, the thoracic duct and the lacteals are very much distended. In an experiment
by Ernest Burdach, a dog was deprived of food and drink for twenty-four hours, after
which he was allowed to drink water, and, in addition, half a pound was injected into
the stomach. The animal was killed a half an hour after, and the thoracic duct was
found engorged with watery lymph, which contained a very small number of lymph-cor-
puscles.

In discussing the question of absorption by the blood-vessels of the intestinal canal,
we alluded to experiments which showed that various poisonous substances introduced
into the intestines produced their characteristic effects upon the system with great
rapidity when the veins leading from the part were intact, while no such effects followed
when the only avenue to the general system was through the lacteals. Without again
discussing these observations in detail, it may be stated, as the general results of experi-
ments on this subject, that few, if any, of the active poisons were found to be absorbed
from the alimentary canal, except by blood-vessels ; and, when soluble coloring matters,
or salts which could be easily recognized, were found in the lacteals or the thoracic duct
after they had been introduced into the intestine, they penetrated in small quantity and
very slowly ; while it has been repeatedly found that the same substances were taken up
by the veins with great rapidity and excreted, in many instances, by the urine.

Absorption from Parts not connected with the Digestive System. — Aside from the
entrance of gases into the blood from the pulmonary surface, physiological absorption is
almost entirely confined to the mucous membrane of the alimentary canal. It is true
that liquids may find their way into the circulation through the skin, the lining mem-
brane of the air-passages, the reservoirs, ducts, and parenchyma of glands, the serous and
other closed cavities, the areolar tissue, the conjunctiva, the muscular tissue, and, in
fact, all parts which are supplied with blood-vessels ; but here the absorption of foreign
matters is an occasional or an accidental circumstance and is not connected with the
general process of nutrition. It is now well known that all parts of the body, except
the epidermis and its appendages, the epithelium, and some other structures which are
regularly desquamated, are constantly undergoing change, and the effete matters which
result from their decay are taken up by what is called interstitial absorption and are car-
ried by the blood to the proper organs, to be excreted. It seems probable that the ves-
sels of these parts would also be capable of taking up soluble foreign substances when
presented to them ; and this is, indeed, the fact with regard to all parts in which the
nutritive processes are even moderately active, or where the structures covering the vas-
cular parts are permeable.

Absorption from the Skin. — It is now generally admitted that absorption can take
place from the general surface, although, at one time, this was a question much discussed
by physiologists and practical physicians. The proofs, however, of the entrance of cer-
tain medicinal preparations from the surface of the body are now entirely conclusive ;
and the constitutional effects of medicines administered in this way are frequently as
marked as when they are taken into the alimentary canal. But the question which is

ABSORPTION BY THE SKIN. 315

of most interest to us as physiologists concerns the normal functions of the skin as an
absorbing surface. Looking at this subject from a purely physiological point of view,
absorption from the skin, under ordinary conditions, must be very slight, if, indeed, it take
place at all. There are a few observations by the older physiologists which would at
first seem to show that a certain amount of water is taken up by the skin when the
atmosphere is unusually moist. In all of these, however, this conclusion is drawn from the
circumstance that the weight is occasionally somewhat increased under these conditions;
but no account is taken of the fact, that, when the surrounding atmosphere is moist, the
amount of the exhalations is greatly decreased. The lungs, also, present an immense
absorbing surface, which is not at all considered. Experiments on this point are not suffi-
ciently definite to warrant any positive conclusions ; but it is evident that, if any articles
enter in this way, the quantity must be excessively minute.

The experiments upon the entrance of water and soluble substances through the skin,
when the body has been immersed for a long time in a bath, are somewhat contradictory.
Most experimenters have noted an increase in the weight, which they attribute to absorp-
tion of water, but others profess to have observed a slight diminution in the weight of the
body. In some experiments on this subject, by Madden, in which all necessary precau-
tions were adopted, the air being respired through a tube passed out of the window of the
room, so that no unusual absorption of moisture could take place by the lungs, the results
were very conclusive. In experiments of this kind, there are many modifying influences
to be guarded against. For example, it has been found to be important to regulate care-
fully the temperature of the bath ; for, when it exceeds that of the body, there may be a
loss of weight by cutaneous transpiration. It is stated by Longet that, when the tem-
perature of the water is lower than that of the body, there is a gain in weight ; but that
the cutaneous exhalation and absorption are balanced when the temperature of the bath
and the body are the same. There is another source of complication in these observa-
tions, which has been brought forward very strongly by a French writer, M. Delore.
This observer has carefully noted the increase in weight of the hair, nails, and epidermis,
after immersion for half an hour in distilled water, and has always found it to be very
considerable. He assumes that this is more than sufficient to account for the increase in
the weight of the entire body after immersion in water for half an hour, which amounts
to about seven hundred grains.

There are, nevertheless, facts which render it certain that water can be absorbed by
the skin. In an elaborate series of experiments by Collard de Martigny, it was proven
conclusively that water could be absorbed in small quantity by the skin of the palm of
the hand. In one experiment, a small bell-glass filled with water was applied hermeti-
cally to the palm. This was connected with a tube bent in the form of a siphon, also
filled with water, the long branch of which was placed in a vessel of mercury. After
the apparatus had been applied for an hour and three-quarters, the mercury was found
sensibly elevated in the tube, showing that a certain quantity of the water had disap-
peared. More recently, a very extended series of observations upon the absorption of
water and soluble substances has been made by Dr. Willemin, in which it is conclusively
proven that water is absorbed in a bath, and that various medicinal substances may be
taken up by the skin in this way and can be detected afterward in the urine. In a large
number of experiments, he found that the weight of the body, after remaining in a tepid
bath for from thirty to forty-five minutes, was generally stationary ; but that sometimes
there was a very slight diminution in weight and sometimes a very slight increase. By
comparative observations, however, he found that the diminution of weight in the bath
was always less than the amount lost by the same subject in the air. Dr. "\\illemin
employed a very delicate apparatus for weighing, and his observations were apparently
conducted with great care. He also confirmed the statement of W. F. Edwards and
others, that transpiration from the general surface goes on in a bath. This he showed
by differences in the composition of the bath before and after immersion of the body.

316 ABSORPTION.

These observations do much to reconcile the contradictory experiments of others, in some
of which a diminution in weight was observed, while in some an increase was noted. In
studying this subject, it must always be remembered that there is a constant loss of
weight by evaporation from the general surface and from the lungs; a fact which was
not taken into account by some of the earlier experimenters.

It has been frequently remarked that the sensation of thirst is always least pressing
in a moist atmosphere, and that it may be appeased to a certain extent by baths. It is
true that, in a moist atmosphere, the cutaneous exhalations are diminished, and this
might account for the maintenance of the normal proportion of fluids in the body with a
less amount of drink than ordinary ; but we could hardly account for an actual allevia-
tion of thirst by immersion of the body in water, unless we assumed that a certain
quantity of water had been absorbed. A striking example of relief of thirst in this way
is given by Captain Kennedy, in the narrative of his sufferings after shipwreck, when lie
and his men were exposed for a long time without water, in an open boat. With regard
to his sufferings from thirst, he says: "I cannot conclude without making mention of
the great advantage I derived from soaking my clothes twice a day in salt-water,
and putting them on without wringing. . . . There is one very remarkable circum-
stance, and worthy of notice, which was, that we daily made the same quantity of urine
as if we had drunk moderately of any liquid, which must be owing to a body of water
absorbed through the pores of the skin. ... So very great advantage did we derive
from this practice, that the violent drought went off, the parched tongue was cured in a
few minutes after bathing and washing our clothes ; at the same time we found ourselves
as much refreshed as if we had received some actual nourishment."

Absorption ly the Respiratory Surface. — In studying the physiological anatomy of
the respiratory apparatus, we have seen how admirably the respiratory surface is calcu-
lated for the introduction of gaseous principles into the blood. The great rapidity with
which the oxygen of the inspired air penetrates through the delicate covering of the pul-
monary vessels has already been fully considered under the head of respiration. Under
natural conditions, the gases of the air are the only principles absorbed by the lungs ; but
examples of the absorption of other gaseous matters are exceedingly common, and this
process has been the subject of numerous experiments by physiologists. The fact of the
absorption of foreign substances by the lungs, also, has long been definitely settled ; but
this belongs to pathology or to therapeutics, rather than to physiology.

It is now almost universally conceded that animal and vegetable emanations may be
taken into the blood by the lungs and produce certain well-marked pathological condi-
tions. It is supposed that many contagious diseases are propagated in this way, as well
as some fevers and other general diseases which are not contagious. With regard to cer-
tain poisonous gases and volatile principles, the effects of their absorption by the lungs
are even more striking. Carbonic oxide and arseniuretted hydrogen produce death al-
most instantly, even when inhaled in small quantity. The vapor of pure hydrocyanic acid
acts frequently with great promptness through the lungs. Turpentine, iodine, and many
medicinal substances may be introduced with great rapidity by inhalation of their va-
pors; and we well know the serious effects produced by the emanations from lead or mer-
cury in persons who work in these articles. Among the most striking proofs of the
absorption of vapors by the lungs are the effects of the inhalation of ether. This passes
into the blood and manifests its characteristic anaesthetic influence almost immediately.
Not only have vapors introduced in this way been recognized in the blood, but many of
the principles thus absorbed are excreted by the kidneys and may be recognized by their
characteristic reactions in the urine.

As would naturally be expected, water and substances in solution, when injected
into the respiratory passages, are rapidly absorbed, and poisons administered in this way
manifest their peculiar effects with great promptness. Experimenters on this subject

ABSORPTION OF FATS AND INSOLUBLE SUBSTANCES. 317

have shown the facility with which liquids may be absorbed from the lungs and the air-
passages, but it must be remembered that the natural conditions are never such as to ad-
mit of this action. The normal function of the lungs is to absorb oxygen and sometimes
a little nitrogen from the air; and the absorption of any thing else by these surfaces is
unnatural and generally deleterious.

Absorption from Closed Cavities, Reservoirs of Glands, etc. — Facts in pathology show-
ing absorption from closed cavities, the areolar tissue, the muscular and nervous tissue,
the conjunctiva, and other parts, are sufficiently numerous. In all cases of effusion of
scrum into the pleural, peritoneal, pericardial, or synovial cavities, in which recovery
takes place, the liquid becomes absorbed. It has been shown by experiment that warm
water injected into these cavities is disposed of in the same way. Effusions into the
areolar tissue are generally removed by absorption. In cases of penetration of air into
the pleura or the general areolar tissue, absorption likewise takes place ; showing that
gases may be taken up in this way as well as liquids. Effusions of blood beneath the
skin or the conjunctiva or in the muscular or nervous tissue may become entirely or in
part absorbed. It is true that these are pathological conditions, but, in the closed cavi-
ties, the processes of exhalation and absorption are constantly going on, although not
very actively. As regards absorption from the areolar tissue, the administration of
remedies by the hypodermic method, which is now so common, is a familiar proof of the
facility with which soluble principles are taken into the blood when introduced beneath
the skin.

Under some circumstances, absorption takes place from the reservoirs of the various
glands, the watery portions of the secretions being generally taken up, leaving the solid
and the organic matters. It is supposed that the bile becomes somewhat inspissated
when it has remained for a time in the gall-bladder, even when the natural flow of the se-
cretion is not interrupted. Certainly, when the duct is in any way obstructed, absorption
of a portion of the bile takes place, as is proven by coloration of the conjunctiva and
even of the general surface. The serum of the blood, under these conditions, is always
strongly colored with bile.

It is probable that some of the watery portions of the urine are reabsorbed by the
mucous membrane of the urinary bladder, when the urine has been long confined in its
cavity, although this resorption is ordinarily very slight. A great many cases of dis-
charge of urinary matters by the stomach and intestines, skin, etc., when the urine has
been long retained, have been reported by the older physiologists and were supposed to
indicate resorption of these principles from the bladder. The mechanism of the excretion
of urinary matters was not understood before the experiments of Prevost and Dumas,
Who showed that urea accumulates in the blood after the extirpation of both kidneys
in the inferior animals. It is now generally admitted that this takes place when the
function of excretion of urine is seriously interfered with, and that an attempt is made
by Nature to remove these effete principles from the system by the stomach, intestine,
skin, and lungs. It is possible, therefore, that the vicarious discharge of urinary matters,
in the cases reported before the true process of excretion by the kidneys was understood,
was due to accumulation of the constituents of the urine in the blood, and not to their
resorption from the urinary passages.

Absorption may take place from the ducts and the parenchyma of glands, although
this occurs chiefly when foreign substances have been injected into these parts.

Absorption of Fats and Insoluble Substances.

The general proposition that all substances capable of being absorbed are soluble in
water or in the digestive fluids must be modified in the case of the fats. These are never
dissolved in any appreciable quantity in digestion, the only change which they undergo
being a minute subdivision in the form of a very fine emulsion. In this condition, the

318

ABSORPTION.

fats are taken up by the lacteals and may be absorbed in small quantity by the blood-
vessels. Although it is now pretty well understood how endosmotic liquids pass through
the walls of the blood-vessels and absorbents, the mechanism of the penetration of fatty
particles, which is no less constant, is still somewhat obscure.

There can be no question with regard to the actual penetration of the minute parti-
cles of the chyle into the lacteals and even into the blood-vessels. In birds, indeed, ac-
cording to Bernard, all the fat which is absorbed is taken up by the blood-vessels, the
lymphatics of the intestine never containing a milky fluid. Confining our discussion to
the mechanism of the absorption of fatty emulsion in mammals, it must be admitted that
the assumption of the existence of orifices in the walls of the lacteals, even if we deny the
actual anatomical demonstration of these openings, becomes almost necessary ; for the
experiments upon the passage of fatty particles through closed membranes are certainly
very unsatisfactory. Taking into consideration all of the facts bearing upon the question,
it seems more probable that orifices exist in the vessels than that the fatty particles pene-
trate by endosmosis; but it must be remembered that this idea rests upon the un-
doubted physiological fact of the absorption of emulsions rather than upon anatomical
grounds ; and, if we were not called upon to explain the absorption of fatty particles, it
is doubtful whether the stomata of the vessels would be so generally admitted. It is not
infrequently the case that we are forced to assume the existence of certain anatomical
arrangements as the only reasonable explanation of physiological phenomena, when act-
ual demonstrations are unsatisfactory. With regard to the lacteals, when we remember
the excessive tenuity of the vessels of origin, the close adhesion of their walls to the
surrounding tissues, the novelty and uncertainty of the staining processes, and the fact
that some anatomists deny that the finest so-called lymphatic plexuses of origin have any
distinct walls, it is readily understood how, as physiologists, we must regard the exist-
ence of stomata in the lymphatics as an idea based upon the necessity of explaining well-
established physiological phenomena, rather than a clearly-demonstrable anatomical fact.
In studying the mechanism of the penetration of fatty particles into the intestinal villi,

it has been ascertained that the epithelial cells
covering the villi play an important part in this
process. It was first ascertained by Goodsir that,
during the digestion of fat, these cells became
filled with fatty granules. This fact has been
confirmed by Gruby and Delafond, Kolliker,
Funke, and others. Funke, in his atlas of physi-
ological chemistry, figures the appearances of the
intestinal epithelium during the digestion of fat,
as contrasted with the epithelium observed dur-
ing the intervals of digestion, showing the cells,
during absorption, filled with fatty granules.

It is true, as a general law, that insoluble sub-
stances, with the exception of the fats, are never
regularly absorbed, no matter how finely they
may be divided. The apparent exceptions to this
^ mercury in & ^ of minute subdivision like

an emulsion, and carbonaceous particles. In the

case of mercury, it is well known that minute particles in the form of unguents may be
introduced into the system by prolonged frictions ; but this cannot be regarded as an
instance of physiological absorption. The passage of small carbonaceous particles
through the pulmonary membrane seems to be purely mechanical. The same thing may
possibly occur when fine, sharp particles of carbon are introduced into the alimentary
canal ; but the experiments of Mialhe with pulverized charcoal, and particularly those
of Berard, Robin, and Bernard with lamp-black introduced into the intestinal canal of

FIG. U.-

.

intestine of the

VARIATIONS AND MODIFICATIONS OF ABSORPTION.

319

animals, showed that, although the intestinal mucous membrane became of a deep black,
this could easily be removed by a stream of water, and no carbonaceous particles could
be discovered in the mesenteric veins, the lacteals, or the mesenteric glands. When the
carbon is used in the form of lamp-black, the particles are very minute and rounded, and
they do not present the sharp points and edges which sometimes enable the grains of
pulverized charcoal to penetrate the vessels mechanically.

FIG. 95. — Epithelium from the duodenum of a rab-
bit, two hours after having been fed with melt-
ed butter. (Fuhke.)

FIG. 96.— Villi, filled with fat. from the small in-
testine of an executed criminal, one hour after
death. (Funke.)

Variations and Modifications of Absorption.

Very little is known concerning the variations in lacteal or lymphatic absorption ;
but, in absorption by blood-vessels, important modifications occur, due, on the one hand,
to different conditions of the fluids to be absorbed, and, on the other, to differences in the
constitution of the blood and in the conditions of the vessels.

The different conditions of the fluids to be absorbed apparently do not always have
the same influence in physiological absorption as in endosmotic experiments made out of
the body. Saccharine solutions of different densities confined in distinct portions of the
intestinal canal of a living animal do not present any marked variations in the rapidity
of their absorption, and they are taken up by the blood, even when their density is
greater than that of the blood-plasma. Solutions of nitrate of potash and sulphate of
soda of greater density than the serum, which would, therefore, attract the endosmotic
current in an endosmometer, are readily taken up by the blood-vessels in a living animal.
Indeed, nearly all soluble substances, whatever be the density of their solutions, may be
taken up by the various absorbing surfaces during life. The woorara poison and most of
the venoms are remarkable exceptions to this rule. In a series of very interesting
experiments upon the absorption of woorara, Bernard has shown that this curious poison,
which is absorbed so readily from wounds or when introduced under the skin, generally
produces no effect when introduced into the stomach, the small intestine, or the urinary
bladder. This result, however, is not invariable, for poisonous effects are produced when
woorara is introduced into the stomach of a fasting animal. This peculiarity in the
absorption of many of the animal poisons has long been observed ; and it is well known
that the flesh of animals poisoned with woorara can be eaten with impunity. It is
curious, however, to see an animal carrying in the stomach without danger a fluid which
would produce death if introduced under the skin ; and the explanation of this is not
readily apparent. The poison is not neutralized by the digestive fluids, for woorara
digested for a long time in gastric juice, or taken from the stomach of a dog, is found to
possess all its toxic properties, as we have frequently shown (repeating the experiment

320 ABSORPTION.

of Bernard) by poisoning a pigeon with woorara drawn by a fistula from the stomach of
a living dog. If we recognize the absorption of this poison simply by its effects upon the
system, it must be assumed that, during digestion, it cannot be absorbed by the mucous
membrane of the stomach . and small intestine, notwithstanding that it is exceedingly
soluble.

It has also been shown that liquids which immediately disorganize the tissues, such as
concentrated nitric or sulphuric acid, cannot be absorbed. Another important peculiar-
ity in absorption has been demonstrated by Mialhe, who has shown that solutions which
readily coagulate the albumen of the circulating fluids are absorbed very slowly. This
is explained on the supposition that there is a coagulation of the albuminous fluids with
which the absorbing membrane is permeated, which interferes with the passage of
liquids. These substances are nevertheless taken up by the blood-vessels, though rather
slowly.

The modifications which are due simply to the physical conditions of liquids to be
absorbed are chiefly manifested out of the body and will be considered in connection with
the subject of endosmosis.

Influence of the Condition of the Blood and of the Vessels on Absorption. — After loss
of blood or deterioration of the nutritive fluid from prolonged abstinence, absorption gen-
erally takes place with great activity. This is well known, both as regards the entrance
of water and alimentary substances and the absorption of medicines. It was at one time
quite a common practice to bleed before administering certain remedies, in order to pro-
duce their more speedy action upon the system.

The rapidity of the circulation has an important influence upon absorption. "We have
already shown, in treating of the action of the blood-vessels on absorption, that this pro-
cess may be impeded or even arrested by the ligation of important vessels. It has been
evident, also, that absorption is generally active in proportion to the vascularity of differ-
ent parts. During the process of intestinal absorption, the increase in the activity of the
circulation in the mucous membrane is very marked and undoubtedly has an influence
upon the rapidity with which the products of digestion are taken up.

Influence of the Nervous System on Absorption. — Experiments upon the influence of
the nervous system on absorption are still very imperfect. It is certain that this process,
especially in the stomach, is subject to variations, which can hardly be dependent upon
any thing but nervous action. Water and other liquids, which usually are readily ab-
sorbed from the stomach, are sometimes retained for a time, and are afterward rejected
in nearly the condition in which they were taken. It is probable, however, that the most
important influences thus exerted by the nervous system are effected through the circu-
lation. The recent experiments of Bernard and others upon the sympathetic system of
nerves and its connection with the muscular coats of the small arteries, by the action of
which the supply of blood in different parts is regulated, point out a line of experimenta-
tion which would probably throw much light upon some of the important variations in
absorption. When it is remembered that the small arteries may become so contracted
under the influence of the sympathetic system that their caliber is almost obliterated,
of course retarding to a corresponding degree the capillary and venous circulation in the
parts, and, again, that, through the sympathetic nerves, the same vessels may be so
dilated as to admit to a particular part three or four times as much -blood as it ordinarily
receives, it becomes apparent that absorption may be profoundly affected through this
system of nerves.

As far as the influence of the cerebro-spinal system is concerned, it has been ascer-
tained that, while section of some of the nerves distributed to the alimentary canal will
slightly retard the absorption of poisonous substances, it is never entirely arrested. Lon-
get found that the operation of strychnine injected into the stomach of a dog in which

IMBIBITION AND ENDOSMOSIS. 321

both pneumogastric nerves had been divided was retarded about five minutes ; but that
the convulsions, when they occurred, were fully as severe as in an animal which had
received an equal dose, without section of the nerves.

Imbibition and Endosmosis.

The ideas of physiologists concerning the mechanism of the absorption of soluble sub-
stances have become radically changed since the beginning of the present century ; and
it is now generally admitted that this process takes place chiefly by blood-vessels, and
that the absorbents have no such wonderful elective power as was attributed to them by
the older writers. This involves the passage of liquids through the coats of the blood-
vessels and lymphatics ; a process which has been the subject of numerous experiments,
resulting in the development of many important physical laws capable of application to
physiological absorption. At the present day, therefore, the history of absorption is not
complete without a consideration of the laws of imbibition and endosmosis.

If liquids can pass through the substance of an animal membrane, it is evident that
the membrane itself must be capable of taking up a certain portion of the liquid by
imbibition; and this must be considered as the starting-point in absorption. Imbibi-
tion is, indeed, a property common to all animal structures. One of the most strik-
ing characteristics of organic principles is that they may lose water by desiccation and
regain it by imbibition. It is also a well-known fact that the tissues do not imbibe all
solutions with the same degree of activity. Distilled water is the liquid which is al-
ways taken up in greatest quantity, and saline solutions enter the substance of the tis-
sues in an inverse ratio to their density. This is also the fact with regard to mixtures
of alcohol and water, imbibition always being in an inverse proportion to the quantity
of alcohol present in the liquid. Among the other circumstances which have a marked
influence upon imbibition, is temperature. It is a familiar fact that dried animal mem-
branes may be more rapidly softened in warm than in cold water ; and, with regard to
the imbibition of liquids by sand, the researches of Matteucci and Cima have shown an
immense increase at a moderately-elevated temperature. While nearly all the structures
of the body, after desiccation, will imbibe liquids, the membranes through which the pro-
cesses of absorption are most active are, as a rule, most easily permeated ; and we shall
see, when we come to study the mechanism of the passage of liquids through these mem-
branes, that the character of the liquid, the temperature, etc., have a great influence
upon the activity of this process. For example, all liquids which have a tendency to
harden the tissues, such as saline solutions, alcohol, etc., pass through with much less
rapidity than pure water. These facts will be found particularly interesting in connec-
tion with observations on the passage of liquids through membranes, in experiments on
endosmosis with artificial apparatus.

Mechanism of the Passage of Liquids through Membranes. — The attention of physi-
ologists was first directed to this subject by the researches of Dutrochet, in 1826. Al-
though not by any means the first to observe the phenomena which he described under
the name of endosmosis, to Dutrochet is generally ascribed the honor of having first
indicated the applications of the laws of endosmosis to the nutrition of plants and ani-
mals. Undoubtedly, Dutrochet was the first to make experiments upon endosmosis which
attracted the attention of scientific men in different parts of the world and which were
immediately repeated and extended ; but the experiments made upon living animals by
Lebkuchner, in 1819, and by Magendie, in 1820, had already demonstrated most conclu-
sively the passage of liquids through the walls of the blood-vessels ; and the explanation
offered by these physiologists was fully as definite as that proposed by Dutrochet.

Dutrochet constructed an instrument called the endosmometer, which consists sim-
ply of a small bell-glass, the lower opening of which is closed by a membrane, the open-
ing above being connected with a long glass tube by which the force with which liquids
21

322 ABSORPTION.

pass through the membrane can be measured. The bell-glass is generally filled with a
liquid capable of attracting a current of water from without, and is immersed in pure
water, so that the membrane is completely covered. Under these circumstances, there
is a current of water through the membrane, whicli will cause the liquid to mount in the
tube, sometimes to the height of several feet ; but, at the same time, there is a feebler
current from the interior of the apparatus to the water. Dutrochet called the stronger,
the endosmotic current, and the feebler, the exosmotic current. This nomenclature,
however, is not strictly accurate ; for, if the position of the liquids be reversed, the
stronger current is exosmotic and the feebler is endosmotic. It must be remembered,
therefore, that the name endosmosis is always to be understood as applied to the princi-
pal current, while the term exosmosis is applied to the current in the opposite direction.
This possible inaccuracy of expression has led to the adoption by Graham and others of
the term osmosis, as applied generally to the currents which take place through mem-
branes ; but the terms first proposed by Dutrochet are most commonly used.

The phenomena of endosmosis, which, since the publication of the researches of Du-
trochet, have been so closely studied by physicists, are chiefly interesting to the physiolo-
gist in their application to absorption. While it is true, perhaps, that all the phenomena
of physiological absorption cannot as yet be explained upon purely physical principles,
it is nevertheless important to ascertain how far physical laws are involved in this pro-
cess. With this end in view, we shall study the physical phenomena of endosmosis,
chiefly with reference to their physiological applications.

It is now definitely ascertained that the following conditions are necessary for the
operation of endosmosis and exosmosis :

1. That both liquids be capable of "wetting" the interposed membrane, or, in other
words, that the membrane be capable of imbibing both liquids. If but one of the liquids
can wet the membrane, the current can take place in only one direction.

2. That the liquids be miscible with each other and be differently constituted. Al-
though it is found that the currents are most active when the liquids are of different den-
sities, this condition is not indispensable ; for currents will take place between solutions
of different substances, such as salt, sugar, or albumen, when they have precisely the
same density.

The physiological applications of the laws of endosmosis can now be more fully
appreciated, as it is evident that the above conditions are fulfilled whenever absorption
takes place, with the single exception of the absorption of fats, which has been specially
considered. For example, all substances are dissolved or liquefied before they are ab-
sorbed, and, in this condition, they are capable of u wetting " the walls of the blood-vessels
All the liquids absorbed are capable, also, of mixing with the plasma of the blood. What
makes this application still more complete, is the behavior of albumen in endosmotic ex-
periments. In physiological absorption, there is always a great predominance of the
endosmotic current, and there is very little transudation, or exosmosis, of the albuminoid
constituents of the blood. On the other hand, there is a constant absorption of albu-
minose, which is destined to be converted into the albuminoid matters of the blood.

Recognizing the fact, which was, indeed, pointed out clearly by Dutrochet, that albu-
men is capable of inducing a more powerful endosmotic current than almost any other
liquid, it has been shown that it never itself passes through membranes in the exosmotic
current; but that albuminoids, after transformation by digestion into albuminose, or
albumen mixed with gastric juice, pass through animal membranes with great facility.
The experiments by which these facts are demonstrated are very conclusive and are
of the highest physiological importance. On removing part of the shell of an egg, so
as to expose its membranes, and immersing it in pure water, the passage of water into
the egg was rendered evident by the projection of the distended membranes; but,
although the surrounding liquid had become alkaline and the appropriate tests revealed
the presence of some of the inorganic constituents of the egg, the presence of albumen

IMBIBITION AND ENDOSMOSIS. 323

could never be detected. "When the contents of the egg were replaced by the serum
of the blood, the same result followed. " After six or eight hours of immersion, the
serum had yielded to the water in the vessel all its saline elements, chlorides, sulphates,
phosphates, which were easily recognized by their peculiar reactions, but
not an atom of albumen."

A very simple apparatus for illustrating endosmotic action can be con-
structed in the following way : Remove carefully a circular portion,
about an inch in diameter, of the shell from one end of an egg, which
may be done without injuring the membranes, by cracking the shell into
small pieces, which are picked off with forceps. A delicate glass-tube,
about six inches in length, is then introduced through a small opening in
the shell and membranes of the other end of the egg, and is secured in a
vertical position by wax, the tube penetrating the yolk. The egg is then
placed in a wine-glass partly filled with water. In the course of half an
hour or an hour, the water will have penetrated the exposed membrane,
and the yolk will rise in the tube.

Influence of Membranes upon Osmotic Currents. — The force with
which liquids pass through membranes, called endosmotic or osmotic
force, is to a great degree dependent upon the influence of the mem-
branes themselves. This influence is always purely physical, in experi-
ments made out of the body ; and physiological absorption can be ex-
plained, to a certain extent, by the same laws. It must be remem-
bered, however, that the properties of organic structures, which are
manifested only in living bodies, are capable of modifying these physical
phenomena to a remarkable degree. For example, all living tissues are
capable of selecting and appropriating from the nutritive fluids the ma-
terials necessary for their regeneration ; and the secreting structures of lustrate endos-
glands also select from the blood certain principles which are used in
the formation of their secretions. At the present day, these phenomena and their modi-
fications through the nervous system cannot be fully explained. This is true, also, of
many of the phenomena of absorption and their modifications, which are probably de-
pendent upon the same kind of action. In view of these undoubted facts, the influence
of the structures through which liquids pass in physiological absorption may be divided
as follows : first, into physical influences, which may be illustrated by endosmotic ex-
periments with organic membranes out of the body ; and second, modifications of these
phenomena, which are presented only in the living organism.

Numerous experiments have demonstrated that both the endosmotic and the exos-
raotic current may be produced by using a porous instead of a membranous septum,
though then they are always comparatively feeble. The phenomena thus presented are
to be explained entirely by the laws of capillary attraction and of the diffusion of liquids.
These laws would enter largely into the explanation of the passage of liquids through
animal membranes, if it could be demonstrated, or even rendered probable, that these
membranes are invariably porous, or provided with capillary openings. It will be neces-
sary, however, to study this question very carefully and to examine all the properties of
animal membranes, both within and without the living organism.

In the first place, is there any proof that all membranes which will admit the passajrc
of liquids are porous? This is a most important question; and it lies at the foundation
of the explanation of the phenomena of endosmosis by the laws of capillary attraction.

In all membranes which possess an anatomical structure discoverable by the micro-
scope, there are undoubtedly interstices between the fibres, cells, etc., of which the tis-
sue is composed; but, on the other hand, animal membranes generally have a layer, like
the basement-membranes of mucous tissues, which is absolutely homogeneous and struct-

324 ABSORPTION.

tireless. In applying the laws of endosmosis to physiological absorption, it is found that
the membranes which are most easily penetrated by fluids are excessively thin and
nearly homogeneous. Take, for example, the walls of the capillary blood-vessels, through
which the greatest part of physiological absorption takes place. This membrane is
from 2g^oo to -reyor ot an incn thick, and is entirely amorphous, with the exception of
the lining epithelium with its nuclei. The assumption that invisible capillary orifices
exist in these thin, amorphous membranes, aside from the so-calle'd stomata, is purely
hypothetical and is unwarrantable. The only circumstance which could lead to such a
supposition is the fact that these membranes can be penetrated by liquids.

It is manifestly unphilosophical and absurd to offer, as an explanation ot endosmosis
through structureless membranes, an hypothesis which has its only support in the exist-
ence of the phenomena which it is intended to explain. This mode of reasoning is all
the more unsound, as the phenomena of endosmosis are very far from being completely
understood, and as many important properties of organic structures, which bear directly
upon the question under consideration, are ignored. For example, physiological absorp-
tion does not always take place in accordance with known physical laws. It undergoes
modifications which can at present only be explained on the supposition that the liquids
become, for the time, part of the living organic structures and partake of their peculiar
properties; one of them, the property by virtue of which they appropriate both the
organic and the inorganic principles necessary to their proper constitution and regenera-
tion, is called by some, vital ; a word which simply expresses ignorance of its essen-
tial character. It must be understood, however, that this remark does not apply to the
general phenomena of endosmosis or absorption, but only to certain of its unexplained
modifications.

A most important property of organic tissues, which is ignored by those who explain
absorption on the principle of capillary attraction, is that of hygrometricity. All the
organic nitrogenized proximate principles are capable of losing their water of composi-
tion by desiccation and of regaining it by imbibition. The water which enters into their
composition is not necessarily contained in interstices in the tissue, but, in the case of
structureless parts especially, is uniformly disseminated, or, we may term it, diffused
throughout the organic substance, of which it forms a constituent part. This action of
certain liquids upon the organic semisolids is something like the diffusion of liquids ; the
difference being that it is the liquid only which is diffused in the semisolid, the semisolid
being incapable of diffusing in the liquid. As it has been found that all liquids are not
equally subject to capillary attraction, so animal tissues imbibe different liquids with dif-
ferent degrees of activity; a fact which will account in a measure for the variations in
the end osmotic currents with different solutions.

Examples are not wanting of endosmosis by imbibition or diffusion, when it cannot
be assumed that there is any such thing as porosity in the septum. The following
experiment of Lhermite fully illustrates this point. A tube was partly filled with a col-
umn of chloroform ; and upon this was poured a layer of water, and above it a layer of
ether. The ether gradually penetrated the layer of water and passed to the chloroform,
mingling with it. After a certain time, all the ether had thus been diffused in the chlo-
roform, and the layer of water retained its original volume. We have repeated this
experiment with some slight modifications, using first a layer of sulphuric acid, then a
layer of water, and finally a solution of blue litmus in alcohol ; and, in a very short
time, the acid penetrated the water and reddened the litmus above. A liquid septum is
certainly not porous, in any sense of the word; and the explanation of the phenomenon
of endosmosis through liquids depends simply upon the law of diffusion of liquids, the
molecules of the liquids being held together so feebly that they will admit the molecules
of other liquids with which they are capable of mixing.

With regard to the passage of liquids through different septa, the following seem to be
the facts which can be considered as definitely settled :

IMBIBITION AND ENDOSMOSIS. 335

The cohesive attraction of the constituent particles of insoluble solids is so great, that
the entrance of fluids is impossible, unless the substance be porous, and this always
involves the law of capillary attraction ; but, in liquids, the cohesive attraction is so
slight as to admit of the penetration and diffusion of certain other liquids.

Homogeneous animal membranes, which are of a semisolid consistence, are capable
of imbibing certain liquids; and any liquid which can pass into such membranes will
pass through them. under proper conditions. The cohesive attraction of the particles of
the membrane is not such as to allow them to imbibe an indefinite quantity of any liquid ;
but it is one of the distinctive properties of organic tissues, that a limited quantity of
liquid can be taken up in this way.

In view of these facts, it is not necessary to assume the existence of infinitely small
capillary openings in homogeneous membranes through which osmotic currents can be
made to take place, in order to explain the mechanism of these currents. In the case of
two liquids capable of diffusing with each other and separated by an animal membrane,
the mechanism of the endosraotic and exosmotic currents is very simple. In the first
place, the membrane imbibes both the liquids, but one is always taken up in greater
quantity than the other. If water and a solution of common salt be employed, the sur-
face of the membrane exposed to the water will imbibe more than the surface exposed to
the saline solution ; but both liquids will meet in its substance. The first step, therefore,
in the production of the currents is imbibition. Once in contact with each other, the
liquids diffuse, the water passing to the saline solution, and vice versa. This takes place
by precisely the same mechanism as that of the passage of liquids through porous septa.

The osmotic currents may be modified with the same liquids by using different mem-
branes. This fact was well illustrated in some of the experiments of Matteucci and Cima,
in which comparative observations were made upon the currents through the skin of the
torpedo, the skin of the frog, and the skin of the eel. The results obtained with these
different membranes showed marked and constant variations. The same observers,
using the mucous membrane of the stomach of the lamb, found a marked difference in the
endosmotic phenomena when the surface exposed to the water was reversed. In two
experiments, with the epithelial surface of the membrane turned toward the interior of
the endosmometer, the elevations of the liquid in an hour and a quarter were forty-
four and fifty-six millimeters ; but, with the membrane reversed, so that the attached sur-
face was turned toward the interior, the elevations during the same period were sixty-six
and seventy-two millimeters. This difference is readily explained by the difference in the
constitution of the two surfaces of the membrane used. From these facts, it is evident
that, while the diffusion of liquids as they meet in the substance of a membrane is the
actual cause of the osmotic currents, which are continued as the liquids diffuse with each
other upon either side of the membrane, the determination of a predominating or endos-
motic current, the ordinary conditions being undisturbed, is effected by the greater at-
tractive force which the membrane exerts upon one of the liquids.

Influence of Different Liquids upon Osmotic Currents. — The action of the liquids be-
tween which endosmotic currents take place is, as we have seen, most intimately con-
nected with the force by which the liquids enter the membrane, be it capillary attraction
or imbibition ; but the attractive force exerted by the membrane is never capable, in itself,
of producing a current. It is evident, therefore, that the properties of the liquids must
have an important influence upon osmosis, both from differences in the attraction of the
membrane for the liquids and their different degrees of diffusibility. In order to appre-
ciate fully all the physical phenomena of osmosis, it will be necessary to study carefully
the laws of diffusion of liquids and the diffusibility of different solutions ; but it will be
sufficient, for our present purpose to state a few general propositions, which will be found
more or less applicable to physiological absorption.

When two liquids, capable of mixing with each other, are brought together, they
diffuse with greater or less rapidity, until the constitution of the mixture becomes uniform.

326 ABSORPTION.

Different liquids possess widely different degrees of diffusibility ; and, as a rule, in
saline solutions, the rate of diffusion increases in proportion to the strength of the solu-
tion, at least when the quantity of salt dissolved does not exceed four or five per cent.
It follows from this that the activity of the endosmotic current toward any saline solution
will be greatest at the beginning of the experiment and will progressively dimmish as the
currents continue and the two liquids assume a more nearly uniform density.

The rate of diffusion of different solutions is generally increased hy a moderate eleva-
tion of temperature.

Bearing in mind these general laws, and remembering that they are applicable to
diffusion as it takes place through animal membranes, we can easily understand how
different liquids and solutions, in an endosmometer, will attract with different degrees of
intensity any given liquid, such as pure water; and how this attractive force, which is
measured by the rapidity and extent of the rise of liquid in an endosmometer, may be
modified by the concentration of the solution, differences in temperature, and other con-
ditions. The influence which the membrane exerts upon the relative intensity of these
currents is dependent to a certain extent upon the diffusion which takes place when the
two liquids come together in its substance.

As a rule to which there are not many exceptions, pure water will penetrate ani-
mal membranes more readily than any other liquid ; and it is consequently from the
water to the liquid contained in the endosmometer that the principal current generally
takes place. Liquids like alcohol, saline solutions, etc., which have this property, are
said to be positively osmotic ; while those with which the current takes place in the
opposite direction, such as oxalic acid, weak hydrochloric acid, bichloride of platinum,
etc., are said to be negatively osmotic. In a series of experiments with different liquids,
if the endosmometer be always the same and if all the liquids used be exposed to the action
of pure water, in a given time a definite change in the quantity of fluid in the endosmom-
eter will be produced, which will be indicated by a certain amount of elevation or de-
pression in its level.

Applications of Physical Laws to the Function of Absorption.

In no experiments performed out of the body, can the conditions favorable to the
passage of liquids through membranes in accordance with purely physical laws be realized
as they exist in the living organism. The vast extent of the absorbing surfaces ; the great
delicacy and permeability of the membranes ; the rapidity with which principles are car-
ried on by the torrent of the circulation, as soon as they pass through these membranes ;
the uniformity of the pressure, notwithstanding the penetration of liquids ; all these favor
the physical phenomena of absorption in a way which cannot be imitated in artificially-
constructed apparatus. It is not necessary to invoke the vital properties of tissues to
explain the ordinary phenomena of absorption. Enough has been learned of the laws
which regulated endosmosis and exosmosis to enable us to explain most of these phe-
nomena upon physical principles. This fact has been apparent in studying these princi-
ples in their relation to absorption in the living body ; but it is an important question to
determine whether this be applicable to all the varied phenomena of physiological ab-
sorption. In other words, are there any modifications in this function which cannot, as
yet, be explained by physical laws ?

Admitting the fact that the general process of absorption takes place in accordance
with the laws of endosmosis, we shall now consider some of the phenomena which ap-
pear to be in opposition to known physical principles, or in which the application of
these principles seems to be imperfectly understood.

It is not easy to understand how particles of emulsified fat find their way through
the walls of the lacteals and blood-vessels, unless we admit the existence of orifices,
such as have been described by recent anatomists. The experiments of Matteucci with
alkaline emulsions seem to show that alkalinity is a condition necessary to the penetra-

IMBIBITION AND ENDOSMOSIS. 327

tion of fatty particles, although they do not offer an explanation of the mechanism by
which these particles pass through membranes. It has been demonstrated that the epi-
thelium which covers these membranes becomes filled with fatty granules during the
absorption of emulsions, and some physiologists invoke the aid of " cell-action," — con-
cerning which it must be confessed that there exists very little definite information — in
explanation of this phenomenon. The penetration of fatty particles through membranes
must be regarded as one of the points which cannot be explained by the laws of endos-

mosis.

There are certain experiments on absorption in the living body, to which a great deal
of importance was attached by Longet, which are seemingly in opposition to physical
laws. This author states that, when solutions of sugar of different densities are secured
in isolated portions of the intestine of a living animal, the denser solutions are absorbed
with as much rapidity as those which are less concentrated. He also shows that saline
solutions of greater density than the blood are absorbed in the living animal, when,
according to physical laws, the current should take place in the opposite direction. The
view that these facts are in opposition to physical laws is very successfully controverted
by Milne-Edwards. This author, referring to some experiments by Von Becker in sup-
port of his position, asserts that there is first an exosmosis of the watery portions of the
blood to these dense solutions, with a feeble penetration of the solutions into the blood-
vessels, until, by the laws of diffusion, the solutions become so diluted as to be readily taken
into the circulation. Such an action as this could not take place between two saline
solutions in an endosmorneter, for both the currents would be equal when the liquids
became of equal density ; but it has been shown that, after endosmosis in an endosmome-
ter has ceased, it may be again induced by simply agitating the liquids. In physiological
absorption, the motion is constant and very rapid, and solutions in their passage along the
alimentary canal are continually exposed to fresh absorbing surfaces. Farthermore, the
albuminoid matters of the blood, which are very slightly exosmotic, will attract an en-
dosmotic current from liquids even when they are of the same density. The kind of
action described by Milne-Edwards would be by no means an isolated example of a
liquid passing out of the blood-vessels to be again absorbed after it has acted upon mat-
ters contained in the alimentary canal. This takes place with all the digestive fluids ;
and the liquid is effused, not by simple exosmosis, but by an act of secretion excited by
the impression made upon the mucous membrane. We are not justified, therefore, in
assuming, with Longet, that the absorption of solutions of greater density than the blood
is always in opposition to the laws of endosmosis.

The imbibition of the coloring matter of the bile by the coats of the gall-bladder
after death, while nothing of the kind takes place during life, is not due to the absence
of so-called vital action. During life, the circulation in the mucous membrane of this
reservoir would readily remove the few particles of coloring matter which might pene-
trate from the bile, and of course there is no time for any coloration to take place.

In treating of the variations and modifications of absorption, we noted an apparent
elective power in the mucous membrane of some portions of the alimentary canal. This
is illustrated in the failure of the mucous membrane to absorb woorara and various of
the animal poisons, which, as a rule, produce their effects only when introduced into a
wound or injected into the areolar tissue. The separation of various soluble substances by
the process known as dialysis may throw some light upon this subject, but as yet we have
no facts which offer a satisfactory explanation of this phenomenon. Certain of these phe-
nomena which show an apparent elective power in absorbing membranes are probably
due to a cell-action resembling secretion ; for all these surfaces are covered with epithe-
lium, which must be penetrated before the fluids can get to the blood-vessels. But, even
with regard to the selection of materials from the blood to form secretions, very little of
a definite character is known.

Those who believe that absorption is often modified by so-called vital action offer this

328 ABSORPTION.

in explanation of the important influence of the nervous system upon this function. Pre-
cisely how the nervous system affects absorption, in all instances, it is impossible, in the
present state of our knowledge, to determine ; but modifications are frequently effected
through the sympathetic nerves. These nerves, as is well known, are capable of pro-
ducing important local changes in the circulation, and can even temporarily arrest the
capillary circulation in some parts ; and it is in this way that many of the variations in
absorption may be produced.

Lymph and Chyle.

To complete the history of physiological absorption, it will be necessary to treat of
the origin, composition, and properties of the lymph and chyle. It is only within a few
years that physiologists have been able to appreciate the importance of the lymph, for
the experiments indicating the enormous quantity of this liquid which is continually
passing into the blood are of recent date. The earlier experimenters never succeeded in
obtaining more than a small quantity of fluid from the lymphatic system. On the other
hand, for the long period during which it was supposed that all the products of diges-
tion entered the system by the thoracic duct, the importance of the chyle was much
exaggerated ; but the researches upon intestinal absorption by Magendie and those who
followed him, and the experiments of Colin on the quantity of fluid which passes into
the blood by the thoracic duct during the intervals of digestion, have enabled physiologists
to form a better estimate of the importance of the lymph and chyle. In studying the
properties of these fluids, the consideration of the lymph naturally precedes that of the
chyle, as the latter consists simply of lymph, to which certain of the products of diges-
tion have been added by absorption from the alimentary canal.

Mode of obtaining Lymph. — The old methods of obtaining this fluid are no longer
employed. In the inferior animals, recently killed, a few drops may be obtained by
pricking the lymphatic glands or by exposing the right lymphatic trunk or the thoracic
duct and collecting the small quantity of fluid which is discharged when these vessels are
punctured. Although a notable quantity of chyle can be obtained from the thoracic duct
of an animal killed during intestinal absorption, it is difficult to collect even a small quan-
tity of fluid during the intervals of digestion. Various occasions have presented them-
selves for obtaining lymph, possessing more or less of its normal characters, from the
human subject during life ; but, in many of these instances, there existed some pathologi-
cal condition of the lymphatic system, and it cannot be assumed that the liquid thus
obtained was in a perfectly healthy condition.

The first successful experiments in which the lymph and chyle were obtained in quan-
tity were made by Colin. This observer, in operating upon large animals, particularly
the ruminants, experienced no great difficulty in isolating the thoracic duct near its junc-
tion with the subclavian vein and introducing a metallic tube of sufficient size to allow
the free discharge of fluid. These experiments, made upon horses and the larger rumi-
nants, were the first to give any clear idea of the quantity of liquids (lymph and chyle)
which pass through the thoracic duct. In an observation upon a cow of medium size, he
succeeded in collecting, in the course of twelve hours, the enormous quantity of 105-3 Ihs.
av. (47,963 grammes) ; and he farther states that a very much greater amount can be
obtained by operating upon ruminants of larger size. Whether this represent the actual
quantity which is normally discharged into the venous circulation, is a question which
will be considered under the head of the probable quantity of lymph and chyle ; but it
certainly shows that the lymph cannot but be regarded as one of the most important of
the animal fluids.

Among the observations upon the fluids discharged from the thoracic duct, which
followed the experiments of Colin, the most interesting are those made in 1859, by Dai-
ton, who operated upon carnivorous as well as herbivorous animals. These experiments

LYMPH AND CHYLE. 329

were performed upon young goats and dogs, and the general results with regard to the
quantity of fluids discharged closely corresponded with those obtained by Colin. The
operation of making the fistula in goats is not very difficult, all that is necessary being
to cut down upon the subclavian vein at the point where the duct empties into it, and to
fix in it a tube of appropriate size ; but, in dogs, the vessels are more deeply situated, and
the operative procedure is much more tedious. This, however, is the only way in which
lymph and chyle can be obtained from the lower animals in any considerable quantity.

Quantity of Lymp h.— Although, the experiments just described might at first seem
sufficient to give a pretty clear idea of the entire quantity of lymph discharged into the
venous system, it is evident that the conditions of the circulation of this fluid must be so
seriously modified by the establishment of a fistula, that the results thus obtained are far
from being entirely satisfactory. In the first place, Colin found that the canal, at its
junction with the subclavian vein, was seldom single ; and, in many of his observations
in which a very large quantity of liquid was obtained, there were several vessels of nearly
equal size emptying into the venous system. In the experiment to which we have
referred, however, the opening was single ; and the quantity of fluid obtained represented
all that passed up the thoracic duct during the time that the observation was continued.
As we should naturally expect, the discharge of liquid was subject to certain variations,
its maximum corresponding with the period of greatest activity in digestion and absorption.

It is not possible to estimate the influence of the unobstructed discharge of lymph
and chyle by a fistulous opening upon the absolute quantity which passes out of the
canal ; and, in the natural course of the circulation, there is a certain amount of obstruc-
tion to its entrance into the vein, which might sensibly retard the current.

According to the estimates of Dalton, deduced from his own observations upon dogs
and the experiments of Colin upon horses, the total quantity of lymph and chyle pro-
duced in the twenty-four hours in a man weighing one hundred and forty pounds is from
six to six and a half pounds. And, again, reasoning from experiments made upon dogs
eighteen hours after feeding, when the fluid which passes up the thoracic duct may be
assumed to be pure, unmixed lymph, the total quantity of lymph alone, produced in the
twenty-four hours by a man of ordinary weight, would be between three and a half and
four pounds (3-864 Ibs.). These estimates can only be accepted as approximative, and
they do not indicate the entire quantity of lymph actually contained in the organism.

There are no very satisfactory recent researches with regard to the physiological
variations in the quantity of lymph. Collard de Martigny made a series of elaborate
investigations a number of years ago, with regard to the effects of starvation upon the
constitution and the quantity of the lymph. He found the lymphatics always distended
with fluid in dogs killed after two days of total deprivation of food. This condition con-
tinued during the first week of starvation ; but, after that time, the quantity in the ves-
sels gradually diminished, and, a few hours before death, the lymphatics and the thoracic
duct were nearly empty. In comparing the quantity of fluid in the lymphatics of the
neck during digestion and absorption with the quantity which they contained soon after
digestion was completed, the same observer found that, while digestion and absorption
were going on actively, the vessels of the neck contained scarcely any fluid ; but the
quantity gradually increased after these processes were completed.

Properties and Composition of Lymph. — Lymph taken from the vessels in various
parts of the system, or the fluid which is discharged from the thoracic duct during the
intervals of digestion, is either perfectly transparent and colorless or of a slightly yellow-
ish or greenish hue. When allowed to stand for a short time, it becomes faintly tinged
with red, and frequently it has a pale rose-color when first discharged. Miscroscopical
examination shows that this reddish color is dependent upon the presence of a few blood-
corpuscles, which are entangled in the clot as the lymph coagulates, thus accounting for

330 ABSOBPTIOF.

the deepening of the color when the fluid has been allowed to stand. The origin of these
red corpuscles has long been a subject of discussion. Their constant presence in lymph
or chyle discharged by fistulous openings has led to the opinion that they are normal
constituents of these fluids ; and this view has been adopted without reserve by those
who assume that the blood-corpuscles are formed from the white corpuscles, or leuco-
cytes. If this view of the formation of the corpuscular elements of the blood be adopted,
there is no good reason why red corpuscles should not be formed from the leucocytes in
the lymph and chyle as well as in the blood itself; particularly as the clear fluid of the
lymph and chyle contains nearly all the principles found in the plasma of the blood. On
the other hand, many physiologists regard the presence of red corpuscles as always acci-
dental ; and, in support of this view, Eobin brings forward the fact that red corpuscles are
never found in lymph taken from a portion of a vessel included between two ligatures.
This is certainly a very strong argument against the constant and normal existence of red
corpuscles in the lymph, particularly as the connection between the lymphatics and the
blood-vessels is very close, and all operations upon the lymphatic system involve dis-
turbances in the circulation. There is no positive evidence of the formation of red cor-
puscles from the leucocytes ; and, if it be the fact that red corpuscles never exist in lymph
taken from a portion of a lymphatic vessel included between two ligatures, it is fair to
assume that the presence of these corpuscles in lymph and chyle is accidental, and that
they are always derived from the blood.

Lymph has no decided or characteristic odor. It is very slightly saline in taste, being
almost insipid. Its specific gravity is much lower than that of the blood. Magendie
found the specific gravity in the dog to be about 1022. Kobin states that the specific
gravity of the defibrinated serum of lymph is 1009. In some recent analyses, by
Dahnhardt, of the lymph taken from dilated vessels in the leg, in the human subject, the
specific gravity was only 1007. The exceedingly low specific gravity in the last instance
would rather lead to the opinion that the fluid was not entirely normal. The difficulty
in obtaining this fluid in a perfectly normal condition from the human subject has ren-
dered it impossible to ascertain its normal specific gravity, even approximative^ ; but it
evidently possesses a density much inferior to that of the blood. The reaction of the
lymph is constantly alkaline.

A few minutes after discharge from the vessels, both the lymph and chyle undergo
spontaneous coagulation. According to Colin, the fluid collected from the thoracic duct
in the large ruminants coagulates at the end of five, ten, or twelve minutes, and sets into
a mass having exactly the form of the vessel in which it is contained. Colin states that
the clot is tolerably consistent, but that there is never any spontaneous separation of
serum. This may be the fact with regard to the lymph and the chyle of the large rumi-
nants, but, in the observations of Dalton, who operated upon dogs and goats, after a few
hours' exposure, the clot contracted to about half its original size, precisely like coagu-
lated blood, expressing a considerable quantity of serum. In one instance, in the dog, the
volume of serum, after twenty-four hours of repose, was about twice that of the contract-
ed clot. Milne- Edwards, quoting from an unpublished memoir presented by Colin to the
Academy of Sciences, in 1858, states that the lymph does not coagulate in the vessels,
even when the circulation is interrupted. This may be the case under ordinary condi-
tions, when the vessels are simply tied ; but it was found by Flandrin, that coagulation
obstructed the tubes which he introduced into the thoracic duct so completely that he
was able to obtain but a small quantity of fluid ; a difficulty which is also mentioned by
Colin, who states that " the clearing of the tube rarely suffices to reestablish the flow, for
the coagnlum formed in the tube is prolonged for a greater or less distance into the in-
terior of the thoracic duct." Coagulation of lymph in the vessels during life, if it occur
at all, must be exceedingly infrequent, notwithstanding that the flow of lymph and chyle
is very slow and irregular, as compared with the circulation of the blood, and is subject,
probably, to frequent interruptions.

COMPOSITION OF LYMPH. 331

Although numerous analyses have been made of lymph from the human subject, the
conditions under which the fluid has been obtained render it probable that, in the ma-
jority of instances, it was not entirely normal. It will be necessary, therefore, to com-
pare these analyses with observations made upon the lymph of the inferior animals ; as,
in the latter, this fluid has been collected under conditions which leave no doubt as to its
normal character. In the experiments of Colin especially, the fluids taken from the tho-
racic duct during the intervals of digestion undoubtedly represented the normal, mixed
lymph collected from nearly all parts of the body ; and the operative procedure in the
large ruminants is so simple as to produce little if any general disturbance. The follow-
ing is an analysis by Lassaigne of specimens of lymph collected by Colin from the thoracic
duct of a cow, under the most favorable conditions :

Composition of Lymph from a Cow.

Water 964*0

Fibrin 0-9

Albumen 28'0

Fatty matter 0'4

Chloride of sodium 5*0

Carbonate, phosphate, and sulphate of soda 1*2

Phosphate of lime 0*5

1,000-0

The proportions given in the table are by no means invariable, the differences in coag-
ulability indicating differences in the proportion of fibrin, and the degree of lactescence
showing great variations in the amount of fatty matters. The table may be taken, how-
ever, as a pretty close approximation of the average composition of the lymph of these
animals, during the intervals of digestion.

The analysis of human lymph which seems to be the most reliable, and in which the
fluid was apparently pure and normal, is that of Gubler and Quevenne. The lymph,
in this case, was collected by Desjardins from a female who suffered from a varicose dila-
tation of the lymphatic vessels in the anterior and superior portion of the left thigh.
These vessels occasionally ruptured, and the lymph could then be obtained in consider-
able quantity. When an opening existed, the discharge of fluid could be arrested at will
by flexing the trunk upon the thigh. Gubler and Quevenne made elaborate analyses of
two different specimens of the fluid, with the following results :

Composition of Human Lymph.

First analysis. Second analysis.

Water 939*87 934'77

Fibrin 0'56 0'63

Caseous matter (with earthy phosphates and traces of iron) 42'75 42*80
Fatty matter (in the second analysis, fusible at 102'3° Fahr.) 3'82 9'20
Hydro-alcoholic extract (containing sugar, and leaving,
after incineration, chloride of sodium, with the phos-
phate and the carbonate of soda) 13-00 12-60

1,000-00 1,000-00

The above analyses show a much larger proportion of solid constituents than was
found by Lassaigne in the lymph of the cow. This excess is pretty uniformly distributed
throughout all the constituents, with the exception of the fatty matters and fibrin; the
former existing largely in excess in the human lymph, especially in the second analysis,
while the latter is smaller in quantity than in the lymph of the cow. It is evident, how-
ever, from a comparison of the two analyses by Gubler and Quevenne, that the composi-

332

ABSORPTION.

tion of the lymph, even when it is unmixed with chyle, is subject to great variations.
The caseous matter given by Gubler and Quevenne is probably equivalent to the albu-
minous matter of other chemists.

The distinctive characters of the different principles found in the lymph do not de-
mand extended consideration, inasmuch as most of them have already been treated of in
connection with the blood. In comparing, however, the composition of the lymph with
tliat of the blood, we are at once struck with the great excess of solid constituents in the
latter fluid.

In all analyses, except those of Lheritier, the organic nitrogenized compounds have
been found to be very much less in the lymph than in the blood. This is generally most
marked with regard to the elements of fibrin ; but, as before stated, the proportion of
all these ingredients is quite variable. On account of this deficiency, lymph is much infe-
rior to the blood in coagulability, and the coagulum, when it is formed, is soft and fria-
ble. There does not appear, however, to be any actual difference between the coagulat-
ing principles of the lymph and of the blood.

Fatty matters have generally been found more abundantly in the lymph than in the
blood ; but their proportion is even more variable than that of the albuminoid substances.
Very little remains to be said concerning the ordinary inorganic constituents of the
lymph. The analyses of Dahnhardt have shown that nearly if not all of the inorganic
matters which have been demonstrated in the blood are contained in the lymph ; and
even a small proportion of iron is given in the analyses by Gubler and Quevenne.

These facts indicate a remarkable correspondence between the composition of the
lymph and that of the blood. All of the constituents of the blood, except the red cor-
puscles, exist in the lymph, the only difference being in their relative proportions.

In addition to the constituents of the lymph ordinarily given, the presence of glucose,
and, more lately, the existence of a certain proportion of urea, have been demonstrated
in this fluid. It has not been ascertained how the sugar contained in the lymph takes its
origin, and its function in this situation is equally obscure.

The presence of urea in considerable quantity in both the chyle and the lymph has
been determined by Wurtz ; and it is thought by Bernard that the lymph is the principal
fluid, if not the only one, by which this excrementitious substance is taken up from the
tissues. Although urea always exists in the blood, its quantity is less than in the lymph.

Corpuscular Elements of the Lymph. — In
every part of the lymphatic system, in addition
to a few very minute fatty granules, there are
found certain corpuscular elements known as
the lymph-corpuscles. These exist, not only in
the clear lymph, but in the opaque fluid con-
tained in the lacteals during absorption. They
are now regarded as identical with the color-
less, globular corpuscles found in the blood,
known under the name of white blood-corpus-
cles, or leucocytes. Although these bodies
have been pretty fully described in treating of
the corpuscular elements of the blood, they
present some peculiarities in the lymphatic sys-
tem, particularly in their mode of development,

PIG. 98.— Chyle taken from the lacteals and tho- which demand consideration.
racic duct of a criminal executed during m-. ,

digestion. (Funke.) Ihe leucocytes found m the lymph and

This figure shows the leucocytes and excessively chyle are rather less uniform in size and gen-
fine granules of fatty emulsion.

eral appearance than the white corpuscles of

Their average diameter is about g-^Yjr of an inch

the blood.

others are as small as

of an inch.

but some are larger, and
Some of these corpuscles are quite clear and

COMPOSITION" OF LYMPH. 333

transparent, presenting but few granulations and an indistinct nuclear appearance in
their centre ; but others are granular and quite opaque. They present the same adhesive
character in the lymph that we have noted in the blood, and frequently they are found
collected in masses in different parts of the lymphatic system. Treated with acetic acid,
the corpuscles generally become swollen and are rendered very transparent, then pre-
senting from one to four or five nuclear concretions in their interior. In all other re-
gards, these bodies present the same characters as the leucocytes of the blood, and they
need not, therefore, be farther described.

We have already alluded to the fact that the lymph-corpuscles are more abundant in
the larger than in the smaller vessels, and that they have been thought to be particu-
larly numerous in the vessels coming from the lymphatic glands. It is nevertheless true
that corpuscles exist even in the smallest vessels, and they are sometimes quite abundant
in lymph which has not passed through the glands. These considerations naturally lead
to the theory of the development of leucocytes in the lymphatics, as well as in the ordi-
nary vascular system, particularly as the constant discharge of lymph and chyle into the
blood-vessels renders it more than probable that most of the leucocytes found in the
blood are derived from the lymph.

The researches of Robin, and of others, by whom his observations have been some-
what extended, have conclusively demonstrated that leucocytes may be developed, under
proper conditions, in a clear, structureless blastema, without the intervention of any
glandular organ ; and, furthermore, it is not necessary that the blastema should be en-
closed in any system of vessels. These facts refute completely the idea that the lymph-
corpuscles are formed exclusively either by the lymphatic glands or by the walls of the
lymphatic vessels. Observations have also shown that leucocytes exist in the blood of the
embryon before any lymphatic vessels can be demonstrated ; a fact which shows that
these bodies may be developed de novo in the blood-plasma.

As regards the lymph, there is no fluid in the body which is placed under conditions
more favorable to the development of leucocytes. It is enclosed in a system of ves-
sels possessing extremely thin walls and undoubtedly subjected to active osmotic cur-
rents. It contains, likewise, a considerable quantity of coagulating matters; and the
proportion of these principles has always been found to influence the rapidity of the devel-
opment of white corpuscles. Its circulation is not very rapid, and the obstacles to the
current which are presented in the lymphatic glands undoubtedly give time for the per-
fection of the structure of leucocytes. It is in this way that the increase in the number
of leucocytes as the lymph passes from the periphery to the larger vessels, and especially
as the fluid passes through the glands, can be explained.

From the fact that leucocytes are developed before the lymphatic system makes its
appearance, that they are found in lymph which has never passed through lymphatic
glands, and from observations showing their spontaneous formation in an amorphous
blastema, it is the inevitable conclusion that nearly if not quite all of the lymph-cor-
puscles are developed by genesis in the clear lymph-plasma, and that their development
goes on as the fluid circulates toward the venous system. With regard to the influence
of the lymphatic glands upon the generation of leucocytes, there is no evidence that the
corpuscles which are developed in the course of the lymph through these organs are not
here, as elsewhere, formed simply from the blastema ; and it is not necessary to invoke
any special formative action taking place in the peculiar structures of the glands.

The function of the lymph-corpuscles is obscure. They are discharged into the blood,
of which they form a constant constituent. Aside from the hypothesis that they are
concerned in the formation of the red blood-disks, no definite and reasonable theory of
their physiological office has been proposed.

In addition to the ordinary leucocytes and a certain number of fatty granules, a few
small, clear globules or granules, about ^Vs °f an iucn m diameter, called sometimes
globulins, are almost constantly present in the lymph. These are insoluble in ether and

334 ABSORPTION".

acetic acid, but are dissolved by ammonia. They are regarded by Robin as a variety of
leucocytes and are described by him as free nuclei. They make their appearance in the
blastema before the larger leucocytes are developed.

Origin and Function of the Lymph. — There can hardly be any doubt concerning the
source of most of the liquid portions of the lymph, for they can be derived only from the
blood. Although the exact relations between the smallest lymphatics and the blood-
vessels have not been made out in all parts of the system, there is manifestly no ana-
tomical reason why the water, mixed with albuminoid matters and holding salts in solu-
tion, should not pass from the blood into the lymphatics ; and this is rendered nearly
certain if it can be demonstrated that the lymphatics partly or entirely surround many
of the blood-vessels, for, under these circumstances, endosmotic and exosmotic currents
would inevitably take place. We have seen, in comparing the composition of the lymph
with that of the plasma of the blood, that the constituents of these fluids are nearly if
not quite identical ; the only variations being in their relative proportions. This is an-
other strong argument in favor of the passage of most of the constituents of the blood
into the lymph.

One of the most important physiological facts in the chemical history of the lymph is
the constant existence of a considerable proportion of urea. This cannot be derived from
the blood, for its proportion is greater in the lymph, notwithstanding that this fluid is
being constantly discharged into the blood-vessels. The urea which exists in the lymph
is derived from the tissues ; it is discharged then into the blood, and is constantly being
removed from this fluid by the kidneys.

The positive facts upon which to base any precise ideas with regard to the general
function of the lymph are not very numerous. From the composition of this fluid, its
mode of circulation, and the fact that it is being constantly discharged into the blood, it
would not seem to have an important function in the active processes of nutrition. The
experiments of Collard de Martigny sustain this view, inasmuch as the quantity and the
proportion of solid constituents of the lymph were rather increased than diminished in
animals that had been deprived of food and drink for several days; while it is well known
that starvation always impoverishes the blood from the first. On the other hand, urea,
one of the most important of the products of destructive metamorphosis of the tissues, is
undoubtedly taken up by the lymph and conveyed in this fluid to the blood. It re-
mains now for future investigations to determine whether other excrementitious princi-
ples may not be taken up from the tissues in the same way — a question of great importance
in its relations to the mechanism of excretion.

What is positively known with regard to the functions of the lymph may be summed
up in a very few words : A great part of its constituents is evidently derived from the
blood, and the relations of these principles to nutrition are not understood. The same
may be said of sugar, also a constant constituent of the lymph, the origin of which, even,
is not known. Urea and, perhaps, other excrementitious matters are taken up from the
tissues by the lymph, and are discharged into the blood, to be removed by the appropriate
organs from the system.

While the blood is evidently the great nutritive fluid of the body, being constantly
regenerated and purified by the absorption of nutritive matters, by respiration, and by the
action of excreting organs, the lymph has an important function in removing from the
tissues some, at least, of the products of physiological decay of the organism.

Chyle.

During the intervals of digestion, the intestinal lymphatics and the thoracic duct carry
ordinary lymph ; but, as soon as absorption of alimentary matters begins, certain nutritive
principles are taken up in quantity by these vessels, and their contents are now known
under the name of chyle. But little remains to be said concerning this fluid, as we have

CHYLE. 335

considered pretty fully the composition and properties of the lymph as well as the different
principles taken up by the lacteal vessels which, with the lymph, form the chyle. Some
general considerations, however, remain concerning the composition and properties of
the chyle as a distinct fluid.

In the human subject and in carnivorous animals, the chyle, taken from the lacteals
near the intestine, where it is nearly pure, or from the thoracic duct, when it is mixed
with lymph, is a white, opaque, milky fluid, of a slightly saline taste, and an odor which
is said to resemble that of the semen. The odor is also said to be characteristic of the
animal from which the fluid is taken ; although this is not very marked, except on the
addition of a concentrated acid, the process employed by Barreul to develop the charac-
teristic odor in the fluids from different animals. Bouisson has found that the peculiar
odor of the dog was thus developed in fresh chyle taken from the thoracic duct.

The chyle taken from a fistula into the thoracic duct is frequently of a more or less
rosy tint ; and it has been a question whether this be due to a peculiar coloring matter or
to the accidental presence of a few red blood-corpuscles. Colin, whose experiments in
collecting chyle from living animals have been very numerous and successful, assumes that
the red coloration is always due to blood-corpuscles coming from the subclavian vein ; the
valve at the orifice of the thoracic duct not being always sufficient to prevent regurgita-
tion. He has never found blood in the fluid taken from the mesenteric vessels or the
receptaculum chyli, and he states, farthermore, that the chyle from these vessels never
becomes colored under the influence of the air or of oxygen.

The reaction of the chyle is either alkaline or neutral. Dalton noted an alkaline re-
action in the chyle of the goat and of the dog ; and a specimen of chyle taken from a
criminal immediately after execution, examined by Rees, was neutral. Leuret and Las-
saigne obtained the fluid from the receptaculum chyli in a man that had died of cerebral
inflammation, and found its reaction to be alkaline.

The specific gravity of the chyle is always less than that of the blood ; but it is very
variable and depends upon the quality of the food and particularly upon the quantity of
liquids ingested. Lassaigne found the specific gravity of a specimen of pure chyle taken
from the mesenteric lacteals of a bull to be 1013, and the specific gravity of the specimen
of human chyle examined by Rees was 1024.

The differences in the appearance of the chyle in different animals depend chiefly upon
the diet. Colin found it excessively milky in the carnivora, especially after fats had been
taken in quantity ; while, hrdogs that were nourished with articles containing but little
fat, its appearance was hardly lactescent. Tiedemann and Gmelin found the chyle almost
transparent in herbivora fed with hay or straw. They also observed the fact that the
chyle was nearly transparent in dogs fed with liquid albumen, fibrin, gelatine, starch, and
gluten ; while it was white in the same animajs fed with milk, meat, bones, etc.

It is impossible to give even an approximative estimate of the entire quantity of pure
chyle taken up by the lacteal vessels. When it finds its way into the thoracic duct, it is
mingled immediately with all the lymph from the lower extremities ; and the immense
quantities of fluid which have been collected from this vessel by Colin and others give
no idea of the quantity of chyle absorbed from the intestinal canal. We cannot, therefore,
attempt to give even an approximate estimate of the absolute quantity of chyle ; but it is
evident that this is variable, depending upon the nature of the food and the quantity of
liquids ingested.

Like the lymph, the chyle, when removed from the vessels, speedily undergoes coagu-
lation. Different specimens of the fluid vary very much as regards the rapidity with
which coagulation takes place. The contents of the thoracic duct taken from the inferior
animals generally coagulate in a few minutes. The first portion of the fluid collected
from the human subject by Dr. Rees (the chyle was collected in this case in two portions)
coagulated in an hour. Received into an ordinary glass vessel, the chyle generally sepa-
rates more or less completely after coagulation into clot and serum, the density and size

336 ABSORPTION.

of the clot indicating the proportion of fibrin. The serum which thus separates is quite
variable in quantity and is never clear. Its milkiness does not depend entirely upon the
presence of particles of emulsified fat, and it is not rendered transparent by ether. It con-
tains, in addition to these particles, numerous leucocytes and organic granules.

Numerous observations have been made with reference to the influence of different
kinds of food upon the chyle ; but these have not been followed by any definite results
that can be applied to the human subject. It is usual to find the chyle fluid in the lac-
teals and in the thoracic duct for many hours after death ; but it soon coagulates after ex-
posure to the air. Although the entire lacteal system is sometimes found, in the human
subject and in the inferior animals, filled with perfectly opaque, coagulated chyle, the
fluid does not often coagulate in the vessels.

Composition of the Chyle. — Analyses of the milky fluid taken from the thoracic duct
during full digestion by no means represent the composition of pure chyle ; and it is only
by collecting the fluid from the mesenteric lacteals, that it can be obtained without a
very large admixture of lymph. In the human subject, it is rare even to have an oppor-
tunity of taking the fluid from the thoracic duct in cases of sudden death during diges-
tion ; and, in most of the inferior animals which have been operated upon, it is difficult to
obtain fluid from the small lacteals in quantity sufficient for accurate analysis. In oper-
ating upon the ox, however, Colin has succeeded in collecting pure chyle in considera-
ble quantity.

The most complete analysis of chyle from the human subject is given by Dr. Eees.
The fluid was taken from the thoracic duct of a vigorous man, a little more than an hour
after his execution by hanging. The subject was apparently in perfect health up to the
moment of his death. The evening before, he ate two ounces of bread and four ounces
of meat. At seven o'clock A. M., precisely one hour before death, he took two cups of
tea and a piece of toast ; and he drank a glass of wine just before mounting the scaffold.
When the dissection was made, the body was yet warm, although the weather was quite
cold. The thoracic duct was rapidly exposed and divided, and about six fluidrachms of
milky chyle were collected. The fluid was neutral and had a specific gravity of 1024.
The following was its proximate composition :

Composition of Human Chyle from the Thoracic Duct.

Water 904*8

Albumen, with traces of fibrinous matter 70-8

Aqueous extractive 5'6

Alcoholic extractive, or osmazome 5'2

Alkaline chlorides, carbonates, and sulphates, with traces of alkaline phosphates

and oxides of iron 4'4

Fatty matters 9-2

1,000-0

Of the constituents of the chyle not given in the ordinary analyses, the most impor-
tant are the urea, which, in all probability, is derived exclusively from the lymph, and
sugar, coming from the saccharine and amylaceous articles of food during the digestion
of these principles.

The difference in chemical composition between the unmixed lymph and the chyle is
very well illustrated in a comparative examination of these two fluids taken from a don-
key. The fluids were collected by Mr. Lane, the chyle being taken from the lacteals
before reaching the thoracic duct. The animal was killed seven hours after a full meal
of oats and beans. The following analyses of the fluids were made by Dr. Rees :

MOVEMENTS OF THE LYMPH AND CHYLE. 337

Composition of Chyle and Lymph before reaching the Thoracic Duct.

Chyle. Lymph.

Water 902'37 965'36

Albuminous matter 35-16 12'00

Fibrinous matter • 3'70 1*20

Animal extractive matter soluble in water and alcohol. . . . , 3-32 2'40

Animal extractive matter soluble in water only 12'33 13-19

Fatty matter 36-01 a trace

g , ( Alkaline chlorides> sulphates, and carbonates, with )

' \ traces of alkaline phosphates, oxide of iron \ " /7'11

1,000-00 1,000-00

The above analyses show a very marked difference in the proportion of solid constitu-
ents in the two fluids. The chyle contains about the same proportion of albumen
and fibrin as the lymph, with a much larger proportion of salts. The proportion of fatty
matters in the chyle is very great, while in the lymph there exists only a trace. The
individual constituents of the chyle given in the above tables do not demand any
farther consideration than they have already received under the head of lymph. The
albuminoid matters are in part derived from the food, and in part from the blood, through
the admixture of the chyle with lymph. The fatty matters are derived in greatest part
from the food. As far as has been ascertained by analyses of the chyle for salts, this
fluid has been found to contain essentially the same inorganic constituents as the
plasma of the blood. All of these principles are rapidly poured into the blood, where
they assist in supplying the material which is being constantly consumed in the process
of nutrition.

The presence of sugar in the chyle was first mentioned by Brande, who described
it, however, rather indefinitely. Glucose was distinctly recognized in the chyle by
Trommer, and its existence in many of the higher orders of animals has since been fully
established by Colin.

Microscopical Characters of the Chyle. — The milky appearance of the chyle as con-
trasted with the lymph is due to the presence of an immense number of excessively
minute fatty granules. The liquid becomes much less opaque when treated with ether,
which dissolves many of the fatty particles. In fact, the chyle of the thoracic duct is
nothing more than lymph to which an emulsion of fat in a liquid containing albuminoid
matters and salts is temporarily added during the process of intestinal absorption. The
quantity of fatty granules in the chyle varies considerably with the diet, and it generally
diminishes progressively from the smaller to the larger vessels, on account of the con-
stant admixture of lymph. The size of the granules is pretty uniformly from g5^00 to
TFT5TF °f an inch. They are much smaller and more uniform in size in the lacteals than
in the cavity of the intestine. Their constitution is not constant; and they are com-
posed of the different varieties of tat which are taken as food, mingled together in varia-
ble proportions.

The ordinary corpuscular elements of the lymph (leucocytes and globulins) are also
found in variable quantity in the chyle. These have already been fully considered.

Movements of the Lymph and the Chyle.

Compared with the current of blood, the movements of the lymph and chyle are
feeble and irregular ; and the character of these movements is such that they are evi-
dently due to a variety of causes. As regards those elements which are derived directly
from the blood, the lymph may be said to undergo a true circulation ; inasmuch as there
is a constant transudation at the peripheral portion of the vascular system, of fluids which
are returned to the circulating blood hy the communications of the lymphatic system
22

338 ABSORPTION.

with the great veins. But we have seen that the lymph is not derived entirely from
the blood, a considerable portion resulting from interstitial absorption in the general lym-
phatic system and from the absorption of certain nutritive matters by the chyliferous
vessels. These are, physiologically, the most important constituents of the lymph and
chyle ; and they are taken up simply to be carried to the blood and do not pass again
from the general vascular system into the lymphatics.

As far as the mode of origin of the lymph and chyle has any bearing upon the move-
ments of these fluids in the lymphatic vessels, there is no difference between the imbibi-
tion of new materials from the tissues or from the intestinal canal, and the transudation
of the liquid portions of the blood; for the mechanism of the passage of liquids from the
blood-vessels is such that the motive power of the blood cannot be felt. An illustration
of this is in the mechanism of the transudation of the liquid portions of the secretions.
The force with which fluids are discharged into the ducts of the glands is enormous and
is independent of the action of the heart, being due entirely to the force of transudation
and secretion. This is combined with the force of imbibition, and with it forms one of
the important agents in the movements of the lymph and chyle. These movements are
studied with great difficulty. One of the first peculiarities to be observed is, that, under
normal conditions, the vessels are seldom distended, and the quantity of fluid which they
contain is subject to considerable variation. As far as the flow in the vessels of medium
size is concerned, the movement is probably continuous, subject only to certain moment-
ary obstructions or accelerations from various causes. But, in the large vessels situated
near the thorax and in those within the chest, the movements are in a marked degree
remittent, or they may even be intermittent. All experimenters who have observed the
flow of lymph or chyle from a fistula into the thoracic duct have noted a constant
acceleration with each act of expiration, and an impulse synchronous with the pulsa-
tions of the heart has been frequently observed.

The fact that the lymphatic system is never distended, and the existence of the
numerous valves by which different portions may become isolated, render it impossible
to estimate the general pressure of fluid in these vessels. This is undoubtedly subject to
great variations in the same vessels at different times, as well as in different parts of the
lymphatic system. It is well known, for example, that the amount of distention of the
thoracic duct is exceedingly variable, its capacity not infrequently being many times
increased during active absorption. At the same time it is difficult to attach a manometer
to any part of the lymphatic system without seriously obstructing the circulation and
consequently exaggerating the normal pressure ; but the force with which liquids pene-
trate these vessels is very great. This is illustrated by the experiment of ligating the
thoracic duct ; for, after this operation, unless communicating vessels exist by which the
fluids can be discharged into the venous system, their accumulation is frequently suffi-
cient to rupture the vessel.

The general rapidity of the current in the lymphatic vessels has never been accurate-
ly estimated. As a natural consequence of the variations in the distention of these ves-
sels, the rapidity of the circulation must be subject to constant modifications. Beclard,
making his calculation from the experiments of Colin, who noted the quantity of fluid
discharged in a given time from fistulous openings into the thoracic duct, estimates that
the rapidity of the flow in this vessel is about one inch per second. This estimate, how-
ever, can be only approximative ; and it is evident that the flow must be much less rapid
in the vessels near the periphery than in the large trunks, as the liquid moves in a space
which becomes rapidly contracted as it approaches the openings into the venous system.

Causes of the Movements of the Lymph and Chyle.

Various influences combine to produce the movements of fluids in the lymphatic sys
tern, some being constant in their operation, and others, intermittent or occasion*
These will be considered, as nearly as possible, in the order of their relative importance.

MOVEMENTS OF THE LYMPH AND CHYLE. 339

Influence of the Forces of Endosmosis and Transudation (vis a tergo). — The forces
of endosmosis and transudation are undoubtedly the main causes of the lymphatic circu-
lation, more or less modified, however, by influences which may accelerate or retard
the current ; but this action is capable in itself of producing the regular movement of
the lymph and chyle. It is a force which is in constant activity, as is seen in cases of
Hgation of the thoracic duct, an operation which must finally abolish all other forces
which aid in producing the lymphatic circulation. When the receptaculum cliyli is rup-
tured as a consequence of obstruction of the thoracic duct, the vessel gives way as the
result of the constant endosmotic action, in the same way that the exposed membranes
of an egg may be ruptured by endosmosis, when immersed in water.

We have already alluded to the influence of transudation from the blood-vessels and
have compared it to the force with which the secretions are discharged into the ducts of
the glands ; and in placing this, with the force of endosmosis, at the head of the list of the
agents which effect the lymphatic circulation, its importance is not over-estimated. This
conclusion can hardly b« avoided when we consider the anatomy of the lymphatic sys-
tem. The situations in which the endosmotic force originates are at the periphery, where
the single, homogeneous wall of the plexus is excessively thin, and where the extent of
absorbing surface is enormous. If liquids can penetrate with such rapidity and force
through the walls of the blood-vessels, where their entrance is opposed by the pressure
of the fluids already in their interior, they certainly must pass without difficulty through
the walls of the lymphatics, where there is no lateral pressure to oppose their entrance,
except that produced by the weight of the column of liquid. This pressure is readily
overcome ; and the numerous valves in the lymphatic system effectually prevent any
backward current. The liquid that passes into the lymphatics by endosmosis or by
transudation produces movement by displacing an equal bulk of liquid contained in the
vessel. We observe with the microscope the rapid filling and rupture of microscopic
cells when immersed in water ; and the rough experiments by which the operation of
endosmosis is ordinarily illustrated, in which the extent of endosmotic surface is infinite-
ly small as compared with that of the lymphatic system, exhibit a current of considerable
force and rapidity. When we remember that the infinitely numerous lymphatic radicles
are bathed in fluids which undoubtedly pass into their interior with great facility, and
when we compare the probable extent of this endosmotic surface with the diameter of the
thoracic duct, we can hardly be surprised that this force should be capable of producing a
movement in the great trunk at the rate of an inch per second. The great elasticity of
the vessels and the fact that they are never completely filled allow of considerable dis-
tention of isolated portions of the lymphatic system when there is any obstruction to the
current that is not readily overcome. In this way we account for the variations in the
flow of the lymph and chyle which are of such constant occurrence.

Influence of the Contractile Walls of the Vessels. — In treating of the anatomy of the
lymphatic system, it has already been observed that the large vessels and those of me-
dium size are provided with unstriped muscular fibres and are endowed with contractil-
ity. This fact has been demonstrated by physiological as well as anatomical investiga-
tions. Beclard states that he has often produced contractions of the thoracic duct by
the application of the two poles of an inductive apparatus. It is not uncommon to see
the lacteals become reduced in size to a mere thread, even while under observation.
Although experiments have generally failed to demonstrate any regular rhythmical con-
tractions in the lymphatic system, it is probable that the vessels contract upon their con-
tvnt*, when they are unusually distended, and thus assist the circulation, the action of the
valves opposing a regurgitating current. This action, however, cannot have any consid-
erable and regular influence upon the general current.

Influence of Pressure from Surrounding Parts. — Contractions of the ordinary vol-
untary muscles, compression of the abdominal organs by contraction of the abdominal

340 ABSORPTION.

muscles, peristaltic movements of the intestines, and pulsations of large arteries situ-
ated against the lymphatic trunks, particularly the thoracic aorta, are all capable of
increasing the rapidity of the circulation of the lymph and chyle. *

The contractions of voluntary muscles assist the lymphatic circulation in precisely
the way in which they influence the flow of blood in the venous system; and we have
nothing to add regarding this action to what has already been said on this subject in
connection with the venous circulation.

Increase in the flow of chyle in the thoracic duct, as the result of compression of the
abdominal organs or of kneading the abdomen with the hands, was observed by Magen-
die, and the fact has been confirmed in all recent experiments on this subject. The same
effect, though probably less in degree, is produced by the peristaltic contractions of the
intestines.

When a tube is introduced into the upper part of the thoracic duct, it is frequently
the case that the fluid is discharged with increased force at each pulsation of the heart.
This was frequently observed by Dalton in his experiments on the thoracic duct, and he
describes the jets as being " like blood coming from a small artery when the circulation
is somewhat impeded." This impulse is due to compression of the thoracic duct as it
passes under the arch of the aorta. Its influence upon the general current of the lymph
and chyle is probably insignificant, but the fact attracted the attention of Haller, who
attached to it a great deal more importance than it is now believed to possess.

Influence of the Movements of Respiration. — While the vis a tergo must be regarded
as by far the most important agent in the production of the lymphatic circulation, the
movements of fluids in the thoracic duct receive constant and important aid from the
respiratory acts. This fact has long been recognized ; and in the works of Haller will
be found a full discussion of the influence of the diaphragm and of the movements of the
thorax upon the circulation of chyle. The observations of Colin on this subject are
most valuable, as he was the first to successfully establish a fistula into the thoracic duct
in large animals. He always found a marked remittency in the flow of chyle from a fis-
tula into the thoracic duct, which was absolutely synchronous with the movements of
respiration. With each act of expiration, the fluid was forcibly ejected, and, with inspira-
tion, the flow was very much diminished or even arrested. These impulses became much
more marked when respiration was interfered with and the efforts became violent. The
intermittency of the current was sometimes so decided, that the pulsations were repeated
in a long elastic tube attached to the canula for the purpose of collecting the fluid.

The amount of influence exerted by the respiratory movements upon the flow of the
lymph and chyle can be best appreciated by examining carefully the mechanism of its
operation.

With each act of inspiration, all the liquids, as well as the air, are drawn toward the
cavity of the thorax. In this way, the thoracic duct is dilated and then becomes most
distended with fluid. At the same time, the flow of lymph from the right lymphatic
duct into the right subclavian vein is increased. After the thoracic duct has been thus
dilated in inspiration, at the moment of expiration, in common with all the other parts
contained within the thorax, it undergoes compression ; the valves prevent the reflux of
its contents, and, as a necessary consequence, the fluid is then discharged with increased
force into the left subclavian vein. It can be readily understood how the act of inspira-
tion, while it has a tendency to fill the thoracic duct from below, opposes the discharge
of fluid from a fistula.

From all these considerations, it is evident that, although there are many circum-
stances capable of modify ing the currents in the lymphatic system, the regular flow of the
lymph and chyle depends chiefly upon the vis a tergo ; but the vessels themselves some-
times undergo contraction, and they are subject to occasional compression from sur-
rounding parts, which, from the existence of numerous valves in the vessels, must favor

SECRETION IN GENERAL. 341

the current toward the venous system. The alternate dilatation and compression of the
thoracic duct with the acts of respiration likewise aid the circulation, and they are more
efficient than any other force, except the vis a tergo. The action of the valves is pre-
cisely the same in the lymphatic as in the venous system.

CHAPTER XI.

SECRETION.

General considerations — Differences between the secretions and fluids containing formed anatomical elements— Classi-
fication of the secretions— Mechanism of the production of the true secretions — Mechanism of the production of
the excretions — General structure of secreting organs — Anatomical classification of glandular organs— Classification
of the secreted fluids— Secretions proper (permanent fluids; transitory fluids)— Excretions — Fluids containing
formed anatomical elements — Physiological anatomy of the serous and synovial membranes — Pericardial, peri-
toneal, and pleural secretions — Synovial fluid — Mucus — Mucous membranes — Mechanism of the secretion of mucus
—Composition and varieties of mucus— Microscopical characters of mucus— General function of mucus— Non-
absorption of certain soluble substances, particularly venoms, by mucous membranes — Sebaceous fluids— Physio-
logical anatomy of the sebaceous, ceruminous, and Meibotnian glands — Ordinary sebaceous matter— Smegma of
the prepuce and of the labia minora — Vernix caseosa — Cerumen— Meibomian secretion — Function of the Meibo-
mian secretion — Mammary secretion — Physiological anatomy of the mammary glands — Condition of the mam-
mary glands during the intervals of lactation — Structure of the mammary glands during lactation — Mechanism
of the secretion of milk — Conditions which modify the lacteal secretion — Quantity of milk — General characters
of milk — Microscopical characters of milk — Composition of milk — Variations in the composition of milk — Colos-
trum—Lacteal secretion in the newly-born.

Secretion in General.

THE phenomena classed by physiologists under the head of secretion are intimately
connected with the general process of nutrition. In the sense in which the term secre-
tion is usually received, it embraces most of the processes in which there is a separation
of material from the blood or a formation of a new fluid out of matters furnished by the
blood. The blood itself, the lymph, and the chyle, are no longer regarded as secre-
tions. These fluids, like the tissues, are permanent constituents of the organism, under-
going those changes only that are necessary to their proper regeneration. They are
likewise characterized by the presence of certain formed anatomical elements, which
themselves undergo the processes of molecular destruction and regeneration. These
characters are not possessed by the secretions. As a rule, the latter are homogeneous
fluids, without formed anatomical elements, except as accidental constituents, such as the
desquamated epithelium in mucus or in sebaceous matter. The secretions are not per-
manent, self-regenerating fluids, except when they perform simply a mechanical function,
as the humors of the eye, or the liquids in serous and synovial cavities. They are either
discharged from the body, when they are called excretions, or, after having performed
their proper function as secretions, are taken up again in a more or less modified form
by the blood.

With the exception of those fluids which have a function almost entirely mechanical,
the relations of the secretions to nutrition are so close, that the production of many of
them forms almost a part of this great function. It is difficult, for example, to con-
ceive of nutrition without the formation of the characteristic constituents of the urine,
the bile, and the perspiration; and it is impossible, indeed, to study satisfactorily the
phenomena of nutrition without considering fully the various excrementitious principles,
such as urea, cholesterine, creatine, creatinine, etc., for the constant formation and dis-
charge of these principles by disassimilation create the necessity for the deposition of
new matter in nutrition. Again, the most important of the secretions, as contradistin-
guished from the excretions, are concerned in the preparation of food by digestion, for
the regeneration of the great nutritive fluid.

342 SECRETION".

As would naturally be supposed, the general mechanism of secretion was very im-
perfectly understood early in the history of physiology, when little was known of the
circulation, the functions of the digestive fluids, and particularly »f nutrition. From its
etymology, the term should signify separation ; hut it is now known that many of the
secreted fluids are formed in the glands and are not simply separated or filtered from
the hlood. Physiologists now regard secretion as the act by which fluids, holding cer-
tain solid principles in solution, and sometimes containing liquid nitrogenized princi-
ples, but not necessarily possessing formed anatomical elements, are separated from the
blood or are manufactured by special organs out of materials furnished by the blood.
These organs may be membranes, follicles, or collections of follicles or tubes. In the
latter instance they are called glands. The liquids thus formed are called secretions;
and they may be destined to perform some function connected with nutrition or may he
simply discharged from the organism.

It is not strictly correct to speak of formed anatomical elements as the results of
secretion, except, perhaps, in the case of the fatty particles in the milk. The leucocytes
found in pus, the spermatozoids of the seminal fluid, and the ovum, which are sometimes
spoken of as products of secretion, are real, anatomical elements developed in the way in
which these structures are ordinarily formed. It has been conclusively demonstrated,
for example, that leucocytes, or pus-corpuscles, are developed in a clear blastema, with-
out the intervention of any special secreting organ, and that spermatozoids and ova are
generated by a true development in the testicles and the ovaries, by a process entirely
different from ordinary secretion. It is important to recognize these facts in studying
the mechanism by which the secretions are produced. It is true that, in some of the
secretions, as the sebaceous matter, a certain quantity of epithelium, more or less disin-
tegrated, is found, but this is to be regarded as an accidental admixture of desquamated
matter and not as a product of secretion.

Classification of the Secretions. — The secretions are capable of a physiological clas-
sification, dependent upon differences in their functions and in the mechanism of their pro-
duction. Investigations within the past few years have shown that these differences are
very distinct.

Certain of the fluids are formed by special organs, and have important functions to
perform which do not involve their discharge from the organism. These may be classed
as the true secretions ; and the most striking examples of such are the digestive fluids.
Each one of these fluids is formed by a special gland or set of glands, which generally
has no other function ; and they are never produced by any other part. It is the gland
which produces the characteristic element or elements of the true secretions out of mate-
rials furnished by the blood ; and the principles thus formed never preexist in the circu-
lating fluid. The function which these fluids have to perform is generally intermittent ;
and, when this is the case, the flow of the secretion is intermittent, taking place only
when its action is required. When the parts which produce one of the true secretiona
are destroyed, as may be sometimes done in experiments upon living animals, the charac-
teristic elements of this particular secretion never accumulate in the blood, nor are they
formed vicariously by other organs. The simple effect of such an experiment is absence
of the secretion and disturbances consequent upon the loss of its function.

Certain other of the fluids are composed of water, holding one or more characteristic
principles in solution, which result from the physiological waste of the tissues. These
principles have no function to perform in the animal economy and are simply separated
from the blood to be discharged from the body. These may be classed as excretions,
the urine being the type of fluids of this kind. The characteristic principles of the excre-
mentitious fluids are formed in the tissues, as one of the results of the constant changes
going on in all organized, living structures. They are not produced in the glands by
which they are eliminated but appear in the secretion as the result of a sort of elective

PRODUCTION OF THE TRUE SECRETIONS. 343

filtration from the blood. They always preexist in the circulating fluid and may be elim-
inated, either constantly or occasionally, by a number of organs. As they are produced
continually in the substance of the tissues and are taken up by the blood, they are con-
stantly discharged into the substance of the proper eliminating organs. When the glands
which thus eliminate these principles are destroyed or when their functions are serious-
ly impaired, the excrementftious matters may accumulate in the blood and give rise to
certain toxic phenomena. These effects, however, are often retarded by the vicarious
discharge of such principles by other organs.

There are some fluids, as the bile, which perform important functions as secretions,
and which nevertheless contain certain excrementitious matters. In these instances, it is
only the excrementitious matters that are discharged from the organism.

In the sheaths of some tendons and of muscles, the substance of muscles, and in
some other situations, are found fluids which simply moisten the parts, and which contain
very little organic matter, with but a small proportion of inorganic salts. Although
these are frequently spoken of as secretions, they are produced generally by a simple,
mechanical transudation of certain of the constituents of the blood through the walls
of the vessels. Still, it is difficult to draw a line rigorously between transudation and
some of the phenomena of secretion; particularly as late experiments upon dialysis have
shown that simple, osmotic membranes are capable of separating complex solutions, allow-
ing certain constituents to pass much more freely than others. This fact explains why
the transuded fluids do not contain all the soluble principles of the blood in the propor-
tions in which they exist in the plasma. All the secreted fluids, both the true secretions
and the excretions, contain many of the inorganic salts of the blood-plasma.

Mechanism of the Production of the True Secretions. — Although the characteristic ele-
ments of the true secretions are not to be found in the blood or in any other of the animal
fluids, they can generally be extracted in quantity from the glands, particularly during
their intervals of repose. This fact has been repeatedly demonstrated with regard to
many of the digestive fluids, as the saiiva, the gastric juice, and the pancreatic juice ; and
artificial fluids, possessing many of the physiological properties of the natural secretions,
have been prepared by simply infusing the glandular tissue in water. There can be no
doubt, therefore, that, even during the periods when the secretions are not discharged,
the glands are taking from the blood matters which are to be transformed into principles
characteristic of the individual secretions, and that this process is constant. Extending
our inquiries into the nature of the process by which these peculiar principles are formed,
it is found to bear a close resemblance to the general act of nutrition. There are certain
anatomical elements in the glands which have the power of selecting the proper material
from the blood and causing them to undergo a peculiar transformation ; in the same way
that the muscular tissue takes from the great nutritive fluid albuminoid matters and
transforms them into its own substance. The exact nature of this property is unex-
plained. It belongs to the class of phenomena observed in living structures only and is
sometimes called vital.

In all of the secreting organs, a variety of epithelium is found, called glandular, which
seems to possess the power of forming the peculiar elements of the different secretions.
Inasmuch as the epithelial cells lining the tubes or follicles of the glands constitute the
only peculiar structures of these parts, the rest being made up of basement-membrane,
connective tissue, blood-vessels, nerves, and other structures which are distributed gen-
erally in the economy, we should expect that these alone would contain the elements of
the secretions. In all probability this Is the fact ; and, with regard to some of the glands,
this has been satisfactorily demonstrated. It has been found, for example, that the liver-
cells contain the glycogenic matter formed by the liver ; and it has been farther shown
that, when the cellular structures of the pancreas have been destroyed, the secretion is
no longer produced. There can be hardly any doubt with regard to the application of

344 SECRETION.

this principle to the glands generally, both secretory and excretory. Indeed, it is well
known to pathologists, that, when the tubes of the kidney have become denuded of their
epithelium, they are no longer capable of separating from the blood the peculiar constitu-
ents of the urine.

With regard to the origin of the principles peculiar to the true secretions, it is impos-
sible to entertain any other view than that they are produced in the epithelial structures
of the glands ; and the old idea that they exist ready-formed in the blood cannot be
maintained. While the secretions contain inorganic salts in solution, transuded from the
blood, the organic constituents, such as pepsin, ptyaline, pancreatine, etc., are readily
distinguished from all other albuminoid principles by their peculiar physiological proper-
ties; although some of them are apparently identical with albumen in their ultimate
composition and in most of their chemical reactions.

It may be stated, then, as a general proposition, that the characteristic elements of
the true secretions, as contradistinguished from the excretions, are formed de novo by the
epithelial structures of the glands, out of material furnished by the blood. Their forma-
tion is by no means confined to what is usually termed the period of functional activity
of the glands, or the time when the secretions are poured out, but it takes place more
or less constantly when no fluid is discharged.

It is more than probable that the formation of the elements of the secretions takes place
with fully as much activity in the intervals of secretion as during the discharge of fluid ;
and most of the glands connected with the digestive system seem to require certain inter-
vals of repose and are capable of discharging their secretions for a limited time only.

When a secreting organ is called into functional activity — like the gastric mucous
membrane, or the pancreas, upon the introduction of food into the alimentary canal — a
marked change in its condition takes place. The circulation in the part is then very
much increased in activity, thus furnishing water and the inorganic elements of the
secretion. This difference in the vascularity of the glands during their activity is very
marked when the organs are exposed in a living animal and is one of the important facts
bearing upon the mechanism of secretion. Beaumont observed this in his experiments
on St. Martin and was the first to show conclusively that the gastric juice is secreted only
when food is taken into the stomach or when some stimulus is applied to its mucous
membrane. Bernard, in his experiments upon the pancreas, noted the pale appearance
of the gland during the intervals of digestion and its reddened and congested condition
whe,n the secretion flowed from the duct ; and these observations have been confirmed
by all who have experimented upon the glands in living animals.

In later experiments upon the circulation in the salivary glands and its relation to
secretion, Bernard has fully investigated the variations in the vascular supply to the
glands, with the most definite and satisfactory results. His observations were made
chiefly upon the submaxillary gland in dogs ; and he has shown that, during the func-
tional activity of this organ, if a tube be introduced into the vein, the quantity of blood
which may be collected in a given time is four or five times that which is discharged in
the intervals of secretion. It was ascertained, also, that the venous blood coming from
the gland contained much less water than the arterial blood ; and, on comparing the
quantity of water lost by the blood in its passage through the gland in a given time with
the quantity discharged in the saliva, they were found to exactly correspond.

The differences in the quality and the composition of the blood coming from the
glands during their repose and their activity have an important bearing upon the mech-
anism of secretion. As far as the composition is concerned, these differences appear to
be dependent mainly upon the modifications in the circulation. When the gland is in
repose, the blood coming from it has the usual dark, venous hue and contains the ordinary
proportion of carbonic acid ; but, during secretion, when the quantity of blood passing
through the organ is increased, the color is nearly as bright as that of arterial blood, and
the proportion of carbonic acid is very small. At this time, also, the blood is frequently

PRODUCTION OF THE TRUE SECRETIONS. 345

discharged from the vein pulsatim to the distance of several inches. The cause of this
difference in color is very easily understood. During the intervals of secretion, the blood
is sent to the gland for the purposes of nutrition and the manufacture of the elements of
the secretion. It then passes through the part in moderate quantity and undergoes the
usual change from arterial to venous, in which a great part of the oxygen disappears and
carbonic acid is formed; but, when secretion commences, the ordinary nutritive changes
are not sufficient to deoxidize the increased quantity of blood, and the venous charatcer
of the blood coming from the part is very much less marked. These facts enable us to
form a pretty clear idea of the mechanism of secretion ; although the exact nature of
the forces which effect the changes of the organic principles of the blood into the charac-
teristic elements of the secretions is not understood. Experiments, however, have shown
that, in the act of secretion, there are two tolerably distinct processes :

1. It may be assumed that, at all times, the peculiar secreting cells of the glands are
forming, more or less actively, the elements of the secretions, which may be washed out
of the part or extracted by maceration ; but, during the intervals of secretion, the quan-
tity of blood received by the glands is relatively small.

2. In obedience to the proper stimulus, when a gland takes on secretion, the quantity
of blood which it receives is four or five times greater than it is during repose. At that
time, water, with certain of the salts of the blood in solution, passes into the secreting
structure, takes up the characteristic elements of the secretion, and fluid is discharged
by the duct.

In all the secretions proper, there are intervals, either of complete repose, as is the
case with the gastric juice or the pancreatic juice, or periods when the activity of the
secretion is very greatly diminished, as in the saliva. These periods of repose seem to
be necessary to the proper performance of the function of the secreting glands ; forming
a marked contrast with the constant action of the organs of excretion. It is well
known, for example, that the function of digestion is seriously disturbed when the act is
too prolonged from the habitual ingestion of an excessive quantity of food.

From the considerations already mentioned, it is evident that the secretions, as a
rule, are formed by the epithelial structures of the glands. There has been a great deal
of speculation with regard to the mechanism of this action of the cells. As we before
remarked, this question cannot be considered as settled. It does not seem probable that
the cells are ruptured during secretion and discharge their contents into the ducts, for,
under these circumstances, we should expect to find some of their structure in the
secreted fluid ; whereas, aside from accidental constituents, the secretions are homogene-
ous and do not contain any formed anatomical elements. There is no good reason for
supposing that this action takes place and that more or less of the glandular epithelium
is destroyed whenever secretion occurs ; and, in the present state of our knowledge, we
can only assume that the secreting cells induce certain transformations in the organic
elements of the blood and modify transudation, without pretending to understand the
exact nature of this process.

The theory, that the discharge of the secretions is due simply to mechanical causes and
is attributable solely to the increase in the pressure of blood, cannot be sustained. Press-
ure undoubtedly has considerable influence upon the activity of secretion ; but the flow
will not always take place in obedience to simple pressure, and secretion may be induced
for a limited time without any increase in the quantity of blood circulating in the gland.

The glands possess a peculiar irritability, which is manifested by their action in
response to proper stimulation. During secretion, they generally receive an increased
quantity of blood; but this is not indispensable, and secretion may be excited without
any modification of the circulation. This irritability will disappear when the artery sup-
plying the part with blood is ligated for a number of hours; and secretion cannot tlu-n
be excited, even when the blood is again allowed to circulate. If the gland be not
deprived of blood for too long a period, the irritability is soon restored; but it may be

346 SECRETION.

permanently destroyed by depriving the part of blood for a long time. These facts
are very striking and they show a certain similarity between glandular and muscular
irritability, although their properties are manifested in very different ways.

Mechanism of the Production of the Excretions. — Certain of the glands have the func-
tion of separating from the blood excreinentitious matters, which are of no use in the
economy and are simply to be discharged from the system. These matters, which will
be fully considered, both in connection with the fluids of which they form a part and
under the head of nutrition, are entirely different in their mode of production from the
characteristic elements of the secretions. The formation of excrementitious principles
takes place in the tissues and is connected with the general process of nutrition ; and in
the excreting glands there is simply a separation of matters already formed. The action
of the excreting organs being constant, there is not that regular, periodic increase in the
activity of the circulation which is observed in secreting organs ; but it has been observed
that the blood which comes from the kidneys is nearly as red as arterial blood, showing
that the quantity of blood which this organ receives is greater than is required for mere
nutrition, the excess, as in the secreting organs, furnishing the water and inorganic salts
that are found in the urine. It has also been shown that, when the secretion of urine is
interrupted, the blood of the renal veins becomes dark, like the blood in the general
venous system.

The function of excretion is not, under all conditions, confined to the ordinary excre-
tory organs. When their action is disturbed, certain of the secreting glands, as the
follicles of the stomach and intestine, may for a time eliminate excrementitious matters ;
but this is abnormal and is analogous to the elimination of foreign matters from the
blood by the glands.

Influence of the Composition and Pressure of the Blood upon Secretion. — Under nor-
mal conditions, the composition of the blood has little to do with the action of the secret-
ing organs, as it simply furnishes the material out of which the characteristic principles
of the secretion are formed ; but, when certain foreign matters are taken into the system
or are injected into the blood-vessels, they are eliminated by the different glandular
organs, both secretory and excretory. These organs seem to possess a power of selection
in the elimination of different substances. Thus, sugar, ferrocyanide of potassium, and
the salts of iron, are eliminated in greatest quantity by the kidneys ; the salts of iron, by
the kidneys and the gastric tubules ; and iodine, by the salivary glands.

The act of secretion is almost always accompanied with an increase in the pressure of
blood in the vessels supplying the glands; and it has been shown, on the other hand,
that an exaggeration in the pressure, if the nerves of the glands do not exert an opposing
influence, increases the activity of secretion. The experiments of Bernard on this point
show the influence of pressure upon the salivary and the renal secretion, particularly the
latter. After inserting a tube into one of the ureters of a living animal, so that the"
activity of the renal secretion could be accurately observed, the pressure in the renal artery
was increased by tying the crural and the brachial. It was then found that the flow of
urine was markedly increased. The pressure was afterward diminished by the abstrac-
tion of blood, which was followed by a corresponding diminution in the quantity of urine.
The same phenomena were observed in analogous experiments upon the submaxillary
secretion. These striking facts, as we have already seen, do not demonstrate that secretion
is due simply to an increase in the pressure of blood in the glands, although this undoubt-
edly exerts an important influence. It is necessary that every condition should be
favorable to the act of secretion for this influence to be effective. Experiments have
shown that pain is capable of completely arresting the secretion of urine, operating
undoubtedly through the nervous system. If the flow of urine be arrested by pain,
an increase in the pressure of blood in the part fails to influence the secretion. To illus-

INFLUENCE OF THE NERVOUS SYSTEM UPON SECRETION. 347

trate this fact more fully, Bernard divided the nerves on one side, through which, the
reflex nervous action was communicated to the kidney, leaving the other side intact. He
then found that increase in the arterial pressure, accompanied with pain, diminished the
flow of urine upon the sound side, through which the nervous action could operate, and
increased it upon the other.

The influence of pressure of hlood upon secretion may, then, he summed up in a few
words : There is always an increase in the activity of secretion when the pressure of
blood in the glands is increased, and a diminution when the pressure is reduced ; except
when there is some modifying influence operating through the nervous system.

Influence of the Nervous System upon Secretion. — The fact that the secretions are gen-
erally intermittent in their flow, being discharged in obedience to impressions which are
made only when there is a demand for the exercise of their functions, would naturally
lead to the supposition that they are regulated, to a great extent, through the nervous
system; particularly as it is now well established that the nerves are capable of modify-
ing and regulating local circulations. The same facts apply, to a certain extent, to the
excretions, which are also subject to considerable modifications. A few years ago,
indeed, there was considerable discussion regarding a subdivision of the reflex system of
nerves, which was supposed to preside over secretion and was called the excito-secre-
tory system. The facts which led to the description of this system of nerves had long
been observed, and they simply illustrated the production of the secretions in response to
irritation.

Experiments have clearly demonstrated the importance of the nervous influence in the
production of the secretions ; but the observations of Bernard show that the effects are
produced mainly by increasing the activity of the circulation in the glands. This takes
place in greatest part through filaments from the sympathetic system, which are dis-
tributed to the muscular coats of the arteries of supply. When these filaments are
divided, the circulation is increased here, as in other situations, and secretion is the result ;
and, if the extremity of the nerve connected with the gland be galvanized, contraction
of the vessels follows, and the secretion is arrested.

With regard to many of the glands, Bernard has shown that the influence of the sym-
pathetic is antagonized by nerves derived from the cerebro-spinal system, which latter he
calls the motor nerves of the glands. The motor nerve of the submaxillary is the chorda
tympani ; and, as both this nerve and the sympathetic, together with the excretory duct
of the gland, can be easily exposed and operated upon in a living animal, most of the
experiments of Bernard have been performed upon this gland. When all these parts are
exposed and a tube is introduced into the salivary duct, division of the sympathetic induces
secretion, with an increase in the circulation in the gland, the blood in the vein becoming
red. On the other hand, division of the chorda tympani, the sympathetic being intact,
arrests secretion, and the venous blood coming from the gland becomes dark. If the
nerves be now galvanized alternately, it will be found that galvanization of the sympa-
thetic produces contraction of the vessels of the gland and arrests secretion, while the
stimulus applied to the chorda tympani increases the circulation and excites secretion.
Enough is known of the nervous influences which modify secretion, to admit of the
inference that all the glands are possessed of nerves through which reflex phenomena,
affecting their secretions, take place. It is the motor, or functional nerve of the gland
through which the reflex action takes place ; the influence of the sympathetic being con-
stant and the same as in other parts where it is distributed to blood-vessels.

As reflex phenomena involve the action of a nervous centre, it becomes an interesting
question to determine whether any particular parts of the central nervous system preside
over the various secretions. We must refer again to the experiments of Bernard for an
elucidation of this question. If a puncture be made in the space included between the
origin of the pneumogastrics and the auditory nerves, in the floor of the fourth ventricle,

348 SECEETION.

there is an increase in the discharge of urine, with an excretion of sugar due to an exag-
geration in the sugar-producing function of the liver. Irritation applied a little higher,
toward the pons Varolii and just posterior to the origin of the fifth pair of nerves, is
followed hy a great increase in the activity of the salivary secretion.

Mental emotions, pain, and various circumstances, the influence of which upon secre-
tion has long been observed, operate through the nervous system. Numerous familial-
instances of this kind are quoted in works on physiology : such as the secretion of tears;
arrest or production of the salivary secretions ; sudden arrest of the secretion of the
mammary glands, from violent emotion ; increase in the secretion of the kidneys or of the
intestinal tract, from fear or anxiety ; with other examples which it is unnecessary to
enumerate.

The effects of destruction of the nerves distributed to the parenchyma of some of the
glandular organs are very curious and interesting. Miiller and Peipers destroyed the
nerves distributed to the kidney and found that, not only was the secretion arrested
in the great majority of instances, but the tissue of the kidneys became softened and
broken down. These experiments have been repeated by Bernard. He found that ani-
mals operated upon in this way died, and that the tissue of the kidney was broken down
into a fetid, semifluid mass. After division of the nerves of the salivary glands, the organs
became atrophied, but they did not undergo the peculiar putrefactive change which was
observed in the kidneys. The same effect was produced when the nerve was paralyzed by
introducing a few drops of a solution of woorara at the origin of the little artery which
is distributed to the submaxillary gland.

General Structure of Secreting Organs. — In treating of the mechanism of secretion
and excretion, it has been evident that all glandular organs must be supplied with blood
to furnish the materials for secretion, and be provided with epithelium, which changes
these matters into the characteristic elements of the secretions. We can understand how
certain of the liquid and saline constituents of the blood can escape by exosmosis through
the homogeneous walls of the capillaries, but the more complex secreted fluids require
for their formation a different kind of action ; although, in the act of secretion, there is
considerable transudation of liquid and saline matters, which take up in their course the
peculiar principles formed by the cells.

Although it is somewhat difficult to draw a line between transudation and the simplest
forms of secretion, it may be assumed, in general terms, that fluids which are exhaled
directly from the blood-vessels, without the intervention of glandular apparatus or of a
secreting membrane, are transudations ; while all fluids produced by simple membranes
or by follicles, or which are discharged from the ducts of glands, are secretions. This
division places the intermuscular fluid and the fluid found in all soft tissues among the
transudations, and the serous and synovia! fluids among the secretions.

The serous and synovial membranes present the simplest form of a secreting apparatus.
Blood is supplied to them in small quantity, and, on their free surfaces, are arranged one
or two layers of epithelial cells which effect the slight changes that take place in the
trans'ided fluids. In some of the serous membranes, as the pleura and peritoneum, the
amount of secretion is very small ; but others, like the serous pericardium and the synovial
membranes, secrete a considerable quantity of fluid. The action of all of these membranes
may become exaggerated, as a pathological condition, and the amount of their secretions
is then very large.

Anatomists have now a pretty clear idea of the structure of what are called the
glandular organs ; and it will be seen that they simply present an arrangement by which
the secreting surface is increased, and at the same time compressed, as it were, into a
comparatively small space. The mucous follicles, for example, are simple inversions of a
portion of the mucous membrane ; while the ordinary racemose glands are nothing more
than collections of follicles around the extremities of excretory ducts. These ideas con-

CLASSIFICATION OF GLANDULAR ORGANS. 349

cerning the general anatomy of the glands date from the observations of Malpighi, who
was the first to correct the old notion that the secretions were discharged into the glan-
dular organs through openings in the blood-vessels. It is evident that nothing could have
been known of the mechanism of secretion before the connection between the arteries
and veins had been ascertained, which, it will be remembered, was also discovered by
Malpighi. Although the ideas of Malpighi were not at first generally received, more
recent observations with the microscope have shown that they were in the main correct;
although, from the imperfection of his optical instruments, Malpighi was unable to inves-
tigate very thoroughly the minute structure of the glands.

Anatomical Classification of Glandular Organs. — The organs which produce the
different secretions are susceptible of a classification according to their anatomical pecu-
liarities, which greatly facilitates their study. They may be divided as follows :

1. Secreting membranes. — Examples of these are the serous and synovial membranes.

2. Follicular glands. — Examples of these are the simple mucous follicles, the follicles
of Lieberkiihn, and the uterine follicles.

3. Tubular glands. — Examples of these are the ceruminous glands, the sudoriparous
glands, and the kidneys.

4. Racemose glands, simple and compound. — Examples of the simple racemose glands
are the sebaceous and Meibomian glands, the tracheal glands, and the glands of Brunner.
Examples of the compound racemose glands are the salivary glands, the pancreas, the
lachrymal glands, and the mammary glands.

5. Ductless, or blood-glands. — Examples of these are the thymus, the thyroid, the
supra-renal capsules, and the spleen.

The liver is a glandular organ which cannot be placed in any one of the above sub-
divisions, as we shall see when we come to treat specially of its anatomy. The lymphatic
glands and other parts connected with the lymphatic and the lacteal system are not
embraced in the above classification. These are sometimes called conglobate glands.

The general structure of secreting membranes and the follicular glands is very simple.
The secreting parts consist of a membrane, generally homogeneous, on the secreting sur-
face of which are found epithelial cells, either tesselated or of the variety called glandular.
Beneath this membrane, ramify the blood-vessels which furnish the elements of the secre-
tions. The follicular glands are simply digital inversions of this structure, with rounded,
blind extremities, the glandular epithelium lining the follicles.

The tubular glands have essentially the same structure as the follicles, except that the
tubes are long and are more or less convoluted. The more complex of these organs con-
tain connective tissue, blood-vessels, nerves, and lymphatics.

The compound racemose glands are composed of branching ducts, around the extrem-
ities of which are arranged collections of rounded follicles, like bunches of grapes. In
addition to the epithelium, basement-membrane, and blood-vessels, these organs contain
connective tissue, fibro-plastic elements, lymphatics, involuntary muscular fibres, and
nerves. In the simple racemose glands the excretory duct does not branch.

The ductless glands contain blood-vessels, lymphatics, nerves, sometimes involuntary
muscular fibres, fibro-plastic elements, and a peculiar structure called pulp, which is com-
posed of fluid with cells and occasionally with closed vesicles. These are sometimes called
blood-glands, because they are supposed to modify the blood as it passes through their
substance.

The testicles and the ovaries are not simply glandular organs ; for, in addition to the
production of mucous or watery secretions, their principal function is to develop certain
anatomical elements, the spermatozoids and the ova. The physiology of these organs
will be considered in connection with the subject of generation

Classification of the Secreted Fluids.— The products of the various glands may be

350

SECRETION.

divided, according to their function, into secretions and excretions. The secreted fluids
may be subdivided into the permanent secretions, which have a more or less mechanical
function, and transitory secretions; some of the latter, like mucus, are thrown off in
small quantity, without being actually excrementitious ; others, like most of the digestive
fluids, are produced intermittently and they rapidly and finally undergo resorption.

Tabular View of the Secreted Fluids.

Serous fluids.

Synovia! fluid.

Aqueous humor of the eye.

Secretions Proper.
Permanent Fluids.

Vitreous humor of the eye.

Fluid of the labyrinth of the internal ear.

Cephalo rachidian, or subarachnoid fluid.

Transitory Fluids.

Mucus, in many varieties.

Sebaceous matter.

Cerumen, the waxy secretion of the external me-

atus.

Meibomian fluid.
Milk and colostrum.
Tears.

Saliva.

Gastric juice.

Pancreatic juice.

Secretion of the glands of Brunner.

Secretion of the follicles of Lieberkiihn.

Secretion of the follicles of the large intestine.

Bile (also an excretion).

Excretions.

Perspiration and the secretion of the axillary
glands.

Urine.

Bile (also a secretion).

Fluids containing Formed Anatomical Elements.

Seminal fluid, containing, beside spermatozoids, the secretions of a number of glandular structures.
Fluid of the Graafian follicles.

Physiological Anatomy of the Serous and Synovial Membranes.

The serous and synovial membranes, which are frequently classed together by anato-
mists, present several well-marked points of distinction, both as regards their structure
and the products of their secretion. The serous membranes are the arachnoid, pleura,
pericardium, peritoneum, and tunica vaginalis testis. The synovial membranes are
found around all the movable articulations. They also form elongated sacs enveloping-
many of the long tendons, and they exist in various parts of the body in the form of
shut sacs, when they are called bursse.

Serous Membranes. — The structure of the serous membranes is very simple. They
consist of a dense tissue of fibres, which is frequently quite closely adherent to the sub-
jacent parts, covered by a single layer of pavement, or tesselated epithelium. The
fibres are mainly of the inelastic variety, arranged in bundles, interlacing each other in
the form of a close net-work, and mingled with small, wavy fibres of elastic tissue and
numerous blood-vessels. It has not been satisfactorily demonstrated that the serous
membranes contain nerves and lymphatics, although the latter are generally quite abun-
dant in the subjacent parts, particularly beneath the serous membranes covering the
viscera. The capillary blood-vessels are in the form of a close, polygonal net-work, with
sharp angles. The epithelium of the serous membranes is pale, regular, with rather
large nuclei, and is easily detached after death. These membranes, as a rule, form closed
sacs, with their opposing or free surfaces nearly in apposition. The secretion, which is
generally very small in quantity, is usually contained in their cavity. The exception to
this rule is the arachnoid membrane, the surfaces of which are exactly in apposition,

PHYSIOLOGICAL ANATOMY OF THE SYNOVIAL MEMBRANES. 351

the fluid being situated beneath both layers. The peritoneum of the female has an open-
ing on either side for the Fallopian tubes.

Synovial Membranes. — The true synovial membranes are found in the diarthrodial, or
movable articulations; but in various parts of the body are found closed sacs, sheaths,
etc., which resemble synovial membranes both in structure and in function. Every mova-
ble joint is enveloped in a capsule, which is closely adherent to the edges of the articu-
lating cartilage and is even reflected upon its surface for a short distance. It was for-
merly thought that these membranes, like the serous sacs, were closed bags, with one
layer attached to the cartilage and the other passing between the bones so as to enclose
the joint ; but it is now the general opinion that the cartilage which incrusts the articu-
lating extremities of the bones, though bathed in synovial fluid, is not itself covered by
a membrane.

The fibrous portion of the synovial membranes is more dense and resisting and less
elastic than the serous membranes. It is composed of white inelastic fibrous tissue, with
a few elastic fibres and blood-vessels. The latter are generally not so numerous as in
the serous membranes. The internal surface is lined with small cells of flattened pave-
ment-epithelium, with rather large, rounded nuclei. These cells exist in from one to two
or four layers.

In most of the joints, especially those of large size, as the knee and the hip, the syno-
vial membrane is thrown into folds which contain a considerable amount of true adipose
tissue. In nearly all the joints, the membrane presents fringed, vascular processes,
called sometimes synovial fringes. These are composed of looped vessels of considerable
size; and when injected they bear a certain resemblance to the choroid plexus. The
edges of these fringes present numerous leaf-like, membranous appendages, of a great
variety of curious forms. They are generally situated near the attachment of the mem-
brane to the cartilage. There is no reason for supposing that either the adipose folds or
the vascular fringes have any special office in the production of the synovial secretion
different from that of other portions of the membrane, although such a theory has been
advanced.

The arrangement of the synovial barsse is very simple. "Wherever a tendon plays
over a bony surface, we find a delicate membrane in the form of an irregularly-shaped,
closed sac, one layer of which is attached to the tendon, and the other, to the bone.
These sacs are lined with an epithelium like that found in the synovial cavities, and they
secrete a true synovial fluid. Numerous bursa) are also found beneath the skin, espe'-
cially in parts where the integument moves over bony prominences, as the olecranon,
the patella, and the tuberosities of the ischium. These sacs, sometimes called bursse
mucosa), are much more common in man than in the inferior animals and have essen-
tially the same function as the deep-seated bursse. The form of both the superficial and
deep-seated bursra is very irregular, and their interior is frequently traversed by small
bands of fibrous tissue. The synovial sheaths, or vaginal processes, line the canals in
which the long tendons play, particularly the tendons of the flexors and extensors of
the fingers and toes. They have essentially the same structure as the bursse, and present
two layers, one of which lines the canal, while the other is reflected over the tendon.
The vascular folds, described in connection with the articular synovial membranes, are
found in many of the bursaa and the synovial sheaths.

Pericardial, Peritoneal, and Pleural Secretions.— In. the normal condition of the true
serous membranes, the amount of secretion is very small ; so small, indeed, that it never
has been obtained in quantity sufficient for ultimate analysis. It is not true that these
membranes produce merely a vaporous exhalation. Their secretion is always liquid,
and, small as it is in quantity, it can be found in the pericardial SMC and sometimes in
the lower part of the abdominal cavity. As the only apparent function of these fluids

352 SECRETION1.

is to moisten the membranes so that the opposing surfaces can move over each other
without undue friction, only enough fluid is secreted to keep these surfaces in a proper
condition. The error frequently committed by authors, in describing the serous exhala-
tions as vaporous, is due to the fact that a vapor is generally given off when the serous
cavities are exposed, either in a living animal or in one recently killed. This vaporous
exhalation takes place after exposure of the parts ; but, if the cavities be observed with-
out exposing the serous surfaces to the air, a certain quantity of liquid can be detected.
Colin always found liquid in the peritoneal, pericardial, and pleural cavities of animals
recently killed or opened during life. In these cavities, the opposite surfaces of the
serous membrane were either in contact or the space between them was filled with
liquid. In one of the small ruminants, he removed the muscles and the elastic tunic
from the lower part of the abdomen, exposing the transparent peritoneum, and through
this membrane he could see liquid collected in the dependent parts.

As far as has been ascertained, the secretions of the different serous membranes bear
a close resemblance to each other. They are either colorless or of a slight amber tinge,
alkaline in reaction, and have a specific gravity of from 1012 to 1020. Their composi-
tion resembles that of the serum of the blood, except that the proportion of water is
very much greater. They contain albumen, chlorides, carbonate and phosphate of soda,
and a little glucose. These facts are the result of observations upon the serous fluids of
some of the inferior animals ; and it is exceedingly difficult to obtain the normal fluids
from the human subject. The elaborate analyses which are sometimes given of the
fluids from the different serous cavities in the human subject are the results of examina-
tions of large morbid accumulations.

The normal quantity of pericardial fluid in the human subject is generally estimated
at from one to two fluidrachms. Colin found that the pericardial sac of the horse con-
tained from two and a half to three and a half fluidounces, the cavity being exposed
immediately after the death of the animal from hemorrhage.

The quantity of fluid found in the peritoneal cavity in horses killed in this way was
from ten to thirty -four fluidounces.

The quantity of fluid in the pleural cavity in the same animal was from three and a
half to seven fluidounces.

These estimates are simply approximative; but they give an idea of the normal
quantity of liquid which may reasonably be supposed to exist in the serous cavities of
the human subject. Judging from the weight of a man of ordinary size as compared
with that of a horse, it may be stated, in general terms, that the pericardial sac contains
from two and a half to three and a half fluidrachms ; the peritoneal cavity, from one to
four fluidounces; and the pleural sac, from three and a half to seven fluidrachms.

The fluid in the cavity of the tunica vaginalis is small in quantity and resembles in
every respect the peritoneal secretion. The cephalo-rachidian, or subarachnoid fluid
will be described in connection with the anatomy of the cerebro-spinal nervous system.

Synovial Fluid. — Although there is a certain similarity between the serous and the
synovial membranes, their secretions differ very considerably in their physical and chemi-
cal characters. Like the serosities, the synovial fluid has simply a mechanical function ;
but it is more viscid and contains a larger proportion of organic matter than the serous
fluids. The quantity of fluid in the joints is sufficient to lubricate freely the articulating
surfaces. In a horse of medium size and in good condition, examined immediately after
death, Colin found T6 fluidrachm in the shoulder-joint; 1-9 drachm in the elbow-
joint; 1'6 drachm in the coxo-femoral articulation; 2*2 in the femoro-tibial articula-
tion; and 1-9 in the tibio-tarsal articulation.

When perfectly normal, the synovial fluid is either colorless or of a pale, yellowish
tinge. It is so viscid that it is with difficulty poured from one vessel into another. This
peculiar character is due to the presence of an organic substance called synovine. "When

COMPOSITION OF THE SYNOVIAL FLUID— MUCUS. 353

this organic matter has been extracted and mixed with water, it gives to the fluid the
peculiar viscidity of the synovial secretion. The reaction of the fluid is faintly alkaline,
on account of the presence of a small proportion of carbonate of soda. The fluid, espe-
cially when the joints have been much used, usually contains in suspension pale epithe-
lial cells and a few leucocytes. The following is the composition of the synovial fluid
of the human subject :

Composition of the Synovial Fluid. (Robin.)

Water 928'00

Synovine (called albumen) 64*00

Principles of organic origin (belonging to the second class of Robin) not estimated.

Fatty matter 0'60

Chloride of sodium

Carbonate of soda

Phosphate of lime 1*50

Ammonio-magnesian phosphate traces.

The observations of Frerichs indicate considerable variations in the composition and
general characters of the synovial fluid, dependent upon use of the joints. In a stall-
fed ox, the proportion of water to solid matter was 969*90 to 30*10 ; and, in animals
that took considerable exercise, the proportions were 948*54 of water to 51*46 of solid
matter. In the latter, the fluid was more viscid and contained a larger proportion of
synovine with a smaller proportion of salts. It was also more deeply colored and con-
tained a larger number of leucocytes.

Like the serous fluids, the synovial secretion is produced by the general surface of the
membrane and not by any special organs. The folds and fringes which have been de-
scribed were at one time supposed to be most active in secreting the organic matter, but
there is no evidence that they have any such special office.

The aqueous humor of the eye and the fluid of the labyrinth of the internal ear resem-
ble the serous secretions in many regards ; but these fluids, with the vitreous humor,
will be considered in connection with the physiological anatomy of the eye and ear.

Mucus.

Mucous Membranes. — The mucous membranes in different situations present impor-
tant peculiarities in structure, many of which have already been considered. "We have
described in detail the mucous membrane of the air-passages and of the alimentary canal,
in connection with the subjects of respiration and digestion; and the membranes in other
parts will necessarily be described in treating of the physiology of the organs in which
they are found. It will be sufficient at present to take a general view of the structure
of these membranes and the mechanism of the production of the various fluids known
under the name of mucus.

A distinct anatomical division of the mucous membranes may be made into two
classes, as follows : First, those provided with pavement-epithelium ; and second, those
provided with columnar or conoidal epithelium. All of the mucous membranes line
cavities or tubes communicating with the exterior by the different openings in the body.

The following are the principal situations in which the first variety of mucous mem-
branes, covered with pavement-epithelium, are found: The mouth, the lower part of the
pharynx, the oesophagus, the conjunctiva, the female urethra, and the vagina. In these
situations, the membrane is composed of a chorion made up of inelastic and elastic
fibrous tissue, a few fibro-plastic elements, with capillaries, lymphatics, and nerves. The
elastic fibres are small and quite abundant. The membrane itself is loosely united to
the subjacent parts by areolar tissue. The chorion is provided with vascular papilla?,
more or less marked ; but, in all situations, except in the pharynx, the epithelial cover-
23

354 SECRETION.

ing fills up the spaces between these papillae, so that the membrane presents a smooth
surface. Between the chorion and the epithelium, is an amorphous basement-membrane.
The mucous glands open upon the surface of the membrane by their ducts, but the glan-
dular structure is situated in the submucous areolar tissue. These glands have many of
them been described in connection with the mucous membrane of the mouth, pharynx,
and oesophagtis. They are generally simple racemose glands, presenting a collection of
follicles arranged around the extremity of a single excretory duct, lined or filled with
rounded, nucleated epithelium. The pavement-epithelium covering these membranes
exists generally in several layers, and presents great variety, both in form and size. The
most superficial layers are of large size, flattened, and irregularly polygonal. The deeper
layers are smaller and more rounded. The size of these cells is from -yfa-y to -g-i^ of an
inch. The cells are pale, slightly granular, and possess a small, ovoid nucleus, with one
or two nucleoli.

The second variety of mucous membranes, covered with columnar epithelium, is found
lining the alimentary canal below the cardiac orifice of the stomach, the biliary passages,
the excretory ducts of all the glands, the nasal passages, the upper part of the pharynx,
the uterus and Fallopian tubes, the bronchi, the Eustachian tubes, and the male urethra.
In certain situations, this variety of epithelium is provided on its free surface with little
hair-like processes called cilia. During life the cilia are in constant motion, producing a
current generally in the direction of the mucous orifices. Ciliated epithelium is found
throughout the nasal passages, commencing about three-quarters of an inch within the
nose ; in the upper part of the pharynx ; the posterior surface of the soft palate ; the Eu-
stachian tube ; the tympanic cavity ; the larynx, trachea, and bronchial tubes, until they
become less than -fa of an inch in diameter ; the neck and body of the uterus ; the Fal-
lopian tubes ; the internal surface of the eyelids ; and the ventricles of the brain. This
variety of mucous membrane is formed of a chorion, a basement-membrane, and epithe-
lium. The chorion is composed of inelastic and elastic fibres, with fibro-plastic ele-
ments, a few unstriped muscular fibres, amorphous matter, blood-vessels, nerves, and lym-
phatics. It is less dense and less elastic than the chorion of the first variety and is gen-
erally more closely united to the subjacent tissue. The surface of these membranes is
generally smooth, the only exception being the mucous membrane of the pyloric portion
of the stomach and the small intestines. These membranes are provided with follicular
glands, extending through their entire thickness and terminating in rounded extremities,
sometimes single and sometimes double, which rest upon the submucous structure. Many
of them are provided also with simple racemose glands, the ducts passing through the
membrane, the glandular structure being situated in the submucous areolar tissue. The
columnar epithelium covering these membranes rests upon an amorphous structure,
called basement-membrane. It generally presents but few layers, and sometimes, as
in the intestinal canal, there is only a single layer. The cells are prismoidal, with a
large, free extremity, and a pointed end which is attached. The lower strata of cells
are shorter and more rounded than those in the superficial layer. The cells are pale,
very closely adherent to each other by their sides, and provided with a moderate-sized,
oval nucleus with one or two nucleoli. The length of the cells is from ^7 to -^-$ of an
inch, and their diameter, from ffos to -gfa^ of an inch. When villosities exist on the
surface of the membranes, the cells follow the elevations and do not fill up the spaces
between them, as in most of the membranes covered with pavement-epithelium.

The mucous membrane of the urinary bladder, the ureters, and the pelvis of the kid-
neys, cannot be classed in either of the above divisions. They are covered with mixed
epithelium, presenting all varieties of form between the pavement and the columnar, some
of the cells being caudate and quite irregular in shape.

Mechanism of the Secretion of Mucus. — Nearly every one of the great variety of
fluids known under the name of mucus is composed of the products of several different

MUCUS. 355

glandular structures. According to Robin, mucus proper is produced by the epithelial
cells of that portion of the membrane situated on the surface, between the opening of
the so-called mucous follicles or glands ; while the secretion of these special glandular
organs always possesses peculiar properties. It is undoubtedly true that certain mem-
branes which do not possess glands, as the mucous lining of the ureters and a great por-
tion of the urinary bladder, are capable of secreting mucus. The mucous membrane of
the stomach produces an alkaline, viscid secretion, during the intervals of digestion,
when the gastric glands do not act ; and the gastric glands, during digestion, secrete a
fluid of an entirely different character. The fluid produced by the follicles of the small
intestine likewise has peculiar digestive properties. These circumstances, and the fact
that the entire extent of the mucous membranes is covered with more or less secretion,
show that the general epithelial covering of these membranes is capable of secreting a
fluid which forms one of the constituents of what is ordinarily recognized as mucus. It
is impossible, however, to separate the secretion of the superficial layer of cells from the
other fluids that are found on the mucous membranes ; and it will be more convenient to
regard as mucus, the secretion which is found upon mucous membranes, except when, as
in the case of the gastric or the intestinal juice, we can recognize a special fluid by cer-
tain distinctive physiological properties.

In the membranes covered with cylinder-epithelium, which are usually provided with
numerous simple follicles, the secretion is produced mainly by these follicles, but in part
by the epithelium covering the general surface. The membranes covered with pavement-
epithelium usually contain but few follicles and are provided with simple racemose glands
situated in the submucous structure, which are to be regarded rather as appendages to
the membrane. The secretion is here produced by the epithelium on the free surface
arid is always mixed with fluids resulting from the action of the mucous glands.

There is nothing to be said with regard to the mechanism of the secretion of mucus
beyond what has already been stated in connection with the general mechanism of secre-
tion. All the mucous membranes are quite vascular, and the cells covering the mem-
brane and lining the follicles and glands attached to it have the property of taking from
the blood the materials necessary for the formation of the secretion. These principles
pass out of the cells upon the surface of the membrane in connection with water and
inorganic salts in variable proportion. Many of the cells themselves are desquamated
and are found in the secretion, together with a few leucocytes, which are produced upon
mucous surfaces with great facility.

Composition and Varieties of Mucus. — In comparing the secretions of the different
mucous membranes, each one will be found to possess certain distinctive peculiarities,
more or less marked ; but there are certain general characters which belong to all varie-
ties of mucus. The fluid is usually a mixture of the secretion from the simple membrane
and the product of its follicles or glandular appendages and always contains a certain
amount of desquamated epithelium ; and it is frequently possible, from the microscopical
characters of the epithelium, to indicate the part from which any given specimen of mucus
has been taken. This desquamation of epithelium must not be regarded as a necessary
condition of the secretion of mucus, any more than the desquamation of the epidermic
scales is to be regarded as a condition necessary to the secretion of perspiration or seba-
ceous matter. It is a property of the epidermis and the epithelial covering of mucous
membranes to be regenerated by the formation of new cells from below, the effete struct-
ures being thrown off, and the admixture of these with mucus is simply accidental.
The leucocytes, formerly called mucus-corpuscles, are the result of irritation of the mu-
cous membrane and are not constant constituents of normal mucus.

All the varieties of mucus are more or less viscid ; but this character is very variable
in the secretions from different membranes, in some of them the secretion being quite
fluid, and in others, almost semisolid. The different kinds of mucus vary considerably in

356 /SECRETION".

general appearance. Some of them are perfectly clear and colorless ; but the secretion
is generally grayish and semitransparent. Examined by the microscope, in addition to
the mixture of epithelium and the occasional leucocytes, which give to the fluid its semi-
opaque character, the mass of the secretion presents a very finely-striated appearance, as
though it were composed of thin layers of a nearly transparent substance, with many
folds. These delicate striae do not usually interlace with each other, and they are ren-
dered more distinct by the action of acetic acid. This appearance, with the peculiar
effect of the acid, is characteristic of mucus. Some varieties of mucus present very
fine, pale granulations and a few small globules of oil.

On the addition of water, mucus is somewhat swollen but is not dissolved. An
exception to this is the secretion of the conjunctival mucous membrane, which is coagu-
lated on the addition of water. As a rule, the reaction of mucus is alkaline ; the only
exception to this being the vaginal mucus, which is very fluid and is distinctly acid.

It is exceedingly difficult to get an exact idea of the proximate composition of nor-
mal mucus, from the fact that the quantity secreted by the membranes in their natural
condition is very small, being just sufficient to lubricate their surface. All varieties, how-
ever, contain a peculiar organic principle, called mucosine, which gives to the fluid its
peculiar viscidity. They likewise present a considerable variety of inorganic salts, as the
chlorides of sodium and potassium, alkaline lactates, carbonate of soda, phosphate of
lime, a small proportion of the sulphates, and, in some varieties, traces of iron and silica.
Of all these constituents, mucosine is the most important, as it gives to the secretion its
characteristic properties. Like all other organic nitrogenized principles, mucosine is
coagulable by various reagents. It is imperfectly coagulated by heat ; and, after desica-
tion, it can be made to assume its peculiar consistence by the addition of a small quantity
of water. It is coagulated by acetic acid and by a small quantity of the strong mineral
acids, being redissolved in an excess of the latter. It is also coagulated by strong alco-
hol, forming a fibrinous clot soluble in hot and cold water. Mucosine may be readily
isolated by adding water to a specimen of normal mucus, filtering, and precipitating with
an excess of alcohol. If this precipitate, after having been dried, be exposed to water,
it assumes the viscid consistence peculiar to mucosine. This property serves to distin-
guish it from albumen and other organic nitrogenized principles.

Nasal Mucus. — The nasal mucus, being subject to so many changes from irritation of
the Schneiderian membrane, presents considerable variation in its appearance and com-
position. Under perfectly normal conditions, it is very viscid, clear or slightly opaque
and grayish, and strongly alkaline. It always contains more or less columnar epithelium.
In its behavior in the presence of various reagents, it presents the characteristics which
we have ascribed to the secretions of the mucous membranes generally. The following
is the composition of the normal secretion :

Composition of JVasal Mucus. (Robin.)

Water 933-00 to 947'00

Mucosine (with a trace of albumen ?) 53*30 " 54'80

Lactate of soda (?) I'OO " 5'00

Organic crystalline principles 2'00 " 1*05

Fatty matters and cholesterine not estimated. 5'01

Chlorides of sodium and potassium 5-60 to 5'09

Calcareous and alkaline phosphates 3 '50 " 2*00

Sulphate and carbonate of soda 0-90 not estimated.

Bronchial and Pulmonary Mucus. — This is the- secretion of the general mucous sur-
face of the larynx and bronchial tubes, mixed with the products of the glands situated in
the substance of these membranes and in the submucous tissue. In addition to this
secretion, there is an exhalation of watery vapor containing traces of organic matter, com-

MUCUS. 357

ing from the air-cells and the bronchial tubes less than -^ of an inch in diameter, which
are not provided with mucous glands. This variety of mucus is alkaline and is quite
similar to nasal mucus in its appearance and general characters.

Mucus secreted by the Mucous Membrane of the Alimentary Canal. — Throughout the
alimentary canal, from the mouth to the anus, the lining membrane secretes a certain
quantity of mucus, which does not differ very much from the mucus found in other situa-
tions. This secretion appears to take place independently of the act of digestion, and
the mucus in most parts of the tract is not known to possess any peculiar digestive prop-
erties. By ligating all of the salivary ducts, the buccal mucus has been procured. This
secretion is produced by the cells covering the general surface of the membrane and is
mixed with the secretion of the isolated follicular and racemose glands of the mouth.
An analogous secretion is produced by the mucous membrane of the pharynx and oesoph-
agus. During the intervals of digestion, a viscid, alkaline secretion covers the mucous
membrane of the stomach. The digestive secretions of the small intestine are so viscid
that it has been found impossible to separate them from the true mucous secretion ; but
undoubtedly a secretion of ordinary mucus is constantly taking place from the lining
membrane of both the small and the large intestine. This secretion probably has a
purely mechanical function, serving to lubricate the membranes and facilitate the move-
ments of the opposing surfaces against each other.

The mucous membrane of the gall-bladder produces quite an abundant secretion ; but
this is always mixed with the bile, and it will be considered in connection with the com-
position of this fluid, although it is not known to possess any peculiar properties.

Mucus of the Urinary Passages. — A small quantity of mucus is secreted by the uri-
nary passages. This is present in the normal urine, in the form of a very slight, cloudy
deposit, which forms after the urine has been allowed to stand for a few hours. A cer-
tain amount of secretion takes place from the mucous membrane of the bladder, which,
as we have seen, does not possess glands except near the neck. This secretion is
produced in very small quantity, and it may be recognized in the urine by the ordinary
microscopical characters of mucus.

Mucus of the Generative Passages. — The vagina secretes a small quantity of mucus,
which differs from the secretions of the other mucous membranes in being distinctly acid
and almost entirely wanting in viscidity. The mucus of the neck of the uterus is clear,
viscid, and distinctly alkaline. This is ordinarily produced in small quantity, but it is very
abundant during pregnancy. It is the result of the action chiefly of the large, rounded
glands found in this situation. The mucus of the body of the uterus and of the Fallopian
tubes is alkaline, of a grayish color, and slightly viscid. The secretions of these parts
are greatly modified during menstruation. These considerations, however, belong prop-
erly to the subject of generation and will be taken up more fully hereafter.

Oonjunctival Mucus. — A small quantity of a viscid secretion constantly covers the
conjunctival mucous membrane, and this is a mixture of the secretion of the membrane
itself with the fluid produced by the little mucous glands found near the internal angle of
the eye. A peculiarity of this variety of mucus is that it becomes white, like coagulated
albumen, by the action of pure water. A peculiarity of the mucus from the conjunctiva,
the urethra of the male, and the vagina, is that they readily become virulent when
secreted in abnormal quantity. They then contain a large number of leucocytes and have
a more or less puriform character.

General Function of Mucus. — The smooth, viscid, and adhesive character of mucus,
forming, as this fluid does, a coating for the mucous membranes, serves to protect these
parts, enables their surfaces to move freely one upon the other, and modifies to a certain
extent the process of absorption. This function is entirely independent of the function
of some of the mucous glands, as the follicles of Lieberkuhn, which produce secretions
only at particular times.

358 SECRETION.

Aside from the mechanical functions of mucus, it has been shown that this fluid, in
connection with the epithelial covering of the mucous membranes, is capable of prevent-
ing the absorption of certain substances. It is well known, for example, that venoms may
be applied with impunity to certain mucous surfaces, while they produce poisonous
effects if introduced into the circulation. These agents are not neutralized by the secre-
tions of the parts, for they will produce their characteristic effects upon the system when
removed from the mucous surfaces and introduced into the circulation ; and it is reason-
able to suppose that the mucous membranes are capable of resisting their absorption.
This fact is proven by the following interesting experiment, detailed by Robin :

Let an endosmometer be constructed, using a fresh mucous membrane, on the surface
of which the epithelium and layer of mucus remain intact, and in the interior of the
apparatus, place a saccharine solution, and let the membrane be exposed to a solution con-
taining some venomous fluid. The liquid will mount in the interior of the apparatus, but
the poison will not penetrate the membrane. If the mucus and epithelium be now
removed with the finger-nail from even a small portion of the membrane, the poison will
immediately pass through that part of the membrane, and an animal may be killed with
the fluid which now penetrates into the interior of the endosmometer.

These facts show that mucus is an important secretion. It not only has a useful me-
chanical function, but it is in all probability closely connected with some of the phenomena
of elective absorption which are so often observed, particularly in the alimentary canal.

Sebaceous Fluids.

The general cutaneous surface is constantly lubricated by a small quantity of a pecul-
iar, oily secretion, called sebum, or sebaceous matter. This secretion is somewhat modi-
fied in certain situations, and an analogous fluid is produced by special glands opening
into the external nleatus of the ear. Another fluid, very much like the ordinary seba-
ceous matter, is smeared upon the edges of the eyelids. These secretions, called respec-
tively cerumen and Meibomian fluid, resemble the secretion of the ordinary sebaceous
glands sufficiently to be classed with it.

Physiological Anatomy of the Sebaceous, Ceruminovs, and Meibomian Glands. — The
true sebaceous glands are found in all parts of the body that are provided with hair ; and,
as nearly every part of the general surface presents either the long, the short, or the
downy hairs, these glands are very generally distributed. They exist, indeed, in greater
or less numbers in all parts of the skin, except the palms of the hands and the soles of
the feet. In the labia minora in the female, and in portions of the prepuce and glans
penis of the male, parts not provided with hair, small, racemose sebaceous glands are
found, which produce secretions differing somewhat from that formed by the ordinary
glands. The glands in the areola of the nipple in the female are very large and are con-
nected with small, downy hairs.

Nearly all of the sebaceous glands are either simple racemose glands, that is, present-
ing a number of follicles connected with a single excretory duct, or compound race-
mose glands presenting several ducts, with their follicles, opening by a common tube.
Although there is this variation in the size and arrangement of the glands of the general
surface, they secrete essentially the same fluid, and their anatomical differences consist
simply in a multiplication of follicles.

The differences in the size of the sebaceous glands bear a certain relation to the size
of the hairs with which they are connected ; and, as a rule, the largest glands are con-
nected with the small, downy hairs. These distinctions in size are so marked, that the
glands may be divided into two classes ; viz., those connected with the long hairs of the
head, face, chest, axilla, and genital organs, and the coarse, short hairs, and those con-
nected with the fine, downy hairs.

SEBACEOUS FLUIDS.

359

The glands connected with the larger hair-follicles are of the simple racemose variety
and are from j^ to TV °f an incn ^n diameter. From two to five of these glands are gen-
erally found arranged around each hair-follicle. They discharge their secretion at about
the junction of the upper third with the lower two-thirds of the hair-follicle. The folli-
cles of the long hairs of the scalp are generally provided each with a pair of sebaceous
glands, measuring from T^ to TV of an inch in diameter. Encircling the hairs of the
beard, the chest, axilla, and genital organs, are large glands, some of them ^ of an inch
in diameter, arranged in groups of from four to eight.

The glands connected with the follicles of the small, downy hairs are so large, as com-
pared with the hair-follicles, that the latter seem rather as appendages to the glandular
structures. These glands are of the compound racemose variety and present sometimes
as many as fifteen culs-de-sac. The largest are found on the nose, the ear, the caruncula
lachrymalis, the penis, and the areola of the nipple, where they measure from /0- to -fa
of an inch. The glands connected with the downy hairs of other parts are usually small-
er. The glands of Tyson, situated upon the corona of the glans penis and behind, upon
the cervix, are sebaceous glands of the compound racemose variety.

FIG. 99.— Sebaceous glands. (Sappey.)

A, a gland in its most rudimentary form : 1, rudimentary hair-follicle: 2, downy hair; 8, simple sebaceous follicle. B,
a gland more developed : 1, hair-follicle ; 2. simple sebaceous follicle. C, a gland with two follicles : 1. hair-follicle ;
2, simple follicle ; 8, follicle imperfectly divided. I), a compound gland : 1. hair-follicle ; 2, lobule with three folli-
cles; 8. lobule with four follicles. E, agland with four lobules: 1. hair-follicle ; 2. 2, first lobule; 3. second lobule;
4, 4, third lobule ; 5, fourth lobule ; 6. excretory duct with a hair passing through it. F, a gland with four lobules :
1, hair-follicle ; 2, 2, first lobule; 8, second lobule ; 4, third lobule ; 5, fourth lobule; 6, excretory duct

The minute structure of the sebaceous glands is very simple. The follicles which
compose the simple glands and the follicular terminations of the simple and compound
racemose glands are formed of a delicate, structureless or slightly granular membrane,

360

SECRETION.

with an external layer of inelastic and small elastic fibres, and are lined by cells. Next
the membrane, the cells are polyhedric, pale, and granular, most of them presenting a
nucleus and a nucleolus ; but the follicle itself contains fatty granules and the other con-
stituents of the sebaceous matter, with cells filled with fatty particles. These cells
abound in the sebaceous matter as it is discharged from the duct. The great quantity of
fatty granules and globules found in the ducts and follicles of the sebaceous glands ren-
ders them dark and opaque when examined with the microscope by transmitted light,
and their appearance is quite distinctive. The larger glands are surrounded with capil-
lary blood-vessels. The glands which open into the larger hair-follicles will be illus-
trated in connection with the anatomy of the hairs.

The ceruminous glands of the ear produce a secretion resembling the sebaceous mat-
ter in many regards, but in their anatomy they are almost identical with the sudoripa-
rous glands. They belong to the variety of glands called tubular, and they consist of a
nearly straight tube which penetrates the skin and a rounded or ovoid coil situated in the
subcutaneous structure. These glands are found only in the cartilaginous portion of the
external meatus, where they exist in great numbers. They are rather more numerous in
the inner than in the outer half of the meatus.

The ducts of the ceruminous glands are short and nearly straight, simply penetrating
the different layers of the skin, and are from y^ to ^7 of an inch in diameter. Their
openings are rounded and about ^fg- of an inch in diameter. They sometimes terminate
in the upper part of one of the hair-follicles. They present an external coat of white
fibrous tissue and are lined with several layers of small, pale, nucleated epithelial cells.

i& a&

FIG. 100. — Ceruminous glands. (Sappey.)

Vertical section of the skin of the external auditory meatus: 1, 1, epidermis; 2, 2, derma; 3, 3, series of hair-follicles
lodged in the substance of the skin ; 4, 4, series of sebaceous glands attached to these follicles ; 5, 5, subcutaneous
areolar layer ; 6, 6, ceruminous glands ; 7, 7, ceruminous glands with the ducts divided ; 8, 8, adipose vesicles.

The glandular coil is an ovoid or rounded, brownish mass, from T|-7 to -^ or •£$ of
an inch in diameter. It is simply a convoluted tube, continuous with the excretory duct
and terminating in a somewhat dilated, rounded extremity. It presents, occasionally,
small, lateral protrusions. The diameter of the tube is from -3-^ to -^^ of an inch. It
possesses a fibrous coat, with a longitudinal layer of involuntary muscular fibres, and
externally a few elastic fibres. It is lined by a single layer of irregularly polygonal cells,
which are from to - of an inch in diameter. These cells contain numerous

SEBACEOUS FLUIDS.

361

brownish or yellowish pigmentary granules. The tube forming the gland contains a clear
fluid mixed with a granular substance containing cells.

In addition to the ceruminous glands of the ear, numerous sebaceous follicles are found
connected with the hair-follicles here, as in other parts provided with hair. The arrange-
ment of the ordinary sebaceous glands and the ceruminous glands, which are situated in
different planes in the subcutaneous structure, is shown in Fig. 100.

The Meibomian glands of the eyelids have essentially the same structure as the ordi-
nary sebaceous glands. Their ducts, however, are longer, and the terminal follicles are
arranged in a peculiar manner by the sides of the tubes along their entire length.
These glands are situated partly in the substance of the tarsal cartilages, between
their posterior surfaces and the conjunctival mucous membrane. They are placed at
right angles to the free border of the eyelids, opening upon the inner edge and occupy-
ing the entire width of the cartilages. From twenty-five to thirty glands are found in the
upper, and from twenty to twenty-five, in the lower lid.

Each Meibomian gland consists of a nearly straight excretory duct, from ^-^ to -^
of an inch in diameter, communicating laterally with numerous compound racemose
acini, or collections of follicles, measuring from -^ to T£¥ of an inch. From fifteen to
twenty of these collections of follicles are found on either side of the duct in glands
of medium length. Most of the excretory ducts are nearly straight, but some are
turned upon themselves near their upper extremity. The general arrangement of these
glands is shown in Fig. 101.

In general structure there is little if any
difference between the terminal follicles of the
Meibomian glands and the follicles of the ordi-
nary sebaceous glands. They are lined with
cells measuring from ^V "o to T^HF °f an mc^ ^n
diameter. These cells contain numerous fatty
globules, but they do not coalesce into large
drops, such as are often seen in the ordinary
sebaceous cells. The follicles and ducts are
filled with the whitish, oleaginous matter which
constitutes the Meibomian secretion, or the
sebum palpebrale.

In addition to the Meibomian secretion, the
edges of the palpebral orifice receive a small
amount of secretion from ordinary sebaceous
glands of the compound racemose variety (cili-
ary glands), which are appended in pairs to each
of the follicles of the eyelashes, and from the
sebaceous glands attached to the small hairs of
the caruncula lachrymalis.

Ordinary Sebaceous Matter. — Although it
may be inferred, from the great number of
sebaceous glands opening upon the cutaneous Fio. ^^^^^^^^^
surface, that the amount of sebaceous matter ^ ^ free border of the Hd ; 2, 2, anterior lip pene-
must be considerable, it has been impossible to
collect the normal fluid in quantity sufficient for
ultimate analysis. In certain parts, as the skin
of the nose, where the glands are particularly
abundant, a certain amount of oily secretion is

sometimes observed, giving to the surface a greasy, glistening aspect. This may be
absorbed by paper, giving it the well-known appearance produced by oily matters, and it

, , ,

trated by the eyelashes ; 8, 3, posterior lip, with
the openings of the Mcil.omian plarnls: 4. n pl.iml
passing obliquely at the summit ; 5 another
gland bent upon itself; 6. 0. two plands in the
form of racemose plands at their onpin ; 7, a
very small gland ; 8, a medium-sized gland.

362 SECRETION.

may be collected in small quantity upon a glass slide and examined microscopically. It then
presents a number of strongly-refracting fatty globules, with a few epithelial cells. The
cells, however, are not numerous in the fluid as it is discharged upon the general surface ;
but, if the contents of the ducts and follicles be examined, cells will here be found in great
abundance. Most of the cells, indeed, remain in the glands, and the oily matter only is
discharged. The object of this secretion is to lubricate the general cutaneous surface
and to give to the hairs that softness which is characteristic of them when in a perfectly
healthy condition.

It is only when the action of the sebaceous glands has become more or less modified,
that the secretion can be obtained in sufficient quantity for chemical analysis ; but we
cannot be certain that the fluid taken under these conditions is perfectly normal. The
analysis by Esenbeck, which is often quoted in works on physiology, was the result of an
examination of the contents of a largely-distended hair-follicle ; and, as the secretion was
confined for a long time, it is evident that it must have undergone material alteration.
We cannot, indeed, refer to any ultimate analysis of the normal sebaceous secretion ; but,
of all tho examinations that have been made of the secretion when it has been consider-
ably increased in quantity, those of Lutz give the best idea of what may be supposed to
be nearly its ordinary composition. This observer analyzed the secretion in a case of
general hypertrophy of the sebaceous system. The fluid which he extracted from the
dilated glands was milky-white, and of about the consistence, when cold, of wax. The
mean of eight analyses of this fluid was as follows :

Composition of Sebaceous Matter.

Water 357

Oleine 270

Margarine 135

Butyric acid and butyrate of soda 3

Caseine 129

Albumen 2

Gelatine 87

Phosphate of soda and traces of phosphate of lime 7

Chloride of sodium 5

Sulphate of soda 5

1,000

This analysis gives the proportions of animal and solid matters, desiccated in a current
of dry air. Robin, who has reviewed at considerable length the analytical process em-
ployed by Lutz, regards the matter supposed to be either caseine or some analogous
albuminoid substance, as the organic matter of the epithelial cells that exist in such gre.it
numbers in distended sebaceous glands. He regards the weight of the substances desig-
nated under the names of albumen, caseine, and gelatine, with a certain quantity of the
water driven off by desiccation, as representing the proportion of epithelium. This view
is very reasonable, as the microscope always shows in these collections great numbers of
epithelial cells. Cholesterine, which is present so frequently in the contents of sebaceous
cysts, does not exist in the normal secretion, nor was it found in the analyses by Lutz.

During the latter months of pregnancy and during lactation, the sebaceous glands of
the areola of the nipple become considerably distended with a grayish-white, opaque
secretion, containing numerous oily globules and granules. Frequently the fluid contains
also a large number of epithelial cells. During the periods above indicated, the secretion
here is always much more abundant than in the ordinary sebaceous glands.

Smegma of the Prepuce and of the Labia Minorca, — In the folds of the prepuce of the
male and on the inner surface and folds of the labia minora in the female, a small quantity

VEKNIX CASEOSA. 363

of a whitish, grumous matter, of a cheesy consistence, is sometimes found, particularly
when proper attention is not paid to cleanliness. The matter which thus collects in
the folds of the prepuce has really little analogy with the ordinary sebaceous secretion.
Examination with the microscope shows that it is composed almost entirely of irregular
scales of pavement-epithelium, which do not present the fatty granules and globules usu-
ally observed in the cells derived from the sebaceous glands. Robin regards the produc-
tion of this substance as entirely independent of the secretion of sebaceous matter, as it
is formed chiefly in parts of the prepuce in which the sebaceous glands are wanting.

The smegma of the labia minora is of the same character as the smegma preputiale ;
but it contains drops of oil and the other products of the sebaceous glands found in these
parts.

Vernix Caseosa.—The surface of the foetus at birth and near the end of gestation is
generally covered with a whitish coating, or smegma, called the vernix caseosa. This is
most abundant in the folds of the skin ; but it usually covers the entire surface with a
coating of greater or less thickness and of about the consistence of lard. There are
great differences in foetuses at term as regards the quantity of the vernix caseosa. In
some the coating is so slight that it would not be observed unless on close inspection.
There are few analyses giving an accurate view of the ultimate composition of this
substance ; and we can form the best idea of its constitution and mode of formation from
microscopical examinations. If a small quantity be scraped from the surface and be spread
out upon a glass slide with a little glycerine and water, it will be found, on microscopical
ex 'lation, to consist of an immense number of epithelial cells, with a very few small,
fa v granules. In the following table, it is seen that these cells, after desiccation, con-
stituted about ten per cent, of the entire mass. The fatty granulations are very few and
do not seem to be necessary constituents of the vernix, as they are of the sebaceous mat-
ter. In fact, the vernix caseosa must be regarded as the residue of the secretion of the
sebaceous glands, rather than an accumulation of true sebaceous matter.

Composition of the Vernix Caseosa. (Robin.)

Water 769-80 to 778-70

Nitrogcnized matter, mucous or caseous , 4'50

Desiccated epithelium 101'30

Cholesterine, \

Oleine and margarine, \ 108'25

Oleates and margarates of potassa and of soda, )

Chloride of sodium, ^

Hydrochlorate of ammonia, 14-9*

Phosphate of soda and of lime, f '

Ammonio-magnesian phosphate, )

The function of the vernix caseosa is undoubtedly protective. If we attempt to make
a microscopical preparation of the cells with water, it becomes evident that the coat-
ing is penetrated by the liquid with very great difficulty, even when mixed with it as
thoroughly as possible. Indeed, we never observe at birth the peculiar effects of pro-
longed contact of the cutaneous surface with water. The protecting coat of vernix caseosa
allows the skin to perform its functions in utero, and, at birth, when this coating is
removed, the surface is found in a condition perfectly adapted to extra-uterine existence.
It is not probable that the vernix caseosa is necessary to facilitate the p.'iss.-iL'v of the child
into the world, for the parts of the mother are always sufficiently lubricated with mucous
secretion.

Cerumen.— A peculiar substance of a waxy consistence is secreted by the glands that
have been described in the external meatus, under the name of ceruminous glands, mixed

364 SECRETION.

with the secretion of sebaceous glands connected with the short hairs in this situation.
It is difficult to ascertain what share these two sets of glands have in the formation of
the cerumen. Robin is of the opinion that the waxy portion of the secretion is produced
entirely by the sebaceous glands, and that the convoluted glands, commonly known as the
ceruminous glands, produce a secretion like the perspiration. He calls the latter, indeed,
the sudoriparous glands of the meatus. This view is, to a certain extent, reasonable ;
for the sebaceous matter is not removed from the meatus by friction, as in other situa-
tions, and would have a natural tendency to accumulate. But the contents of the ducts
of the ceruminous glands differ materially from the fluid found in the ducts of the ordi-
nary sudoriparous glands, containing granules and fatty globules, such as exist in the
cerumen. Although the glands of the ear are analogous in structure, and, to a certain
extent, in the character of their secretion, to the sudoriparous glands, the fluid which they
produce is peculiar. We shall see, also, that the perspiratory glands of the axilla and of
some other parts produce secretions differing somewhat from ordinary perspiration. As
far as can be ascertained, the cerumen is produced by both sets of glands. The sebaceous
glands attached to the hair-follicles probably secrete most of the oleaginous and waxy
matter, while the so-called ceruminous glands produce a secretion of much greater fluid-
ity, but containing a certain amount of granular and fatty matter.

The consistence and general appearance of cerumen are quite variable within the lim-
its of health. When first secreted, it is of a yellowish color, about the consistence of
honey, becoming darker and much more viscid upon exposure to the air. It has a very
decided and bitter taste. It readily forms a sort of emulsive mixture with water.

Examined microscopically, the cerumen is found to contain semisolid, dark granula-
tions of an irregularly polyhedric shape, with epithelium from the sebaceous glands, and
epidermic scales, both isolated and in layers. Sometimes, also, a few crystals of choles-
terine are found.

Chemical examination shows that the cerumen is composed of oily matters fusible at
a low temperature, a peculiar organic matter resembling mucosine, with salts of soda
and a certain quantity of phosphate of lime. The yellow coloring matter is soluble in
alcohol; and the residue after evaporation of the alcohol is very soluble in water and
may be precipitated from its watery solution by the neutral acetate of lead or the chloride
of tin. This extract has an exceedingly bitter taste.

The cerumen lubricates the external meatus, accumulating in the canal around the
hairs. Its peculiar bitter taste is supposed to be efficient in preventing the entrance of
insects.

Meibomian Secretion. — Very little is known concerning any special properties of the
Meibomian fluid, except that it mixes with water in the form of an emulsion more readily
than the other sebaceous secretions. It is produced in small quantity, mixed with a cer-
tain amount of mucus and the secretion from the ordinary sebaceous glands attached to
the eyelashes (ciliary glands) and the glands of the caruncula lachrymalis, and smears
the edges of the palpebral orifice. This oily coating on the edges of the lids, unless the
tears be produced in excessive quantity, prevents their overflow upon the cheeks and
directs the excess of fluid into the nasal duct.

Mammary Secretion.

The mammary glands are among the most remarkable organs in the economy ; not
only from the peculiar character of their secretion, which is unlike the product of any
other of the glands, but from the great changes which they undergo at different periods,
both in size and structure. Rudimentary in early life and in the male at all periods of
life, these organs are fully developed in the adult female, only in the latter months of
pregnancy and during lactation. It is true that, in the female, after puberty, the mam-
mary glands undergo a marked and rapid increase in size ; but even then they are not

PHYSIOLOGICAL ANATOMY OF THE MAMMARY GLANDS. 365

fully developed, and, if examined with the microscope, they are found to lack the essential
anatomical characters of secreting organs. The physiological anatomy of the mammary
glands consequently possesses peculiar interest, aside from the great importance of their
secretion.

It will be found convenient to consider these organs in three stages of development;
viz., in their rudimentary condition, as they exist in the male and in the female before
puberty ; in the partially-developed state, as they are found in the unimpregnated female
after puberty and during the intervals of lactation; and, finally, in the fully-developed
condition, when milk is secreted.

Physiological Anatomy of the Mammary Glands.

The form, size, and situation of the mammae in the adult female are too well known
to demand more than a passing mention. These organs are almost invariably double
and are situated on the anterior portion of the thorax, over the great pectoral mus-
cles. In women who have never borne children, they are generally firm, nearly hemi-
spherical, with the nipple at the most prominent point. In women who have borne
children, the glands, during the intervals of lactation, are usually larger, are held more
loosely to the subjacent parts, and are apt to become flabby and pendulous. The areola
of the nipple is also darker.

In both sexes, the mammary glands are nearly as fully developed at birth as at any
time before puberty. They make their appearance at about the fourth month, in the
form of little elevations of the structure of the true skin, which soon begin to send off
processes beneath the skin, which are destined to be developed into the lobes of the
glands. In the foetus at term, the glands measure hardly more than one-third of an inch
in diameter. At this time, there are from twelve to fifteen lobes in each gland, and
each lobe is penetrated by a duct, with but few branches, composed of fibrous tissue
and lined with columnar epithelium. The ends of these ducts are frequently somewhat
dilated ; but what have been called the gland- vesicles do not make their appearance
before puberty. In the adult male, the glands are from half an inch to two inches
broad, and from -^ to £ of an inch in thickness. In their structure, however, they pre-
sent little if any difference from the rudimentary glands of the infant.

As the period of puberty approaches in the female, the rudimentary ducts of the differ-
ent lobes become more and more ramified. Instead of each duct having but two or three
branches, the different lobes, as the gland enlarges, are penetrated by innumerable rami-
fications, which have gradually been developed as processes from the main duct. It is
important to remember, however, that these branches are never so numerous or so long
during the intervals of lactation as they are when the organ is in full activity. The ordina-
ry condition of the gland, as compared with its structure during activity, is one of atrophy.

Condition of the Mammary Glands during the Intervals of Lactation. — At this
time the glands are not secreting organs. They present the ducts, ramifying, to a certain
extent, in the substance of the lobes into which the structure is divided, but their branches
are short and possess but few of the glandular acini that are observed in every part of
the organs during lactation. This difference in the structure of the glands is most
remarkable ; and, as they pass from a secreting to a non-secreting condition at the end of
lactation, the ducts retract in all their branches, and most of the secreting culs-de-sac
disappear. At this time, the glandular tissue is of a bluish-white color and loses the
granular appearance which it presents during functional activity. The ducts are then
lined with a small, nucleated, pavement-epithelium, which is not found during the secre-
tion of milk. These changes, pointed out by Robin, whose observations have been veri-
fied and extended by Sappey, are confined almost exclusively to the secreting structure of
the glands. The interstitial tissue remains about the same, the blood-vessels, only, being
increased in number during lactation.

366 SECRETION.

Structure of the Mammary Glands during Lactation. — Between the fourth and the
fifth month of utero-gestation, the mammary glands begin to increase in size ; and, at
term, they are very much larger than during the unimpregnated state. At this time, the
breasts become quite hard, and the surface near the areola is somewhat uneven, from
the great development of the ducts. The nipple itself is increased in size, the papillae
upon its surface and upon the areola are more largely developed, and the areola becomes
larger, darker, and thicker. The glandular structure of the breasts during the latter half
of pregnancy becomes so far developed, that, if the child be born at the seventh month,
the lacteal secretion may generally be established at the usual time after parturition.
Even when parturition takes place at term, a few days elapse before secretion is fully
established, and the first product of the glands, called colostrum, is very different from the
fully-formed milk.

The only parts of the covering of the breasts that present any peculiarities are the
areola and the nipple. The surface of the nipple is covered with papillaa, which are
very largely developed near the summit. It is covered by epithelium in several layers,
the lower strata being filled with pigmentary granules. The true skin covering the nip-
ples is composed of inelastic and elastic fibres, containing a large number of sebaceous
glands, but no hair-follicles or sudoriparous glands. According to Sappey, these glands,
which are from eighty to one hundred and fifty in number, are always of the racemose
variety, and they never exist in the form of simple follicles, as they are described by most
anatomists. The nipple contains the lactiferous ducts, fibres of inelastic and elastic tis-
sue, with an immense number of non-striated muscular fibres. The muscular fibres have
no definite direction, but are so numerous that, when they are contracted, the nipple
becomes very firm and hard. The nipple, although it may thus become hard upon the
application of cold or other stimulus, presents none of the anatomical characteristics of
the true erectile organs, as is erroneously supposed by some authors ; and its hardening
is simply due to contraction of its muscular fibres.

The areola does not lie, like the general integument covering the gland, upon a bed
of adipose tissue, but it is closely adherent to the subjacent glandular structure. The
skin here is much thinner and more delicate than in other parts, and the pigmentary
granules are very abundant in some of the lower strata of epidermic cells, particularly
during pregnancy. The true skin of the areola is composed of inelastic and elastic fibres
and lies upon a distinct layer of non-striated muscular fibres. The arrangement of the
muscular fibres (sometimes called the subareolar muscle) is quite regular, forming con-
centric rings around the nipple. These fibres are supposed to be useful in compressing
the ducts during the discharge of milk. The areolar presents the following structures :
numerous papilla, considerably smaller than those upon the nipple ; hair-follicles, con-
taining small, rudimentary hairs ; sudoriparous glands ; and sebaceous glands connected
with the hair- follicles. The sebaceous glands in this situation are very large, and their
situation is indicated by little prominences on the surface of the areola, which are espe-
cially marked during pregnancy.

The mammary gland itself is of the compound racemose variety. It is covered in
front by a subcutaneous layer of fat, and posteriorly it is enveloped in a fibrous membrane
loosely attached to the pectoralis major muscle. A considerable amount of adipose tissue
is also found in the substance of the gland between the lobes.

Separated from the adipose and fibrous tissue, the mammary gland is found divided
into lobes, from fifteen to twenty-four in number. These, in their turn, are subdivided
into lobules made up of a greater or less number of acini, or culs-de-sac. The secreting
structure is of a reddish-yellow color and is distinctly granular, presenting a decided
contrast to the pale and uniformly fibrous appearance of the gland during the intervals
of lactation. If the ducts be injected from the nipple and be followed into the substance
of the gland, each one will be found distributing its branches to a distinct lobe ; so that
the organ is really made up of a number of glands, in their structure identical with each

PHYSIOLOGICAL ANATOMY OF THE MAMMARY GLANDS. 367

other. It will be most convenient, in studying the intimate structure of the gland, to
begin at the nipple and follow out one of the ducts to the termination of its branches in
the secreting culs-de-sac.

The canals which discharge the milk at the nipple are called lactiferous or galac-
tophorous ducts. They vary in number from ten to fourteen. The openings of the ducts
at the nipple are very small, measuring only from -£-$ to ^ of an inch. As each duct
passes downward, it enlarges in the nipple to ^ or T*¥ of an inch in diameter, and beneath
the areola it presents an elongated dilatation, from $ to |-of an inch in diameter, called the
sinus of the duct. During lactation, a considerable quantity of milk collects in these sinuses,
which serve as reservoirs. Beyond the sinuses, the caliber of the ducts measures from
yV to £ of an inch. They penetrate the different lobes, branching and subdividing, to
terminate finally in the collections of culs-de-sac which form the acini. Most modern
observers are agreed that there is no anastomosis between the different lactiferous ducts,
and that each one is distributed independently to one or more lobes.

r

FIG. 102. — Mammary gland of the human female, (Liepeois.)

a, nipple, the central portion of which is retracted ; 6, areola; c, c, c. c, c, lobules of the pland : 1, sinus, or dilated
portion of one of the lactiferous ducts; 2, extremities of the lactiferous ducts.

The intimate structure of the lactiferous ducts is interesting and important. They
are possessed of three distinct coats. The external coat is composed of anastomosing
fibres of elastic tissue, with some inelastic fibres. The middle coat is composed of non
striated muscular fibres, arranged longitudinally and existing throughout the duct, froip
its opening at the nipple to the secreting culs-de-sac. The internal coat is an amor
phous membrane, lined with roundish or elongated cells during the intervals of lactation
and even during pregnancy, but deprived of epithelium during the period when the lac-
teal secretion is most active.

The acini of the gland, which are very numerous, are visible to the naked eye, in the
form of small, rounded granules, of a reddish-yellow color. Between these acini, there
exist a certain quantity of the ordinary white fibrous tissue and quite a number of adi-

368 SECRETION.

pose vesicles. The presence of adipose tissue in considerable quantity in the substance
of the glandular structure is peculiar to the mammary glands. Each acinus is made up
of from twenty to forty secreting vesicles, or culs-de-sac. These vesicles are irregular in
form, often varicose, and sometimes they are enlarged and imperfectly bifurcated at their
terminal extremities. During lactation, their diameter is from ^ to -^ of an inch. Dur-
ing pregnancy, and when the gland has just arrived at its full development, the secreting
vesicles are formed of a structureless membrane, lined with small, nucleated cells of
pavement-epithelium. The nuclei are relatively large, ovoid, and are embedded in a small
amount of amorphous matter, so that they almost touch each other. Sometimes the epi-
thelium is segmented, and sometimes it exists in the form of a continuous nucleated
sheet. When the secretion of milk becomes active, the epithelium entirely disappears,
and it reappears as the secretion diminishes. This observation is due to Robin and has an
important bearing upon the mechanism of the secretion of milk.

During the intervals of lactation, as the lactiferous ducts become retracted, the glan-
dular culs-de-sac disappear ; and, in pregnancy, as the gland takes on its full develop-
ment, the ducts branch and extend themselves, and the vesicles are gradually developed
around their terminal extremities. These changes in the development of the mamma3 at
different periods are most remarkable and are not observed in any other of the glandu-
lar organs.

Mechanism of the Secretion of Milk. — With the exception of water and inorganic
principles, all the important and characteristic constituents of the milk are formed in the
substance of the mammary glands. The secreting structures have the property of sep-
arating from the blood a great variety of inorganic principles ; and we shall see, when
we come to study the composition of the milk more minutely, that it furnishes all the
inorganic matter necessary for the nutrition of the infant, containing, even, a small quan-
tity of iron. Precisely how the secreting vesicles separate the proper quantity of these
principles from the circulating fluid, we are unable, in the present state of our knowl-
edge, to state. It is unsatisfactory enough to say that the membranes of the vesicles
have an elective action, but this expresses the extent of our information on the subject.

The lactose, or sugar of milk, the caseine, and the fatty particles, are all produced
de novo in the gland. The peculiar kind of sugar here found does not exist anywhere
else in the organism. Even when the secretion of milk is most active, different varieties
of sugar, such as glucose or cane-sugar, injected into the blood-vessels of a living animal,
are never eliminated by the mammary glands, as they are by the kidneys; and their
presence in the blood does not influence the quantity of lactose found in the milk. All
that can be said with regard to the formation of sugar of milk is that it is produced in
the mammary glands. The mechanism of its formation is not understood.

Caseine is produced in the mammary glands, probably by a peculiar transformation of
the albuminoid constituents of the blood. This principle does not exist in the blood,
although its presence here has been mentioned by some observers. It is well known that
the caseine of milk is precipitated by an excess of sulphate of magnesia ; but the so-
called caseine of the blood is not affected by this salt and passes through it like albumen.

The fatty particles of the milk are likewise produced in the substance of the gland,
and the peculiar kind of fat which exists in this secretion is not found in the blood. The
mechanism of the production of fat in the mammary glands is obscure. The particles
are not produced in cells and set free by their rupture, by a process analogous to that
which takes place in the formation of the fatty particles found in the sebaceous matter,
for, during the time when the secretion of milk is most active, the epithelium of the
secreting culs-de-sac has entirely disappeared. The butter is produced by the action of
the amorphous walls of the vesicles, in the same way, probably, as fat is produced by
the vesicles of the ordinary adipose tissue. At least, this is all that is known regarding
the mechanism of its production.

PHYSIOLOGICAL ANATOMY OF THE MAMMARY GLANDS. 369

As regards the mechanism of the formation of the peculiar and characteristic con-
stituents of the milk, the mammary glands are to be classed among the organs of secre-
tion and not with those of elimination or excretion; for none of these elements preexist
in the blood, and they all appear first in the substance of the glands.

During the period of secretion, the glands receive a much larger supply of blood than
at other times. Pregnancy favors the development of the secreting portions of the
glands but does not induce secretion. On the other hand, when pregnancy occurs dur-
ing lactation, it diminishes, modifies, and it may arrest the secretion of milk. The secre-
tion is destined, however, for the nourishment of the child and not for use in the economy
of the mother — an important point of distinction from all other secretions — and its pro-
duction presents one or two interesting peculiarities.

In the first place, the secreting action of the mammary glands is nearly continuous.
When the secretion of milk has become fully established, while there may be certain
periods when it is formed in greater quantity than at others, there is no absolute inter-
mitteucy in its production.

Again, in all the other glandular organs, the epithelial cells found in their secreting
portion seem to be the active agents in the production of the secretions; but, in the mam-
mary glands, as we have already noted, the epithelium entirely disappears from the secret-
ing culs-de-sac during the period of greatest functional activity of the gland, and nothing
is left to perform the work of secretion but the amorphous membrane of the vesicles.

Conditions which modify the Lacteal Secretion. — Very little is known concerning the
physiological conditions which modify the secretion of milk. When lactation is fully
established, the quantity and quality of the milk secreted become adapted to the require-
ments of the child at different periods of its existence. In studying the composition of
the milk, therefore, it will be found to vary considerably in the different stages of lacta-
tion. It is evident that, as the development of the child advances, a constant increase of
nourishment is demanded; and, as a rule, the mother is capable of supplying all the
nutritive requirements of the infant for from eight to twenty months.

During the time when such an amount of nutritive matter is furnished to the child,
the quantity of food taken by the mother is sensibly increased ; but observations have
shown that the secretion of milk is not much influenced by the nature of the food. It is
necessary that the mother should be supplied with good, nutritious articles ; but, as far as
solid food is concerned, there seems to be no great difference between a coarse and a deli-
cate alimentation, and the milk of females in the lower walks of life, when the general
condition is normal, is fully as good as in women who are able to live luxuriously. It
is, indeed, a fact generally recognized by physiologists, that the secretion of milk is little
influenced by any special diet, provided the alimentation be sufficient and of the quality
ordinarily required by the system and that it contain none of the few articles of food
which are known to have a special influence upon lactation. So long as the mother is
healthy and well-nourished, the milk will take care of itself; and the appetite is the
surest guide to the proper variety, quality, and quantity of food. It is very common,
however, for females to become quite fat during lactation ; which shows that the fatty
elements of the food do not pass exclusively into the milk, but that there is a tendency,
at the same time, to a deposition of adipose tissue in the ordinary situations in which it
is found. It is a matter of common experience, that certain articles, such as acids and
fermentable substances, often disturb the digestive organs of the child without producing
any change in the milk, that can be recognized by chemical analysis. The individual
differences in women, in this regard, are very great.

The statements with regard to solid food do not apply to liquids. During lactation,

there is always an increased demand for water and for liquids generally ; and, if these be

not supplied in sufficient quantity, the secretion of milk is diminished, and its quality is

almost always impaired. It is a curious fact, which has been fuUy established by obser-

24

370 SECRETION.

vations upon the human subject and the inferior animals, that, while the quantity of
milk is increased by taking a large amount of simple water, the solid constituents are
also increased, and the milk retains all of its qualities as a nutritive fluid.

Alcohol, especially when largely diluted, as in malt-liquors and other mild beverages,
is well known to exert an influence upon the secretion of milk. Drinks of this kind
almost always temporarily increase the activity of the secretion, and sometimes they pro-
duce a certain amount of effect upon the child ; but direct and accurate observations on
the actual passage of alcohol into the milk are wanting. During lactation, the moderate
use of drinks containing a small proportion of alcohol is frequently beneficial, particu-
larly in assisting the mother to sustain the unusual drain upon the system. There are.
however, few instances of normal lactation in which their use is absolutely necessary.

It is well known that the secretion of milk may be profoundly affected by violent
mental emotions. This is the case in many other secretions, as the saliva and the
gastric juice. It is hardly necessary, however, to cite the numerous instances of modifi-
cation or arrest of the secretion from this cause, which are quoted in many works. Ver-
nois and Becquerel mention a very striking case, in which a hospital wet-nurse, who had
lost her only child from pneumonia, became violently affected with grief and presented,
as a consequence, an immediate diminution in the quantity of her milk, with a great
reduction in the proportion of salts, sugar, and butter. In this case the proportion of
caseine was increased. Sir Astley Cooper mentions two cases in which the secretion of
milk was instantaneously and permanently arrested from terror. These cases are types
of numerous others, which have been reported by writers, of the effects of mental emo-
tions upon secretion.

In the present state of our knowledge, we can comprehend the influence of men-
tal emotions upon secretion, only by assuming that they operate through the nervous
system ; and, in many of the glands, the influence of the nerves has been clearly demon-
strated by actual experiment. Direct observations, however, upon the influence of the
nerves upon the mammary glands are few and unsatisfactory. The operation of dividing
the nerves distributed to these glands, which has occasionally been practised upon ani-
mals in lactation, has not been observed to produce any sensible diminution in the quan-
tity of the secretion. It is difficult, however, to operate upon all the nerves distributed
to these organs.

Quantity of Milk. — It is very difficult to form a reliable estimate of the average quan-
tity of milk secreted by the human female in the twenty -four hours. The amount un-
doubtedly varies very much in different persons ; some women being able to nourish two
children, while others, though apparently in perfect health, furnish hardly enough food
for one. Cooper, as the result of direct observation, states that the quantity that can be
drawn from a full breast is usually about two fluidounces. This may be assumed to be
about the quantity contained in the lactiferous ducts when they are moderately distended.
Lehmann, taking for the basis of his calculations the observations of Lampe'rierre, who
found, as the result of sixty-seven experiments, that from fifty to sixty grammes of milk
were secreted in two hours, estimates that the average quantity discharged in twenty-
four hours is 1,320 grammes, or about 44'5 fluidounces. Taking into consideration the
evident variations in the quantity of milk secreted by different women, it may be
assumed that the daily production is from two to three pints.

Certain conditions of the female are capable of materially influencing the quantity of
milk secreted. It is evident that the secretion is usually somewhat increased within the
first few months of lactation, when the progressive development of the child demands an
increase in the quantity of nourishment. If the menstrual function become reestablished
during lactation, the milk is usually diminished in quantity during the periods, but some-
times it is not affected, either in its quantity or composition. Should the female become
pregnant, there is generally a great diminution in the quantity of milk, and that which

PROPERTIES AND COMPOSITION OF THE MILK. 371

it secreted is ordinarily regarded as possessing little nutritive power. In obedience to a
popular prejudice, apparently well-founded, the child is usually taken from the breast as
soon as pregnancy is recognized. Authors have not noted any marked and constant
variations in the quantity of milk in females of different ages.

Properties and Composition of the Milk.

The general appearance and characters of ordinary cow's milk are sufficiently famil-
iar and may serve as a standard for comparison with the milk of the human female.
Human milk is neither so white nor so opaque as cow's milk, having ordinarily a slightly
bluish tinge. The milk of different healthy women presents some variation in this
regard. After the secretion has become fully established, the fluid possesses no visicidty
and is nearly opaque. It is almost inodorous, of a peculiar soft and sweetish taste,
and, when perfectly fresh, has a decidedly alkaline reaction. The taste of human milk
is sweeter than that of cow's milk. A short time after its discharge from the gland, the
reaction of milk becomes faintly acid ; but this change takes place more slowly in
human milk than in the milk of most of the inferior animals.

The average specific gravity of human milk, according to Yernois and Becquerel, is
1032 ; although this is subject to considerable variation, the minimum of eighty-nine
observations being 1025, and the maximum, 1046. The observations of most physiological
chemists have shown that this average is nearly correct.

Milk is not coagulated by heat, even after prolonged boiling ; but a thin pellicle then
forms on the surface, which is probably due to the combined action of heat and the
atmosphere upon the caseine. Although a small quantity of albumen exists in the milk,
this does not coagulate on the surface by the action of the heat, for the scum does not
form when the fluid is heated in an atmosphere of carbonic acid or of hydrogen, or in a
vacuum.

When the milk is coagulated by any substance acting upon the caseine, or when it
coagulates spontaneously, it separates into a curd, composed of caseine with most of the
fatty particles, and a nearly clear, greenish-yellow serum, called whey. This separation
occurs spontaneously, at a variable time after the discharge of the milk, taking place
much more rapidly in warm than in cold weather. It is a curious fact that fresh milk is
frequently coagulated during a thunder-storm, a phenomenon which has never been sat-
isfactorily explained.

On being allowed to stand for a short time, the milk separates, without coagulating,
into two tolerably distinct portions. A large proportion of the globules rises to the top,
forming a yellowish-white and very opaque fluid, called cream, leaving the lower portion
poorer in globules and of a decidedly bluish tint. In healthy milk, the stratum of cream
forms from one-fifth to one-third of the entire mass of the milk. In the human subject,
the skim-milk is not white and opaque, but it is nearly as transparent as the whey. A
very good method of testing the richness of milk is by the use of little graduated glasses,
called lactometers, by which we can measure the thickness of the layer of cream. The
specific gravity of the cream from milk of the average specific gravity of 1032 is about
1024. The specific gravity of skim-milk is about 1034.

Microscopical Characters of the Milk. — If a drop of milk be examined with a magni-
fying power of from three hundred to six hundred diameters, the cause of its opacity
will bo apparent. It contains an immense number of minute globules, of great refractive
power, held in suspension in a clear fluid. These are known under the name of milk-
globules and are composed of margarine, oleine, and a fatty matter, peculiar to milk,
called butyrine. In human milk the particles are perfectly spherical ; but in cow's milk
they are often polyhedric from mutual compression. This difference is due to the softer
consistence of the butter in human milk, the globules containing a much larger propor-
tion of oleine ; and, if cow's milk be warmed, the particles also assume a spherical form.

372

SECRETION.

FIG. 108. — Human milk-globules, from a healthy
lying-in woman, eight days after delivery.
(Funke.)

The human milk-globules measure from 25^00 to y^- of an inch in diameter. They are
usually distinct from each other, but they may occasionally become collected into groups
without indicating any thing abnormal. In a perfectly normal condition of the glands,

when the lacteal secretion has become fully es-
tablished, the milk contains nothing but a clear
fluid with these globules in suspension. The
proportion of fatty matter in the milk is from
twenty -five to forty-eight parts per thousand,
and this gives an idea of the proportion of
globules which are seen on microscopical ex-
amination.

There has been a great deal of discussion
with regard to the anatomical constitution of
the milk-globules. In many late works it is
stated that these are true anatomical elements,
composed of fatty matters surrounded by an
albuminoid membrane ; but some writers as-
sume that the fat is merely in the form of an
emulsion and is simply divided into globules
and held in suspension, like the fatty particles
of the chyle. No one, however, has assumed
to have seen the investing membrane of the milk-globules, and its existence is only
inferred from the behavior of these little particles in the presence of certain reagents.
It is unnecessary to review in detail the numerous opinions that have been advanced
on this subject. As far as can be ascertained by simple examination, even with the
highest magnifying powers, the globules appear perfectly homogeneous ; and the burden
of proof rests with those who profess to be able to demonstrate the existence of an
investing membrane. Robin, one of the highest authorities on these subjects, argues
against the existence of a membrane and opposes the observations of those who assume
to have demonstrated it, by explanations of the phenomena produced by reagents, which
do not involve, as a necessity, the presence of such a structure. The arguments in favor
of its existence are not very satisfactory ; and the experiments upon which they are
based relate chiefly to the action of ether upon the globules before and after the action
of other reagents.

If a quantity of milk be shaken up with an equal volume of ether, the mixture
remains opaque ; but, if a little potash be added, the fatty matters are dissolved, and the
mixture then becomes more or less clear. These facts are all that can be observed with-
out following out the changes with the microscope. Robin has shown that the fatty
particles are acted upon when the milk is thoroughly agitated with ether alone ; and
that the opacity is then due to the fact that the ether, with the fat in solution, is itself
in the form of an emulsion. If the opaque mixture of milk and ether be examined
with the microscope, globules are seen, larger than the ordinary milk-globules, paler,
and possessing much less refractive power. These he supposes to be composed of fat
and ether. If potash be added, either before or after the addition of ether, the consti-
tution of the whole mass of liquid is changed, and it becomes somewhat transparent,
though by no means perfectly clear. It is assumed that, in the first instance, the ether
does not attack the globules, because it has no effect upon the membrane which is sup-
posed to exist, and that the potash acts upon the membrane, allowing the ether then to
take up the fat; but, if the observations of Robin be correct, it is evident that this view
cannot be sustained.

If dilute acetic acid be added to a specimen of milk under the microscope, the glob-
ules become deformed, and some of them show a tendency to run together ; an appear-
ance which is supposed by Henle, who was the first to study closely the action of acetic

COMPOSITION OF HUMAN MILK. 373

acid upon the milk-globules, to indicate the existence of a memhrane. This deduction,
however, is not justifiable. Acetic acid readily coagulates the caseine, a principle which
is most efficient in maintaining the fat in its peculiar condition. The coagulating caseine
then presses upon the globules, and produces, in this way, all the changes in form that
have been observed.

Most of the other arguments in favor of the existence of a membrane have no support
from direct observation, and consequently they do not demand special consideration;
while all the facts which we have been able to find relating to this subject go to show
that the fatty matters in the milk are in the condition of a simple emulsion. The precise
condition, however, of the fluid immediately surrounding the globules is not fully under-
stood. Certain of the constituents of fluids capable of forming emulsive mixtures with
liquid fats may form a coating of excessive tenuity immediately around the globules, but
they never constitute distinct membranes capable of resisting the action of solvents upon
the fats; and, in the case of the milk, they do not prevent the mechanical union of the
globules into masses, as occurs in the process of churning. Milk-globules less than ^Vs of
an inch in diameter present under the microscope that peculiar oscillating motion known
as the Brownian movement. This is arrested on the addition of acetic acid, by coagula-
tion of the caseine. From these facts, it is evident that the milk-globules are composed
simply of fat in the form of a fine emulsion. They are not true anatomical elements,
originating by a process of genesis in a blastema, undergoing physiological decay, and ca-
pable of self-regeneration from materials furnished by the menstruum in which they are
suspended, like the blood-corpuscles or leucocytes. They are simply elements of secretion.

Composition of the Milk. — "We do not propose, in treating of the composition of the
milk, to consider the various methods of analysis which have been employed by different
chemists. The only constituent that has ever presented much difficulty in the estimation
of its quantity is caseine ; but the various processes now employed for its extraction have
led to nearly identical results. The following table, compiled by Eobin from the analy-
ses of various chemists, gives the constituents of human milk :

Composition of Human Milk.

Water 902-717 to 863-149

Caseine (desiccated) 29-000 " 39*000

Lacto-proteine I'OOO " 2-770

Albumen traces " 0-880

rMargarine 17'000 " 26-840

Butter, 25 to 38 -I Oleine 7'600 " H'400

[fiutyrine, caprine, caproine, capriline 0*500 " 0'760

Sugar of milk (lactine, or lactose) 37'000 " 49-000

Lactafe of soda(?) 0-420 " 0-450

Chloride of sodium 0'240 " 0'340

Chloride of potassium 1-440 " 1'830

Carbonate of soda 0-053 " 0'056

Carbonate of lime 0-069 " 0-070

Phosphate of lime of the bones 2-310 " 3'440

Phosphate of magnesia 0'420 " 0'640

Phosphate of soda 0-225 " 0-230

Phosphate of iron (?) 0-032 " 0-070

Sulphate of soda 0-074 " 0'075

Sulphate of potassa traces.

( Oxygen 1'29 } 1,000-000 1,000'000

Gases in solution < Nitrogen 12-17 > 30 parts per 1,000 in volume. (Hoppe.)

( Carbonic acid. 16 '54 )

374 SECRETION.

The proportion of water in milk is subject to a certain amount of variation, but this
is not so considerable as might be expected from the great variations in the entire quan-
tity of the secretion. In treating of the quantity of milk in the twenty-four hours, we
have seen that the influence of drinks, even when nothing but pure water has been taken,
is very marked ; and, although the activity of the secretion is much increased by fluid
ingesta, the quality of the milk is not usually affected, and the proportion of water to the
solid matters remains about the same.

Nitrogenized Constituents of Milk. — Very little remains to be said concerning the
nitrogenized constituents of human milk, after what has been stated under the head of
alimentation. The different principles of this class undoubtedly have the same nutritive
function and they appear to be identical in all varieties of milk, the only difference being
in their relative proportion. It is a matter of common experience, indeed, that the milk
of many of the lower animals will take the place of human milk, when prepared so as to
make the proportions of its different constituents approximate the composition of the nat-
ural food of the child. A comparison of the composition of human milk and cow's milk
shows that the former is poorer in nitrogenized matters and richer in butter and sugar ;
and consequently, the upper strata of cow's milk, appropriately sweetened and diluted
with water, very nearly represent the ordinary breast-milk.

Caseine is by far the most important of the nitrogenized principles of milk, and it sup-
plies nearly all of this kind of nutritive matter demanded by the child. Lacto-proteine,
a principle described by Millon and Cornmaille, is not so well defined, and albumen
exists in the milk in very small quantity. That albumen always exists in milk, can readily
be shown by the following process described by Bernard : If milk, treated with an
excess of sulphate of magnesia sp as to form a thin paste, be thrown upon a filter, the case-
ine and fatty matters will be retained, and the clear liquid that passes through shows a
marked opacity upon the application of heat or the addition of nitric acid.

The coagulation of milk depends upon the reduction of caseine from a liquid to a
semisolid condition. When milk is allowed to coagulate spontaneously, or sour, the
change is effected by the action of the lactic acid which results from a transformation of a
portion of the sugar of milk. Caseine, in fact, is coagulated by any of the acids, even
the feeble acids of organic origin. It differs from albumen in this regard and in the fact
that it is not coagulated by heat. It has been suggested that, in fresh milk, the caseine
exists in combination with carbonate of soda, and that coagulation always takes place
from the action of acids upon this salt, by which the caseine is set free. It is true that
coagulated caseine may be readily dissolved in a solution of carbonate of soda, but it has
been shown that coagulation may be induced by the agency of certain neutral principles,
while the milk retains its alkaline reaction. If fresh milk be slightly raised in tempera-
ture and be treated with an infusion of the gastric mucous membrane of the calf, coagu-
lation will take place in from five to ten minutes, the clear liquid still retaining its alka-
line reaction. Simon has observed that the mucous membrane of the stomach of an
infant a few days old, that had recently died, coagulated woman's milk more readily than
the mucous membrane of the stomach of the calf.

Non- Nitrogenized Constituents of Milk. — Non-nitrogenized matters exist in abun-
dance in the milk. The liquid caseine and the water hold the fats, as we have seen, in
the condition of a fine and permanent emulsion. This fat has been separated from the
milk and analyzed by chemists and is known under the name of butter. In human
milk, the butter is much softer than in the milk of many of the inferior animals, particu-
larly the cow ; but it is composed of essentially the same constituents, although in differ-
ent proportions. In different animals, there are developed, even after the discharge of
the milk, certain odorous principles, which are more or less characteristic of the animal
from which the butter is taken.

The greatest part of the butter consists of margarine. It contains, in addition, oleine,
with a small quantity of peculiar fats, which have not been very well determined, called

VARIATIONS IN THE COMPOSITION OF THE MILK. 375

butyrine, caprine, caproine, and capriline. The margarine and oleine are principles found
in the fat throughout the body ; but the last-named substances are peculiar to the milk.
These are especially liable to acidification, and the acids resulting from their decomposi-
tion give the peculiar odor and flavor to rancid butter.

Sugar of milk, sometimes called lactine, or lactose, is the most abundant of the solid
constituents of the mammary secretion. It is this principle that gives to the milk its
peculiar sweetish taste, although this variety of sugar is much less sweet than cane-sugar.
The chief peculiarities of milk-sugar are that it readily undergoes change into lactic acid
in the presence of nitrogenized ferments and takes on alcoholic fermentation slowly and
with difficulty. At one time, indeed, it was supposed that milk-sugar could not be de-
composed into alcohol and carbonic acid ; but it is now well established that this change
can be induced, the only peculiarity being that it takes place very slowly. In some parts
of the world, intoxicating drinks are made by the alcoholic fermentation of milk.

A consideration of the nutritive action of the fatty and saccharine constituents of milk
belongs properly to the subjects of alimentation and nutrition. It may be stated here,
however, that these principles seem to be as necessary to the nutrition of the child as the
nitrogenized principles; although the precise manner in which they affect the develop-
ment and regeneration of the tissues has not been ascertained.

Inorganic Constituents of Milk. — It is probable that many inorganic principles exist
in the milk which are not given in the table ; and the separation of these principles from
their combinations with organic matters is one of the most difficult problems in physio-
logical chemistry. This must be the case for, during the first months of extra-uterine
existence, the child derives all the inorganic, as well as the organic matters necessary to
nutrition and development, from the breast of the mother. The reaction of the milk
depends upon the presence of the alkaline carbonates, and these principles are important
in preserving the fluidity of the caseine. It is not determined precisely in what form iron
exists in the milk, but its presence here is undoubted. A comparison of the composition
of the milk with that of the blood shows that most of the important inorganic prin-
ciples found in the latter fluid exist also in the milk.

Hoppe has indicated the presence of carbonic acid, nitrogen, and oxygen, in solution
in milk. Of these gases, carbonic acid is the most abundant. It is well known that
the presence of gases in solution in liquids renders them more agreeable to the taste,
and carbonic acid increases very materially their solvent properties. Aside from these
considerations, the precise function of the gaseous constituents of the milk is not ap-
parent.

A study of the composition of the milk fully confirms the fact, which we have already
had occasion to state, that this is a typical alimentary fluid and presents in itself the
proper proportion and variety of material for the nourishment of the body during the
period when the development of the system is going on with its maximum of activity.
The form in which its different nutritive constituents exist is such that they are easily
digested and are assimilated with great rapidity.

Variations in the Composition of the Milk.

Vernois and Becquerel have indicated a certain amount of variation at different ages
and at different periods in lactation, but they show, at the same time, that the fluid is not
subject to changes in its composition sufficiently great to influence materially the nutrition
of the child.

If the composition of the milk be compared at different periods of lactation, it will be
found to undergo great changes during the first few days. In fact, the first fluid secreted
after parturition is so different from ordinary milk, that it has been called by another name.
It is then known as colostrum, the peculiar properties of which will be considered more
fully hereafter, under a distinct head. As the secretion of milk becomes established, the
fluid, from the first to the fifteenth day, becomes gradually diminished in density and

376 SECRETION.

in its proportion of water and of sugar, while there is a progressive increase in the pro-
portion of most of the other constituents, viz., butter, caseine, and the inorganic salts.
The milk, therefore, as far as we can judge from its composition, as it increases in
quantity during the first few days of lactation, is constantly increasing in its nutritive
properties.

The differences in the composition of the milk, taken from month to month during the
entire period of lactation, are not so distinctly marked. It is difficult, indeed, to indicate
any constant variations of sufficient importance to lead to the view that the milk varies
much in its nutritive properties at different times, during the ordinary period of lactation.
The differences noted between the milk of primipara and multipart were very slight and
unimportant. As a rule, however, the milk of priiniparse approaches more nearly the
normal standard.

The menstrual periods, when they occur during lactation, have been found by most
observers to modify considerably the composition and properties of the milk; and it is
well known to practical physicians that the secretion is then liable to produce serious
disturbances of the digestive system of the child, although frequently these effects are not
observed. The changes in the composition of the milk which commonly occur during
menstruation are, great increase in the quantity of caseine, increase in the proportion of
butter and the inorganic salts, and a slight diminution in the proportion of sugar. The
common impression that the milk is unfit for the nourishment of the child if pregnancy
occur during lactation is undoubtedly well-founded, although analyses of the milk of
pregnant women have never been made upon an extended scale.

In normal lactation, there is no marked and constant difference in composition between
milk that has been secreted in great abundance and milk which is produced in compara-
tively small quantity ; nor do we observe that difference between the milk first drawn
from the breast and that taken when the ducts are nearly empty, which is observed in
the milk of the cow.

The influence of alimentation and the taking of liquids upon lactation relates chiefly to
the quantity of milk and has already been considered.

In treating of the influences which modify the secretion of milk, we have already
alluded to the effects of violent mental emotions upon the production and the composition
of this fluid. The very remarkable case of profound alteration of the milk by violent
grief, detailed by Vernois and Becquerel, is the only one in which the secretion in this
condition has been carefully analyzed. The changes thus produced in its composition
have already been referred to, the most marked difference being observed in the propor-
tion of butter, which became reduced from 23'79 to 5'14 parts per 1,000.

Colostrum.

Near the end of utero-gestation, during a period which varies considerably in different
women and has not been accurately determined, a small quantity of a thickish, stringy
fluid may frequently be drawn from the mammary glands. This bears little resemblance
to perfectly-formed milk. It is small in quantity and is usually more abundant in multi-
part than in primipara). This fluid, with that secreted for the first few days after
delivery, is called colostrum. It is yellowish, semiopaque, of a distinctly alkaline reaction,
and is somewhat mucilaginous in its consistence. Its specific gravity is considerably above
that of the ordinary milk, being from 1040 to 1060. As lactation progresses, the charac-
ter of the secretion rapidly changes, until it becomes loaded with true milk-globules and
assumes the characters of ordinary milk.

The opacity of the colostrum is due to the presence of a number of different cor-
puscular elements. Milk-globules, very variable in size and number, are to be found in
the secretion from the first. These, however, do not exist in sufficient quantity to render
the fluid very opaque, and they are frequently aggregated in rounded and irregular
masses, held together, apparently, by some glutinous matter. Peculiar corpuscles, first

COMPOSITION OF COLOSTRUM.

377

The smaller globules are globules of milk ; the larger
globules, a, a, filled with granulations, are coios-
triim-corpuscles. As lactation advances, the co-
lostrum-corpuscles gradually disappear, and the
milk-globules become more numerous, smaller,
and more uniform in size.

accurately described by Donne, under the name of " granular bodies," and supposed to
be characteristic of the colostrum, always exist in this fluid. These are now known as
colostrum-corpuscles. They are spherical, varying in size from -gjini to -s^s °f an inch, are
sometimes pale, but more frequently quite gran-
ular, and they contain very often a large num-
ber of fatty particles. They behave in all respects
like leucocytes and are described by Kobin as a
variety of these bodies. Many of them are pre-
cisely like the leucocytes found in the blood,
lymph, or pus. We now know, however, that
the so-called mucus-corpuscle does not differ
from the pus-corpuscle or the white corpuscle
of the blood ; and leucocytes generally, when
confined in liquids that are not subject to
movements, are apt to undergo enlargement,
to become fatty, and, in short, they may pre-
sent all the different appearances observed in
the colostrum-corpuscles. In addition to these
corpuscular elements, a small quantity of muco-
sine may frequently be observed in the colos-
trum on microscopical examination.

On the addition of ether to a specimen of
colostrum under the microscope, most of the
fatty particles, both within and without the
colostrum-corpuscles, are dissolved. Ammonia

added to the fluid renders it stringy, and sometimes the entire mass assumes a gelati-
nous consistence.

In its proximate composition, colostrum presents many points of difference from
true milk. It is sweeter to the taste and contains a greater proportion of sugar and
of the inorganic salts. The proportion of fat is at least equal to the proportion in the
milk and is generally greater. Instead of caseine, pure colostrum contains a large
proportion of albumen ; and, as the character of the secretion changes in the process of
lactation, the albumen becomes gradually reduced in quantity and caseine takes its place.

The following, deduced from the analyses of Clemm, may be taken as the ordinary
composition of colostrum of the human female :

Composition of Colostrum.

Water 945-24

Albumen, and salts insoluble in alcohol , 29'81

Butter 7-07

Sugar of milk, extractive matter, and salts soluble in alcohol 17'27

Loss 0-61

1,000-00

Colostrum ordinarily decomposes much more readily than milk and takes on putre-
factive changes very rapidly. If it be allowed to stand for from twelve to twenty-four
hours, it separates into a thick, opaque, yellowish cream and a serous fluid. In an
observation by Sir Astley Cooper, nine measures of colostrum, taken soon after partu-
rition, after twenty -four hours of repose, gave six parts of cream to three of milk.

The peculiar constitution of the colostrum, particularly the presence of an excess of
sugar and inorganic salts, renders it somewhat laxative in its effects, and it is supposed
to be useful, during the first few days after delivery, in assisting to relieve the infant of
the accumulation of meconium.

378 SECRETION.

As the quantity of colostrum that may be pressed from the mammary glands during
the latter periods of utero-gestation, particularly the last month, is very variable, it
becomes an interesting and important question to determine whether this secretion have
any relation to the quantity of milk that may be expected after delivery. This has been
made the subject of careful study by Donne, who arrived at the following important
conclusions :

In women in whom the secretion of colostrum is almost absent, the fluid being in
exceedingly small quantity, viscid, and containing hardly any corpuscular elements, there
is hardly any milk produced after delivery.

In women who, before delivery, present a moderate quantity of colostrum, contain-
ing very few milk-globules and a number of colostrum-corpuscles, after delivery the milk
will be scanty or it may be abundant, but it is always of poor quality.

When the quantity of colostrum produced is considerable, the secretion being quite
fluid and rich in corpuscular elements, particularly milk-globules, the milk alter delivery
is always abundant and of good quality.

From these observations, it would seem that the production of colostrum is an indi-
cation of the proper development of the mammary glands ; and the early production of
fatty granules, which are first formed by the cells lining the secreting vesicles, indicates
the probable activity in the secretion of milk after lactation has become fully estab-
lished.

The secretion of the mammary glands preserves the characters of colostrum until
toward the end of the milk-fever, when the colostrum-corpuscles rapidly disappear, and
the milk-globules become more numerous, regular, and uniform in size. It may be stated,
in general terms, that the secretion of milk becomes fully established and all the charac-
ters of the colostrum disappear at from the eighth to the tenth day after delivery. A few
colostrum-corpuscles and masses of agglutinated milk-globules may sometimes be dis-
covered after the tenth day, but they are very rare. After the fifteenth day, the milk
does not sensibly change in its microscopical or its chemical characters.

Lacteal Secretion in the Newly-Born.

It is a curious fact that in infants of both sexes there is generally a certain amount
of secretion from the mammary glands, commencing at birth or from two to three days
after, and continuing sometimes for two or three weeks. The quantity of fluid that may
be pressed out at the nipples at this time is very variable. Sometimes only a few drops
can be obtained, but occasionally the fluid amounts to one or two drachms. Although
it is impossible to indicate the object of this secretion, which takes place when the glands
are in a rudimentary condition, it has been so often observed and described by physiolo-
gists, that there can be no doubt with regard to the nature of the fluid and the fact that
the secretion is almost always produced in greater or less quantity. The following is an
analysis by Quevenne of the secretion obtained by Gubler. The observations of Gubler
were very extended and were made upon about twelve hundred children. The secretion
rarely continued for more than four weeks, but in four instances it persisted for two
months.

Composition of the Milk of the Infant.

Water , 894'GO

Caseine 26'40

Sugar of milk 62-20

Butter 14-00

Earthy phosphates 1 -20

Soluble salts (with a small quantity of insoluble phosphates) 2'20

1,000-00

GENERAL CONSIDERATIONS. 379

This fluid docs not differ much in its composition from ordinary milk. The propor-
tion of butter is much less, but the amount of sugar is greater, and the quantity of case-
ine is nearly the same.

Of the other fluids which are enumerated in the list of secretions, the saliva, gastric
juice, pancreatic juice, and the intestinal fluids have already been considered in connec-
tion with digestion. The physiology of the lachrymal secretion will be taken up in con-
nection with the eye, and the bile will be treated of fully under the head of excretion.

CHAPTER XII.

EXCRETION BY THE SKIN AND KIDNEYS.

Differences between the secretions proper and the excretions— Physiological anatomy of the skin— Physiological
anatomy of the nails and hairs— Sudden blanching of the hair— Uses of the hairs— Perspiration— Sudoriparous
glands — Mechanism of the secretion of sweat — Properties and composition of the sweat — Peculiarities of the
sweat in certain parts— Physiological anatomy of the kidneys— Distribution of blood-vessels in the kidneys
—Lymphatics and nerves of the kidneys— Mechanism of the production and discharge of urine— Formation
of the excrementitious constituents of the urine in the tissues, absorption of these principles by the blood,
and separation of them from the blood by the kidneys— Effects of removal of both kidneys from a living animal
—Effects of tying the ureters in a living animal— Extirpation of one kidney— Influence of blood-pressure, the
nervous system, etc., upon the secretion of urine— Alternation in the action of the kidneys upon the two sides-
Changes in the composition of the blood in passing through the kidneys— Physiological anatomy of the urinary
passages — Mechanism of the discharge of urine — Properties and composition of the urine— General physical prop-
erties of the urine— Quantity, specific gravity, and reaction of the urine— Composition of the urine— Gases of
the urine— Variations in the composition of the urine— Variations produced by food— Urina potus, urina cibi,
and urina sanguinis — Influence of muscular exercise upon the urine — Influence of mental exertion.

IN entering upon the study of the elimination of effete matters, it is necessary to
appreciate fully the broad distinctions between the secretions proper and the excretions,
in their composition, the mechanism of their production, and their destination. These
considerations are again referred to, for the reason that they have not ordinarily received
that attention in works upon physiology which their importance seems to demand. The
mechanism of excretion is inseparably connected with the function of nutrition, and it
forms one of the great starting-points in the study of all the modifications of nutrition in
diseased conditions.

Taking the urine as the type of the excrementitious fluids, it is found to contain none
of those principles included in the class of non-crystallizable, organic nitrogenized mat-
ters, but is composed entirely of crystallizable matters, simply held in solution in water.
The character of these principles depends upon the constitution of the blood and the gen-
eral condition of nutrition, and not upon any formative action in the glands. The principles
themselves represent the ultimate physiological changes of certain constituent parts of the
living organism, and they are in such a condition that they are of no farther use in the
economy and are simply discharged from the body. Certain inorganic matters are found
in the excrementitious fluids, are discharged with the products of excretion, and are thus
associated with the organic principles of the economy in their physiological destruction,
as well as in their deposition in the tissues. Coagulable organic matters, or albuminoid
principles, never exist in the excrementitious fluids under normal conditions ; except as
the products of other glands may become accidentally or constantly mixed with the
excrementitious fluids proper. The same remark applies to the non-nitrogenized matters
(sugars and fats), which, whether formed in the organism or taken as food, are consumed
as such in the process of nutrition. The production of the excretions is constant, being-
subject only to certain modifications in activity, which are dependent upon varying con-
ditions of the system. All of the elements of excretion preexist in the blood, either in
the precise condition in which they are discharged or in some slightly-modified form.

380 EXCRETION.

Under the head of excretion, it is proposed to consider the general properties and
composition of the different excrementitious fluids; but the relations of the excremen-
titious matters themselves to the tissues will be more fully treated of in connection with
nutrition.

The urine is a purely excrementitious fluid. The perspiration and the secretion of the
axillary glands are excrementitious fluids, but they contain a certain amount of the secre-
tion of the sebaceous glands. Certain excrementitious matters are found in the bile, but,
at the same time, this fluid contains principles manufactured in the liver and has an impor-
tant function as a secretion, in connection with the process of digestion.

Physiological Anatomy of the Skin.

The skin is one of the most complex and important structures in the body, and it pos-
sesses a variety of functions. In the first place, it forms a protective covering for the
general surface. It is quite thick over the parts most subject to pressure and friction, is
elastic over movable parts and those liable to variations in size, and, in many situations,
is covered with hair, which affords an additional protection to the subjacent structures.
The skin and its appendages are imperfect conductors of caloric, are capable of resisting
very considerable variations in temperature, and they thus tend to maintain the normal
standard of the animal heat. As an organ of tactile sensibility, the skin has an important
function, being abundantly supplied with sensitive nerves, some of which present an
arrangement peculiarly adapted to the nice appreciation of external impressions. The
skin assists in preserving the external forms of the muscles. It also relieves the abrupt
projections and depressions of the general surface and gives roundness and grace to the
contours of the body. In some parts it is very closely attached to the subjacent struct-
ures, while in others it is less adherent and is provided with a layer of adipose tissue.

As an organ of excretion, the skin is very important ; and, although the quantity of
excrementitious matter exhaled from it is not very great and probably not subject to
much variation, the evaporation of water from the general surface is always considerable
and is subject to such modifications as may become necessary from the varied conditions
of the animal temperature. Thus, while the skin protects the body from external influ-
ences, its function is important in regulating the heat produced as one of the numerous
phenomena attendant upon the general process of nutrition.

As the skin presents such a variety of functions, its physiological anatomy is most
conveniently considered in connection with different divisions of the subject of physi-
ology. For example, under the head of secretion, we have already taken up the struct-
ure of the different varieties of sebaceous glands ; and the anatomy of the skin as an organ
of touch will be most appropriately considered in connection with the nervous system.
In this connection, we shall describe the excreting organs found in the skin ; and here it
will be most convenient to study briefly its general structure and the most important
points in the anatomy of the epidermic appendages. A full and connected description of
the skin and its appendages belongs properly to works upon anatomy.

Extent and Thickness of the Slcin. — Sappey has made a number of very careful
observations upon the extent of the surface of the skin. Without detailing the measure-
ments of different parts, it may be stated, as the general result of his observations, that
the cutaneous surface in a good-sized man is equal to a little more than sixteen square feet;
and, in men of more than ordinary size, it may extend to twenty-one or twenty-two
square feet. In women of medium size, as the mean result of three observations, the
surface was found to equal about twelve square feet. When we consider the great extent
of the cutaneous surface, it is not surprising that the amount of secretion, under certain
conditions, should be enormous. Indeed, under all circumstances, the amount of elimina-
tion is very considerable, and the skin is really one of the most important of the organs
of excretion.

PHYSIOLOGICAL ANATOMY OF THE SKIN. 381

The thickness of the skin varies very much in different parts. Where it is exposed
to constant pressure and friction, as on the soles of the feet or the palms of the
hands, the epidermis becomes very much thickened, and in this way the more delicate
structure of the true skin is protected. It is well known that the development of the
epidermis, under these conditions, varies in different persons, with the amount of press-
ure and friction to which the surface is habitually subjected. The true skin is from T^
to £ of an inch in thickness ; but in certain parts, particularly in the external auditory
meatus, the lips, and the glans penis, it frequently measures not more than T^ of
an inch.

Layers of the Slcin. — The skin is naturally divided into two principal layers, which
may be readily separated from each other by maceration. These are, the true skin (cutis
vera, derma, or corium), and the epidermis, cuticle, or scarf-skin. The true skin is at-
tached to the subjacent structures, more or less closely, by a fibrous structure called the
subcutaneous areolar tissue, in the meshes of which we commonly find a certain quantity
of fatty tissue. This layer is sometimes described under the name of the panniculus adi-
posus. The thickness of the adipose layer varies very much in different parts of the
general surface and in different persons. There is no fat beneath the skin of the eyelids,
the upper and outer part of the ear, the penis, and the scrotum. Beneath the skin of
the cranium, the nose, the neck, the dorsum of the hand and foot, the knee, and the
elbow, the fatty layer is about -fa of an inch in thickness. In other parts it usually
measures from | to ^ of an inch. In very fat persons it may measure one inch or more.
Upon the head and the neck, in the human subject, are muscles attached more or less
closely to the skin. These are capable of moving the skin to a slight extent. Muscles
of this kind are largely developed and quite extensively distributed in some of the lower
animals.

There is no sharply-defined line of demarcation between the cutis and the subcuta-
neous areolar tissue ; and the under surface of the skin is always irregular, from the
presence of numerous fibres which are necessarily divided in detaching it from the sub-
jacent structures. The fibres which enter into the composition of the skin become looser
in their arrangement near its under surface, the change taking place rather abruptly,
until they present large aveolaD, which generally contain a certain amount of adipose
tissue.

The layer called the true skin is subdivided into a deep, reticulated, or fibrous layer,
and a superficial portion, called the papillary layer. The epidermis is also divided into
two layers, as follows : an external layer, called the horny layer ; and an internal layer,
called the Malpighian, or the mucous layer, which is in contact with the papillary layer
of the corium.

The Corium, or True Slcin. — The reticulated and the papillary layer of the true skin are
quite distinct. The lower stratum, the reticulated layer, is much thicker than the papil-
lary layer and is dense, resisting, quite elastic, and slightly contractile. It is composed of
numerous bundles of white fibrous tissue interlacing with each other in every direction,
generally at acute angles. Distributed throughout this layer, are found numerous anas-
tomosing, elastic fibres of the small variety, and with them a number of non-striated
muscular fibres. This portion of the skin contains, in addition, a considerable quantity
of amorphous matter, which serves to hold the fibres together. The muscular fibres are
particularly abundant about the hair-follicles and the sebaceous glands connected with
them, and their arrangement is such that, when they are excited to contraction by cold
or by electricity, the follicles are drawn up, projecting upon the general surface and
producing the appearance known as " goose-flesh." Contraction of these fibres is par-
ticularly marked about the nipple, producing the so-called erection of this organ, and
about the scrotum and penis, wrinkling the skin of these parts. The peculiar arrange-

382 EXCRETION.

ment of the little muscles around the hair-follicles, forming little bands attached to the
surface of the true skin and the base of the follicles, explains fully the manner in which
the " goose-flesh " is produced. (See Fig. 107, page 387.) Contraction of the skin, in
obedience to the stimulus of electricity, has been repeatedly demonstrated, both in the
living subject and in executed criminals immediately after death.

The papillary layer of the skin passes insensibly into the subjacent structure and
presents no well-marked line of division. It is composed chiefly of amorphous mat-
ter like that which exists in the reticulated layer. The papillae themselves appear to
be simple elevations of this amorphous matter, although they may contain a few fibres.
In this layer, we find a number of fibro-plastic nuclei, with a few little corpuscular bodies
called by Kobin, cytoblastions.

As regards their form, the papilla? may be divided into two varieties ; the simple and
the compound. The simple papillae are conical, rounded, or club-shaped elevations of
the amorphous matter and are irregularly distributed on the general surface. The
smallest are from Ti^ to ^-5- of an inch in length and are found chiefly upon the face.
The largest are on the palms of the hands, the soles of the feet, and the nipple. These
measure from ^-¥ to ^¥ of an inch. Large papillae, regularly arranged in a longitudinal
direction, are found beneath the nails. The regular, curved lines observed upon the
palms of the hands and the soles of the feet, particularly the palmar surfaces of the last
phalanges, are formed by double rows of compound papillae, which present two, three,
or four points attached to a single base. In the centre of each of these double rows of
papillae, is an excessively fine and shallow groove, in which are found the orifices of the
sudoriferous ducts.

The papillaa are abundantly supplied with blood-vessels, terminating in looped capil-
lary plexuses, and with nerves. The termination of the nerves is peculiar and will be fully
described in connection with the organs of touch. The arrangement of the lymphatics,
which are very numerous in the skin, has already been indicated in the general descrip-
tion of the lymphatic system.

The Epidermis and its Appendages. — The epidermis, or external layer of the skin, is
a membrane composed exclusively of cells, containing neither blood-vessels, nerves, nor
lymphatics. Its external surface is marked by exceedingly shallow grooves, which cor-
respond to the deep furrows between the papillaa of the derma. Its internal surface is
applied directly to the papillary layer of the true skin and follows closely all its
inequalities. This portion of the skin is subdivided into two tolerably-distinct layers.
The internal layer is called the rete mucosum, or the Malpighian layer, and the external
is called the horny layer. These two layers present certain important distinctive char-
acters.

The Malpighian layer is composed of a single stratum of prismoidal, nucleated cells,
containing a certain amount of pigmentary matter (melanine), which are applied directly
to all the inequalities of the derma, and of a number of layers of rounded cells containing
no pigment. The upper layers of cells, with the scales of the horny layer, are semi trans-
parent and nearly colorless ; and it is the pigmentary layer chiefly which gives to the
skin its characteristic color and the peculiarities in the complexion of different races and
of different individuals. In the negro, this layer is nearly black ; and, when the epider-
mis is removed, the true skin does not present any marked difference from the skin of
the white race. All the epidermic cells are somewhat colored in the dark races, but the
upper layers contain no pigmentary granules. The cells of the pigmentary layer are from
ToW to WTRT of an incn in length and from -5-^ to ^Vtr of an inch in their short diame-
ter. The rounded cells in the upper layers are from ^Vo" to WTRT °f an inc^ m diameter.
The absolute thickness of the rete mucosum is from -^^ to -^ of an inch.

The horny layer is composed of numerous strata of hard, flattened cells, irregularly
polygonal in shape, generally without nuclei, and measuring from -^-^ to yfg of an inch

PHYSIOLOGICAL ANATOMY OF THE SKIN. 383

in diameter. The deeper cells are thicker and more rounded than those of the super-
ficial layers.

The epidermis serves as a protection to the more delicate structure of the true skin,
and its thickness is proportionate to the exposure of the different parts. It is conse-
quently much thicker upon the soles of the feet and the palms of the hands than in other
portions of the general surface, and its thickness is very much increased in those who
are habitually engaged in manual labor. Upon the face, the eyelids, and in the exter-
nal auditory passages, the epidermis is most delicate, measuring from ¥^ to -^ of an
inch in thickness. Upon the palm it is from ^ to ^ of an inch thick, and upon the sole
of the foot it measures from T^ to % of an inch. These variations in thickness depend
entirely upon the development of the horny layer. The thickness of the rete rnucosum,
although it presents considerable variation in different parts, is rather more uniform.

There is constantly more or less desquamation of the epidermis, particularly of the
horny layer, and the cells are regenerated by a blastema exuded from the subjacent vas-
cular parts. It is probable that there is a constant formation of cells in the deeper strata
of the horny layer, which become flattened as they near the surface ; but there is no direct
evidence that the cells of the rete mucosum undergo transformation into the hard, flat-
tened scales of the horny layer.

Physiological Anatomy of the Nails and Hairs. — It is unnecessary, in this connec-
tion, to discuss very minutely the anatomy of the nails and hairs. They are ordi-
narily regarded as appendages of the epidermis, produced by certain peculiar organs
belonging to the true skin ; and an elaborate study of these parts belongs strictly to
descriptive and general anatomy. To complete, however, the physiological history of
the skin, it will be necessary to consider briefly the general arrangement of the cuticular
appendages.

The nails are situated on the dorsal surfaces of the distal phalanges of the fingers and
toes. They serve to protect these parts, and, in the fingers, they are quite important in
prehension. The general appearance of the nails is so familiar that it requires no special
description. In their study, anatomists have distinguished a root, a body, and a free
border.

FIG. 105. — Anatomy of the nails. CSappey.)

A, nail in sift/ : 1, cutaneous fold covering1 the root of the nail ; 2, section of this fold, turned back to show the root
of the nail ; 3, lunula ; 4, nail. B, concave or adherent surface of the nail: 1, border of the root ; 2, lunula and
root; 3, body ; 4, free border. 0, longitudinal section of the nail: 1, 2, epidermis; 8, superficial layer of the
nail; 4, epidermis of the pulp of the finger ; 5, 6, true skin ; 7, 11, bed of the nail ; 8, Malpighian layer of the
pulp of the finger; 9, 10, true skin on the dorsal surface of the finger ; 12, true skin of the pulp of the finger ;
13, last phalanx of the finger.

The root of the nail is thin and soft, terminating in rather a jagged edge, which is
turned slightly upward and is received into a fold of the skin extending around the nail
to its free edge. The length of the root of course varies with the size of the nail, but it
is generally from one-fourth to one- third of the length of the body.

The body of the nail extends from the fold of skin which covers the root to the free
border. This portion of the nail, with the root, is closely adherent by its under surface
to the true skin. It is marked by fine but distinct longitudinal striao and very faint

384

EXCRETION.

transverse lines. It is usually reddish in color, from the great vascularity of the subja-
cent structure. At the posterior part, is a whitish portion of a semilunar shape, called
the lunula, which has this appearance simply from the fact that the corium in this part is
less vascular and the papillae are not so regular as in the rest of the body. That portion
of the skin situated beneath the root and the body of the nail is called the matrix. It
presents highly vascular papillae, arranged in regular, longitudinal rows, and it receives
into its grooves corresponding ridges on the under surface of the nail.

The free border of the nail begins at the point where the nail becomes detached from
the skin. This is generally cut or worn away and is constantly growing ; but, if left to
itself, it attains in time a definite length, which may be stated, in general terms, to be
from an inch and a half to two inches.

FIG. 106.— Section of the nail, etc. (Sappey.)

A, section of the nail : 1, 1, superficial layer ; 2, deep layer ; 8. 3, 4, 4, section of the grooves on the attached sur-
face ; 5, 5, union of the superficial with the deep layer ; 6, 6, dark line between the two layers. B, cells of the
superficial layer, lateral view. C, cells of the superficial layer, flat view. D, cells of the deep layer.

Examining the nail in a longitudinal section, the horny layer, which is usually
regarded as the true nail, is found to increase progressively in thickness from the root to
near the free border. If the nail be examined in a transverse section, it will also be
found much thicker in the central portion than near the edge, and that part which is
received into the lateral portions of the fold becomes excessively thin like the rest of the
root. The thickness of the true nail at the root is from ^^ to -^ of an inch ; and, in
the thickest portion of the body, it usually measures from ^ to -£$ of an inch. The nail
becomes somewhat thinner at and near the free border.

Sections of the nails show that they are composed of two layers, which correspond
to the Malpighian and the horny layer of the epidermis, although they are much more

PHYSIOLOGICAL ANATOMY OF THE NAILS. 385

distinct. The Malpighian layer is applied directly to the ridges of the bed of the nail
and presents upon its upper surface ridges much less strongly marked than those of the
underlying true skin. This layer is rather thinner than the horny layer, is whitish in
color, and is composed of numerous strata of elongated, prismoidal, nucleated cells,
arranged perpendicularly to the matrix. These cells are from ^Vfr to T^TF °f an ^ncn m
length.

The horny layer, which constitutes the true nail, is applied by its under surface
directly to the ridges of the Malpighian layer. It is dense and brittle and is composed of
numerous strata of flattened cells, which cannot be isolated without the use of reagents.
If the different strata of this portion of the nail be studied after boiling in a dilute solu-
tion of soda or potash, it becomes evident that here, as in the horny layer of the epider-
mis, the lower cells are somewhat rounded, while those nearer the surface are flattened.
These cells are nearly all nucleated and measure from -j-^Vo to T^ of an inch in diame-
ter. The thickness of this layer varies in different portions of the nail, while that of
the Malpighian layer is nearly uniform. This layer is constantly growing, and it consti-
tutes the entire substance of the free borders of the nails.

The connections of the nails with the true skin resemble those of the epidermis ; but
the relations of these structures to the epidermis itself are somewhat peculiar. Up to
the fourth month of foetal life, the epidermis covering the dorsal surfaces of the last
phalanges of the fingers and toes does not present any marked peculiarities ; but, at
about the fourth month, the peculiar hard cells of the horny layer of the nails make
their appearance between the Malpighian and the horny layer of the epidermis, and at
the same time the Malpighian layer beneath this plate, which is destined to become the
Malpighian layer of the nails, is somewhat thickened, and the cells assume more of an
elongated form. The horny layer of the nails constantly thickens from this time ; but,
until the end of the fifth month, it is covered by the horny layer of the epidermis. After
the fifth month, the epidermis breaks away and disappears from the surface ; and, at the
seventh month, the nails begin to increase in length. Thus, at one time, the nails are
actually included between the two layers of the epidermis ; but, after they have become
developed, they are simply covered at their roots by a narrow border of the horny
layer, the epidermis commencing again under the nail where the free border leaves the
bed. The nails are therefore to be regarded as modifications of the horny layer of
the epidermis, possessing certain anatomical and chemical peculiarities. The Malpighian
layer of the nails is continuous with the same layer of the epidermis, but the horny lay-
ers are, as we have seen, distinct.

One of the most striking peculiarities of the nails is in their mode of growth. The
Malpighian layer is stationary, but the horny layer is constantly growing, if the nails be
cut, from the root and bed. It is evident that the nails grow from the bed, as their
thickness progressively increases in the body from the root to near the free border ; but
their longitudinal growth is by far the more rapid. Indeed, the nails are constantly
pushing forward, increasing in thickness as they advance. Near the end of the body of
the nail, as the horny layer becomes thinner, the growth from below is diminished.

Hairs, varying greatly in size and development, cover nearly every portion of the
cutaneous surface. The only parts in which they are not found are the palms of the
hands and soles of the feet, the palmar surface of the fingers and toes, the dorsal surface
of the last phalanges of the fingers and toes, the lips, the upper eyelids, the lining of the
prepuce, and the glans penis. Some of the hairs are long, others are short and stiff, and
others are fine and downy. These differences have led to a division of the hairs into
three varieties :

The first variety includes the long, soft hairs, which are found on the head, on the
face in the adult male, around the genital organs and under the arms in both the male
and the female, and sometimes upon the breast and over the general surface of the body
and extremities, particularly in the male.
25

386 EXCRETION".

The second variety, the short, stiff hairs, is found at the entrance of the nostrils,
upon the edges of the eyelids, and upon the eyebrows.

The third variety, the short, soft, downy hairs, are found on the general surface
not occupied by the long hairs, and in the caruncula lachryraalis. In early life, and ordi-
narily in the female at all ages, the trunk and extremities are covered with downy
hairs ; but, in the adult male, these frequently become developed into long, soft hairs.

The hairs are usually set obliquely in the skin and take a definite direction as they
lie upon the surface. Upon the head and face, and, indeed, the entire surface of the
body, the general course of the hairs may be followed out, and they present currents
or sweeps that have nearly always the same direction.

The diameter and length of the hairs are exceedingly variable in different persons,
especially in the long, soft hairs of the head and beard. It may be stated in gen-
eral terms that the long hairs attain the length of from twenty inches to three feet,
in women, and considerably less in men. There are instances, however, in women, in
which the hairs of the head measure considerably more than three feet, but these are
quite unusual. Like the nails, the hair, when left to itself, attains in three or four years
a definite length, but when it is habitually cut it grows constantly. The short, stiff
hairs are from one quarter to one half an inch in length. The soft, downy hairs
measure ordinarily from one-twelfth to one-half an inch. Hairs that have never been
cut terminate in pointed extremities ; and sometimes in hairs that have been cut, the
ends become somewhat pointed, although they are never so sharp as in the new hairs.

Of the long hairs, the finest are upon the head, where they average about ^^ of
an inch in diameter, the extremes being from T^V<5- to TOT °f an mcn f°r tne finest,
and from ^i^ *° ilir °f an incn f°r tne coarsest. The hair is ordinarily coarser in
women than in men. Dark hair is generally coarser than light hair ; and, upon the
same head, the extremes of variation are sometimes observed. The hairs of the beard
and the long hairs of the body are coarser than the hairs of the head. Wilson esti-
mates that the average number of hairs upon a square inch of the scalp is about 1,000,
and the number upon the entire head, about 120,000.

The short, stiff hairs are from -^ to T-f7 of an inch in diameter, and the fine, downy
hairs, from ^THF to y^Vg- of an inch. The variations in the color of the hairs in different
races and in different individuals of the same race are sufficiently familiar.

When the hairs are in a perfectly normal condition, they are very elastic and may be
stretched to from one-fifth to one-third more than their original length. Their strength
varies with their thickness, but an ordinary hair from the head will bear a weight of
six or seven ounces. A well-known property of the hair is that of becoming strongly
electric by friction ; and this is particularly well-marked when the weather is cold and
dry. The electricity thus excited is negative. Sections of the shaft of the hairs show
that they are oval, but their shape is very variable, straight hairs being nearly round,
while curled hairs are quite flat. Another peculiarity of the hairs is that they are
strongly hygrometric. They readily absorb moisture and become sensibly elongated, a
property which has been made use of by physicists in the construction of delicate hy-
grometers.

Roots of the Hairs and Hair-follicles. — The roots of the hairs are embedded in fol-
licular openings in the skin, which differ in the different varieties only in the depth to
which they penetrate the cutaneous structure. In the downy hairs, the roots pass only
into the superficial layers of the true skin ; but, in the thicker hairs, the roots pass
through the skin and penetrate the subcutaneous cellulo- adipose tissue.

The root of the hair is softer, rounder, and a little larger than the shaft. It be-
comes enlarged into a rounded bulb at the bottom of the follicle and rests upon a fungi-
form papilla, constricted at its base, to which it is closely attached. In describing the
connection between the hairs and the skin, anatomists mention three membranes forming
the walls of the hair-follicles, and two membranes that envelop the roots of the hair in

PHYSIOLOGICAL ANATOMY OF THE HAIRS.

387

the form of a sheath. The study of these parts is much simplified by keeping constant-
ly in view the correspondence between the different layers of the follicles and the layers
of the true skin, and the relations of the root-sheaths with the epidermis.

The follicles are tubular inversions of the structures that compose the corium, and
their walls present three membranes. Their length is from T^ to £ of an inch. The

FIG. 107.— Hair and 'hair-follicle. (Sappey.)
root of the hair; 2, bulb of the hair, covering the papilla
of the hair-follicle; 3, internal root-sheath: 4, external
root-sheath ; 5, membrane of the hair-follicle, composed
of fusiform, nucleated fibres arranged transversely (the
internal, amorphous membrane of the follicle is very deli-
cate and is not represented in the figure) ; 6, external
membrane of the follicle, composed chiefly of longitudinal
fibres : 7, 7, muscular bands attached to the follicle ; 8, 8,
extremities of these bands passing to the skin ; 9, com-
pound sebaceous gland, with its duct (10) opening into
the upper third of the follicle ; 11, simple sebaceous gland ;
12, opening of the hair-follicle.

FIR. 108.— Root of the hair. (Sappey.)
1, root of the hair; 2, hair-bulb; 3, pa-
pilla of the follicle; 4, opening of
the follicle ; 5, 5, internal root-sheath ;
6, external root-sheath ; 7, 7, B€WWe-
ous glands ; 8, 8, excretory ducts of
the sebaceous glands.

membrane that forms the external coat of the follicles is composed of inelastic fibres,
arranged for the most part longitudinally, provided with blood-vessels and a few nerves,
containing some fibro-plastic elements, but deprived entirely of elastic tissue.

This is

388

EXCRETION".

the thickest of the three membranes and is closely connected with the corium. Next to
this, is a fibrous membrane composed of fusiform, nucleated fibres arranged transversely.
These resemble the non-striated muscular fibres. The internal membrane is structure-
less and corresponds to the amorphous layer of the true skin. The papilla at the bottom
of the hair-sac varies in size with the size of the hairs and is connected with the fibrous
layers of the walls of the follicle. It is composed of amorphous matter, with a few
granules and nuclei, and it probably contains blood-vessels and nerves, although these
are not very distinct.

Although the different membranes of the hair-follicles are sufficiently recognizable, it
is evident that the hair-sac is nothing more than an inversion of the corium, with some
slight modifications in the character and arrangement of its anatomical elements. The
fibrous membranes correspond to the deeper layers of the true skin, without the elastic
elements, and they present a peculiar arrangement of its inelastic fibres, the external
fibres being longitudinal and the internal fibres transverse. The structureless membrane
corresponds to the upper layers of the true skin, which are composed chiefly of amorphous
matter. The hair-papilla corresponds to the papilla on the general surface of the corium.

The investment of the root of the hair presents two distinct layers called the external
and internal root-sheaths. The external root-sheath is three or four times as thick as
the inner membrane, and it corresponds exactly with the Malpighian layer of the epider-
mis. This sheath is continuous with the bulb of the hair. The internal root -sheath is a
transparent membrane, composed of flattened cells, mostly without nuclei. This extends
from the bottom of the hair- follicle and covers the lower two-thirds of the root.

Structure of the Hairs. — The different varieties of hairs present certciin peculiarities
in their anatomy, but all of them are composed of a fibrous structure forming the great-
er part of their substance, covered by a thin layer of imbricated cells. In the short,
stiff hairs, and in the long, white hairs, there is a distinct medullary substance ; but this
is wanting in the downy hairs and is indistinct in many of the long, dark hairs.

FIG. 109.— Human hair from the head of a white
child ; magnified 370 diameters. (From a photo-
graph taken at the United States Army Medical
Museum.) This figure shows the imbricated ar-
rangement of the epidermis of the hair.

FIG. 110.— Transverse section of a human hair from
the beard of a white adult ; magnified 370 diam-
eters. (From a photograph taken at the United
States Army Medical Museum.)

The fibrous substance is composed of hard, elongated, longitudinal fibres, which can-
not be isolated without the aid of reagents. They may be separated, however, by macer-
ation in warm sulphuric acid, when they present themselves in the form of dark, irregu-
lar, spindle-shaped plates, from ^ to ^ of an inch long, and from j-fa* to WOTT of
an inch wide. These contain pigmentary matter of various shades, occasional cavities

GROWTH OF THE HAIRS. 389

filled with air, and a few nuclei. The pigment may be of any color, from a light yellow
to an intense black, and it is this substance that gives to the hair the great variety in
color which is observed in different persons. In the lower part of the root the fibres
are much shorter, and at the bulb they become transformed, as it were, into the soft,
rounded cells found in this situation covering the papilla.

The epidermis of the hair is excessively thin and is composed of flattened, quadran-
gular plates, overlying each other from below upward. These scales, or plates, are with-
out nuclei, and they exist in a single layer over the shaft of the hair and the upper part
of its root ; but, in the lower part of the root, the cells are thicker, softer, are frequent-
ly nucleated, and they exist in two layers.

The medulla is found in the short, stiff hairs, and it is often beautifully distinct in
the long, white hairs of the head. It occupies from one-fourth to one-third of the diam-
eter of the hair. The medulla can be traced, under favorable circumstances, from just
above the bulb to near the pointed extremity of the hair. It is composed of small,
rounded cells, from -^^ to T^V^ of an inch in diameter, nucleated, and frequently con-
taining dark granules of pigmentary matter. Mixed with these cells are numerous air-
globules ; and frequently the cells are interrupted for a short distance and the space is
occupied with air. The dark granules of the medullary cells are supposed by Kolliker
to be globules of air. The medulla likewise contains a glutinous fluid between the cells
and surrounding the air-globules.

Growth of the Hairs. — Although not provided with blood and deprived of sensibility,
the hairs are connected with vascular parts and are nourished by imbibition from the
papilla?. Each hair is first developed in a closed sac, and at about the sixth month its
pointed extremity perforates the epidermis. These first-formed hairs are afterward shed,
like the milk-teeth, being pushed out, as it were, by new hairs from below, which arise
from a second and a more deeply-seated papilla. This shedding of the hairs usually takes
place from two to six months after birth.

The difference in the color of the hair depends upon differences in the quantity and
the tint of the pigmentary matter; and, in old age, the hair becomes white or gray from
a blanching of the cortex and medulla.

Sudden Blanching of the Hair. — It is an interesting question, in connection with the
nutrition of the hair, to examine the instances so often quoted of sudden blanching of the
hair from violent emotions or other causes. Some physiologists are of the opinion that
the hair may become almost white in the course of a few hours, and this, indeed, is a
popular impression ; but others assume that such sudden changes never take place,
although it is certain that the hair frequently turns gray in the course of a few weeks.
In examining the literature of this subject, it is difficult to find, in the older works, well-
authenticated cases of these sudden changes, and most of those that have been quoted are
taken upon the loose authority of persons evidently not in the habit of making scientific
observations. Such instances, unsupported by analogous cases of a reliable character,
must necessarily be rejected as not fulfilling the rigid requirements demanded in scientific
inquiries, in which all possible sources of error should be carefully excluded. It is not
necessary, therefore, to quote the instances of sudden blanching of the hair recorded by
the ancient writers, or those well-known cases of later date, so often detailed in scien-
tific works, such as that of Marie Antoinette or Sir Thomas More ; and it seems proper
to exclude, also, cases in which the blanching of the hair has been observed only by
friends or relatives ; for in most of them the statements with regard to time are conflict-
ing and unsatisfactory.

Regarding the subject, however, from a purely scientific point of view, there are a
few instances of late date, in which sudden blanching of the hair has been observed and
the causes of this remarkable phenomenon fully investigated by competent observers;
and it is almost unnecessary to say that a single well-authenticated case of this kind
demonstrates the possibility of its occurrence and is interesting in connection with the

390 EXCRETION.

reported instances which have not been subjected to proper investigation. One of these
cases is reported in Virchow's Archiv, for April, 1866, by Dr. Landois, as occurring under
the observation of himself and Dr. Lohmer. In this case, the blanching of the hair oc-
curred in a hospital in a single night, while the patient was under the daily observation
of the visiting physician. As this is one of the few well-authenticated instances of sudden
blanching of the hair, we shall give, in a few words, its essential particulars :

The patient, a compositor, thirty-four years of age, with light hair and blue eyes, was
admitted into the hospital, July 9, 1865, suffering apparently from an acute attack of
delirium tremens. A marked peculiarity in the disease was excessive terror when any
person approached the patient. He slept for twelve hours on the night of the llth
of July, after taking thirty drops of laudanum. Up to this time nothing unusual had
been observed with regard to the hair. On the morning of July 12th, it was evident to
the medical attendants and all who saw the patient that the hair of the head and beard
had become gray. This fact was also remarked by the friends who visited the patient,
and he himself called for a mirror and remarked the change with intense astonishment.
The patient continued in the hospital until September 7th, when he was discharged, the
hair remaining gray. An interesting point connected with this case is the fact that the
hairs were submitted to careful microscopical examination. The white hairs were found
to contain a great number of air-globules in the medulla and in the cortical substance,
but the pigment was everywhere preserved. The presence of air gave the hairs a dark
appearance by transmitted light and a white appearance by reflected light. Dr. Landois
quotes, in this connection, instances of blanching of the hair, in which each hair pre-
sented alternate rings of a white and a brown color. Another very curious case of this
kind was lately reported to the Royal Society by Mr. Erasmus Wilson. In this case, the
white portions presented, on microscopical examination, great bubbles of air ; but there
was no diminution in the quantity of pigmentary matter.

The microscopical examinations by Dr. Landois and others leave no doubt as to the
cause of the white color of the hair in cases of sudden blanching ; and the instances we
have just quoted show that the fact of the occurrence of this phenomenon can no longer
be called in question. All are agreed that there is no diminution in the pigment, but that
the greater part of the medulla becomes filled with air, small globules being also found
in the cortical substance. The hair in these cases presents a marked contrast with hair
that has become gray gradually from old age, when there is always a loss of pigment in
the cortex and medulla. How the air finds its way into the hair in sudden blanching, it
is difficult to imagine ; and the views that have been expressed on this subject by different
authors are entirely theoretical.

The fact that the hair may become white or gray in the course of a few hours renders
it probable that many of the cases reported upon unscientific authority actually occurred ;
and these have all been supposed to be connected with intense grief or terror. The terror
was very marked in the case reported by Dr. Landois. In the great majority of recorded
observations, the sudden blanching of the hair has been apparently connected with intense
mental emotion ; but this is all that can be said on the subject of causation, and the
mechanism of the change is not understood.

Uses of the Hairs. — The hairs serve an important purpose in the protection of the
general surface and in guarding certain of the orifices of the body. The hair upon the
head and the face protects from cold and shields the head from the rays of the sun during
exposure in hot climates. Although the amount of hair upon the general surface is small,
as it is a very imperfect conductor of caloric, it serves in a degree to maintain the heat
of the body. It also moderates the friction upon the surface. The eyebrows prevent the
perspiration from running from the forehead upon the lids ; the eyelashes protect the
surface of the conjunctiva from dust and other foreign matters ; the mustache protects
the lungs from dust, a function very important in persons exposed to dust in long journeys
or in their daily work ; and the short, stiff hairs at the openings of the ears and nose pro-

PERSPIRATION.

391

tect these orifices. It is difficult to assign any special office to the hairs in some other
situations, but their general uses are sufficiently evident.

Perspiration.

In the fullest acceptation of the term, perspiration embraces the entire function of the
skin as an excreting organ and includes the exhalation of carbonic acid as well as of
watery vapor and organic matter. The office of the skin as an eliminator is undoubtedly
very important ; but the quantity of excrementitious matters with the properties of which
we are well acquainted, such as carbonic acid and urea, thrown off from the general sur-
face is small as compared with the amount exhaled by the lungs and discharged by the
kidneys. If the surface of the body be covered with an impermeable coating, death
occurs in a very short time ; but the phenomena which precede the fatal result are diffi-
cult to explain. All that we can say upon this point is that death takes place when the
heat of the body has been reduced to about 70° Fahr., and that suppression of the
function of the skin in this way is always followed by a depression of the animal tem-
perature. The cause of death has never been satisfactorily explained, partly for the
reason that we are unacquainted with the nature and properties of all the excrementitious
matters exhaled from the skin ; and it is not easy to understand why coating the surface
should be followed by such a rapid diminution in the general temperature. The experi-
mental facts, however, indicate that the skin probably possesses important functions with
which we are entirely unacquainted. Physiological chemists have detected urea and some
other effete matters in the perspiration, but it is probable that some volatile principles
are eliminated by the general surface, which have thus far escaped observation.

Sudoriparous Glands. — The most numerous and the most important glands of the
skin are those which secrete the sweat. The other glands, which have been already
considered, have rather a mechanical function, serving to keep the skin and its append-
ages in a proper condition for the protection of the subjacent parts ; but it is the perspir-
atory apparatus chiefly which is concerned in the great function of elimination.

With few exceptions, every portion of the skin is provided with sudoriparous glands.
They are not found, however, in the skin covering the concave surface of the concha of
the ear, the glans penis, the inner lamella of the prepuce, and, unless the ceruminous glands
be regarded as sudoriparous organs, in the external auditory meatus.

On examining the surface of the skin with a low
magnifying power, especially on the palms of the
hands and the soles of the feet, the orifices of the
sudoriferous ducts may be seen in the middle of the
papillary ridges, forming a regular line in the shal-
low groove between the two rows of papilke. The
tubes always open upon the surface obliquely. If
a thin section of the skin be carefully made and
examined microscopically, the ducts are seen pass-
ing through the different layers and terminating
in rounded, convoluted coils in the subcutaneous
structure. These little, rounded or ovoid bodies,
which constitute the sudoriparous, or sweat-pro-
ducing apparatus, may be seen attached to the un-
der surface of the skin, when it has been removed
from the subjacent parts by maceration. The per-
spiratory apparatus consists, indeed, of a simple
tube, presenting a coiled mass beneath the skin, the
sudoriparous portion, and a tube of greater or less length, in proportion to the thickness
of the cutaneous layers, which is the excretory duct, or the sudoriferous portion.

FIG. 111.— Surface of the palm of the Jianrf ;

a portion of the *kin attout one-lmlf

an inch squwe, magnified 4 diameters.

(Sappey.)
1, 1, 1, 1, openings of the sudoriferous ducts; 2,

2 2, 2, grooves between the papilla) of the

skiii.

392

EXCRETIOK

The glandular coils vary in size from T|T to ^ of an inch ; the smallest coils being
found beneath the skin of the penis, the scrotum, the eyelids, the nose, and the convex
surface of the concha of the ear, and the largest, on the areola of the nipple and the peri-
neum. Very large glands are found mixed with smaller ones in the axilla, but these
produce a peculiar secretion which will be specially considered. The coiled portion of
the tube is about T|7 of an inch in diameter and forms from six to twelve convolutions.
It consists of a sharply-defined, strong, external membrane, from -^ -^ ~0- to ¥7Vo °f an mcn
in thickness, very transparent, uniformly granular, and sometimes indistinctly striated.
This is of uniform diameter throughout the coil and terminates in a very slightly dilated,
rounded, blind extremity. It is filled with epithelium in the form of finely granular mat-
ter, usually not segmented into cells, and provided with small, oval nuclei. The glandu-
lar mass is surrounded by a plexus of capillary blood-vessels, which send a few small
branches between the convolutions of the coil. Sometimes the coil is enclosed in a deli-
cate fibrous envelope.

The excretory duct is simply a continuation of the glandular coil. Its course through
the layers of the true skin is nearly straight. It then passes into the epidermis between
the papilla of the corium, and presents, in this layer, a number of spiral turns. The
spirals vary in number according to the thickness of the epidermis. Sappey has
found from six to ten in the palms of the hands and from twelve to fifteen in the soles
of the feet. As it emerges from the glandular coil, the excretory duct is somewhat nar-
rower than the tube in the secreting portion ; but, as it passes through the epidermis, it

again becomes larger. It possesses the same external
membrane as the glandular coil and is lined generally
by two layers of cells of pavement-epithelium.

In a section of the skin and the subcutaneous tissue,
involving several of the sudoriparous glands with their
ducts, it is seen that the glandular coils are generally
situated at different planes beneath the skin, as is indi-
cated in Fig. 112.

Robin has described a variety of sudoriparous glands
in the axilla, which do not differ so much from the
glands in other parts in their anatomy as in the charac-
ter of their secretion. The coil in these glands is much
larger than in other parts, measuring from ^V to TF °f
an inch ; the walls of the tube are thicker, and they
present an investment of fibrous tissue with an internal
layer of longitudinal, unstriped muscular fibres; and,
finally, the tubes of the coil itself are lined with cells
of pavement-epithelium. They are very numerous in
the axilla, forming a continuous layer beneath the skin,
^lixed with these, are a few glands of the ordinary va-
riety.

Estimates have been made by different writers of
the absolute number of sudoriparous glands in the body
and the probable extent of the exhalant surface of the
skin. One of the most careful, and probably the most
reliable of these estimates, is that made by Krause;
but, like all estimates of this kind, the results are to
be taken as merely approximative. Krause found
great differences in the number of perspiratory open-
ings in different portions of the skin, and he estimated the number in a square inch in
certain parts, as follows : On the forehead, he found 1,258 glands to a square inch ; on
the cheeks, 548; on the anterior and lateral portions of the neck, 1,303; on the breast

FIG. 112. — Siidori 'parmtK glands; mag-
nified 20 diameters. (Sappey.)

1. 1, epidermis ; 2. 2. mucous layer ; 3. 3,
papillae; 4,4, derma; 5. 5. subcutane-
ous areolar tissue; 6, 6, 6, 6, sudoripa-
rous erlands ; 7. 7. adipose vesicles ; 8, 8,
excretory ducts in the derma; 9, 9, ex-
cretory ducts divided.

PERSPIRATION. 393

and abdomen, 1,136 ; on the back of the neck, the back, and the nates, 417; on the fore-
arm, inner surface, 1,123, and the outer surface, 1,093; on the hand, palmar surface,
2,736, and dorsal surface. 1,490 ; on the upper part of the thigh, inner surface, 576, outer
surface, 554; on the lower part of the thigh, inner surface, 576; on the foot, plantar
surface, 2,685, and dorsal surface, 924. From these figures, it is estimated that the
entire number of perspiratory glands is 2,381,248; and, assuming that each coil when
unravelled measures about -j-1^ of an inch, the entire length of the secreting tubes is
about 2£ miles. It must be remembered, however, that the length of the secreting coil
only is given, and that the excretory ducts are not included.

Mechanism of the Secretion of Sweat. — The action of the skin as a glandular organ is
continuous and not intermittent ; but, under ordinary conditions, the sweat is exhaled
from the general surface in the form of vapor. With regard to the mechanism of its sepa-
ration from the blood, nothing is to be said in addition to the general remarks upon the
subject of secretion ; and it is probable that the epithelium of the secreting coils is the
active agent in the selection of the peculiar matters which enter into its composition.
There are no examples of the separation by glandular organs of vapor from the blood,
and the perspiration is secreted as a liquid, and only becomes vaporous as it is discharged
upon the surface.

The influence of the nervous system upon the secretion of sweat is remarkable. It is
well known, for example, that an abundant production of perspiration is frequently the
result of mental emotions. Bernard has shown, in a series of interesting experiments, that
the nervous influence may be propagated through the sympathetic system. In one of these
observations, he divided the sympathetic in the neck of a horse, producing, as a conse-
quence, an elevation in temperature and an increase in the arterial pressure in the part
supplied with branches of the nerve. He found, also, that the skin of the part became
covered with a copious perspiration. Upon galvanizing the divided extremity of the nerve,
the secretion of sweat was arrested. When the skin is in a normal condition, after exer-
cise or whenever there is a tendency to elevation of the animal temperature, there is a
determination of blood to the surface, accompanied with an increase in the secretion of
sweat. This is the case when the body is exposed to a high temperature ; and it is by
an increase in the transpiration from the surface that the animal heat is maintained at the
normal standard.

Quantity of Cutaneous Exhalation. — The amount of cutaneous exhalation is subject
to great variations, depending upon conditions of temperature and moisture, exercise, the
quantity and character of the ingesta, etc. Most of these variations relate to the func-
tion of the skin in regulating the temperature of the body ; and it is probable that the
elimination of excrementitious matters by the skin is not subject, under normal condi-
tions, to the same modifications, although positive experiments upon this point are want-
ing. It is not designed, in this connection, to discuss all the experiments that have been
made upon the quantity and the modifications of the cutaneous exhalations, and we shall
consider only what appear to be the most reliable of the numerous recorded observations
upon this subject. The classical experiments of Sanctorius were among the first at-
tempts to determine by the balance the relations of the ingesta to the exhalations ; but
these were necessarily imperfect, on account of the difficulty in constructing proper in-
struments for the investigations, and the cutaneous and pulmonary exhalations were esti-
mated together. When there is such a wide range of variation in different individuals
and in the same person under different conditions of season, climate, etc., it is only pos-
sible to give approximate estimates of the quantity of sweat secreted and exhaled in the
twenty-four hours ; and more recent observations have shown that the calculations of
Seguin and Lavoisier, made in 1790, are very nearly correct. These observers estimated
the daily quantity of cutaneous transpiration at about two pounds (one pound and four-

394 EXCKETION".

teen ounces). The estimates of Krause and of Valentin are a little less, but the difference
is not considerable.

Under violent and prolonged exercise, the loss of weight by exhalation from the skin
and lungs may become very considerable. It is stated by Mr. Maclaren, the author of
an excellent work on training, that, in one hour's energetic fencing, the loss by perspira-
tion and respiration, taking the average of six consecutive days, was about three pounds,
or, accurately, forty ounces, with a range of variation of eight ounces.

When the body is exposed to a very high temperature, the amount of exhalation from
the surface is immensely increased ; and it is by this rapid evaporation that persons have
been able to endure for several minutes a dry heat considerably exceeding that of
boiling water. Dr. South wood Smith made some very interesting observations with
regard to this point upon workmen employed about the furnaces of gas-works and exposed
to intense heat ; and he found that, in an hour, the loss of weight amounted to from two
to four pounds, this being chiefly by exhalation of watery vapor from the skin. In such
instances, the loss of water by transpiration is supplied constantly by the ingestion of
large quantities of liquid.

Properties and Composition of the Sweat. — A very complete and satisfactory analysis
of the sweat was made by Favre, in 1853. After taking every precaution to obtain the
secretion in a perfectly pure state, he collected a very large quantity, nearly thirty pints
(fourteen litres), the result of six transpirations from one person, which he assumed to
represent about the average in composition. The liquid was perfectly limpid, colorless,
and of a feeble but characteristic odor. Almost all observers have found the reaction of
the sweat to be acid ; but it readily becomes alkaline on being subjected to evaporation,
showing that it contains some of the volatile acids. In the experiments of Favre, it was
found that the fluid collected during the first half-hour of the observation was acid, during
the second half-hour it was neutral or feebly alkaline, and during the third half-hour, con-
stantly alkaline. The specific gravity of the sweat is from 1003 to 1004. The following
is the composition of the fluid collected by Favre :

Composition of the Sweat.

Water 995-573

Urea 0-043

Fatty matters 0'014

Alkaline lactates 0-317

Alkaline sudorates T562

Chloride of sodium, } 2'230

Chloride of potassium, 0'244

Alkaline sulphates, L soluble in water 0*012

Alkaline phosphates, I a trace.

Alkaline albuminates, J 0'005

Alkaline earthy phosphates (soluble in acidulated water) a trace.

Epidermic debris (insoluble) a trace.

1,000-000

We have already alluded to the functions of the skin as a respiratory organ and its
office in regulating the temperature of the body by the evaporation of what is known as
the insensible perspiration ; but the composition of the sweat indicates clearly that the skin
is an important organ of excretion. Urea is now known to be a constant constituent of
the sweat, and the compounds of sudoric acid are probably excrementitious in their char-
acter, although they have not yet been detected in the blood or in any of the tissues.
The quantity of urea, under ordinary conditions, is not large ; but it is well known that its
proportion in the sweat is very much increased when there is deficient elimination by the

PHYSIOLOGICAL ANATOMY OF THE KIDNEYS. 395

kidneys. The sudoric acid, obtained by decomposition of the sudorates of soda and of
potassa, is a nitrogenized substance, with a formula, according to Favre, who first de-
scribed it, of CioH8Oi3 N. The nature of the volatile acid has not yet been determined.
The fatty matters are probably produced by the sebaceous glands, and the ordinary
nitrogenized matters are derived from the epidermic scales. With regard to the in-
organic constituents, there is no great interest attached to any but the chloride of sodium,
which exists in a proportion many times greater than that of all the other inorganic mat-
ters combined.

Peculiarities of the Sweat in Certain Parts. — In the axilla, the inguino-scrotal region
in the male, and the inguino-vulvar region in the female, and between the toes, the sweat
always has a peculiar odor, more or less marked, which, in some persons, is excessively
disagreeable. Donne has shown that whenever the secretion has an odor of this kind
its reaction is distinctly alkaline ; and he is disposed to regard its peculiar characters as
due to a mixture of the secretion of the other follicles found in these situations. Some-
times the sweat about the nose has an alkaline reaction. In the axillary region, the
secretion is rather less fluid than on the general surface and frequently has a yellowish
color, so marked, sometimes, as to stain the clothing. The odor is probably due to the
presence of volatile, odorous compounds of the fatty acids, like the caproates, the vale-
rates, or the butyrates ; but the presence of these principles has never been accurately
determined.

Physiological Anatomy of the Kidneys.

The urine is generally regarded by physiologists as the type of the excrementitious
fluids, it having no function to perform in the economy, but being simply retained in
the bladder to be voided at convenient intervals. All the remarks, indeed, that have
been made concerning excretion in general may be applied without reserve to the action
of the kidneys; and there are few subjects in physiology of greater interest than the
process of urinary excretion, with its relations to nutrition and disassimilation. In
entering upon the study of the functions of the kidneys, it will be found useful to con-
sider certain points in their anatomy.

The kidneys are symmetrical organs, situated in the lumbar region beneath the peri-
toneum, invested by a proper fibrous coat, and always surrounded by more or less adipose
tissue. They usually extend from the eleventh or twelfth rib downward to near the
crest of the ilium, and the right is always a little lower than the left. In shape, the
kidney is very aptly compared to a bean ; and the concavity, the deep, central portion
of which is called the hilum, looks inward toward the spinal column The weight of
each kidney is from four to six ounces, usually about half an ounce less in the female
thjn in the male. The left kidney is nearly always a little heavier than the right.

Outside of the proper coat of the kidney, is a certain amount of fatty tissue enclosed
in a loose fibrous structure. This is sometimes called the adipose capsule; but the
proper coat consists of a close net-work of the ordinary white fibrous tissue, interlaced
with numerous small fibres of the elastic variety. This coat is thin and smooth and may
be readily removed from the surface of the organ. At the hilum, it is continued inward
to line the pelvis of the kidney, covering the calices and blood-vessels. This coat, how-
ever, is not continued into the substance of the kidney.

On making a vertical section of the kidney, it presents a cavity at the hilum, bounded
internally by the dilated origin of the ureter. This is called the pelvis. It is lined by
a smooth membrane, which is simply a continuation of the proper coat of the kidney,
and which forms little cylinders, called calices^into which the apices of the pyramids are
received. Some of the calices receive the apex of a single pyramid, while others are
larger and receive two or three. The calices unite into three short, funnel-shaped tubes,
called infundibula, corresponding respectively to the superior, middle, and inferior por-
tions of the kidney. These finally open into the common cavity, or pelvis. The sub-

396

EXCRETION.

stance of the kidney is composed of two distinctly-marked portions called the cortical

substance, and the medullary, or pyramidal substance.

The cortical substance is reddish and gran-
ular, rather softer than the pyramidal sub-
stance, and is about one-sixth of an inch in
thickness. This occupies the exterior of the
kidney and sends little prolongations (col-
umns of Bertin) between the pyramids. The
surface of the kidney is marked by little po-
lygonal divisions, giving it a lobulated appear-
ance. This, however, is simply due to the
arrangement of the superficial blood-vessels.
The medullary substance is arranged in the
form of pyramids, sometimes called the pyra-
mids of Malpighi, from twelve to fifteen or
eighteen in number, their bases presenting
toward the cortical substance, and their apices
being received into the calices at the pelvis.
Ferrein subdivided the pyramids of Malpighi
into smaller pyramids (the pyramids of Fer-
-* rein), each formed by about one hundred
tubes radiating from the openings at the
summit of the pyramids toward their bases.
The tubes composing these pyramids were
supposed to pass into the cortical substance,
forming corresponding pyramids of convo-
FIG. 113.— VetticM section of the kidney. (Sappey.) luted tubes, thus dividing this portion of the

kidney into lobules, more or less distinct.

the calices ; 6, 6, columns of Bertin ; 7, pelvis of The medullary substance is firm, of a dark-

the kidney ; 8, upper extremity of the ureter. 11^1.1 ..• i i_ j. i

er red color than the cortical substance, and

is marked by tolerably distinct strise, which take a nearly straight course from the bases
to the apices ol the pyramids. As these striaa indicate the direction of the little tubes
that constitute tne greatest part of the medullary substance, this is sometimes called the
tubular portion of the kidney.

From the arrangement of the secreting portion of the kidneys, they are classed
among the tubular glands, presenting a system of tubes, or canals, some of which are
supposed simply to carry off the urine, while others separate the excrementitious con-
stituents of this tiuid from the blood. It is difficult to determine precisely where the
secreting tubes merge into the excretory ducts, but it is the common idea, which is
probably correct, that the cortical substance is the active portion, while the tubes of
the pyramidal portion simply carry off the excretion.

Pyramidal Substance. — Each papilla, as it projects into the pelvis of the kidney, pre-
sents from ten to twenty-five little openings, measuring from -g-i^ to ^ of an inch in
diameter. The tubes leading from the pelvis immediately divide at very acute angles,
generally dichotomously, until a bundle of tubes arises, as it were, from each opening.
These bundles constitute the pyramids of Ferrein. In their course, the tubes are slightly
wavy and are nearly parallel with each other. These are called the straight tubes of the
kidney, or the tubes of Bellini. They extend from the apices of the pyramids to their
bases and pass then into the cortical substance. The pyramids contain, in addition to
the straight tubes, a delicate fibrous matrix and numerous blood-vessels ; which latter,
for the most part, pass beyond the pyramids, to be finally distributed in the cortical
substance. Recent researches have shown that some of the convoluted tubes dip down

PHYSIOLOGICAL ANATOMY OF THE KIDNEYS.

397

into the pyramids, returning to the cortical substance in the form of loops. This ar-
rangement will be fully described in connection with the cortical substance.

The tubes of the pyramidal substance are composed of a strong, structureless base-
ment-membrane, lined with granular, nucleated cells. According to the researches of
Bowman, the tubes measure from ^J-g- to -^ of an inch in diameter at the apices, and
near the bases of the pyramids their diameter is about -^ of an inch. The membrane
of the tubes is dense and resisting, and portions of it with the epithelial lining removed
can generally be seen in microscopical examinations, when the pyramidal substance has
been simply lacerated with needles. This membrane is from ^-gj «7 to -^Q^-Q of an inch
in thickness.

The cells lining the straight tubes exist in a single layer applied to the basement-
membrane. They are thick, irregularly polygonal in shape, and contain numerous albu-
minoid granules. They present one, and occasionally, though rarely, two granular nuclei,
with one or t\vo nucleoli. They are very liable to alteration and are only seen in the

FIG. 114 (A). — Longitudinal section of the pyram-
idal substance of the kidney of the fu&tus.
(Sappey.)

1, trunk of a lan^e urinifcrous tube ; 2, 2. primary
branches of this tube ; 3, 3. 3, secondary branches";
4, 4, 5, 5, 6, 6, 7, 7, 7, 7, branches becoming smaller
and smaller ; 8, 8, 8, 8, loops of the tubes of Henle.

FIG. 114 (B).— Longitudinal action of the cortical sub-
stance of the same kidney. (Sappey.)
1, 1, limit of the cortical substance and base of the pyra-
mids ; 2. 2, 2. tubes passim: toward the surface of tho
kidney ; 3. •'!. :i. \ S. 8, convoluted tubes : 4. 4, 4. 4. •>.
Malpiirhian bodies: <!. <;. artery, with its branches (i, <,
7) ; 9, 9, fibrous covering of the kidney.

normal condition in a perfectly fresh, healthy kidney. Their diameter is about T7Vs- of
an inch. The caliber of the tubes is reduced by the thickness of their lining epithe-
lium to -- or i-- of an inch.

398

EXCRETION.

Cortical Substance.— In the cortical portion of the kidney, are found numerous tubes,
differing somewhat from the tubes of the pyramidal portion in their size and in the char-
acter of their epithelial lining, but presenting the most marked difference in their direc-
tion. These tubes are somewhat larger than the tubes of pyramidal substance and are very
much convoluted, interlacing with each other inextricably in every direction. Scattered
pretty uniformly throughout this portion of the kidney, are rounded or ovoid bodies, about
four times the diameter of the convoluted tubes, known as the Malpighian bodies. At
one time there was considerable difference of opinion with regard to the relation of
these bodies to the tubes ; but the researches of Bowman, Isaacs, and later anatomists,

have established, without doubt, the fact that
they are simply flask-like, terminal dilatations
of the tubes themselves.

As the result of recent researches, the cor-
tical portion of the kidney is now regarded as
presenting a delicate fibrous matrix, which
forms a sort of skeleton for the support of
the secreting portion with its blood-vessels.
The tubes of this portion are convoluted and
somewhat larger than the straight tubes, but
are continuous with them, terminating finally
in the Malpighian bodies. The researches of
late anatomists, however, particularly in Ger-
many, have shown that this simple view of
the course and termination of the tubes of the
cortical substance must be somewhat modified ;
although, as far as the anatomy of the organ
has any bearing upon our ideas concerning the
mechanism of the secretion of urine, the views
of physiologists need undergo no material
change.

The tubes of the cortical substance present
considerable variations in size, and, instead of
a single system continuous with the straight
tubes and terminating in the Malpighian bod-
ies, we can distinguish three well-defined varie-
ties :

1. The ordinary convoluted tubes, directly
connected with the Malpighian bodies. 2.
Small tubes, continuous with the convoluted
tubes, dipping down into the pyramids and
returning to the cortical portion in the form of
loops. 3. Large, communicating tubes, form-
ing a plexus connecting the different varieties
of tubes with each other and finally with the
straight tubes of the pyramidal portion.

The relation of these tubes can be readily
understood by reference to Fig. 115. In trac-
ing out the course of the tubes, which recent
observati°ns h*ve shown to be somewhat intri-

cate, it will be found most convenient to COm-

mence with a description of the Malpighian

bodies and to follow the course of the tubes from these bodies to their connections with
the straight tubes of the pyramidal substance.

FIG. 115. — Diagrammatic view of the Malpighian

bodies and tubes of the kidney. (Sappey.)
1, 1. 2, straight tube of Bellini ; 3, 3, 3, other straight
tubes opening into the tube 1, 1 ; 4, 4, 4, 4, 4, Mal-
pighian bodies ; 5, 5, 5, 5, 5, convoluted tubes ; 6,
6, (5, 6, 6, descending portions
or' llenle; 7. 7, 7, 7, 7, a
Henle; 8,

looped tubes

dd inh

cortical and of the pyramidal substance.

PHYSIOLOGICAL ANATOMY OF THE KIDNEYS. 399

Malpighian Bodies. — Thes3 are ovoid or rounded terminal dilatations of the convo-
luted tubes, of somewhat variable size, measuring from ^r^ to Tfg- of an inch in diam-
eter. They are composed of a membrane continuous with the external membrane of
the convoluted tubes, of the same homogeneous character, but somewhat thicker, meas-
uring about ^o^o-o °f an inch- This sac, called the capsule of Muller, encloses a mass of
convoluted blood-vessels and is lined with a layer of nucleated epithelial cells. In
addition to the cells lining the capsule, there are other cells which are applied to the
blood-vessels. The theory advanced by Bowman in 1842, that the Malpighian bodies are
chiefly concerned in the transudation of water, with, perhaps, a small quantity of inor-
ganic salts, while the epithelium of the tubes separates the solid excrementitious principles
from the blood, has lately been confirmed (1874) by the experiments of Ileidenhain, and
is now generally accepted.

The cells attached to the capsule of Muller are smaller and more transparent than
those lining the convoluted tubes. They are ovoid, nucleated, and finely granular. The
cells covering the vessels, however, are larger and more opaque, and they resemble the
epithelium lining the tubes. They measure from T¥Vo- to Wo o of an incn m diameter, by
about ^yVo- of an inch in thickness.

Tales of the Cortical Substance. — Following out the tubes in the cortical substance
from the Malpighian bodies, we find first a short, constricted portion, called the neck
of the capsule. The tube soon dilates to the diameter of about -5-^ of an inch, when
its course becomes exceedingly intricate and convoluted. These are what are known
as the convoluted tubes of the kidney. The membrane of these tubes is transparent
and homogeneous, but quite firm and resisting. It measures about ^^^ of an inch in
thickness. It is lined throughout with a single layer of rounded epithelial cells, from
T_i__ to y-jjVs- of an inch in diameter, somewhat larger, consequently, than the cells lining
the straight tubes. These cells are nucleated and usually quite granular. It has heen
found that, in many of the lower orders of animals, the cells lining the neck of the
capsule are provided with vibratilo cilia ; and it is possible that they may exist in man,
although their presence has never been actually demonstrated.

Kecent researches, particularly those of Heidenhain, have shown that the greatest
part if not all of the solid excrementitious constituents of the urine, such as urea and the
urates, is separated from the blood by the cells of the convoluted tubes of the cortical
substance and perhaps by the dilated portions of the tubes of Henle, while the water of
the urine transudes through the blood-vessels in the Malpighian bodies. This view was
first advanced by Bowman in 1842.

Narrow Tubes of Henle. — According to the most recent observations, the convoluted
tubes above described, after a long and tortuous course in the cortical substance, invari-
ably become continuous, near the pyramids, with tubes of much smaller diameter, which
form loops, extending to a greater or less depth into the pyramids. The loops formed
by these canals (the narrow tubes of Henle) are nearly parallel with the tubes of Bel-
lini and are much greater in number near the bases of the pyramids than toward the
apices. The diameter of these tubes is very variable, and they present enlargements at
irregular intervals in their course. The narrow portions are about s fa ff of an inch in
diameter, and the wide portions, about twice this size. The narrow portion is lined by
small, clear cells with very prominent nuclei. The wider portions are lined by larger,
granular cells. Near the bases of the pyramids, the wide portion sometimes forms the
loop ; but, near the apices, the loop is always narrow. The difference in the size of the
epithelium is such, that, while the diameter of the tube is variable, its caliber remains
nearly uniform. The membrane of these tubes is quite thick, thicker, even, than the
membrane of the tubes of Bellini.

Intermediate Tubes.— After the narrow tubes of Henle have returned to the cortical
substance, they communicate with a system of flattened, ribbon-shaped canals, measuring
from TIVfr to T^Vff of an inch in diameter, with excessively thin, fragile walls, lined by

400 EXCRETION.

clear pavement-epithelium. These tubes take an irregular and somewhat angular course
between the true convoluted tubes and finally empty into the branches of the straight
tubes of Bellini, thus establishing a communication between the tubes coming from the
Malpighian bodies and the tubes of the pyramidal substance. They are called the inter-
mediate tubes, or the canals of communication. Some observers have described them as
forming an anastomosing plexus, but this disposition is not definitely established.

The tubes into which the intermediate canals open join with others, generally two by
two, and then pass in a nearly straight direction into the pyramids, where they continue
to unite with each other in their course, becoming, consequently, less and less numerous,
until they open at the apices of the pyramids into the infundibula and the pelvis of the
kidney.

Distribution of Blood-vessels in the Kidney. — The renal artery, which is quite volumi-
nous in proportion to the size of the kidney, enters at the hilum and divides into four
branches. By numerous smaller branches it then penetrates between the pyramids and
ramifies in the columns of cortical substance which occupy the spaces between the pyra-
mids (columns of Bertin). The main vessels, which are generally two in number, occupy
the centre of the columns of Bertin, sending off in their course, at short intervals, regular
branches on either side, toward the pyramids. When these branches reach the boundary
of the cortical substance, they turn upward and follow the periphery of the pyramid to
its base. Here the vessels form an arched, anastomosing plexus, situated exactly at the
boundary which separates the rounded base of the pyramid from the cortical substance.
This plexus presents a convexity looking toward the cortical substance, and a concavity,
toward the pyramid. It is so arranged that the interstices are just large enough to admit
the collections of tubes that form the so-called pyramids of Ferrein.

From the arterial arcade, branches are given off in two opposite directions. From
its concavity, numerous small branches, measuring at first from T2V^ to y|7 of an inch in
diameter, pass downward toward the papillae, giving off small ramifications at very acute
angles and becoming reduced in size to about ^rVs- of an inch. These vessels — called
sometimes the arteriolse rectos — surround the straight tubes and pass into capillaries in
the substance of the pyramids and at their apices.

From the convex surface of the arterial arcade, numerous branches are given off at
nearly right angles. These pass into the cortical substance, breaking up into a large num-
ber of little arterial twigs, from Y^TT to TTS- °f an incn *n diameter, each one of which
penetrates a Malpighian body at a point opposite to the origin of the convoluted tube.
Once within the capsule, the arteriole breaks up into from five to eight branches, which
then divide dichotomously into vessels measuring from ^Vo to ysVo °f an iQcn in diame-
ter, arranged in the form of coils and loops, constituting a dense, rounded mass (the
Malpighian coil), filling the capsule. These vessels break up into capillaries without
anastomoses. Their coats are amorphous and are provided with numerous nuclei rather
shorter than those found in the general capillary system.

The blood is collected from the vessels of the Malpighian bodies by veins, sometimes
one, and frequently three or four, which pass out of the capsule and form a second capil-
lary plexus surrounding the convoluted tubes. When there is but one vein, it generally
emerges from the capsule near the point of penetration of the arteriole. The walls of
the vein are much more fragile than those of the arteriole, and, consequently, in ordinary
microscopical preparations of the cortical substance, the arteriole is left attached, while
the veins are torn off.

The efferent vessels, immediately after their emergence from the capsule, break up
into a very fine and delicate plexus of capillaries, closely surrounding the convoluted
tubes. These form a true plexus, the branches anastomosing freely in every direction ;
and the distribution of vessels in this part resembles essentially the vascular arrangement
in most of the glands. Bowman has called the branches which connect together the

MECHANISM OF THE PRODUCTION OF URINE.

401

vessels of the Malpighian tuft and the capillary plexus surrounding the tubes, the portal
system of the kidney. These intermediate vessels form a coarse plexus surrounding the
prolongations of the pyramids of Ferrein into
the cortical substance.

The renal, or emulgent vein takes its origin
in part from the capillary plexus surrounding the
convoluted tubes and in part from the vessels
distributed in the pyramidal substance. A few
branches come from vessels in the envelopes of
.the kidney, but these are comparatively unim-
portant. The plexus surrounding the convoluted
tubes empties into venous radicles, which pass
to the surface of the kidney, and these present a
number of little radiating groups, each converg-
ing toward a central vessel. This arrangement
gives to the vessels of the fibrous envelope of the
kidney a peculiar stellate appearance. These are
sometimes called the stars of Verheyn. The
large trunks which form the centres of these
stars then pass through the cortical substance to
the rounded bases of the pyramids, where they
form a vaulted, venous plexus corresponding to
the arterial plexus already described. The ves-
sels distributed upon the straight tubes of the
pyramidal substance form a loose plexus around
these tubes, except at the papillae, where the net-
work is much closer. They then pass into the
plexus at the bases of the pyramids to join with
the veins from the cortical substance. From this
plexus, a number of larger trunks arise and pass
toward the hilum in the centre of the inter-py-
ramidal substance, enveloped in the same sheath
with the arteries. Passing thus to the pelvis of
the kidney, the veins converge into from three
to four great branches, which unite to form the
renal, or emulgent vein. A preparation of all
the vessels of the kidneys shows that the veins
are much more voluminous than the arteries.

The lymphatics of the kidney are few, and,
according to Sappey, they only exist in the sub-
stance of the organ, converging toward the hilum.
This author does not admit the existence of su-
perficial lymphatics.

The nerves are quite abundant and are de-
rived from the solar plexus, their filaments following the artery in its distribution in the
interior of the organ and ramifying upon the walls of the vessels.

FIG. 116.— Blood-vessels of the Malpighian bodies
and convoluted tubes of the kidney. (Sappey.)

1, 1, Malpighian bodies surrounded by the capsules
of M filler; 2, 2, 2, convoluted tubes connected
with the Malpighian body ; 3, artery branch-
ing to go to the Malpighian bodies ; 4, 4, 4,
branches of the artery ; 6, 6, Malpighian bodies
from which a portion of the capsules has been
removed; 7. 7, 7, vessels passing out of the
Malpighian bodies ; 8, vessel, the branches ol
which (9) pass to the capillary plexus (10).

Mechanism of the Production and Discharge of Urine.

The striking peculiarities which the kidney presents in its structure, as compared with

the true glands, and the fact of the voluntary discharge of its secretion at certain intervals,

would naturally lead to a closer study of the mechanism of the production and discharge

of the urine than we have given under the general head of the mechanism of the formation

26

402 EXCRETION.

of the excretions. The composition of the urine, also, will be found to be exceedingly
complex, and its various ingredients bear the closest relation to the processes of nutrition
and disassimilation ; all of which considerations render it of the greatest importance to
ascertain the precise mode of its formation and to study all the conditions by which this
process may be modified. In the present state of our knowledge, we must certainly re-
gard the excrementitious constituents of the urine as formed essentially in the system at
large, being merely separated from the blood by the kidneys ; and a consideration of these
eifete principles belongs to the subject of nutrition. It remains for us, then, in this con-
nection, to treat, in general terms, of the way in which these substances find their way
into the urine.

The most important constituent of the urine is urea, a crystallizable, nitrogenized
substance, which is discharged by the skin as well as by the kidneys. This has long been
recognized as an excrementitious principle ; but the first observations that gave any defi-
nite idea of the mechanism of its production were made by Prevost and Dumas, in 1821.
At the time these experiments were made, chemists were not able to detect urea in the
normal blood ; but Prevost and Dumas extirpated the kidneys from living animals (dogs
and cats), and found an abundance of urea in the blood, after certain symptoms of blood-
poisoning had been manifested. The first experiments were performed by removing one
kidney by an incision in the lumbar region, and, at the end of three or four days, after
the animal had recovered from the first operation, removing the other. After the second
operation, the animals lived for from five to nine days. For the first two or three days
there were no symptoms of blood-poisoning. Watery discharges from the stomach and
intestinal canal occurred after a few days, and finally stupor and other marked evidences
of nervous disturbance supervened, when the presence of urea in the blood could be easily
determined. These observations were confirmed and extended by Segalas and Vauque-
lin, in 1822, who presented to the French Academy of Medicine a specimen of nitrate
of urea extracted from the blood of a dog, taken sixty hours after extirpation of the kid-
neys, giving its proportion to the weight of blood employed. Since that time, as the
processes for the determination of urea in the animal fluids have been improved, this
substance has been detected in minute quantity in the normal blood. Picard carefully
estimated and compared the proportions of urea in the renal artery and the renal vein,
and he found that the quantity in the blood was diminished by about one-half in its passage
through the kidneys. Still later, urea has been found by Wurtz to exist in the lymph
and chyle in larger quantity, even, than in the blood. These facts, which have been
almost universally regarded as established, have led physiologists to adopt the view that
the peculiar excrementitious principles found in the urine are not produced by the kid-
neys, but are formed in the system by the general process of disassimilation, are taken up
from the tissues by the blood, either directly or through the lymph, and are merely
separated from the blood in the kidneys ; and it has consequently been pretty generally
assumed that nearly, if not all, the constituents of the urine preexist in the circulating
fluid. There is, indeed, no well-defined principle in the urine that has not been actually
demonstrated in the blood. As an additional argument in favor of this view of the
mechanism of urinary excretion, it has been ascertained that, when the kidneys are
interrupted in their function, there is a tendency to the elimination of the excrementitious
principles of the urine by the lungs, skin, and alimentary canal ; and that these matters
accumulate in the blood only after this vicarious effort has failed to effect their complete
discharge. These ideas have seemed to be so completely justified by facts, that they have
been applied to the mechanism of excretion by other organs, such as the skin and the liver ;
but, within a few years, the older observations with regard to nephrotomized animals
have been discredited. It has been asserted, as the result of experiment, that urea and
the urates do not accumulate in the blood after removal of the kidneys, and that this
only occurs when both ureters have been tied. The experiments upon which this idea
is based have been applied mainly to the pathology of ursemic intoxication, but it is evi-

MECHANISM OF THE PRODUCTION OF URINE. 493

dent that they bear directly upon the mechanism of excretion. It is not assumed, how-
ever, that excrementitious principles are not formed by the disassimilation of the tissues,
but it is asserted that urea and the urates are produced in the kidneys by a transforma-
tion of excrementitious matters which exist in the blood.

The original experiments of Pre" vost and Dumas are very strong arguments in favor
of the view that has been so long almost unquestioned, viz., that urea is simply separated
from the blood by the kidneys ; but the more recent observations of Bernard and Barres-
wil, Robin, and many others, while they confirm the first experiments on this subject,
have added very considerably to our knowledge of the mechanism of uraemic poisoning
after extirpation of the kidneys. The kidneys, it has been found, can readily be removed
from living animals (dogs, cats, rabbits, etc.) without any great disturbance immediately
following the operation. Bernard and Barreswil found that animals from which both
kidneys had been removed did not usually present any distinctive symptoms for a day or
two after, except that they vomited and passed an unusual quantity of liquid from the
intestinal canal. During this period, the blood never contained an abnormal quantity
of urea ; but the contents of the stomach and intestine were found to be highly ammo-
niacal. During this time, also, the secretions from the stomach and intestines, particu-
larly the stomach, became continuous, as well as increased in quantity. Animals oper-
ated upon in this way usually live for four or five days, and they then die in coma follow-
ing upon convulsions. Toward the end of life, the secretion of gastric and intestinal fluids
becomes arrested, probably from the irritating effects of ammoniacal decomposition of
their contents, and then, and then only, urea is found to accumulate enormously in the
blood.

It is thought by Bernard that the hypersecretion by the gastric and intestinal mucous
membrane, in nephrotomized animals, is an effort on the part of the system to eliminate
urea, which is decomposed by contact with these membranes into carbonate of am-
monia. This view is sustained by the fact that, when urea is introduced into the alimen-
tary canal in living animals, it disappears almost immediately and is replaced by the am-
moniacal salts. Consequently, after removal of the kidneys, we should not expect to find
an increased quantity of urea in the blood until its elimination by the mucous membrane
of the alimentary canal has ceased ; but the fact that it then accumulates in large
quantity cannot be doubted.

The results obtained by other experimenters generally correspond with those of Ber-
nard and Barreswil. It has also been ascertained, as was shown by Segalas and Vau-
quelin, that urea is an active diuretic when injected in small quantity into the veins of a
healthy animal ; and that, in this case, it does not produce any poisonous effects, but is
immediately eliminated. But, when urea is injected into the vascular system of a ne-
phrotomized animal, it produces death in a very short time, with the characteristic symp-
toms of ura3mic poisoning. We have frequently removed both kidneys from dogs, and,
when the operation is carefully performed, the animals live for from three to five days.
In some instances, they have been known to live for twelve days or even longer; but
death always takes place finally with symptoms of blood-poisoning.

The experiments which are supposed to show that urea and the urates are actually
formed in the kidneys, to which we have already alluded, were made with the view of
comparing the effects of removal of both kidneys with those produced by tying the
ureters. According to these observations, the blood contains much more urea after the
ureters are tied than after removal of the kidneys. These experiments, which are di-
rectly opposed in their results to the well-considered observations of Pre"vost and Du-
mas, Bernard and Barreswil, Segalas, and many others, cannot be accepted, unless it
be certain that all the necessary physiological conditions have been fulfilled. In the
first place, it was positively demonstrated, as early as 1847, that urea does not accumu-
late in the blood immediately after removal of the kidneys, but that this occurs only
toward the end of life, and then urea is found in enormous quantity. In the second

404 EXCRETION.

place, it is well known that the operation of tying the ureters is followed by an immense
pressure of urine in the kidneys, which not only disturbs the eliminative action of these
organs, but affects most seriously the general functions. Since the influence of the ner-
vous system upon the secretions has been closely studied, it is evident that the pain and
disturbance consequent upon the accumulation of urine above the ligated ureters must
have an important reflex action upon the secretions; and this would probably inter-
fere with the vicarious elimination of urea and other excrementitious principles by
the stomach and intestines. It is well known to practical physicians that an arrest
of these secretions, in cases of organic disease of the kidneys, is liable to be followed
immediately by evidences of uraemia, and that grave ursemic symptoms are frequently
relieved by the administration of remedies that act promptly and powerfully upon the
intestinal canal. As an additional evidence of the great disturbance of the system — aside
from the mere accumulation of excrementitious principles in the blood — which must
result from tying the ureters, we have the intense distress and general prostration,
always so prominent in cases of nephritic colic in which there may be merely temporary
obstruction of one ureter.

From a careful review of the important facts bearing upon the question under con-
sideration, there does not seem to be any valid ground for a change in our ideas concern-
ing the mode of elimination of urea and the other important excrementitious constituents
of the urine. There is every reason to suppose that these principles are produced in
the various tissues and organs of the body during the process of disassimilation, are
taken up by the blood, and are simply separated from the blood by the kidneys. There
may be unimportant modifications of some of these principles in the kidneys or in the
urine, such as the conversion of a certain amount of creatine into creatinine, but the great
mass of excrementitious matter is separated from the blood by the kidneys unchanged.

Extirpation of one kidney from a living animal is not necessarily fatal. We have fre-
quently performed this operation as a class-demonstration, and have kept the animal for
weeks and months, without observing any indications of disturbance in the eliminative
functions. If the operation be carefully performed, the wound will generally heal with-
out difficulty, and in most instances the remaining kidney seems sufficient for the elimi-
nation of urine for an indefinite period. In all of our experiments, save one, the ani-
mals, killed long after the wound had healed, never presented any marked symptoms of
retention of excrementitious matters in the blood. It is a noticeable fact, however,
that in many instances they showed a marked change in disposition, and the appetite
became voracious and unnatural. These animals would sometimes eat fa3ces, the flesh
of dogs, etc., and, in short, presented certain of the phenomena so frequently observed
after extirpation of the spleen. After extirpation of one kidney, it has been observed
that the remaining kidney increases in weight, although recent investigations show that
this is due mainly to an increase in the amount of blood, lymph, and urinary princi-
ples, and not to a new development of renal tissue. It is reasonable to suppose that
Nature has provided, in the kidneys, more working substance than is ordinarily required
for the elimination of the excrementitious constituents of the urine ; and that, even
when one kidney is removed, the other is competent to eliminate the amount of excre-
mentitious matter that is produced, under ordinary conditions of the system. The
exceptional experiment in which the animal died after extirpation of one kidney is quite
interesting : October 6, 1864, we removed one kidney from a small cur-dog, about
nine months old, by an incision in the lumbar region. The animal did not appear
to suffer from the operation, and the wound healed kindly. The only marked effects
were great irritability of disposition and an exaggerated and perverted appetite. He
would attack the other dogs in the laboratory without provocation, and would eat with
avidity, faeces, putrid dog's flesh, and articles which the other animals would not touch,
and which he did not eat before the operation. On the morning of November 18th,
forty-three days after the operation, the dog appeared to be uneasy, cried frequently, and

VARIATIONS. IN THE SECRETION OF URINE. 4Q5

at 12 o'clock went into convulsions, which continued until 3£ p. M., when he died.
In one other instance, in which a dog was kept for more than a year after extirpa-
tion of one kidney, it was occasionally observed that the animal was rather quiet and
indisposed to move for a day or two, hut this always passed off, and when he was
killed he was as well as before the operation.

Influence of the Nervous System, Blood-pressure, etc., upon the Secretion of Urine. —
There are many instances in which very marked and sudden modifications in the
action of the kidneys take place under the influence of fear, anxiety, hysteria, etc.,
when the impression must have been transmitted through the nervous system. Although
little is known of the final distribution of the nerves in the kidney, it has been ascertained
that here, as elsewhere, filaments from the sympathetic system ramify upon the walls of
the blood-vessels, and they are undoubtedly capable of modifying the quantity and the
pressure of blood in these organs.

It may be stated as a general proposition, that an increase in the pressure of blood in
the kidneys increases the flow of urine, and that, when the blood-pressure is lowered,
the flow of urine is correspondingly diminished. This fact will in a measure account for
the increase in the flow of urine during digestion ; but it cannot serve to explain all of
the modifications that may take place in the action of the kidneys. The fact above
stated, although it has been long recognized by physiologists, has lately been very fully
illustrated by the experiments of Bernard. This observer measured the pressure of blood
in the carotid artery of a dog and carefully noted the quantity of urine discharged in the
course of a minute from one of the ureters. Afterward, by tying the two crural, the two
brachial, and the two carotid arteries, he increased the blood-pressure about one-half, and
the quantity of urine discharged in a minute was immediately increased by a little more
than fifty per cent. In another animal, he diminished the pressure by taking blood from
the jugular vein, and the quantity of urine was immediately reduced about one-half.
His later observations on this subject showed that the increase in the quantity of urine
produced by exaggerated pressure of blood in the kidneys was capable of being modified
through the nervous system. In these experiments, the nerves going to one kidney were
divided, which produced an increase in the arterial pressure and a consequent exaggera-
tion in the quantity of urine from the ureter on that side. The pressure was then farther
increased by stopping the nostrils of the animal. The quantity of urine was increased by
this on the side on which the nerves had been divided, but the pain and distress from
want of air arrested the secretion upon the sound side.

The precise influence which special nerves exert upon the secretion of urine has not
yet been positively ascertained. Some important facts, however, bearing upon this sub-
ject have been developed of late years. In his interesting and novel experiments upon
artificial diabetes in animals, Bernard found that, when irritation was applied to the floor
of the fourth ventricle, in the median line, exactly in the middle of the space comprised
between the origin of the pneumogastrics and the auditory nerves, the urine was in-
creased in quantity and became strongly saccharine. When the irritation was applied a
little above this point, the urine was simply increased in quantity, but it contained no
sugar ; and, when the puncture was made a little below, sugar appeared in the urine,
without any increase in the quantity of the secretion. It has also been observed that
section of the spinal cord in the upper part of the dorsal region arrests, for a time, the
secretion of urine.

The final effect of division of all the nerves going to the kidney is very curious. The
immediate effect of destruction of these nerves is to increase largely the amount of blood
sent to the kidney, the organ then pulsating like an aneurismal tumor. In experiments
upon this subject, by Miiller and Peipers, the flow of urine was sometimes arrested by divi-
sion of these nerves, but occasionally it continued. In these observations, the nerves
were destroyed by applying a ligature tightly to the vessels as they enter at the hiluni,

406 EXCRETION.

including every thing but the ureter. The ligature was then loosened, so as to admit the
blood, but the nerves had been bruised and destroyed. The secretion of urine continues,
however, under these circumstances, for only a few hours. It then ceases, and the nutri-
tion of the kidney becomes profoundly affected, its tissue breaking down into a putrid,
semifluid mass, which probably enters the blood and is the cause of death.

The other physiological conditions that affect the urinary excretion influence the com-
position of the urine and the quantity of excrementitious matters separated by the kid-
neys. These will be more appropriately considered under the head of nutrition and dis-
assimilation. It is sufficient to remark, in this connection, that, during digestion, when
the composition of the blood is modified by the absorption of nutritive matters, the quan-
tity of urine is usually increased. This is particularly marked when a large amount of
liquid has been taken.

As the excrementitious principles eliminated by the kidneys are being constantly pro-
duced in the tissues by the process of disassimilation, the formation of urine is constant ;
presenting, in this regard, a marked contrast with the intermittent flow of most of the
secretions proper, as distinguished from the excretions. It was noted by Erichsen, in a
case of extroversion of the bladder, and it has been farther shown by experiments upon
dogs, that there is an alternation in the action of the kidneys upon the two sides. Ber-
nard exposed the ureters in a living animal and fixed a small silver tube in each, so that
the secretion from each kidney could be readily observed ; and he noted that a large
quantity of fluid was discharged from one side for from fifteen to thirty minutes, while
the flow from the other side was slight and in some instances was entirely arrested. The
flow then commenced with activity upon the other side, while the discharge from the
opposite ureter was diminished or arrested. We are already familiar with this alterna-
tion of action in the parotid glands.

Changes in the Composition of the Blood in passing through the Kidneys. — Some of
the changes in the blood in its passage through the kidneys have already been noted.
The most important of these consist in a diminution in the proportion of urea, the urates,
and other of the excrementitious principles found in the urine. This would be expected,
inasmuch as these principles are constantly present in the urine, and they have been shown
to be derived exclusively from the blood. It has been ascertained, also, that the blood
of the renal veins contains less water than the blood of any other part of the venous sys-
tem. The constant separation of water from the blood by the kidneys, for the purpose
of carrying off the soluble excrementitious principles, is an explanation of this fact. It
was also observed by Simon, a number of years ago, that the blood of the renal veins
does not coagulate readily, and that it is impossible to obtain fibrin from it in the ordinary
way by stirring with rods.

Reference has already been made to the researches of Bernard, showing that the
blood coming from many of the glands during their functional activity is but little dark-
er than arterial blood. The action of the kidneys is constant, and the quantity of blood
which they receive is enormous. Unless the function of these organs be disturbed, the
blood passing through them cannot be deoxygenated, and it is consequently red, contain-
ing a large quantity of oxygen and a very small proportion of carbonic acid. This fact
we have often noted, and it has been observed by all who have examined the renal veins
in living animals. In comparative analyses for gases of the blood of the renal artery and
vein, Bernard found, in one examination, no carbonic acid in either specimen, the pro-
portion of oxygen being 12 parts per hundred in volume for the artery, and 10 parts
for the vein. These observations were made at a temperature of from 50° to 53° Fahr.
Making the analyses at about the temperature of the body (104° to 113°), the quantity
of carbonic acid was 3 parts for the artery and 3*13 parts for the vein, and the propor-
tion of oxygen was 19 '46 parts for the artery and 1T26 parts for the vein. When the
secretion of urine was arrested by irritation of the kidney, the blood became black in

PHYSIOLOGICAL ANATOMY OF THE URINARY PASSAGES. 407

the vein, and the quantity of oxygen diminished, with a corresponding increase in the
proportion of carbonic acid. These observations show that during secretion most of the
blood sent to the kidneys is for the purpose of furnishing water and the excrementitious
principles of the urine, and that but little is used for ordinary nutrition. Secretion ap-
pears to have no marked influence upon the consumption of oxygen and the production
of carbonic acid.

Physiological Anatomy of the Urinary Passages. — The chief physiological interest
attached to the anatomy of the urinary passages is connected with the discharge of the
urine from the kidneys into the bladder, and with the process of micturition; and it will
be necessary, consequently, to give but a brief account of the structure of these parts.

The excretory ducts of the kidneys (the ureters) commence each by a funnel-shaped
sac, the pelvis, which is applied to the kidney at the hilum. This sac presents little tu-
bular processes, called calices, into which the apices of the pyramids are received. The
ureters themselves are membranous tubes of about the diameter of a goose-quill, becom-
ing much reduced in caliber as they penetrate the coats of the bladder. They are from
sixteen to eighteen inches in length, passing from the kidneys to the bladder behind the
peritoneum. They have three distinct coats : an external coat, composed of fibrous tis-
sue, the ordinary white fibres mixed with elastic fibres of the small variety ; a middle
coat, composed of different layers of non- striated muscular fibres ; and a mucous coat.

The external coat requires no special description. It is prolonged into the calices and
is continuous with the fibrous coat of the kidney at the apices of the pyramids.

The fibres of the muscular coat present two principal layers ; an external longitudi-
nal layer, and an internal transverse, or circular layer, to which is added near the blad-
der a layer of longitudinal fibres, internal to the circular fibres.

The mucous lining is thin, smooth, and without any follicular glands. It is thrown
into slight longitudinal folds, when the tube is flaccid, which are easily effaced by dis-
tention. The epithelium exists in several layers and is remarkable for the irregular
shape of the cells. They present, usually, numerous dark granulations and one or two
clear nuclei with distinct nucleoli. Some of the cells are flattened, some are rounded,
and some are caudate, with one or two prolongations.

Passing to the base of the bladder, the ureters become constricted, penetrate the coats
of this organ obliquely, their course in its walls being a little less than an inch in
length. This valvular opening allows the free passage of the urine from the ureters, but
compression or distention of the bladder closes the orifices and renders a return of
the fluid impossible.

' The bladder, which serves as a reservoir for the urine, varies in its relations to the
pelvic and abdominal organs as it is empty or more or less distended. When perfectly
empty, it lies deeply in the pelvic cavity and is then a small sac, of an irregularly trian-
gular form. As it becomes filled, it assumes a globular or ovoid form, rises up in the
pelvic cavity, and, when excessively distended, it may project into the abdomen. When
the urine is voided at normal intervals, the bladder, when filled, contains about a pint
of liquid ; but, under pathological conditions, it may become distended so as to con-
tain ten or twelve pints, and, in some instances of obstruction, it has been found to con-
tain even more. The bladder is usually more capacious in the female than in the male.
It is held in place by certain ligaments and folds of the peritoneum, which it is unneces-
sary to describe in this connection, but which are so arranged as to allow of the various
changes in volume and position which the organ- is liable to assume under different de-
grees of distention.

The anatomy of the coats of the bladder possesses a certain amount of physiological in-
terest. These are three in number. The external coat is simply a reflection of the peri-
toneum, covering the posterior portion completely, from the openings of the ureters to the
summit, about one-third of the lateral portion, and a small part of the anterior portion.

408 EXCRETION.

The middle, or muscular coat, consists of fibres of the non-striated or involuntary
variety, arranged in three tolerably distinct layers.

The external muscular layer is composed of longitudinal fibres, which arise from parts
adjacent to the neck, and pass anteriorly, posteriorly, and laterally over the organ, so
that when they are contracted they diminish its capacity chiefly by shortening its verti-
cal diameter. The anterior fibres of this layer arise from the body of the pubis and the
symphysis, by tendinous bands, known to most anatomists as the anterior ligaments.
These tendinous fibres spread out upon the prostate and are attached to its anterior sur-
face. As the fibres on the anterior surface pass over the summit of the bladder, they in-
terlace, and some of them are continuous with the fibres coming from the posterior sur-
face. The posterior fibres arise from the base of the prostate, and, after forming a dis-
tinct band an inch or an inch and a quarter in breadth, spread out upon the posterior sur-
face of the bladder. The lateral fibres arise from the sides of the prostate and spread
out upon the lateral surfaces of the bladder. In the female, the posterior fibres arise
from the dense fibrous membrane between the neck of the bladder and the vagina, and
the lateral fibres, from the perineal aponeurosis, the anterior fibres arising from the pubis,
as in the male. The fibres of the external layer are of a pinkish hue, being much more
highly colored than the other layers.

The middle muscular layer is formed of circular fibres, arranged, on the anterior sur-
face of the bladder, in distinct bands at right angles to the superficial fibres. They are
thinner and less strongly marked on the posterior and lateral surfaces.

The internal muscular layer is composed of excessively pale fibres arranged in longi-
tudinal fasciculi, the anterior and lateral bundles anastomosing with each other as they
descend toward the neck of the bladder, by oblique bands of communication, and the
posterior bundles interlacing in every direction, forming an irregular plexus. Here they
are not to be distinguished from the fibres of the middle layer. This arrangement has
given to these fibres the name of the plexiform layer, and it gives to the interior of the
bladder its reticulated appearance. This layer is continuous with the muscular fibres of
the urachus, the ureters, and the urethra.

The sphincter vesica3 is composed of a band of smooth fibres, about half an inch in
breadth and one-eighth of an inch in thickness, embracing the neck of the bladder and
the posterior half of the prostatic portion of the urethra. The tonic contraction of these
fibres prevents the flow of urine, and, during the ejaculation of the seminal fluid, it offers
an obstruction to its passage into the bladder.

It is seen, from the arrangement of the muscular fibres of the bladder, that they are
capable by their contraction of expelling the greatest part of the urine when the sphinc-
ter is relaxed.

The mucous membrane of the bladder is smooth, rather pale, thick, and loosely ad-
herent to the submucous tissue, except over the corpus trigonum. The epithelium exists
in several layers and presents the same diversity in form as that observed in the pelvis
of the kidney and the ureters ; viz., the deeper cells are elongated and resemble the co-
lumnar epithelium, while the cells on the surface are flattened. In the neck and fundus
of the bladder are a few mucous glands, some in the form of simple follicles, and others
collected to form glands of the simple racemose variety.

The corpus trigonum is a triangular body, lying just beneath the mucous membrane
at the base of the bladder and extending from the urethra in front to the openings of
the ureters. It is composed of white fibrous tissue, with a few elastic and muscular
fibres. At the opening of the urethra, it presents a small projecting fold of mucous
membrane, which is sometimes called the uvula vesicas. Over the whole of the surface
of the trigone, the mucous membrane is very closely adherent, and it is never thrown into
folds, even when the bladder is entirely empty.

The blood-vessels going to the bladder are ultimately distributed to its mucous mem-
brane. They are not very numerous, except at the fundus, where the mucous mem-

MECHANISM OF THE DISCHARGE OF URINE.

409

brane is tolerably vascular. Lymphatics have been described as existing in the walls of
the bladder, but Sappey, whose researches in the lymphatic system have been very ex-
tended and successful, has failed to demonstrate them in this situation. The nerves of
the bladder are derived from the hypogastric plexus.

The urethra is provided with muscular fibres, and it is lined by a mucous membrane,
the anatomy of which will be more fully considered in connection with the function of
generation. In the female the epithelium of the urethra is like that of the bladder. In
the male the epithelial cells are small, pale, and of the columnar variety.

Mechanism of the Discharge of Urine. — In some of the lower orders of animals in
which the urine is of a semisolid consistence, the movement of vibratile cilia in the uri-
niferous tubes probably aids in the discharge of the excretion ; but, in the human subject,
the existence, even, of cilia is doubtful, and the urine is discharged into the pelves of the
kidneys and the ureters by pressure due to the act of separation of the fluid from the
blood. Once discharged into the ureters, the course of the urine is determined in part by
the vis a tergo, and in part, probably, by the action of the muscular coats of these canals.
Miiller has found that the ureters can be made to undergo a powerful local contraction
upon the application of a galvanic current ; and Bernard has shown that this may be
produced by galvanization of the anterior root of the eleventh dorsal nerve.

When the urine has accumulated to a certain extent in the bladder, a peculiar sensa-
tion is felt which leads to the act for its expulsion. The intervals at which it is experi-
enced are exceedingly variable. The urine is
usually voided before retiring to rest and upon
rising in the morning, and generally two or
three times, in addition, during the day. The
frequency of micturition, however, depends
very much upon habit, upon the quantity of
liquids ingested, and upon the degree of ac-
tivity of the skin.

Evacuation of the bladder is accomplished
by the muscular walls of the organ itself, aid-
ed by contractions of the diaphragm and the
abdominal muscles with certain muscles which
operate upon the urethra, and it is accompa-
nied by relaxation of the sphincter vesica3.
This act is at first voluntary, but, once begun,
it may be continued by the involuntary con-
traction of the bladder alone. During the first
part of the process, the distended bladder is
compressed by contraction of the diaphragm
and the abdominal muscles ; and this, after a
time, excites the action of the bladder itself.
A certain period usually elapses then before
the urine begins to flow. When the bladder
contracts, aided by the muscles of the abdo-
men and the diaphragm, the resistance of the
sphincter is overcome, and a jet of urine flows from the urethra. All voluntary action
may then cease for a time, and the bladder will nearly empty itself; but the force of the
jet may be considerably increased by voluntary effort.

Toward the end of the expulsive act, when the quantity of liquid remaining in the
bladder is small, the diaphragm and the abdominal muscles are again called into action,
and there is a convulsive, interrupted discharge of the small quantity of urine that re-
mains. At this time, the impulse from the bladder, and, indeed, the influence of the ab-

FIG. 116*. — Diagram shoicinfl the mechanism of mic-
turition. (Kiiss.)

5; but the walls cannot approach nearer the base
without the aid of the abdominal muscles, which, by
a voluntary effort, bring the summit to the position
indicated by the line 6.

410 EXCRETION.

dominal muscles and diaphragm, are very slight, and the flow of urine along the urethra
is aided by the contractions of its muscular walls and the action of some of the perineal
muscles, the most efficient being the accelerator urinse; but with all this muscular action
a few drops of urine generally remain in the male urethra after the act of urination is
accomplished. The process of evacuation of urine in the female is essentially the same
as in the male, with the exception of the slight modifications due to differences in the di-
rection and length of the urethra.

The movements of the bladder are under the control of the nervous system. Accord-
ing to the researches of Budge, the influence of the nervous system operates through the
sympathetic, and he has described a centre in the spinal cord, which presides over the con-
tractions of the lower part of the intestinal canal, the bladder, and the vasa deferentia.
This he calls the genito-spinal centre, and he has located it, in experiments upon rabbits,
in the spinal cord, at a point opposite the fourth lumbar vertebra. From this centre, the
nervous filaments pass through the sympathetic nerve communicating with the ganglion
which corresponds to the fifth lumbar vertebra.

Properties and Composition of the Urine.

The importance of an exact knowledge of the properties and composition of the urine
has long been recognized by physiologists; and our literature is full of observations, more
or less valuable, upon this subject, dating from the discovery of urea, by Hillaire Eouelle,
in the latter part of the last century, to the present time. It is impossible, however, to
follow out in detail even the most important of the chemical researches upon the differ-
ent urinary constituents, without exceeding the limits of pure human physiology ; and
the observations of the earlier authors have now little more than an historical interest.
But this can hardly be said of the analysis of the urine by Berzelins, made early in the
present century; for, even in recent authoritative works upon physiology, these are
quoted as the most elaborate and reliable of the quantitative examinations of the renal
excretion. In treating of this subject, we propose to give simply the chemistry of the
urine as it is understood at the present day, dwelling particularly upon its relations to the
physiology of nutrition and disassimilation. In doing this it will be necessary to con-
sider carefully the quantity, specific gravity, reaction, etc., of the urine, with the varia-
tions observed under different physiological conditions.

General Physical Properties of the Urine. — The color of the urine is very variable
within the limits of health, and it depends to a considerable extent upon the character of
the food, the quantity of drink, and the activity of the skin. As a rule, the color is yel-
lowish or amber, with more or less of a reddish tint. The fluid is perfectly transparent,
free from viscidity, and exhales, when first passed, a peculiar, aromatic odor, which is by
no means disagreeable. Soon after the urine cools, it loses this peculiar odor and has the
odor known as urinous. This odor remains until the liquid begins to undergo decomposi-
tion. The color and odor of the urine are usually modified by the same physiological
conditions. When the fluid contains a relatively large amount of solid matters, the color
is more intense and the urinous odor is more penetrating; and, when its quantity is
increased by an excess of water, the specific gravity is low, the color pale, and the odor
faint. The urine passed in the morning is usually more intense in color than that passed
during the day.

It is somewhat difficult to measure the exact temperature of the urine at the moment
of its emission. In the observations on this subject, by Dr. Byasson, in which a very
delicate thermometer was used and extraordinary care was taken to prevent any change
in temperature before the estimate was made, the temperature, under physiological con-
ditions, varied but a small fraction of a degree from 100° Fahr. It is important to know
the normal temperature of the urine, as it is liable to vary very considerably in certain
diseases.

PROPERTIES AND COMPOSITION OF THE URINE. 4H

Quantity, Specific Gravity, and Reaction of the Urine. — In estimating the total quan-
tity of urine discharged in the twenty-four hours, it is important to take into considera-
tion the specific gravity, as an indication of the amount of solid matter excreted hy the
kidneys. We have already alluded to some of the variations in quantity constantly oc-
curring in health, as depending upon the proportion of water ; but the amount of solid
matters excreted is usually more nearly uniform. It must also be taken into account that
differences in climate, habits of life, etc., in different countries, have an important influ-
ence upon the daily quantity of urine. Dr. Parkes has collected the results of twenty-six
series of observations made in America, England, France, and Germany, and he finds the
average daily quantity of urine in healthy male adults, between twenty and forty years
of age, to be fifty-two and a half fluidounces, the average quantity per hour being two
and one-tenth fluidounces. The extremes were thirty-five and eighty-one ounces.

In attempting to decide the question whether a certain quantity of urine passed be
abnormal or within the limits of health, it is important to recognize, if possible, certain
limits of physiological variation. Becquerel states that the variations in the proportion
of water in the urine likely to occur in health are between twenty-seven and fifty fluid-
ounces ; but his average of the total quantity in the twenty-four hours is only forty-four
ounces, which is rather lower than the one we are disposed to adopt. The circumstances
that lead to a diminution in the proportion of water are usually more efficient in their
operation than those which tend to an increase ; and the range below the healthy standard
is rather wider than it is above. All these estimates, however, are merely approxima-
tive. Assuming that the usual quantity in the male is about fifty ounces, it may be stated,
in general terms, that the range of normal variation is between thirty and sixty ; and
that, when the quantity varies much from these figures, it is probably due to some patho-
logical condition.

According to the researches of Becquerel, the quantity of water discharged by the
kidneys in the twenty-four hours is a little greater in the female than in the male ; but
in the female the specific gravity is lower, and the amount of solid constituents is rela-
tively and absolutely less.

The specific gravity of the urine should always be estimated in connection with the
absolute quantity in the twenty-four hours. Those who assume that the daily quantity
is about fifty ounces give the ordinary specific gravity- of the mixed urine of the twenty-
four hours, at 60° Fahr., as about 1020. The specific gravity is liable to the same vari-
ations as the proportion of water, and the density is increased precisely as the amount of
water is diminished. The ordinary range of variation in specific gravity is between 1015
and 1025 ; but, without positively indicating any pathological condition, it may be as low
as 1005 or as high as 1030.

The reaction of the urine is acid in the carnivora and alkaline in the herbivora. In
the human subject, it is usually acid at the moment of its discharge from the bladder ;
although at certain periods of the day it may be neutral or feebly alkaline, the reaction
depending upon the character of the food. The acidity may be measured by carefully
neutralizing the urine with an alkali, in a solution that has previously been graduated
with a solution of oxalic acid of known strength ; and the degree of acidity is usually
expressed by calling it equivalent to so many grains of crystallized oxalic acid.

As the result of numerous observations made by Vogel and under his direction, the total
quantity of acid in the urine of the twenty-four hours in a healthy adult male is equal to
from two to four grammes, or, omitting fractions, to from thirty to sixty grains of oxalic
acid. The hourly quantity in these observations was equal, in round numbers, to from
one and a half to three grains of acid. The proportion of acid was found to be very vari-
able in the same person at different periods of the day. In one individual, upon whom
the greatest number of observations was made, the average hourly quantity of acid at
night was 2'9 grains ; in the forenoon, 2 grains; and in the afternoon, 2*3 grains. " In
a series of experiments made upon four different persons, the quantity was found to be

412 EXCRETION.

greatest at night, least in the forenoon, and between these extremes in the afternoon."
In estimating the degree of acidity of the urine, it is necessary to test the fluid as soon as
possible after it is discharged from the bladder ; for its acidity rapidly increases after
emission — until ammoniacal decomposition sets in — by the formation of organic acids, par-
ticularly the lactic.

There has been considerable discussion and difference of opinion among physiological
chemists with regard to the cause of the acid reaction of the urine. At the moment of
its discharge from the bladder, it is distinctly and even strongly acid ; but it will not de-
compose the carbonates, like most acid solutions. The weight of chemical authority upon
this point is in favor of the view that there is no free acid in the urine when it is first
passed, although the lactic acid, the acid lactates, and, perhaps, some other of the organic
acids may be produced after emission, as the result of decomposition ; but nearly all
authors agree that it contains the acid phosphate of soda. The phosphates exist in the
fluids of the body in at least three different conditions. The basic phosphate of soda, for
example, possesses three atoms of the base and has an alkaline reaction. In contact
with carbonic acid, this salt may lose one atom of the base, forming the carbonate of
soda and what is called the neutral phosphate, the latter, however, having a feebly alka-
line reaction. In contact with uric acid, the neutral phosphate may lose still another
atom of base, forming the urate of soda and the acid phosphate ; and, according to most
authorities, it is in this form that it exists in the urine, and the presence of this salt is the
cause of its acidity. The acid phosphate of soda may or may not be associated, in the
human subject, with the acid phosphate of lime, which ordinarily gives the intensely acid
reaction to the urine of the carnivora.

Composition of the Urine.

Regarding the excrementitious constituents of the urine as a measure, to a certain
extent, of the general process of disassimilation, it is probably more important to recog-
nize the absolute quantity of these principles discharged in a definite time than to learn
simply their proportions in the urine ; and, in making out a table of the composition of
the urine, we shall give, as far as possible, the absolute quantity of its different constitu-
ents excreted in twenty-four hours. This latter point, however, will be more elaborately
considered in connection with the characters of the individual excrementitious principles
and their variations under physiological conditions. In compiling this table, we have
taken advantage of the elaborate bibliographical and experimental researches of Prof.
Robin, contained in his recent work upon the humors,1 but we have ventured to make
some changes and corrections in his list of urinary constituents :

1 EOBIN, Lefons swr lea humeurs, Paris, 1874. In the table given by Eobin (p. 762), there is evidently a very
serious error in one of the figures giving the proportion of water and an error in the proportion of oxygen. We have
omitted some of the constituents given by Robin, which are stated to be doubtful or accidental, or are noted as present
under pathological conditions.

Although the table represents, very nearly, the latest and most reliable observations upon the relative and abso-
lute quantities of the urinary constituents, there are a few minor points that demand some explanation. For example,
Eobin estimates the proportion of hippurates at a little less than the proportion of urates, while many writers of high
authority speak of the hippurates as excreted in rather larger quantity ; but the investigations with regard to the
daily excretion of hippuric acid have not been so definite and satisfactory as those upon which the estimates of the ex-
cretion of uric acid are based. Kobin gives, also, the proportion of creatine as 1-4 to 2'6 parts per 1,000, and of crea-
tinine, 0-2 to 0'4 per 1,000 ; and most authors give in the urine a larger proportion of creatinine. This difference, how-
ever, is not important, for, as far as the process of excretion is concerned, these two substances may be regarded as a
single principle, creatine being readily converted into creatinine in the urine by simple decomposition. In our endeavor
to make this table as complete as possible, we have reduced the figures given by many authors to represent the amounts
of uric acid, phosphoric acid, sulphuric acid, chlorine, etc., to the quantity of the salts as they actually exist. This is
particularly important in a work on physiology, for chlorine and the various acids just enumerated are not proximate
constituents of the urine, except when combined with bases. It is simply a matter of convenience to estimate them
separately, and the proportions of salts are readily calculated from the combining equivalents of the different ele-
ments.

COMPOSITION OF THE URINE. 413

Composition of the Human Urine.

Water (in 24 hours, 27 to 50 fluidounces — Becquerel) ...................... 967'47 to 940'36

Urea (in 24 hours, 355 to 463 grains— Robin) ............................. lo'OO u 23'00

Uric acid, accidental, or traces ..........................................

Urate of soda, neutral and acid ................... ^ (In 24 hours, 6 to 9

Urate of ammonia, neutral and acid (in small quantity) | grs. of uric acid — Bec-

Urate of potassa ................................ j> querel— or 9 to'l4 grs. 1-00 " 1*60

Urate of lime ................................... of urates, estimated as

Urate of magnesia .............................. J neut. urate of soda.)

Hippurate of soda ............. ) (In 24 hours, about 7'5 grs. of hippuric

Hippurate of potassa .......... > acid — Thudichum — equivalent to about 8*7 I'OO " 1'40

Hippurate of lime ............. ) grs. of hippurate of soda.)

Lactate of soda ............... \

Lactate of potassa ............ >• (Daily quantity not estimated) ........... 1'50 " 2'60

Lactate of lime ............... )

Creatine ..................... ) (In 24 hours, about 11 '5 grains of both —

Creatinine .................. \ Thudichum) ............................ 1'60 " 3*00

Oxalate of lime (daily quantity not estimated) ............................. traces " I'lO

Xanthine ................... , ....................................... not estimated.

Margarine, oleine, and other fatty matters ................................ O'lO to 0'20

Chloride of sodium (in 24 hours, about 154 grains — Robin) .................. 3'00 " 8'00

Chloride of potassium ................................................. traces.

Hydrochlorate of ammonia ............................................. 1*50 to 2*20

Sulphate of soda .......... } V* U hours, 23 to 38 grains of sulphuric acid

Sulphate of potassa ....... -Thudichum. About equal part, of sulphate „

-j. /i [ of soda and sulphate of potassa — Robin — equiv-

Sulphate of lime (traces). . .

J alent to from 22'5 to 37'5 grains of each.)

Phosphate of soda, neutral. . . . )

Phosphate of soda, acid ....... ( ^ ^^ n<>t e8t'mated) ............ ™°

Phosphate of magnesia (in 24 hours, 7'7 to ITS grains — Neubauer) .......... 0'50 " I'OO

Phosphate of lime, acid ...... ) grains-Neubauer). . 0'20 « 1-80

Phosphate of lime, basic ..... )

Ammonio-magnesian phosphate (daily quantity not estimated) ............... 1'50 " 2'40

(Daily excretion of phosphoric acid, about 56 grains — Thudichum.)
Silicic acid ........................................................... 0-03 " 0'04

Urrosacine

Mucus from the bladder

1,000-00 1,000-00

Proportion of solid constituents, from 32'63 to 59'89 parts per 1,000.

)

) '

Gases of the Urine. (Parts per 1,000, in volume.)

Oxygen, in solution 0'90 " I'OO

Nitrogen, in solution 7'00 " 10-00

Carbonic acid, in solution 45 " 50*00

Urea. — As regards quantity, and probably as a measure of the activity of the general
process of disassimilation, urea is the most important of the urinary constituents ; and
this substance, with the changes which, it undergoes in the urine and the mode of its
production in the system, has been most carefully studied by physiologists. Regarding
the daily excretion of urea as a measure of nutritive force and physiological waste, its
consideration would come properly under the head of nutrition, in connection with all
other substances known to be the results of disassimilation ; but it is more convenient to
treat of its general physiological properties, and some of its variations in common with
other excrementitious principles separated by the kidneys, in connection with the com-
position of the urine.

414

EXCRETION.

The formula for urea, showing the presence of a large proportion of nitrogen, would
lead us to suppose that this substance is one of the products of the waste of the nitrogen -
ized principles of the body. It is found, under normal conditions, in the urine, the lymph
and chyle, the blood, the sweat, and the vitreous humor. Its presence has lately been de-
monstrated, also, in the substance of the healthy liver in both carnivorous and herbivorous
animals ; and it has farther been shown by Zalesky that it exists in minute quantity in
the muscular juice. Under pathological conditions, as has been already intimated, urea
finds its way into various other fluids, such as the secretion from the stomach, the serous
fluids, etc.

In connection with the chemical properties of urea, it is interesting to note that it is
one of the few organic proximate principles that can be produced synthetically in the
laboratory of the chemist. As early as 1828, Wohler obtained urea by adding sulphate
of ammonia to a solution of cyanate of potassa. The products of this combination are
sulphate of potassa, with cyanic acid and ammonia in a form to constitute urea. The
cyanate of ammonia is isomeric with urea, and the change is effected by a simple re-
arrangement of its elements. It has long been known that urea, in contact with certain
animal substances, is readily convertible into carbonate of ammonia. This transformation
is theoretically accomplished by adding to urea four atoms of water. It has recently been
stated by Kolbe, that carbonate of ammonia, when heated in sealed tubes to the tem-
perature at which urea commences to decompose, is converted into urea. The decom-
position of urea resulting in the carbonate of ammonia may be easily effected by various
chemical means. As this occurs in the spontaneous decomposition of urea in the urine
and elsewhere, it has been supposed that the symptoms of blood-poisoning following re-
tention of the urinary constituents, in cases of disease of the kidneys, are due to the
decomposition of the urea into carbonate of ammonia, and not to the presence of the urea
itself in the blood. Many interesting experiments and observations have been made upon
this subject, but it is now pretty generally admitted that the weight of evidence is against
the carbonate-of-ammonia theory of ursemia.

Except as regards the probable changes that take place in the process of transforma-
tion of certain constituents of the tissues into urea, the chemical history of this substance
does not present much physiological interest. Urea may be readily extracted from the
urine, by processes fully described in all the modern works upon physiological chemistry ;
and its proportion may now be easily estimated by the new methods of volumetric anal-
ysis. It is not so easy, however, to separate it
from the blood or the substance of any of the
tissues, on account of the difficulty in getting
rid of the other organic matters and the great
facility with which it undergoes decomposi-
tion.

When perfectly pure, urea crystallizes in
the form of long, four -sided, colorless, and
transparent prisms, which are without odor,
neutral, and in taste resemble saltpetre. These
crystals are very soluble in water and in alco-
hol, but they are entirely insoluble in ether.
In its behavior to reagents, urea acts as a base,
combining readily with certain acids, particu-
larly nitric and oxalic. It also forms combi-
nations with certain salts, such as the oxide

^tattized^m an aqueous so- of mercury, chloride of sodium, etc. It exists
in the economy in a state of watery solution,
with perhaps a small portion of it modified by the presence of chloride of sodium.

of Urea. — There are two probable sources of urea in the economy, assuming

COMPOSITION OF THE URINE. 415

that it always preexists in the blood and is not formed in the kidneys. One of these is
in the disassimilation of the nitrogenized constituents of the tissues, and the other, in a
transformation in the blood of an excess of the nitrogenized elements of food. Urea, as
we have already seen, exists in considerable quantity in the lymph and chyle, and it is
found, also, in small proportion, in the blood. It has lately been detected in still smaller
quantity in the muscular tissue ; but chemists have thus far been unable to extract it
from any other of the solid tissues, under normal conditions, except the substance of the
liver. The fact that it exists in the liver has led to the supposition that this is the organ
chiefly concerned in its production; but this opinion, which is based mainly upon the
analyses of Cyon and of Meissner, has lately been shown to be incorrect by the experi-
ments of Gscheidlen, who has demonstrated important errors in previous analyses. We
cannot, therefore, accept the view that the liver produces urea while the kidneys are the
organs chiefly concerned in its elimination ; but, if it be true that urea is the result of the
physiological wear of the nitrogenized elements of the body, the liver would probably
produce its share, in the ordinary process of disassimilation. The fact that urea has not
yet been detected in normal muscular tissue is by no means a conclusive argument against
its formation in this situation. We have lately shown that, although the liver is constant-
ly producing sugar, none can be detected in its substance, for the reason that it is washed
out as fast as it is formed, by the current of blood. In the case of the muscles, it is by
no means improbable that the lymph and perhaps the blood washout the urea constantly
and keep these parts free from its presence during normal conditions. In some late ex-
periments by Meissner, urea was found in dogs and rabbits, after removal of the kidneys,
not only in the liver but in the muscles and brain.

Although our experimental knowledge does not warrant the unreserved conclusion
that urea is produced primarily in the nitrogenized parts of the organism, particularly
the muscular tissue, this view is exceedingly probable ; and we must wait for farther
information on this subject, until physiological chemists are able to follow out more
closely the exact atomic changes that intervene between the functional operation of or-
ganized parts and the change of their substance into excrementitious matters.

When we come to consider the influence of food upon the composition of the urine, it
will be seen that an excess of nitrogenized matter taken into the alimentary canal causes
a proportionate increase in the quantity of urea discharged. This fact has led to the
supposition that a part of the urea contained in the urine is the result of a direct trans-
formation in the blood of the nitrogenized alimentary principles. This view must be
regarded as purely hypothetical. We do not even know the nature of the process by
which the nitrogenized elements of the tissues are transformed into excrementitious mat-
ter, and we are still more ignorant of the essential characters of nutrition proper. When
more nitrogenized food is taken than is absolutely necessary, it is evident that the excess
must be discharged from the system. This is never discharged in the form in which
it enters, like an excess of chloride of sodium or other inorganic matter, but it is well
known that a series of complicated changes are necessary, even before organic matters
can be taken into the blood by absorption. There is no evidence of the direct transfor-
mation of these principles into urea before they have become part of the organized struct-
ures, except in a comparison of the proportions of nitrogen ingested and discharged ; and
this proves nothing with regard to the nature of the intermediate processes. At the
present time, the most rational supposition is, that the nitrogenized elements of food
nourish the corresponding constituents of the body, which are constantly undergoing
conversion into excrementitious matters. Observations which have appeared to demon-
strate the formation of urea directly from albuminoid substances have not been confirmed.

There are certain arguments, based upon comparisons of the atomic constitution of
urea with the elements of uric acid, creatine, and creatinine, in favor of the view that
urea is the product of a higher degree of oxidation of the other excrementitious matters
above mentioned. It has been found, also, that urea may be formed artificially from uric

416 EXCRETION.

acid, creatine, creatinine, xanthine, hypoxanthine, and some other bodies of similar nature.
That certain bodies are mutally convertible by the addition or subtraction of a few elements
of water, there can be no doubt. Examples of these simple transformations are, the
change of starch, dextrine, etc., into glucose, the change of creatine into creatinine, etc.,
but the atomic changes necessary for the conversion into urea of the principles from
which this substance has been assumed to be produced are much more complicated.
There is no positive proof that the proportion of these various principles in the muscles,
blood, and urine, bears an inverse ratio to the proportion of urea. Again, the argument
that the excrements of reptiles contain an excess of uric acid because the activity of oxi-
dation is less than in the mammalia is met by the fact that, in birds, in which the amount
of oxygen consumed is greater, the proportion of urates is enormous ; and urea is not
generally found in this class, but is contained only in the excrements of the rapacious
birds, and here only in small quantity.

There are no sufficient reasons for regarding urea as the final result of oxidation of cer-
tain of the tissues of the body, uric acid, creatine, etc., being substances in an intermediate
stage of transformation ; and we are forced to admit that this principle is formed during
the general process of disassirnilation, probably from the nitrogenized elements of the
body, by a destructive action, with the exact nature of which we are as yet imper-
fectly acquainted.

The daily amount of urea excreted is subject to very great variations. It is given in
the table as ranging between 355 and 463 grains. This is much less than the estimates
frequently given ; but, when the quantity has been very large, it has generally depended
upon an unusual amount of exercise or of nitrogenized food, or the weight of the body
has been above the average. Parkes gives the results of twenty-five different series of
observations upon this point. The lowest estimate is 286*1 grains, and the highest, 688'4
grains.

Uric Acid and its Compounds. — Uric acid seldom if ever exists in a free state in
normal urine. It is exceedingly insoluble, requiring from fourteen to fifteen thousand
times its volume of cold water, and from eighteen to nineteen hundred parts of boiling
water for its solution. It was at one time supposed to exist in the urine in sufficient
quantity to give it its acid reaction ; but it has since been ascertained that its solution
does not redden litmus. Its presence in the urine uncombined must be regarded as a
pathological condition ; still, it is often found in urinary deposits, where it is interesting
to study the peculiar and varied forms of its crystals. Frequently, in tables of the com-
position of the urine, the proportion of uric acid is given, but this is simply a matter of
convenience, and it has precisely the same signification as the estimates of the proportions
of sulphuric or of phosphoric acid. None of these acids constitute, of themselves, prox-
imate principles of the urine, but they are always combined with bases.

In normal urine, uric acid is combined with soda, ammonia, potassa, lime, and mag-
nesia. Of these combinations, the urate of soda and the urate of ammonia are by far the
most important and constitute the great proportion of the urates, the urates of potassa,
lime, and magnesia existing only in minute traces. The urate of soda is very much more
abundant than the urate of ammonia. The union of uric acid with the bases is very
feeble. If from any cause the urine become excessively acid after its emission, a deposit
of uric acid is liable to occur. The addition of a very small quantity of almost any acid
is sufficient to decompose the urates, when the uric acid appears, after a few hours, in a
crystalline form.

Uric acid, probably in combination with bases, was found in the substance of the liver
in large quantity by Cloetta, and his observations have been confirmed by recent, Ger-
man authorities. It is more than probable that the urates also exist in the blood and
pass ready-formed into the urine ; but their proportion in the blood is so slight, under
normal conditions, that their presence in this fluid has not been definitely determined,

COMPOSITION OF THE URIKE.

417

except in birds, in which Meissner has lately found it in considerable quantity. The fact
that the urates exist in the liver, and in no other part — except, perhaps, the spleen — has
led Meissner to the opinion that this organ is the principal seat of the formation of uric
acid. However this may be — and the facts do not seem sufficiently definite to lead to
such an exclusive opinion — it is certainly not formed in the kidneys, but is simply sepa-

FIG. 118.— Crystals of uric acid obtained partly
by the solution and subsequent precipitation
of chemically pure acid, and partly by de-
composition of the uratea by nitric or acetic
acid. (Funke.)

FIG. 119.— Urate of soda. (Funke.)

rated by these organs from the blood. Meissner did not succeed in finding uric acid in
the muscular tissue, although the specimens were taken from the same animals in which
he had found large quantities in the liver.

We have already discussed the theory of the change of uric acid into urea. In the
present state of our knowledge, we must regard the urates, particularly the urate of soda,
as among the products of disassimilation of the nitrogonized constituents of the body ;
and we should admit that as yet we are unable to designate the precise seat of their
formation or to follow out all the processes involved in their production.

The daily excretion of uric acid, given in the table, is from six to nine grains ; which
is equal to from nine to fourteen grains of urates estimated as neutral urate of soda. Like
urea, the proportion of the urates in the urine is subject to certain physiological varia-
tions, which will be considered farther on.
|

Hippuric Acid, Hippurates, and Lactates. — The compounds of hippuric acid, which
are so abundant in the urine of the herbivora, are now known to be constant constitu-
ents of the human urine. Hippuric acid is always to be found in the urine of children,
but it is sometimes absent temporarily in the adult. The hippurates have been de-
tected in the blood of the ox by Verdeil and Dolfuss, and they have since been found in
the blood of the human subject. There can be scarcely any doubt that they pass, ready-
formed, from the blood into the urine. With regard to the exact mode of origin of the
hippurates, we have even less information than upon the origin of the other urinary con-
stituents already considered. Experiments have shown that the proportion of hippuric
acid in the urine is greatest after taking vegetable food ; but it is found after a purely
animal diet, and probably it also exists during fasting. We must be content at present
simply to class the hippurates among the products of disassimilation, without attempting to
specify their exact mode of origin. The daily excretion of hippuric acid amounts to
about 7*5 grains, which is equivalent to about 8'7 grains of hippurate of soda.

Hippuric acid itself, unlike uric acid, is quite soluble in water and in a mixture of
27

418

EXCRETION.

hydrochloric acid. It requires six hundred parts of cold water for its solution, and a
much smaller proportion of warm water. Under pathological conditions, it is sometimes
found free in solution in the urine.

The lactates of soda, potassa, and lime, exist in very considerable proportion in the
normal urine. They are undoubtedly derived immediately from the blood, passing
ready-formed into the urine, where they exist in simple watery solution. According to
Robin, the lactates are formed in the muscles, in the substance of which they can be
readily detected. We have no positive information with regard to the precise mode of
formation of these salts. It is probable, however, that the lactic acid is the result of

FIG. 120.— Crystals ofhippuric acid. (Funke.)

FIG. 121.— Lactate of lime, from chemically pure
lactic acid and carbonate of lime, crystal-
lised from a hot, watery solution. (Funke.)

transformation of glucose. As a curious chemical fact, it is interesting to note that the
lactic acid contained in the lactates extracted from the muscular substance is not abso-
lutely identical with the acid resulting from the transformation of the sugars. The for-
mer have been called sarcolactates, and they contain one equivalent of water less than
the ordinary lactates. According to Robin, the compounds of lactic acid in the urine are
in the form of sarcolactates.

Although the inosates have never been detected in the urine, Robin is of the opinion
that traces of these salts are separated from the blood by the kidneys, from the fact that
they exist normally in the blood and in the muscular tissue.

We have little or no information with regard to the relations of the inosates to ex-
cretion.

Creatine and Creatinine. — Creatine and creatinine are undoubtedly identical in their
relations to the general process of disassimilation, for one is easily converted into the
other, out of the body, by very simple chemical means ; and there is every reason to
suppose that, in the organism, they are the products of physiological waste of the same
tissue or tissues. These principles have been found in the urine, blood, muscular tissue,
and brain. Scherer has demonstrated the presence of creatine in the amniotic fluid. By
certain chemical manipulations, both creatine and creatinine may be converted into urea ;
and the fact that these substances are now known to be constant constituents of the
urine leaves no doubt that they are to be classed among the excrementitious principles.
Chevreul, who first discovered creatine in the extract of muscular tissue, regarded it as
one of the nutritive principles of meat ; but the subsequent researches of Heintz, Liebig,
and others, who found it in the urine, revealed its true character. Verdeil and Marcet
have since found both creatine and creatinine in the blood ; and these principles are now

COMPOSITION OF THE URINE. 419

generally regarded as excrementitious matters, taken from the tissues by the blood, to be
eliminated by the kidneys.

Oreatine has a bitter taste, is quite soluble in cold water (one part in seventy-five), and
is much more soluble in hot water, from which it separates in a crystalline form on cool-
ing. It is but slightly soluble in alcohol and is insoluble in ether. A watery solution
of creatine is neutral. It does not readily form combinations as a base ; but it has lately
been made to form crystalline compounds with some of the strong mineral acids, the
nitric, hydrochloric, and sulphuric. When boiled for a long time with baryta, it is changed
into urea and sarcosine ; but the recent researches of Voit have pretty conclusively shown
that this change does not take place in the living organism, and that probably none of the
urea of the urine is produced in this way. When boiled with the strong acids, creatine
loses four atoms of water and is converted into crea'tinine. This change takes place very
readily in decomposing urine, which contains neither urea nor creatine but a large quan-
tity of creatinine, when far advanced in putrefaction.

FIG. 122.— Creatine, extracted from the, muscular FIG. 123.— Creatinine, formed from creatine by

ftttiM, and crystallised from a hot, watery digestion, with hydrochloric acid, and crystal-

solution. (Funke.) Used from a hot, watery solution. (Funke.)

Creatinine is more soluble than creatine, and its watery solution has a strongly alka-
line reaction. It is dissolved by eleven parts of cold water and is even more soluble in
boiling water. It is slightly soluble in ether and is dissolved by one hundred parts of
alcohol. This substance is regarded as one of the most powerful of the organic bases,
readily forming crystalline combinations with a number of acids. According to Thudi-
chum, who has very closely studied the physiological relations of these substances, crea-
tine is the original excrementitious principle produced in the muscular substance, and
creatinine is formed in the blood by a transformation of a portion of the creatine, some-
where between the muscles and the kidneys ; " for, in the muscle, creatine has by far the
preponderance over creatinine ; in the urine, creatinine over creatine."

In the present state of our knowledge, there is very little to be said with regard to
the physiological relations of creatine and creatinine, except that they are probably to be
classed among the excrementitious principles resulting from the disassimilation of the
muscular tissue. As they exist in considerable quantity in the muscular substance, it be-
comes a question whether, in the urine of carnivorous animals, they be not derived from
the food ; but they could have no such origin in the herbivora or in the urine of starving
animals.

It has been assumed by many authors that, inasmuch as the muscular tissue of the
heart is in almost constant action, it should contain more creatine than any other portion
of the muscular system ; but late observations on this point show that the reverse of this

420

EXCRETION.

is the case. In comparing the proportion of creatine in the heart and in the muscles of
the extremities, in oxen and in the human subject, the quantity has been found to be
much less in the heart ; still, the proportion of creatine has been found to be greater in
tetanized muscles than in the muscular tissue after repose.

From the meagreness of our facts with regard to the physiological relations of creatine
and creatinine, it is evident that there is much to be learned before we can understand
the process of their formation in the healthy organism and the probable results of their
retention or deficient elimination in disease. At present we can only say that these prin-
ciples are probably produced in greatest part in the muscular tissue. The fact that cre-
atine has lately been demonstrated in the brain would lead to the supposition that it is
also one of the products of disassimilation of the nervous substance.

The average daily excretion of creatine and creatinine is estimated by Thudichum at
about 11*5 grains. Of this he estimates that 4'5 grains consist of creatine, and 7 grains,
of creatinine.

Oxalate of Lime. — This salt is not constantly present in the normal human urine,
although it may exist in considerable quantity without indicating any pathological condi-
tion. It is exceedingly insoluble, and the appearance of its crystals, which are commonly
in the form of small, regular octahedra, is quite characteristic. According to Eobin, a
trace may be retained in solution by the chlorides and the alkaline phosphates in the
urine. This salt may find its way out of the system by the kidneys, after it has been
taken with vegetable food or with certain medicinal substances. The ordinary rhubarb,
or pie-plant, contains a large quantity of oxalate of lime, which, when this article is taken,
will pass into the urine. It is probable, however, that a certain quantity of oxalate of lime
may be formed in the organism. Pathologists now recognize a condition called oxaluria,
characterized by the appearance of oxalate-of-lime crystals in the urinary sediments ; and
sometimes the quantity in the urine is so large, and its presence is so constant, that it
forms vesical calculi of considerable size.

FKJ. 124.— Crystals of oxalate of lime, deposited
from the normal human urine, on the addition,
to the urine, of oxalate of ammonia. (Funke.)

FIG 125 —Crystals of leucine. (Funke.)

Inasmuch as pathological facts have shown pretty conclusively that oxalic acid may
appear in the system without being introduced with the food, some physiologists have
endeavored to show how it may originate from a change in certain other of the proximate
principles from which it can be produced artificially out of the body. One of the sub-
stances from which oxalic acid can be thus formed is uric acid. It remains, however, to
show that this can take place in the living organism. Woehler and Frerichs injected

COMPOSITION OF THE URINE.

421

into the jugular vein of a dog a solution containing about twenty-three grains of urate of
ammonia. In the urine, taken a short time after, there was no deposit of uric acid but
there appeared numerous crystals of oxalate of lime. The same result followed in the
human subject, on the administration of sixty-seven grains of urate of ammonia by the
mouth. These questions have more of a pathological than a physiological interest; for
the quantity of oxalate of lime in the normal urine is insignificant, and this salt does not
seem to be connected with any of the well-known processes of disassunilation.

Xanthine, Hypoxanthine, Leucine, Tyrosine, and Taurine. — Traces of xanthine have
been found in the normal human urine, but its proportion has not been estimated, and
we are as yet but imperfectly acquainted with its physiological relations. Under patho-

FIG. 126.— Crystals of tyrosine. (Funke.)

Jio. 127.— Crystals of taurine, (Fuake.)

logical conditions, it occasionally exists in sufficient quantity to form urinary calculi. It
has been found in the liver, spleen, thymus, pancreas, muscles, and brain. It is in-
soluble in water but is soluble in both acid and alkaline fluids. Hypoxanthine has never
been found in normal urine, although it exists in the muscles, liver, spleen, and thymus.
Leucine exists in the pancreas, salivary glands, thyroid, thymus, suprarenal capsules,
lymphatic glands, liver, lungs, kidneys, and in the gray substance of the brain. It has
never been detected in the normal urine. The same remarks apply to tyrosine (although
it is not so extensively distributed in the economy), to taurine and cystine. The last two,
however, contain sulphur, and they may have peculiar physiological and pathological
relations that we do not at present understand.

These various substances are mentioned, although some of them have not been demon-
strated in the normal urine, for the reason that there is evidently much to be learned
with regard to the various products of disassimilation as they are represented by the
composition of the urine. While some of these may not be actual proximate principles,
but substances produced by the processes employed for their extraction, some, which
have thus far been discovered only under pathological conditions, may yet be found in
health, and they represent, perhaps, important physiological acts.

Fatty Matters.— Fat and fatty acids are said to exist in the normal urine in certain
quantity. Their proportion, however, is small, and the mere fact of their presence,
only, is of physiological interest.

Inorganic Constituents of the Urine.

It is by the kidneys that the greatest quantity and variety of inorganic principles are
discharged from the organism; and it is probable that even now we are not acquainted

422

EXCRETION.

with the exact proportion and condition of all the principles of this class contained in
the urine. In all the processes of nutrition, it is found that the inorganic constituents of
the hlood and tissues accompany the organic matters in their various transformations,
although they are themselves unchanged. In fact, the condition of union of the inorganic
with the organic principles is so intimate, that they cannot be completely separated with-
out incineration. In view of these facts, it is evident that a certain part, at least, of the
inorganic salts of the urine is derived from the tissues, of which, in combination with
organic matters, they have formed a constituent part. As the kidneys frequently elimi-
nate from the blood foreign matters taken into the system and are capable sometimes of
throwing off an excess of the normal principles which may be introduced into the cir-
culation, it can be readily understood how a large proportion of some of the inorganic
matters of the urine may be derived from the food.

From the fact that the inorganic matters discharged in the urine are generally the
same as those introduced with the food, and that they vary in proportion with the con-
stitution of the food, it is difficult to ascertain how far their presence and quantity in the
urine represent the processes of disassimilation. One thing, however, is certain : that
the organic constituents of the food, the blood, the tissues, and the urine, are never with-
out inorganic matter in considerable variety ; and it is more than probable that the pres-
ence of these salts in a tolerably definite proportion influences the processes of absorption
and secretion and has an important bearing upon nutrition ; but we are as yet so imper-
fectly acquainted with the processes of nutrition of the tissues, that we cannot follow
out all the relations of the inorganic matters, first to nutrition, and afterward to disas-
similation.

Chlorides. — Almost all of the chlorine in the urine is in the form of chloride of so-
dium, the amount of chloride of potassium being insignificant and not of any special

physiological importance. It is unnecessary, in
this connection, to describe the well-known
properties of common salt, and the methods for
determining its presence and proportion in the
urine are fully treated of in works upon physi-
ological chemistry. All that we have to con-
sider is its importance and significance as a uri-
nary constituent.

By reference to the table of the composition
of the urine, it is seen that the proportion of
chloride of sodium is subject to very great vari-
ations, the range being from three to eight parts
per thousand. This at once suggests the idea
that the quantity excreted is dependent to a
considerable extent upon the amount taken in
with the food ; and, indeed, it has been shown
by numerous observations that this is the fact.
The proportion of chloride of sodium in the blood
seems to be tolerably constant; and any excess that maybe introduced is thrown off
chiefly by the kidneys. It has been shown conclusively that deprivation of common salt
in the food after a time is followed by serious disturbances in the general process of
nutrition ; and it is an acknowledged fact that this proximate principle is a constituent
of every tissue of the body, except the enamel of the teeth. As the chlorides are de-
posited with the organic matter in all the acts of nutrition, they are found to be elimi-
nated constantly with the products of disassimilation of the nitrogenized parts, and their
absence from the food does not completely arrest their discharge in the urine. Accord-
ing to Robin, by suppressing salt in the food, its daily excretion may be reduced to from

FIG. 128.— Crystals of chloride of sodium.
(Funke.)

INORGANIC CONSTITUENTS OF THE URINE.

thirty to forty-five grains, the normal quantity being from one hundred and fifty to one
hundred and sixty grains. This quantity is less than the amount contained in the
ingesta, and under these circumstances there is a gradual diminution in the nutritive
activity. " This fact demonstrates the necessity of adding chloride of sodium to the
food." It is an interesting pathological fact that, in all acute febrile disorders, the pro-
portion of chlorine in the urine rapidly diminishes and is frequently reduced to one hun-
dredth of the normal amount. The quantity rapidly increases to the normal standard
during convalescence. Most of the chlorides of the urine are in simple watery solution ;
but a certain proportion of the chloride of sodium exists in combination with urea.

The daily elimination of chloride of sodium is about one hundred and fifty-four grains
(Robin). The great variations in its proportion in the urine, under different conditions
of alimentation, etc., will explain the differences in the estimates given by various
authorities.

Sulphates. — There is very little to be said regarding the sulphates, beyond the general
statements we have made concerning the inorganic principles of the urine. The propor-
tion of these salts in the urine is very much greater than in the blood, in which there
exists only about 0*28 of a part per thousand. Inasmuch as the proportion in the urine is
from three to seven parts per thousand, it seems probable that the kidneys eliminate
these principles as fast as they find their way into the circulating fluid, either from the
food or from the tissues. Like other principles derived in great part from the food, the
normal variations in the proportion of sulphates in the urine are very great. It is unne-
cessary to consider in detail the variations in the amount of sulphates discharged in the
urine, depending upon the ingestion of different salts or upon diet, for all the recorded
observations have been followed by the same results, and they show that the ingestion of
sulphates in quantity is followed by a corresponding increase in the proportion eliminated.

Thudichum estimates the daily excretion of sulphuric acid at from 23 to 38 grains.
Assuming, with Robin, that the sulphates consist of about equal parts of sulphate of
potassa and sulphate of soda, with traces of sulphate of lime, the quantity of salts would be
from 22-5 to 37*5 grains of sulphate of potassa and an equal quantity of sulphate of soda.

Phosphates. — The urine contains phosphates in a variety of forms; but, inasmuch as
it is not known that any one of the different combinations possesses peculiar relations to
the process of disassimilation, as distinguished from the other phosphates, the phosphatic
salts may be considered together.

The remarks which we have just made with regard to the chlorides and the sulphates
are applicable, to a certain extent, to the phosphates. These salts exist constantly in the
urine, and they are derived in part from the food and in part from the tissues. Like other
inorganic matters, they are united with the nitrogenized elements of the organism, and,
when these are changed into excrementitious principles and are separated from the blood
by the kidneys, they pass with them and are discharged from the organism.

It becomes a question of importance, now, to consider how far the phosphates are
derived from the tissues, and what proportion comes directly from the food. This point
is peculiarly interesting, from the fact that phosphorus has been shown to exist in the
nerve-tissue, and it has been inferred that the excretion of phosphates represents, to some
extent, the physiological wear of the nervous system.

All observers agree that the quantity of phosphates in the urine is in direct relation
to the proportion in the food, and that an excess of phosphates taken into the stomach is
immediately thrown off by the kidneys. It is a familiar fact, indeed, that the phosphates
are deficient and the carbonates predominate in the urine of the herbivora, while the
reverse obtains in the carnivora, and that variations, in this respect, in the urine, may be
produced by feeding animals with different kinds of food. Verdeil made some very
interesting comparative analyses of the blood for the alkaline phosphates in the herbivora,

424 EXCRETION.

the carnivora, and in man. He found the proportion very small in the ox, as compared
with the dog, and intermediate in the human subject. The proportion of phosphates in
the blood of the dog was greatly diminished by feeding with potato. Deprivation of food
diminishes the quantity of phosphates in the urine, but a certain proportion is discharged,
which is derived exclusively from the tissues. We have already noted the fact that the
products of disassimilation of the nitrogenized principles are never discharged in health
without being accompanied with certain inorganic salts, such as the chlorides, sulphates,
and phosphates.

In connection with the fact that phosphorus exists (in precisely what condition it is
not known) in the nervous matter, it has been stated that mental exertion is always
attended with an increase in the elimination of phosphates ; and this has been advanced to
support the view that these salts are specially derived from disassimilation of the brain-
substance. Experiments show that it is not alone the phosphates that are increased in
quantity under these conditions, but urea, the chlorides, sulphates, and inorganic matters
generally ; and, in point of fact, any physiological conditions which increase the pro-
portion of nitrogenized excrementitious principles increase as well the elimination of
inorganic matters. It cannot be assumed, therefore, that the discharge of phosphates is
specially connected with the activity of the brain. "We learn nothing from pathology
upon this point, for, although numerous observations have been made upon the excretion
of phosphoric acid in disease — Vogel having made about one thousand different analyses
in various affections — no definite results have been obtained. From these facts it is seen
that there is no physiological reason why we should connect the elimination of the phos-
phates with the disassimilation of any particular tissue or organ, especially as these salts
in some form are universally distributed in the organism.

Observations have been made upon the hourly variations in the discharge of phos-
phoric acid at different periods of the day ; but these do not appear to bear any absolute
relation to known physiological conditions, not even to the process of digestion.

Of the different phosphatic salts of the urine, the most important are those in which
the acid is combined with soda. These exist in the form of the neutral and acid phos-
phates. The acid salt has one equivalent of the base and is supposed to be the source of
the acidity of the urine at the moment of its emission. The so-called neutral salt is
slightly alkaline and has two equivalents of the base. The proportion of the phosphates
of soda in the urine is larger than that of any of the other phosphatic salts, but the daily
amount excreted has not been estimated. The phosphate of magnesia is a constant con-
stituent of the urine, as well as the acid and the basic phosphate of lime. The daily
excretion of phosphate of magnesia amounts to from 7*7 to 11'8 grains, and that of the phos-
phates of lime, from 4'7 to 5*7 grains. According to Robin, there always exists in the
urine a small quantity of the ammonio-magnesian phosphate, but it never, in health,
exists in sufficient quantity to form a crystalline deposit. The daily excretion of the phos-
phates is, as we have seen, subject to great variations, but the average quantity of phos-
phoric acid excreted daily may be estimated at about fifty grains, or, more accurately,
fifty-six grains.

The urine contains, in addition to the inorganic principles above described, a small
quantity of silicic acid ; but, as far as we know, this has no physiological importance.

Coloring Matter and Mucus.

The peculiar color of the urine is due to the presence of a nitrogenized principle,
known to physiological chemists under a variety of names. We have mentioned it in the
table as urrosacine. It is also called urochrome, uroha9matine, uroxanthine, and purpu-
rine. We have no accurate account of its ultimate composition, and all that is known
about its constituents is that it contains carbon, oxygen, hydrogen, and nitrogen, and
probably iron. Although its exact ultimate composition is not absolutely settled, its con-
stituents are supposed to be nearly the same as those of the coloring matter of the blood,

GASES OF THE URINE. 425

the proportion of oxygen being very much greater. These facts point to the probability
of the formation of urrosacine from heemaglobine.

The quantity of coloring matter in the normal urine is very small. It is subject to
considerable variation in disease, and almost always it is fixed by deposits and calculi of
uric acid or the urates, giving them their peculiar color. This principle first makes its
appearance in the urine and is probably formed in the kidneys. So little is known of its
physiological or pathological relations to the organism, that it does not seem necessary to
follow out all of the chemical details of its behavior in the presence of different reagents.

The normal urine always contains a small quantity of mucus, with more or less epi-
thelium from the urinary passages, and a few leucocytes. These form a faint cloud in
the lower strata of healthy urine after a few hours' repose. The properties of the differ-
ent kinds of mucus have already been considered. An important peculiarity, however,
of the mucus contained in normal urine is that it does not seem to excite decomposition
of the urea, and that the urine may remain for a long time in the bladder without under-
going any putrefactive change.

Gases of the Urine.

In the process of separation of the urine from the blood by the kidneys, a certain
proportion of the gases in solution in the circulating fluid is also removed. For a long
time, indeed, it has been known that the normal human urine contained different gases,
but lately some very interesting observations on this subject have been made by M.
Morin, in which the proportions of the free gases in solution have been accurately esti-
mated. By using the method employed by Magnus in estimating the gases of the blood,
Morin was able to extract about two and a half volumes of gas from a hundred parts of
urine. By careful experiments, he ascertained that a certain quantity of gas remained in
the urine and could not be extracted by his ordinary process. This amounted to about
one-fifth of the whole volume of gas. Adding this to the quantity of gas extracted, he
obtained the proportions to one litre of urine, in cubic centimetres, which are given in
the table, viz. :

Oxygen 0-824

Nitrogen 9'589

Carbonic acid 19'620

These proportions represent the average of fifteen observations upon the urine secreted
during the night.

The proportion of these gases was found by Morin to be subject to certain variations.
For example, after the ingestion of a considerable quantity of water or any other liquid,
the proportion of oxygen was considerably increased (from 0'824 to 1'024), and the car-
bonic acid was diminished more than one-half. The most interesting variations, how-
ever, were in connection with muscular exercise. After walking a long distance, the
exercise being taken both before and after eating, the quantity of carbonic acid was found
to be double that contained in the urine after repose. The proportion of oxygen was
very slightly diminished, and the nitrogen was somewhat increased. The variations of
these gases, however, were insignificant.

Morin explains the great increase in the proportion of carbonic acid, by the greater
respiratory activity during exercise. It is well known, indeed, that muscular exercise
largely increases the proportion of carbonic acid in the blood and the quantity eliminated
by the lungs; and, as the carbonic acid of the urine is undoubtedly derived from the
blood, we should expect that the same conditions would increase its proportion in this
secretion.

It is not probable that the kidneys are very important as eliminators of carbonic acid
from the system, but it is certain that the presence of this gas in the urine assists in the
solution of some of the saline constituents of this fluid, notably the phosphates.

426 EXCRETION.

Variations in the Composition of the Urine.

The urine represents, in its varied constituents, not only a great part of the physiolo-
gical disintegration of the organism, but it contains elements evidently derived from the
food. Its constitution is varying with every different condition of nutrition, with exer-
cise, bodily and mental, with sleep, age, sex, diet, respiratory activity, the quantity of
cutaneous exhalation, and, indeed, with every condition that affects any part of the sys-
tem. There is no fluid in the body that contains such a variety of principles, as a con-
stant condition, but in which the proportion of these principles is so variable. It is for
this reason that we have given in the table of the composition of the urine the ordinary
limits of variation of its different constituents ; and it has been found necessary, in treat-
ing of the individual excrementitious principles, to refer to some of the variations in their
proportion in the urine. In treating more specially of the physiological variations of the
urine, we shall only refer in general terms to conditions that produce wide and important
changes in the proportion of its constituents ; and, under the head of nutrition, we shall
consider how far the absolute quantities of the urinary principles and other excrementi-
tious substances represent the physiological waste which is always coincident with the
repair of the parts.

Variations with Age and Sex. — There are decided differences in the composition of
the urine at different periods of life and in the sexes. These undoubtedly depend in
part upon the different conditions of nutrition and exercise, and in part upon differences
in the food. Although the quantities of excrementitious matters present great varia-
tions, their relations to the organism are not materially modified, except, perhaps, at an
early age ; and the influence of sex and age operates merely as these conditions affect the
diet and the general habits of life.

It is stated by most authors that the urine of the foetus is highly albuminous and con-
tains no urea ; but examinations of the urine in the foetus and newly born have been so
few that we know very little regarding its constitution and normal variations. The re-
searches of the authorities on this subject, quoted by Parkes, leave the question of the
composition of the urine in the foetus and during the first days of extra-uterine life
still uncertain. In a specimen of urine taken from a still-born child delivered with for-
ceps, examined by Drs. Elliot and Isaacs, the presence of urea was determined. Dr.
Beale found urea in a specimen taken at the seventh month.

"With our present imperfect knowledge of the composition of the urine at the earliest
periods of existence, it is impossible to deduce any conclusions regarding the production
of the excrementitious principles at this time ; and it would be unprofitable to detail the
unsatisfactory and conflicting examinations to be found in works devoted specially to the
urine. Observations upon children between the ages of three and seven are more definite.
At this period of life, the amount of urea excreted in proportion to the weight of the body
is about double that in the adult. The amount of chlorine in children is about 'three
times the quantity in the adult; and the proportionate amount of other solid matters is
also greater. The amount of water excreted by the kidneys in children, in proportion
to the weight of the body, is very much greater than in the adult, being more than
double. From eight years of age to eighteen, the urinary excretion becomes gradually
reduced to the adult standard. It has been observed that crystals of oxalate of lime
are much more frequent in the urine of children between four and fourteen years of
age than in the adult.

There are not many definite observations on record upon the composition of the urine
in the later periods of life. It has been shown, however, that there is a decided dimi-
nution, at this time, in the excretion of urea, and that the absolute quantity of urine is
somewhat smaller.

The absolute quantity of the urinary excretion in women is less than in men, and the

VARIATIONS IN THE COMPOSITION OF THE URINE. 427

same is true of the proportionate amount of these principles to the weight of the body ;
still, the differences in the proportionate excretion are not very marked, and the amount
of all these principles being subject to modifications from the same causes as in men, the
small deficiency, in the few direct observations upon record, may be in part, if not
entirely, explained by the fact that women usually perform less mental and physical work
than men, and that their digestive system is generally not so active.

Variations at Different Seasons and at Different Periods of the Day. — The changes
in the quantity and composition of the urine which may be directly referred to the con-
ditions of digestion, temperature, sleep, exercise, etc., have long been recognized by
physiologists ; but it is difficult, if not impossible, so to separate these influences, that
the true modifying value of each can be fully appreciated. For example, there is nothing
which produces such marked variations in the composition of the urine as the digestion
of food. So marked, indeed, is its influence, that some writers of authority incline to
the belief that the greatest part of what have been regarded as the most important
excrementitious matters is derived from the food and not from physiological disintegration
of the tissues. Under strictly physiological conditions, the modifying influence of diges-
tion must always complicate observations upon the effects of exercise, sleep, season,
period of the day, etc. ; and the urine is continually varying in health, with the physio-
logical modifications in the other processes and conditions of life. It will be sufficient
for our purpose to note the most important of these variations and to endeavor to appre-
ciate the conditions which combine to produce them, assigning to each one its proper
value.

At different seasons of the year and in different climates, the urine presents certain
variations in its quantity and composition. It seems necessary that a tolerably definite
quantity of water should be discharged from the body at all times ; and, when the tem-
perature or the hygrometric condition of the atmosphere is favorable to the action of the
skin, as in a warm, dry climate, the quantity of water in the urine is diminished, and its
proportion of solid matters is correspondingly increased. On the other hand, the reverse
obtains when the action of the skin is diminished from any cause. This fact is a matter
of common remark as well as of scientific observation.

At different periods of the day, the urine presents constant and important variations.
It is evident that the specific gravity must be constantly varying with the proportion of
water and solid constituents. According to Dalton, the urine first discharged in the
morning is dense and highly colored ; that passed during the forenoon is pale and of a
low specific gravity ; and in the afternoon and evening it is again deeply colored, and its
specific gravity is increased. The acidity is also subject to tolerably definite diurnal
variations, which have already been noted.

Variations produced ly Food. — An immense number of observations have been made
upon the influence of ordinary food and upon diet restricted to particular articles. These
facts have necessarily been considered more or less fully in connection with the origin
of the urinary constituents ; but it is important, in studying the influence of muscular
exercise, mental effort, etc., to constantly bear in mind the variations occurring under
the influence of the ingesta.

Water and liquids generally increase the proportion of water in the urine and dimin-
ish the specific gravity. This is so marked after the ingestion of large quantities of
liquids, that the urine passed under these conditions is sometimes spoken of by phys-
iologists as the urina potus. This must be borne in mind in clinical examinations of
the urine. It is a curious fact, however, that, when an excess of water has been taken
for purposes of experiment, the diet being carefully regulated, the absolute amount of
solid matters excreted is considerably increased. This is particularly marked in the
urea, but it is noticeable in the sulphates and phosphates, though not to any great

428 EXCRETION.

extent in the chlorides. The results of experiments upon this point seem to show that
water taken in excess increases the activity of disassimilation.

The ordinary meals invariably increase the solid constituents of the urine, the most
constant and uniform increase being in the proportion of urea. This, however, depends
to a great extent upon the kind of food taken. The increase is usually noted during the
first hour after a meal, and it attains its maximum at the third or fourth hour. The inor-
ganic matters are increased as well as the excrementitious principles proper. The urine
passed after food has been called urina cibi, under the idea that it is to be distinguished
from the urine supposed to be derived exclusively from disassimilation of the body, which
is called the urina sanguinis.

It is an interesting and important question to determine the influence of different
kinds of food upon the composition of the urine, particularly the comparative effects of a
nitrogenized and a non-nitrogenized diet. Lehmann has made some very striking obser-
vations upon this point, and his results have been fully confirmed by many other physi-
ologists of authority. Without discussing elaborately all of these observations, it is
sufficient to state that the ingestion of an excess of nitrogenized principles always pro-
duced a great increase in the proportion of the nitrogenized constituents of the urine,
particularly the urea. On a non-nitrogenized diet, the proportion of urea was found to
be diminished more than one-half. The results of the experiments of Lehmann are so
striking that we quote them in full :

"My experiments show that the amount of urea which is excreted is extremely
dependent on the nature of the food which has been previously taken. On a purely ani-
mal diet, or on food very rich in nitrogen, there were often two-fifths more urea excreted
than on a mixed diet ; while, on a mixed diet, there was almost one-third more than on
a purely vegetable diet ; while, finally, on a non-nitrogenous diet, the amount of urea
was less than half the quantity excreted during an ordinary mixed diet.

" In my experiments on the influenc3 of various kinds of food on the animal organism,
and especially on the urine, I arrived at the above results, which in mean numbers may
be expressed as follows : On a well-regulated mixed diet I discharged, in twenty-four
hours, 32-5 grammes of urea (I give the mean of fifteen observations) ; on a purely ani-
mal diet, 53-2 grammes (the mean of twelve observations) ; on a vegetable diet, 22-5
grammes (the mean of twelve observations) ; and on a non-nitrogenous diet, 15-4 grammes
(the mean of three observations)."

With regard to the influence of food upon the inorganic constituents ot the urine, it
may be stated in general terms that the ingestion of mineral substances increases their
proportion in the excretions. We have already alluded to this fact in treating of the
different inorganic salts.

There are certain articles which, when taken into the system, the diet being regular,
seem to retard the process of disassimilation ; or, at least, they diminish, in a marked
manner, the amount of matters excreted, particularly urea. Alcohol has a very decided
influence of this kind. Its action may be modified by the presence of salts and other
matters in the different alcoholic beverages, but, in nearly all direct experiments, alco-
hol, either taken under normal conditions of diet, when the diet is deficient, or when it
is in excess, diminishes the excretion of urea. The same may be stated in general terms
of tea and coffee.

Influence of Muscular Exercise. — There can be no doubt that muscular exercise, under
ordinary conditions of diet, increases the proportion of many of the solid constituents of
the urine, particularly the urea ; but it must be remembered, in considering the effects
of exercise upon the elimination of excrementitious matters, that the modifications in the
urine produced by food are very considerable. We have purposely considered the influ-
ence of food before taking up other modifying conditions, so as to make apparent an
important element of error in some recent observations which are at variance with the

VARIATIONS IN THE COMPOSITION OF THE URINE. 429

prevailing ideas on this subject. When, for example, it has been shown that restriction
to a non-nitrogenous diet will immediately diminish the daily elimination of urea more
than one-half, it is evident that the diet must always be fully considered in experiments
upon the effects of exercise or of other modifying circumstances.

There is another important point, also, which is not always taken into consideration
in comparative observations upon the absolute quantities of urea eliminated during exer-
cise and repose ; and that is the elimination of this principle by the cutaneous surface.
We have already seen that urea is a constant constituent of the sweat. Speck, who
found that exercise usually increased the elimination of excrementitious matters, noted
the fact that urea was not increased in the urine when the sweat was very abundant.

A very elaborate analysis of the principal observations on this subject by Parkes
shows the discrepancies in the experiments of different authors and points out several of
the sources of error. The weight of experimental evidence formerly was decidedly in
favor of an increase in the elimination of urea by exercise ; and the observations opposed
to this view involved inaccuracies which would explain, in part at least, the contradictory
results obtained. Lately, however, new observations have been made, which are assumed
by some to show an actual diminution by exercise in the quantity of urea excreted. Fick
and Wislicenus, Frankland, and Haughton, have attempted to show that this is the fact,
and these physiologists have come to the conclusion that muscular force involves chiefly
the consumption of non-nitrogenous principles and the production of carbonic acid.
While the experiments upon this subject have been so meagre, it would be unprofitable to
enter into an elaborate discussion of their merits, particularly as they have not been
directed specially to the influence of exercise upon the composition of the urine, but to
the amount of muscular power developed by different kinds of food. This subject has
not been reduced to such an absolute certainty that we are able to calculate mathemati-
cally the heat-units, the digestion-coefficients, and the amount of " work " produced by
any given quantity of food ; and such calculations cannot, as yet, take the place of actual
experimental observations. What we want to know is the measurable influence of mus-
cular exercise upon the proportion of certain of the constituents of the urine, under nor-
mal alimentation, every other modifying condition being taken into account. There can
be no doubt that, under an ordinary mixed diet, the elimination of urea is increased by
exercise. Fick and Wislicenus made their observations, extending over a period of between
one and two days, under a diet of non-nitrogenized matter ; and Prof. Haughton com-
pared his observations, made in July, with an average of experiments made at different
seasons, taking no account of the action of the skin. It may be true that, with a purely
non-nitrogeneous diet, exercise fails to increase the quantity of urea eliminated by the
kidneys, as appears from the observations of Fick and Wislicenus ; but farther experi-
ments are necessary to settle even this point, and the recent observations by Parkes show
that this is not always the case.

With regard to the influence of muscular exercise upon the other constituents of the
urine, experiments are somewhat contradictory. Sometimes the water is lessened and
sometimes it is increased ; this difference probably depending upon the activity of the
cutaneous exhalation. Sometimes the uric acid is increased and sometimes it is dimin-
ished. The sulphates, phosphates, and chlorides, are generally increased.

The general result of experimental observations on the effects of exercise upon the
urine may be summed up in the proposition that this condition increases the activity of
the nutritive processes, and produces a corresponding activity in the function of disas-
similation, as indicated by the amount of excrementitious matters separated by the
kidneys.

We have had an opportunity of settling definitely the vexed question of the influence
of muscular exercise upon the elimination of nitrogen.1 In 1870, we made an exceedingly

* FLINT, JK., On the Physiological Effects of Severe and Protracted Muscular Exercise.— New York Medical
Journal, 1S71, vol. xiii., p. 609, et seq.; and Source of Muscular Power, New York, 1878.

430 EXCRETION".

elaborate series of observations upon "Weston, the pedestrian. \ Of these we can here
give only a brief summary. Weston walked for five consecutive days as follows : First
day, 92 miles; second day, 80 miles; third day, 57 miles; fourth day, 48 miles; fifth
day, 40^- miles. The nitrogen of the food was compared with the nitrogen excreted for
three periods; viz., five days before the walk, five days walking, and five days after the
walk. A trusty assistant was with Mr. Weston day and night for the fifteen days ; the
food was weighed and analyzed ; the excreta were collected ; and other observations
were made during the entire period. The analyses were made independently by a com-
petent chemist who had no idea of the results until we had classified and tabulated
them. The conclusions were most decided, and, as far as possible, all the physiological
conditions were fulfilled. As regards the proportion of nitrogen eliminated to the nitro-
gen of the food, the general results were as follows :

For the five days before the walk, with an average exercise of about eight miles daily,
the nitrogen eliminated was 92*82 parts for 100 parts of nitrogen ingested. For the five
days of the walk, for every hundred parts of nitrogen ingested, there were discharged
153-99 parts. For the five days after the walk, when there was hardly any exercise, for
every hundred parts of nitrogen ingested, there were discharged 84-63 parts. During
the walk, the nitrogen excreted was in direct ratio to the amount of exercise; and, what
was still more striking, the excess of nitrogen eliminated over the nitrogen of food almost
exactly corresponded with a calculation of the nitrogen of the muscular tissue wasted,
as estimated from the loss of weight of the body. Full details of the method of investi-
gation, the processes employed, etc., are given in our original paper.

In 1876, Dr. F. W. Pavy made a series of observations upon Weston, similar to
those which we made in 1870. The actual results of these observations did not differ
materially from our own; but Dr. Pavy's interpretation of his results was entirely
different. Taking Dr. Pavy's actual figures, however, we cannot regard his experiments
as conflicting at all with -our own conclusions, and, in point of fact, -his observations
fully confirm those which we published in 1871. We have given an elaborate review
of the recent observations in a little work on The Source of Muscular Power, published
in 1878, in which we have made a careful comparison of Dr. Pavy's figures with our own.

In Dr. Pavy's experiments, the figures certainly show an increase in the proportionate
elimination of nitrogen, due to the excessive muscular work.

Influence of Mental Exertion. — Although the influence of mental exertion upon the
composition of the urine has not been very closely studied, the results of the investiga-
tions which have been made upon this subject are, in many regards, quite satisfactory.
It is a matter of common remark that the secretion of urine is often modified to a
considerable extent through the nervous system. Fear, anger, and various violent emo-
tions, sometimes produce a sudden and copious secretion of urine containing a large
amount of water, and this phenomenon is often observed in cases of hysteria. Intense
mental exertion will occasionally produce the same result. We have often observed
a frequent desire to urinate during a few hours of intense and unremitting mental labor ;
and, on one occasion, being struck with the amount of urine voided, it was found, on
examination, to present scarcely any acidity, and a specific gravity of about 1002. The
interesting point in this connection, however, is to observe the influence of mental labor
upon the elimination of solid matters, as contrasted with the amount of excretion during
complete repose, the conditions of alimentation in the two instances being identical.

In a very interesting work upon the influence of cerebral activity upon the composi-
tion of the urine, Byasson found that by mental exertion the quantity of urine was
increased ; the amount of urea was also increased ; the phosphoric acid was increased
about one-third ; the sulphuric acid was more than doubled ; and the chlorine was
nearly doubled.

PHYSIOLOGICAL ANATOMY OF THE LIVER. 431

CHAPTER XIII.

FUNCTIONS OF THE LIVER.

Physiological anatomy of the liver— Distribution of the portal vein, the hepatic artery, and the hepatic duct-
Origin and course of the hepatic veins— Structure of a lobule of the liver — Arrangement of the bile-ducts in
the lobules — Anatomy of the excretory biliary passages — Nerves and lymphatics of the liver — Mechanism of
the secretion and discharge of bile — Quantity of bile — Variations in the flow of the bile — Discharge of bile from
the gall-bladder— General properties of the bile— Composition of the bile— Origin of the biliary salts— Choles-
terine— Biliverdine — Tests for bile — Excretory function of the liver — Origin of cholesterine — Experiments show-
ing the passage of cholesterine into the blood as it circulates through the brain— Elimination of cholesterine by
the liver — Cholesteramia — Production of sugar in the liver — Evidences of a glycogenic function in the liver —
Does the liver contain sugar during life? — Mechanism of the production of sugar by the liver— Glycogenic mat-
ter— Variations in the glycogenic function — Production of sugar in fetal life — Influence of digestion and of differ-
ent kinds of food upon glycogenesis — Influence of the nervous system, etc., upon glycogenesis — Artificial dia-
betes— Destination of sugar — Alleged production of fat by the liver — Changes in the albuminoid and the corpus-
cular elements of the blood in their passage through the h'ver.

Physiological Anatomy of the Liver.

THE liver, by far the largest gland in the body, is now known to have several entirely
distinct functions ; and one of the most important of these has already been fully con-
sidered, in connection with digestion. It is true that we know very little with regard to
the exact office of the bile in digestion, but that this function is essential to life, there
can be no doubt. We have, however, more positive information with regard to the
excrementitious function of the liver and the changes which the blood undergoes in pass-
ing through its substance ; and the study of these functions is closely connected with
the anatomy of the liver and the chemical constitution of the bile.

It is unnecessary, in this connection, to dwell upon the ordinary descriptive anatomy of
the liver. It is sufficient to state that it is situated just below the diaphragm, in the right
hypochondriac region, and is the largest gland in the body, weighing, when moderately
filled with blood, about four and a half pounds. Its weight is somewhat variable, but it
is stated by Sappey that, in a person of ordinary adipose development, its proportion to
the weight of the body is about as one to thirty-two. In early life, the liver is relatively
larger, its proportion to the weight of the body, in the new-born child, being as one to
eighteen or twenty.

The liver is covered externally by peritoneum, folds or duplicatures of this mem-
brane being formed as it passes from the surface of the liver to the adjacent parts. These
constitute four of the so-called ligaments that hold the liver in place. The proper coat
of the liver is a very thin but dense and resisting fibrous membrane, adherent to the sub-
stance of the organ, but detached without much difficulty, and very closely united to the
peritoneum. This membrane is of variable thickness at different parts of the liver, being
especially thin in the groove for the vena cava. At the transverse fissure, it surrounds
the duct, blood-vessels, and nerves, and it penetrates the substance of the organ in the
form of a vagina, or sheath, surrounding the vessels and branching with them. This
membrane, as it ramifies in the substance of the liver, is called the capsule of Glis-
son. It will be more fully described in connection with the arrangement of the hepatic
vessels.

The substance of the liver is made up of innumerable lobules, of an irregularly ovoid
or rounded form, and about ^ of an inch in diameter. The space which separates these
lobules is about one-quarter of the diameter of the lobule and is occupied with the blood-
vessels, nerves, and ramifications of the hepatic duct, all enclosed in the fibrous sheath.
In a few animals, as, for example, the pig and the polar bear, the division of the hepatic
substance can be readily made out with the naked eye; but, in man and in most of the

432 EXCRETION.

mammalia, the lobules are not so distinct, although their arrangement is essentially the
same. Although the lobules are intimately connected with each other from the fact that
branches going to a number of different lobules are given off from the same interlobular
vessels, they are sufficiently distinct to represent, each one, the general anatomy of the
secreting substance of the liver ; but, before we study the minute structure of the lobules,
it will be convenient to follow out the course of the vessels and the duct, after they have
penetrated at the transverse fissure. In this description we shall follow, in the main,
the observations of Kiernan, who has given, probably, the most accurate account of the
vascular arrangement in the liver.

At the transverse fissure, the portal vein, collecting the blood from the abdominal
organs, and the hepatic artery, a branch of the coeliac axis, penetrate the substance of
the liver, with the hepatic duct, nerves, and lymphatics, all enveloped in the fibrous
vagina, or sheath, known as the capsule of Glisson. The portal vein is by far the larger
of the two blood-vessels, and its caliber may be roughly estimated at from eight to ten
times that of the artery.

The vagina, or capsule of Glisson, is composed of fibrous tissue, in the form of a dense
membrane, closely adherent to the adjacent structure of the liver, and enveloping the
vessels and nerves, to which it is attached by a loose areolar tissue. The attachment of
the blood-vessels to the sheath is so loose, that the branches of the portal vein are col-
lapsed when not filled with blood ; thus presenting a striking contrast to the hepatic
veins, which are closely adherent to the substance of the liver and remain open when
they are cut across. This sheath is prolonged over the vessels as they branch and it fol-
lows them in their subdivisions. It varies considerably in thickness in different animals.
In man and in the mammalia generally, it is rather thin, becoming more and more delicate
as the vessels subdivide, and it is entirely lost before the vessels are distributed in the
interlobular spaces.

The vessels distributed in and coming from the liver are the following :

1. The portal vein, the hepatic artery, and the hepatic duct, passing in at the trans-
verse fissure, to be distributed in the lobules. The blood-vessels are continuous in the
lobules with the radicles of the hepatic veins. The duct is to be followed to its branches
of origin in the lobules.

2. The hepatic veins ; vessels that originate in the lobules, and collect the blood dis-
tributed in their substance by branches of the portal vein and of the hepatic artery.

Branches of the Portal Vein, the Hepatic Artery, and the Hepatic Duct. — These
vessels follow out the branches of the capsule of Glisson, become smaller and smaller, and
they finally pass directly between the lobules. In their course, however, they send off
lateral branches to the sheath ; and those who follow exactly the description of Kiernan
call this the vaginal plexus. The arrangement of the vessels in the sheath is not in the
form of a true, anastomosing plexus, although branches pass from this so-called vaginal
plexus between the lobules. These vessels do not anastomose or communicate with each
other in the sheath.

The portal vein does not present any important peculiarity in its course from the
transverse fissure to the interlobular spaces. It subdivides, enclosed in its sheath, until
its small branches go directly between the lobules, and, in its course, it sends branches
to the sheath (vaginal vessels), which afterward go between the lobules. The distri-
bution of the hepatic artery, however, is not so simple. This vessel has three sets of
branches. As soon as it enters the sheath with the other vessels, it sends off minute
branches (vasa vasorum), to the walls of the portal vein, to the larger branches of the artery
itself, to the walls of the hepatic veins, and a very rich net-work of branches to the hepatic
duct. When the hepatic artery is completely injected, the walls of the hepatic duct are
seen almost covered with vessels. In its course, the hepatic artery also sends branches
to the capsule of Glisson (capsular branches), which join with the branches of the portal

PHYSIOLOGICAL ANATOMY OF THE LIVER. 433

vein, to form the so-called vaginal plexus. From these vessels, a few arterial branches
are given off which pass between the lobules. The hepatic artery cannot be followed
beyond the interlobular spaces. The terminal branches of the hepatic artery are not
directly connected with the radicles of the hepatic veins, but they empty into small
branches of the portal vein within the capsule of Glisson.

FIG. 129.— Lobules of the liver, interlobular vessels, and intralobular veins. (Sappey.)

1, 1, 1 1, 3, 4, lobules ; 2, 2, 2, 2, intralobular veins, injected with white ; 5, 5, 5, 5, 5, interlobular vessels, filled with a

dark injection.

The hepatic duct follows the general course of the portal vein ; but its structure and
relations are so important and intricate that they will be described separately.

Interlobular Vessels. — Branches of the portal vein, coming from the terminal ramifi-
cations as the vessel branches within the capsule and from the branches in the walls of
the capsule, are distributed between the lobules, constituting the greatest part of the
so-called interlobular plexus. These are situated between the lobules and surround them ;
each vessel, however, giving off branches to two or three lobules, and never to one alone.
They do not anastomose, and consequently they are not in the form of a true plexus. The
diameter of these interlobular vessels varies from ysVfr to Tlhr °f an inch. In this distribu-
tion, the blood-vessels are followed by branches of the duct, which are much less numer-
ous and smaller, measuring only -^^ of an inch ; and some, even, have been measured
that are not more than -g-^Vs of an inch in diameter.

Lobular Vessels. — In the interlobular plexus, the ramifications of the hepatic artery
are lost, and this can no longer be traced as a distinct vessel. One of the peculiarities
of its arrangement, as we have seen, is that the artery does not empty into the radicles
of the efferent vein but joins the portal vessels as they are about to be distributed in a
true capillary plexus in the substance of the lobules. In the lobules themselves, conse-
quently, we have only to study the arrangement of the portal plexus, with the mode of
origin of the hepatic veins and the relations of the hepatic duct.

The arrangement of the lobular plexus of blood-vessels is very simple. From the
interlobular veins, a number of branches (eight to ten) are given off arid penetrate the
lobule. As the interlobular vessels are situated between different lobules, each one
sends branches into two and sometimes three of these lobules ; so that, as far as vascular
supply is concerned, these divisions of the liver are never absolutely distinct.

After passing from the interlobular plexus icto the lobules, the vessels immediately
break up into a close net-work of capillaries, from ^TF to *sW of an inch in diameter,
which occupy the lobules with a true plexus. These vessels are very numerous ; and,
28

434

EXCKETIOJST.

when they are fully distended by artificial injection, their diameter is greater than that
of the intervascular spaces. It must be remembered, however, that, in the study of the
liver by minute injections, as in other parts, the vessels probably are distended so that
they occupy more space than they ever do under the physiological conditions of the cir-
culation. The blood, having been distributed in the lobules by this lobular plexus, is col-
lected by venous radicles of considerable size into a single central vessel situated in the
long axis of the lobule, called the intralobular vein. A single lobule, surrounded with
an interlobular vessel, showing the lobular capillary plexus, and the central vein (the
intralobular vein* cut across, is represented in Fig. 130.

//J *

FIG. 130. — Transverse section of a single hepatic lobule. (Sappey.)

1, intralobular vein, cut across ; 2, 2, 2, 2, afferent branches of the intralobular vein ; 3. 8, 8, 3, 3, 3, 3, 3, 3, interlobuhr
branches of the portal vein, with its capillary branches, forming the lobular plexus, extending to the radicles of
the intralobular vein.

"With regard to the mode of origin of the hepatic duct in the substance of the lobule,
recent researches have shown that it begins by a very fine, anastomosing plexus of ves-
sels, with amorphous walls, situated between the liver-cells ; but there are many differ-
ent opinions on this subject, and we shall defer its full consideration until we take up the
anatomy of the secreting structures in the lobules.

Origin and Course of the Hepatic Veins. — The blood distributed in the lobular capil-
lary plexus furnishes the materials for the formation of bile and undergoes those changes
produced by the action of the liver as a ductless gland ; in other words, it is in and
around this plexus that all the physiological functions of the liver are performed. It is.
then only necessary that the blood should be carried from the liver to go to the right
side of the heart ; and the arrangement of the hepatic veins is accordingly very simple.

Intralolular Veins. — The innumerable capillaries of the lobules converge into three
or four venous radicles (represented in Fig. 130), which empty into a central vessel, from
TtfW t° 4-itf of an inch in diameter. This is the intralobular vein. If a liver be carefully
injected from the hepatic veins, and if sections be made in various directions, it will be
seen that the intralobular veins follow the long axis of the lobules, receiving vessels in
their course, until they empty into a larger vessel, situated at what may be termed the
base of the lobules. These vessels have been called, by Kiernan, the sublobular veins.
They collect the blood in the manner just described from all parts of the liver, unite
with others, becoming larger and larger, until finally they form the three hepatic veins,
which discharge the blood from the liver into the vena cava ascendens.

PHYSIOLOGICAL ANATOMY OF THE LIVER.

435

The hepatic veins differ somewhat in their structure from other portions of the venous
system. Their walls are thinner than those of the portal veins, they are not enclosed
in a sheath, and they are very closely adherent to the hepatic tissue. It is this provision
which makes the force of aspiration from the thorax so efficient in the circulation in
the liver. Here, indeed, a force added to the action of the heart is specially necessary;
for the blood is passing into the liver through a second capillary plexus, having already
been distributed in the capillaries of the alimentary canal and other abdominal organs,
before it is received into the portal vein. It has also been noted that the hepatic veins
possess a well-marked muscular tunic, very thin in man, but well-developed in the pig,
the ox, and the horse, and composed of unstriped muscular fibres interlacing with each
other in every direction.

In addition to the blood-vessels just described, the liver receives venous blood from
vessels which have been called accessory portal veins, coming from the gastro-hepatic
omentum, the surface of the gall-bladder, the diaphragm, and from the anterior abdominal
walls. These vessels penetrate at different portions of the surface of the liver, and they
may serve as derivatives, when the circulation through the portal vein is obstructed.

Structure of a Lobule of the Liter. — Each hepatic lobule, bounded and more or less
distinctly separated from the others by the inteiiobular vessels, contains blood-vessels,
radicles of the hepatic ducts, and the so-called hepatic cells. The arrangement of the
blood-vessels has just been described ; but, in all preparations made by artificial injec-
tion, the space occupied by the blood-vessels is exaggerated by excessive distention, and
the difficulties in the study of the relations of the ducts and the liver-cells are thereby
much increased. As the important problem in the minute anatomy of the lobules has
been the relations of the cells to the radicles of the bile-ducts, we shall first take up the
structure of the cells.

Hepatic Cells. — If a scraping from the cut surface of a fresh liver be examined with a
moderately high magnifying power, the field
of view will be found filled with numerous
rounded, ovoid, or irregularly polygonal cells,
measuring from T3Vjr to -j^Vo" of an inch in
diameter. In their natural condition, they are
more frequently ovoid than polygonal; and,
when- they have the latter form, the corners
are always rounded. These cells present one
and sometimes two nuclei, sometimes with and
sometimes without nucleoli. The presence of
numerous small pigmentary granules gives to
the cells a peculiar and characteristic appear-
ance; and, in addition, nearly all of them
contain a few granules or small globules of fat.
Sometimes the fatty and pigmentary matter is
so abundant as to obscure the nuclei. The
addition of acetic acid renders the cells pale
and the nuclei more distinct. By appropriate *

reagents, animal starch (probably glycogenic matter) has been demonstrated in the sub-
stance of the cells.

Arrangement of the Bile-ducts in the Lolules.—In describing the plexus of origin of
the biliary ducts, we shall not discuss the views of Kiernan, Leidy, Beale, and others, as
recent researches have conclusively shown that these were entirely erroneous. Late
researches have shown that the following is probably the true relation of the ultimate
ramifications of the bile-ducts in the lobules to the hepatic cells :

In the substance of the lobules, is an exceedingly fine and regular net- work of vessels,

FIG. 131.— Liver-cells, from a Jivman, fatty lirer.
(Funke.)

436

EXCRETION.

ois uniform size, about TG^S of an inch in diameter, which surround the liver-cells, each
cell lying in a space bounded by inosculating branches of these canals. This plexus is
entirely independent of the blood-vessels, and it seems to enclose in its meshes each indi-
vidual cell, extending from the periphery of the lobule (where it is in communication

with the interlobular bile-ducts) to the intra-
lobular vein in the centre. The vessels prob-
ably have excessively thin, homogeneous
walls — although the existence of their mem-
brane has not been positively demonstrated —
and are without any epithelial lining, being
much smaller, indeed, than any epithelial
cells with which we are acquainted. This
arrangement, as far as is known, has no ana-
logue in any other secreting organ.

Although it is within a few years only
that the reticulated bile-ducts of the lobules
have attracted much attention, they were dis-
covered in the substance of the lobules, near
the periphery, by Gerlach, in 1848. It is evi-
dent, from an examination of his figures and
description, that he succeeded in filling with

injection that portion of the lobular net- work
FIG. 132. — Portion of a transverse section of an 7ie- J.-L-UJ r ru i v i Ji^^i

tic lobule of tie raNM; magnified 400 diame- near the borders of the lobules, and he demon-

(Kolliker.)

Z>, &, &, capillary blood-vessels; g, g, g
ducts ; I, I, I, liver-cells.

gr, capillary bile-

strated the continuity of their vessels with
the interlobular ducts ; but he did not recog-
nize the vessels nearer the centre of the lob-
ule. It is now demonstrated, beyond a doubt, that there are either canals or interspaces
between the liver-cells in the lobules, and that these open into the interlobular hepatic
ducts. It is still a question of discussion, however, whether these passages be simple
spaces between the cells or true vessels lined by a membrane ; but this point has no great
physiological importance, and we can readily imagine that it would be exceedingly diffi-
cult to demonstrate a membrane forming the wall of a tube, the whole measuring but

TFOTT5- °f an mcn-

A peculiarly favorable opportunity for observing the bile-ducts in the lobules was
presented in the livers of animals that died of the so-called " Texas cattle-disease." This
was taken advantage of by the late Dr. R. C. Stiles, who was able to verify, in the most
satisfactory manner, the facts which have lately been established by the German anato-
mists. In these livers, the finest bile-ducts were found filled with bright yellow bile,
and their relations to the liver-cells were exceedingly distinct. In the examination of
these specimens, the presence of what appeared to be detached fragments of these little
canals is an argument in favor of the view that they are lined by a membrane of exces-
sive tenuity. These interesting anatomical points were demonstrated by Dr. Stiles before
the New York Academy of Medicine, and we have since been able to verify them in every
particular.

Anatomy of the Excretory Biliary Passages. — There can be scarcely any doubt of the
connection between the intercellular biliary plexus in the substance of the lobules and
the interlobular ducts. We shall see, farther on, that the ducts, in their course from the
lobules to the intestine, are provided with numerous small, racemose glands, which prob-
ably secrete a mucus that is mixed with the bile ; but, in all probability, the peculiar
elements of the bile are formed in the lobules, and the canals situated bet ween the lobules
and leading from them to the larger ducts are merely excretory.

Between the lobules, the ducts are very small, the smallest measuring about -^^ of

PHYSIOLOGICAL ANATOMY OF THE LIVER. 437

an inch in diameter. They are composed of a delicate membrane, lined with small, flat-
tened epithelium. The ducts larger than y^Vs of an inch have a fibrous coat, formed of
inelastic with a few elastic elements, and, in the larger ducts, there are, in addition, a few
non-striated muscular fibres. The epithelium lining these ducts is of the columnar variety,
the cells gradually undergoing a transition from the pavement-form as the ducts increase
in size. In the largest ducts, there is a distinct mucous membrane, with mucous glands.
Throughout the whole extent of the biliary passages, from the interlobular canals to
the ductus choledochus, are little utricular or racemose glands, varying in size in differ-
ent portions of the liver, called by Robin, the biliary acini. These are situated, at short
intervals, by the sides of the canals. The glands connected with the smallest ducts are
simple follicles, from -^ to ¥^y of an inch long. The larger glands are formed of groups
of these follicles, and they measure from ^-^ to -3-^ of an inch in diameter. The glands are
only found connected with the ducts ramifying in the substance of the liver, and they do
not exist in the hepatic, cystic, and common ducts. They are composed of a homogeneous
membrane, lined with small, pale cells of pavement-epithelium. If the ducts in the sub-
stance of the liver be isolated, they are found covered with these little groups of follicles
and have the appearance of an ordinary racemose gland, except that the acini are rela-
tively small and scattered. This appearance is represented in Fig. 133.

FIG. 133. — Anastomoses, and racemose glands attached to the biliary ducts of the pig; magnified 18 diameters.

(Sappey.)

moses in arches ; 7, 7, 7, angular anastomoses ; 8, 8, 8, 8, anastomoses by transverse branches.

The excretory biliary ducts, from the interlobular vessels to the point of emergence
of the hepatic duct, present numerous anastomoses with each other in their course.

Vasa Aberrantia. — In the livers of old persons, and occasionally in the adult, certain
vessels are found ramifying on the surface of the liver, but always opening into the bil-
iary ducts, which have been called vasa aberrantia. These are never found in the foetus
or in children. They are, undoubtedly, appendages of the excretory system of the liver,
and are analogous in their structure to the ducts, but are apparently hypertrophied, with
thickened, fibrous walls, and present, in their course, irregular constrictions, not found
in the normal ducts. The racemose glands attached to them are always very much atro-
phied. Sappey is of the opinion that these are ducts leading to lobules on the surface of
the liver, which have become atrophied.

Gall-Madder, Hepatic, Cystic, and Common Ducts.— The hepatic duct is formed by

438

EXCRETION.

the union of two ducts, one from the right and the other from the left lobe of the liver.
It is about an inch and a half in length and joins at an acute angle with the cystic duct,
to form the ductus communis choledochus. The common duct is about three inches in
length, of the diameter of a goose-quill, and it opens into the descending portion of the
duodenum. It passes obliquely through the coats of the intestine and opens into its
cavity, in connection with the principal pancreatic duct. The cystic duct is about an
inch in length and is the smallest of the three canals.

20 12 19

728 3 27 7

FIG 134. — Gall-bladder, hepatic, cystic, and common ducts. (Sappey )

1, 2, 3, duodenum ; 4, 4, 5, 6, 7, 7, 8, pancreas and pancreatic ducts ; 9, 10, 11, 12, 13, liver ; 14, gall-bladder; 15, hepatic
duct; 16, cystic duct; Uncommon duct; 18, portal vein; 19, branch from the creliac axis ; 20, hepatic artery ; 21,
coronary artery of the stomach ; 22, cardiac portion of the stomach ; 23, splenic artery ; 24, spleen ; 25, left kidney ;
26, right kidney ; 27, superior mesenteric artery and vein; 28, inferior vena cava.

The structure of these ducts is essentially the same. They have a proper coat, formed
of white fibrous tissue, a few elastic fibres, and a few non-striated muscular fibres. The
muscular tissue is not sufficiently distinct to form a separate coat. The mucous mem-
brane is always found tinged yellow with the bile, even in living animals. It is marked
by numerous minute excavations and is covered with cells of columnar epithelium. This
membrane contains numerous mucous glands.

The gall-bladder is an ovoid or pear-shaped sac, about four inches in length, one inch
in breadth at its widest portion, and capable of holding from an ounce to an ounce and a
half of fluid. Its fundus is covered entirely with peritoneum, but this membrane passes
only over the lower surface of its body.

The proper coat of the gall-bladder is composed of white fibrous tissue with a few
elastic fibres. In some of the lower animals there is a distinct muscular coat, but a few
scattered fibres only are found in the human subject. The mucous coat is of a yellowish
color and marked with numerous very small, interlacing folds, which are exceedingly
vascular. Like the membrane of the ducts, the mucous lining of the gall-bladder is cov-
ered with columnar epithelium. In the gall-bladder, are found numerous small racemose
glands, formed of from four to eight follicles lodged in the submucous structure. These
are essentially the same as the glands opening into the ducts in the substance of the liver,
and thev secrete a mucus which is mixed with the bile.

MECHANISM OF THE SECRETION OF BILE. 439

Nerves and Lymphatics of the Liver. — The nerves of the liver are derived from the
pneumogastric, the phrenic, and the solar plexus of the sympathetic. The branches of
the left pneumogastric penetrate with the portal vein, while the branches from the right
pneumogastric, the phrenic, and the sympathetic surround the hepatic artery and the
hepatic duct. All of these nerves penetrate at the transverse fissure and follow the
blood-vessels in their distribution. They have not been traced farther than the terminal
ramifications of the capsule of Glisson, and their exact mode of termination is unknown.

The lymphatics of the liver are very numerous. They are divided into two layers:
the superficial layer, situated just beneath the serous membrane ; and the deep layer,
formed of a plexus surrounding the lobules and situated outside of the blood-vessels.
The superficial lymphatics from the under surface of the liver, and that portion of the deep
lymphatics which follows the hepatic veins out of the liver, pass through the diaphragm
and are connected with the thoracic glands. Some of the lymphatics from the superior
or convex surface join the deep vessels that emerge at the transverse fissure and pass
into glands below the diaphragm, while others pass into the thoracic cavity.

Mechanism of the Secretion and Discharge of Bile. — The liver has no analogue in the
glandular system, either in its anatomy or in its physiology. There is no gland in the
economy which we know to have two distinct functions, such as the secretion of bile and
the production of certain elements destined to be taken up by the current of blood as it
passes through. In other words, there is no organ in the body which has at the same
time the functions of an ordinary secreting gland and a ductless gland. If we regard the
liver-cells as the anatomical elements which produce the bile, it is evident that their
number is very much out of proportion to the amount of bile secreted ; and the liver
itself is an organ of much greater size than it seems to us would be required for the mere
secretion of bile. We explain this disproportionate size by the fact that the liver has
other functions, which are those of a ductless gland.

There is no gland in which the arrangement of secreting tubes is the same as in the
liver. It is hardly possible that the intercellular plexus of fine tubes in the lobules should
be any thing but the plexus of origin, or the secreting portion of the hepatic duct. These
are certainly not blood-vessels, and the only vessels that could have the appearance we
have described, except the bile-ducts, are the lymphatics ; but the communication be-
tween these vessels and the excretory bile-ducts, and the fact that they have been seen
distended with bile in icteric livers, are pretty conclusive evidence of their nature. This
arrangement, then, must be regarded as peculiar to the liver, as the arrangement of a
capillary plexus surrounded with cells and enveloped in a dilated extremity of a secreting
tube is peculiar to the kidney and is found in no other glandular organ.

Do the liver-cells, situated outside of the plexus of origin of the biliary duct, secrete
the bile, which is taken up by these delicate vessels and carried to the excretory biliary
passages? There are very good reasons for answering this question in the affirmative ;
although, if we do, we must recognize the fact that the same cells produce glycogenic
matter. As far as we are able to understand the mechanism of secretion (except in the
production of milk), it seems necessary that a formed anatomical element, known as a
secreting cell, should elaborate, from materials furnished by the blood, the elements of
secretion ; and this cannot be accomplished by a structureless membrane like that which
forms the walls of the bile-ducts. Under this view, assuming that bile, as bile, first
makes its appearance in these little lobular tubes, the liver-cells are the only anatomical
elements capable of producing the secretion. With regard to the mechanism of this
secreting action, we have nothing to say beyond our general remarks in a previous
chapter. With the view we have just expressed, certain elements of the bile are sep-
arated from the blood, and others are manufactured out of materials furnished by the
blood by the liver-cells and are taken up by the delicate plexus of vessels situated between
the cells. The discharge of the fluid is like the discharge of any other of the secretions,

440 EXCRETION.

except that a portion is temporarily retained in a diverticulum from the main duct, the
gall-bladder.

The two distinct functions of the liver now recognized by many physiologists, namely,
the secretion of bile and the formation of sugar, have led to the question of the existence
in the liver of two anatomically distinct portions or organs, corresponding to its double
physiological function. This view, indeed, has been advanced by several eminent anato-
mists. Robin recognizes two distinct parts in the liver ; a biliary organ and a glycogenic
organ. He regards the lobules, with their liver-cells and blood-vessels, as the parts con-
cerned in the glycogenic function of the liver, and the little glands which open into the
biliary ducts all along their course (see Fig. 133) and are arranged on the duct " in the
form of leaves of fern," as the biliary organ. The same independence of the glycogenic
and biliary portions of the liver has been argued by others.

The fact that bile is found in the lobular canals and the demonstration of the direct
communication of these canals with the excretory biliary ducts are powerful arguments
in favor of the view that the bile is formed in the lobules, and probably by the liver-cells.
What, then, is the function of the little acini connected exclusively with the biliary ducts?
The similarity of their structure to that of the ordinary mucous glands, and to the mucous
glands of the gall-bladder especially, would lead to the supposition that they secrete a
mucous fluid. It is well known that the bile taken from the gall-bladder contains more
mucus than that discharged directly from the liver ; but the bile of the hepatic duct in
most animals is somewhat viscid and contains a certain amount of mucus. This is the
view entertained by Sappey, who states that the bile is viscid in different animals in pro-
portion to the development of these little glands ; and, in the rabbit, in which the glands
do not exist, the bile is remarkably fluid.

Inasmuch as there is no direct evidence that the racemose glands attached to the
excretory biliary passages have any thing to do with the secretion of the essential con-
stituents of the bile, and as they are not even to be found in some animals that produce a
considerable quantity of bile, we must regard the question of the isolation of two organs
in the liver, one for the secretion of bile and the other for the production of sugar, as still
unsettled. There is no evidence, indeed, that the bile is secreted anywhere but in the
hepatic lobules.

Secretion of Bile from Venous or Arterial Blood. — Numerous experiments have been
made with the view of determining whether the bile be secreted from the blood brought
to the liver by the portal vein or from the blood of the hepatic artery. The immense
quantity of blood distributed in the liver by the portal vein led first to the opinion that
the impurities were separated from this blood to form the bile, and that the hepatic
artery had little or nothing to do with the secretion. But, since Bernard discovered the
glycogenic function of the liver, this subject has assumed additional importance ; and it
becomes a question whether the materials for the secretion of bile may not be furnished
by one vessel (the hepatic artery), while the other (the portal vein) is specially con-
cerned in the formation of glycogenic matter. This theoretical view, however, is not
carried out by well-established anatomical facts or by physiological experiments. It is
not yet possible to separate the liver anatomically into two organs, one for the secretion
of bile and the other for the production of sugar. It seems certain, also, from numerous
experiments, that bile may be secreted from the blood of the portal vein after a ligature
has been applied to the hepatic artery ; and it is equally certain, from the recent experi-
ments of Ore, that, if the portal vein be obliterated so gradually that the animal does not
die from the operation, bile is secreted from the blood of the hepatic artery. In support
of this view, several instances of obliteration of the portal vein in the human subject are
cited in works upon physiology. In a note to the communication of Ore in the Comptes
rendus, Andral reports the case of a patient that died of dropsy, and on post-mortem
examination the portal vein was found obliterated. In this instance the gall-bladder

MECHANISM OF THE SECKETION OF BILE. 441

was found full of bile. In addition, instances in which the portal vein emptied into
the vena cava have been reported, and in none was there any deficiency in the secretion
of bile.

If the experiments upon the effects of tying the hepatic artery, and the observations
of instances of obliteration of the portal vein and of congenital malformation, in which
the portal vein does not go to the liver, be equally reliable, there is but one conclusion
to be drawn from them ; and that is, that bile may be secreted from either venous or
arterial blood. This view is not inconsistent with what we know of the general process
of secretion and its applications to the production of bile. Regarding the bile as in part
an excrementitious fluid, its effete element, cholesterine, is contained both in the blood
of the portal vein and the hepatic artery. Its recrementitious principles, glycocho-
lates, taurocholates, etc., we suppose are produced de now in the liver, out of materials
furnished by the blood. The exact nature of the production of elements of secretion by
glandular cells we do not understand ; but there is no good reason to suppose that the
principles necessary for the formation of bile may not be furnished by the blood of the
portal vein, as well as by the hepatic artery.

The view most nearly in accordance with all the facts bearing on the question is, that
bile is produced in the liver from the blood distributed in its substance by the portal vein
and the hepatic artery, and not from either of these vessels exclusively ; and that the bile
may continue to be secreted, if either one of these vessels be obliterated, provided the
supply of blood be sufficient.

Quantity of Bile. — The estimates of the daily quantity of bile in the human subject
must be merely approximative ; and our only ideas on this point are derived from experi-
ments upon the inferior animals. The most complete and reliable observations upon this
subject are those of Bidder and Schmidt, which were made upon animals with a fistula into
the gall-bladder, the ductus communis having been tied. These observers found great
variations in the daily quantity in different classes of animals, the quantity in the car-
nivora being the smallest. Applying their results to the human subject, assuming that
the amount is about equal to the quantity secreted by the carnivora, the daily secretion
in a man weighing one hundred and forty pounds would be about two and a half pounds.

Variations in the Flow of the Bile. — We have already considered, under the head of
digestion, the variations in the flow of bile and their relation to the process of intestinal
digestion. It is sufficient in this connection to repeat that the discharge from a biliary fis-
tula in a dog increases immediately after eating ; that it is at its maximum from the second
to the eighth hour, during which time it does not vary to any great extent ; after the eighth
hour it begins to diminish ; and, from the twelfth hour to the time of feeding, it is at its
minimum. These facts show that, while the bile is discharged much more abundantly
during intestinal digestion than during the intervals of digestion, its production and dis-
charge are constant. This, as we shall see farther on, is a strong argument in favor of
the view that the liver has an excrementitions function.

The bile is stored up in the gall-bladder to a considerable extent during the intervals
of digestion. If an animal be killed at this time, the gall-bladder is always distended ;
but it is found empty, or nearly so, in animals killed during digestion.

The influence of the nervous system upon the secretion of bile has been very liftlo
studied, and the question is one of great difficulty and obscurity. The liver is supplied
very abundantly with nerves, both from the cerebro- spinal and the sympathetic system,
and some observations have been made upon the influence of the nerves upon its glycogenic
function ; but, with regard to the secretion of bile, we can only apply our general remarks
concerning the influence of the nervous system on secretion.

The bile is discharged through the hepatic ducts like the secretion of any other gland.
During digestion, the fluid accumulated in the gall-bladder passes into the ductus com-

442 EXCRETION.

munis, in part by contractions of its walls, and in part, probably, by compression exerted
by the distended and congested digestive organs adjacent to it. It seems that this fluid,
which is necessarily produced by the liver without intermission, separating from the blood
certain excrementitious matters, is retained in the gall-bladder for use during digestion.

Functions of the Bile.

Although the function of the bile in intestinal digestion is essential to life, we know
very little of its mode of action ; and we have thought proper to defer until now a full
consideration of the properties and composition of this secretion. For an account of what
is known of its digestive function, the reader is referred to the chapters treating of diges-
tion. We shall show, in this connection, that the liver excretes one of the most important
of the effete principles ; but, before taking up the relations of the bile as an excretion, it
will be necessary to study its general properties and composition.

General Properties of the Bile. — The secretion, as it comes directly from the liver, is
somewhat viscid ; but, after it has passed into the gall-bladder, its viscidity is much
increased from a farther admixture of mucus.

The color of the bile is very variable within the limits of health. It may be of any
shade between a dark, yellowish-green and a reddish-brown. It is semitransparent, ex-
cept when the color is very dark. In different classes of animals, the variations in color
are very great. In the pig it is bright-yellow ; in the dog it is dark-brown ; and in the
ox it is greenish -yellow. As a rule, the bile is dark-green in the carnivora and greenish-
yellow in the herbivora.

The specific gravity of the human bile is from 1020 to 1026. When the bile is per-
fectly fresh, it is almost inodorous, but it readily undergoes putrefactive changes. It
has an excessively disagreeable and bitter taste. It is not coagulated by heat. When
mixed with water and shaken, it becomes frothy, probably on account of the tenacious
mucus and its saponaceous constituents.

It is generally stated that the bile is invariably alkaline. This is true of the fluid dis-
charged from the hepatic duct, although the alkalinity is not strongly marked ; but the
reaction varies after it has passed into the gall-bladder. Bernard found it sometimes acid
and sometimes alkaline in the gall-bladder, in animals (dogs, and rabbits) killed under
various conditions ; but many of these animals were suffering from the effects of severe
operations. In the hepatic ducts the reaction is always alkaline ; and there are no obser-
vations on human bile that show that the fluid is not alkaline in all of the biliary passages.

We have already noted the fact that the epithelium of the biliary passages is strongly
tinged with yellow, even in living animals. This is due to the remarkable facility with
which the coloring principle of the bile stains the animal tissues. This is very well illus-
trated in icterus, when even a small quantity of this coloring matter finds its way into the
circulation.

Perfectly normal and fresh bile, examined with the microscope, presents a certain
amount of mucus, the characters of which we have already described. There are no
formed anatomical elements characteristic of this fluid. The fatty and coloring matters
are in solution and not in the form of globules or granules.

Composition of the Bile.

It is a remarkable fact, that, although the bile, in a perfectly fresh and normal con-
dition, may be obtained from the inferior animals with the greatest facility, no satisfac-
tory analyses of its characteristic principles were made before the examinations of ox-
gall by Strecker, in 1848. The bile is, however, one of the most important, but least
understood, of the animal fluids ; and our scanty information with regard to its func-
tions has been in a measure due to the want of an exact knowledge of its physiological

COMPOSITION OF HUMAN BILE. 443

chemistry. "We shall study the composition of the bile very closely, and shall show that
it contains two classes of constituents : one class — elements of secretion — which is reab-
sorbed ; and another — an element of excretion — which is discharged in a modified form
in the faeces. The latter involves a newly-described function of the liver, but our infor-
mation is much more positive and definite concerning it than with regard to the digestive
action of the bile. In treating of the subject of digestion, we have already indicated
some of the difficulties, which have been but imperfectly overcome, in the study of the
action of the bile as a true secretion, or a recrementitious fluid. The reason why the
same obscurity has prevailed with regard to the function of the bile as an excretion is
that physiologists have regarded what are known as the biliary salts as the only really
important constituents ; and these salts have eluded chemical investigation after the dis-
charge of the bile into the small intestine. Our recent positive knowledge of the excre-
mentitious function of the liver is due to the recognition of cholesterine, an invariable
constituent of the bile, as one of the most important of the elements of excretion.

Composition of Human JSile. (Robin.)

Water 916-00 to 819-00

Taurocholate, or choleate of soda 56'60 " 106'00

Glycocholate, or cholate of soda traces.

Cholesterine 0'62 to 2'66

Biliverdine 14-00 " SO'OO

Lecithene. .

O.OA « SI "00

Margarine, oleine, and traces of soaps.. r

Choline. . . , traces.

Chloride of sodium 2'7Y to 3*50

Phosphate of soda 1'60 " 2'50

Phosphate of potassa 0'75 " 1-50

Phosphate of lime 0'50 " 1'35

Phosphate of magnesia 0'45 " 0'80

Salts of iron 0'15 " 0'30

Salts of manganese traces " 0*12

Silicic acid '. 0'03 " 0'06

Mucosine traces.

Loss 3-43 to 1-21

1,000-00 1,000-00

There are no peculiarities in the composition of the bile, as regards its inorganic con-
stituents, which demand more than a passing mention. It contains no coagulable organic
principle, except mucosine, and all of its constituents are simply solids in solution. The
quantity of solid matter is very large, and the proportion of water is relatively small ; but,
in comparing its proportion of water with that of other fluids in the body, as the blood-
plasma, lymph and chyle, milk, etc., it must be remembered, as is suggested by Robin,
that all of these contain water entering into the composition of their coagulable prin-
ciples ; so that their proportion of water, as it is ordinarily given, is really not greater
than in the bile. Among the inorganic salts, we find chloride of sodium in considerable-
quantity and a large proportion of phosphates. We also note the presence of salts of
iron, of manganese, and a small proportion of silicic acid.

The fatty and saponaceous matters demand hardly any more extended consideration.
A small quantity of margarine and oleine are held in solution, partly by the small pro-
portion of soaps, but chiefly by the taurocholate of soda, These principles sometimes
exist in larger quantity, when they may be discovered in the form of globules. The pro-
portion of soaps is very small. Lecithene, a phosphorized fat, is mentioned by Robin and
others, but its constitution is not definitely settled. All that is known of this principle

444 EXCRETION.

is that it is a neutral fatty substance extracted from the bile, and is capable of being
decomposed into phosphoric acid and glycerine. Choline is a peculiar alkaloid found in
the bile in exceedingly minute quantity.

Biliary Salts. — The principles which we have called biliary salts are compounds of
soda with peculiar organic acids, found nowhere but in the liver, and undoubtedly pro-
duced in this organ from materials furnished by the blood. The fact that the bile pos-
sesses peculiar principles has long been recognized. It is unnecessary, however, to
follow out in detail the earlier chemical investigations into their properties; for the
biliary matter of Berzelius and the picromel and biliary resin of Thenard are now known
to be composed of several distinct proximate principles. Our exact knowledge of these
substances dates from the analyses of ox-bile by Strecker. He obtained two peculiar
acids, cholic and choleic acid, which he found in the bile, in combination with soda. In
the subsequent researches of Lehmann, these acids are called, respectively, glycocholic
and taurocholic acid, and the salts, glycocholate and taurocholate of soda.

In human bile, the proportion of glycocholate of soda is very small, the biliary mat-
ter existing almost entirely in the form of the taurocholate. The taurocholate may be
precipitated from an alcoholic extract of bile by ether, in the form of dark, resinous
drops. These do not crystallize, and the amount of glycocholate, which is precipitated
in the same way and soon assumes a crystalline form, is very slight. Prof. Dalton, who
has studied the biliary salts very closely, at first was unable to obtain any crystalline
matter from human bile, but he has lately found it in minute quantity.

Taurocholate of Soda. — There is some doubt whether the resinous drops obtained by
the addition of an excess of ether to a strong alcoholic extract of bile consist of a proxi-
mate principle in a perfectly pure state. These drops are not crystallizable, and this has
led to the opinion that they are impure. In fact, even now, there is a certain amount of
obscurity with regard to the character of these peculiar biliary salts. In ox-bile, the
non-crystallizable and the crystallizable salts exist together ; but, in human bile, the
greatest part is in the form of what we know as the taurocholate of soda.

These salts may be readily obtained from ox-bile and separated from each other by
the following process : The bile is first evaporated to dryness and pulverized. The dry
residue is then extracted with absolute alcohol and filtered. In this part of the process,
Dr. Dalton uses five grains of the dry residue to one fluidrachm of alcohol. The filtered
fluid is of a clear, yellowish color, and it contains fats and coloring matter, in addition to
the biliary salts. To precipitate the biliary salts, a small quantity of ether is added,
which produces a dense, white precipitate that redissolves by agitation. Another small
quantity of ether is again added, and the precipitate thus produced is dissolved by shak-
ing the mixture. This process is repeated carefully, adding the ether and shaking the
mixture after each step, until the precipitate becomes permanent. An excess of ether —
from eight to ten times the bulk of the alcoholic extract used— is then added, the test-
tube or flask is carefully corked, and the mixture is set aside to crystallize. Gradually
the dense, white precipitate falls to the bottom of the vessel or becomes attached in the
form of resinous drops to the sides of the glass ; and in from six to twenty-four hours it
begins to form delicate, acicular crystals, arranged in rosettes. These are crystals of the
glycocholate of soda ; and the non-crystallizable matter remaining is the taurocholate of
soda.

To separate the biliary salts from each other, the ether is rapidly poured off, and the
crystalline and resinous residue is dissolved in distilled water. On the addition to this
solution of a little acetate of lead, the glycocholate is decomposed and precipitated in the
form of glycocholate of lead, leaving the taurocholate in solution. The glycocholate of
lead is then separated by filtration, and the subacetate of lead is added to the filtered
fluid. This decomposes the taurocholate, and the taurocholate of lead is precipitated.
The subacetate of lead will decompose both the glycocholate and the taurocholate, but

BILIARY SALTS.

445

the glycocbolate only is acted upon, by the acetate of lead. The glycocholate and the
taurocholate of lead are then carefully washed and treated separately with the carbonate
of soda, which gives the original salts in nearly a pure state.

The taurocholate of soda is a proximate principle of the bile ; and it is not necessary
to describe fully in detail the purely chemical processes by which it is decomposed.
With a little care, the taurocholic acid may be obtained in a state of tolerable purity, and,
by prolonged boiling with potash, it may be decomposed into a new acid and taurine.
Some confusion exists in the books about the name of this new acid. Strecker calls it
choleic acid, and he applies the name of cholic acid to what we have described as glyco-
cholic acid. As we have adopted the nomenclature of Lehmann, we shall call it cholic
acid. It must be remembered, however, that these substances are formed artificially and
are not true proximate principles. They have been described in explanation of the name
taurocholic acid, which has been applied to this acid on the assumption that the different
biliary acids are formed of cholic acid united with taurine or other basic substances.

If human bile be treated in the manner just described, frequently no crystalline mat-
ter is obtained, and, when it exists, it is in very small quantity. The great mass of the
precipitate is composed of the taurocholate of soda. This, when it has been thoroughly

FIG. 135.— Crystals of glycoclwlate of soda; magnified 100 diameters. (Robin.)

purified, is whitish and gummy, very soluble in water and alcohol, and insoluble in ether.
It is melted with slight heat and is inflammable. Its reaction is neutral. It has a pecul-
iar sweetish -bitter taste. The proportion of this principle in the bile is always very large,
although it is subject to considerable variation. It has very little in common with the
salts of fatty origin, either in its general properties or composition, inasmuch as it is
entirely insoluble in ether, and its acid contains nitrogen. Another peculiarity in its

446 EXCRETION.

composition, and one which serves to distinguish it from the glycocholate of soda, is that
it contains two atoms of sulphur. One of its important properties in the bile is that it
aids in the solution of the fats contained in this fluid, and to a certain extent, probably,
in the solution of cholesterine.

Glycocholate of Soda. — We have necessarily described the process for the extraction
of the glycocholate of soda, in connection with the tauro<jholate. The glycocholate is
crystallizable and is more easily obtained in a condition of purity. The chemical points
of difference between these salts are, that the glycocholate is precipitated by the acetate
of lead as well as the subacetate, the acetate having no effect upon the taurocholate of
soda, and that the glycocholic acid does not contain sulphur. By treating glycocholic
acid with potash at a high temperature, it is decomposed into cholic acid and glycine, or
glycocoll. It is this which has given it the name of glycocholic acid. In their physio-
logical relations, the two biliary salts are, as far as we know, identical.

Origin of the Biliary Salts. — There can be no doubt that these principles are ele-
ments of secretion and are produced de now in the substance of the liver. In no
instance have they ever been discovered in the blood in health ; and, although they pre-
sent certain points of resemblance with some of the constituents of the urine, they have
never been found in the excreta. In experiments made by Mtiller, Kunde, Lehmann, and
Moleschott, on frogs, in which the liver was removed and the animal survived several
days, and, in the observations of Moleschott, between two and three weeks, it was found
impossible to determine the accumulation of the biliary salts in the blood. There is no
reason, therefore, for supposing that these principles are products of disassimilation.
Once discharged into the intestine, they undergo certain changes and can no longer be
recognized by the usual tests ; but experiments have shown that, changed or unchanged,
they are absorbed with the elements of food. They are probably the elements con-
cerned in the digestive function of the bile.

Cholesterine. — Before the publication, in 1862, of a memoir on a new excretory func-
tion of the liver, the function and relations of cholesterine were not known, and this sub-
stance was hardly mentioned in most works on physiology. As we believe that it must
now be recognized as one of the most important of the products of disassimilation, it
becomes interesting and important to study its properties more closely.

Cholesterine is now recognized as a normal constituent of various of the tissues and
fluids of the body. Most authors state that it is found in the bile, blood, liver, nervous
tissue, crystalline lens, meconium, and fsecal matter. We have found it in all these situa-
tions, with the exception of the faeces, where it does not exist normally, being trans-
formed into stercorine in its passage down the intestinal canal.

In the fluids of the body, cholesterine exists in solution ; but by virtue of what con-
stituents it is held in this condition, is a question that is not entirely settled. It is stated
that the biliary salts have the power of holding cholesterine in solution in the bile, and
that the small amount of fatty acids contained in the blood holds it in solution in that
fluid ; but direct experiments on this point are wanting. In the nervous substance and
in the crystalline lens, it is united " molecule d molecule " to the other elements which go
to make up these tissues. After it is discharged into the intestinal canal, when it is not
changed into stercorine, it is to be found in a crystalline form, as in the meconium and
in the faeces of animals in a state of hibernation. In pathological fluids and in tumors,
it is found in a crystalline form and may be detected by microscopical examination.

Cholesterine is usually described as a non-nitrogenized principle, having all the prop-
erties of the fats, except that of saponification with the alkalies. It is neutral, inodor-
ous, crystallizable, insoluble in water, soluble in ether, very soluble in hot alcohol, though
sparingly soluble in cold alcohol. It is inflammable and burns with a bright flame. It
is not attacked by the alkalies, even after prolonged boiling. When treated with strong

CIIOLESTERIKE.

447

FIG. 13G.—C7iole8tenne extracted from the Hie
objective.

\inch

The determination of the fusing-point is

sulphuric acid, it strikes a peculiar red color, which is mentioned by some as characteristic
of cholesterine. We have found that it possesses this character in common with the so-
called seroline.

Cholesterine may easily and certainly be recognized by the form of its crystals, the char-
acters of which can be made out by means of the microscope. They are rectangular or
rhomboidal, exceedingly thin and transparent, of variable size, with distinct and generally
regular borders, and frequently are arranged
in kyers, with the borders of the lower stra-
ta showing through those which are super-
imposed. This arrangement of the crystals
takes place when cholesterine is present in
considerable quantity. In pathological speci-
mens, the crystals are generally few in num-
ber and isolated. The plates of cholesterine
are frequently marked by a cleavage at one
corner, the lines running parallel to the bor-
ders; and frequently they are broken, and
the line of fracture is generally undulating.
Frequently the plates are rectangular, and
sometimes they are almost lozenge-shaped.
It is by the transparency of the plates, the
parallelism of their borders, and their ten-
dency to break in parallel lines, that we rec-
ognize cholesterine. Crystals of cholesterine
melt at 293° Fahr., but they are formed again
when the temperature falls below that point,
one of the means of distinguishing cholesterine from seroline, which latter fuses at 90° 8'.

Without considering in detail the processes which have been employed by other
observers for the extraction of cholesterine from the blood, bile, and various tissues of the
body, we shall simply describe the method which has been found most convenient in the
various analyses we have made for this substance. In analyses of gall-stones, the process
is very simple ; all that is necessary being to pulverize the mass, extract it with boiling
alcohol, and filter the solution while hot, the cholesterine being deposited on cooling.
If the crystals be colored, they may be redissolved and filtered through animal charcoal.
It is only when this substance is mixed with fatty matters, that its isolation is a matter
of any difficulty. In extracting cholesterine from the blood, we have operated on both
the serum and clot, and, in this way, we have been able to demonstrate it in greater quan-
tities in this fluid than have been observed by others, who have employed only the serum.
The following is the process for quantitative analysis, which was fixed upon after a
number of experiments :

The blood, bile, or brain, as the case may be, is first carefully weighed, then evaporated
to dryness over a water-bath, and afterward pulverized in an agate mortar. The powder
is then treated with ether, in the proportion of about a fluidounce for every hundred grains
of the original weight, for from twelve to twenty-four hours, agitating the mixture occa-
sionally. The ether is then separated by filtration, throwing a little fresh ether on the
filter so as to wash through every trace of the fat, and the solution is set aside to evaporate.
If the fluid, especially the blood, have been carefully dried and pulverized, when the ether
is added it divides it into a very fine powder and penetrates every part. After the ether
has evaporated, the residue is extracted with boiling alcohol, in the proportion of about
a fluidrachm for every hundred grains of the original weight of the specimen, filtered
while hot into a watch-glass, and allowed to evaporate spontaneously. To keep the fluid
hot while filtering, the whole apparatus may be placed in the chamber of a large water-
bath, or, as the filtration is generally rapid, the funnel may be warmed by plunging it

448 EXCRETION.

into hot water, or steaming it, taking care that it be carefully wiped. We now have the
cholesterine mixed with a certain quantity of saponifiable fat. After the fluid has evapo-
rated, we can see the cholesterine crystallized in the watch-glass, mingled with masses
of fat. This we remove by saponification with an alkali ; and, for this purpose, we add
a moderately strong solution of caustic potash, which we allow to remain in contact
with the residue for one or two hours. If much fat be present, it is best to heat the
mixture to a temperature a little below the boiling-point ; but in analyses of the blood
this is not necessary. The mixture is then to be largely diluted with distilled water,
thrown upon a small filter, and thoroughly washed till the fluid which passes through is
neutral. We then dry the filter and fill it up with ether, which, in passing through,
dissolves out the cholesterine. The ether is then evaporated, the residue extracted with
boiling alcohol as before, the alcohol collected on a watch-glass previously weighed, and
allowed to evaporate. The residue consists of pure cholesterine, the quantity of which
may be estimated by weight.

The accuracy of this process may be tested by means of the microscope ; for the crys-
tals have so distinctive a form that it is easy to determine, by examining the watch-glass,
that the cholesterine is perfectly pure. In making this analysis quantitatively, it is
necessary to be very careful in all the manipulations ; and, for determining the weight of
such minute quantities, an accurate and delicate balance, one, at least, that will turn with
the thousandth of a gramme, carefully adjusted, must be employed. With these precau-
tions, the quantity of cholesterine in any fluid or solid may be determined with perfect
accuracy ; and the estimate may be made in a quantity of blood not exceeding fifteen or
twenty grains. In analyzing the brain and bile, we found it necessary to pass the first
ethereal solution through animal charcoal, in order to get rid of the coloring matter.
In doing this, the charcoal must be washed with fresh ether until the solution which
passes through is brought up to the original quantity. The other manipulations are the
same as in the analyses of the blood. In examining the meconium, we found that the
cholesterine which crystallized from the first alcoholic extract was so pure that it was
not necessary to subject it to the action of an alkali.

The proportion of cholesterine in the bile is not very large. In the table, it is esti-
mated at from 0*62 to 2'66 parts per thousand. In a single examination of the human
bile, we found the proportion 0'618 of a part per thousand.

The origin and destination of this principle involve, as we believe, an office of the
liver which has not hitherto been recognized by physiologists; and we shall consider
these questions specially, under the head of the excretory function of the liver.

Biliverdine. — The coloring matter of the bile bears a certain resemblance to the color-
ing matter of the blood and is supposed to be formed from it in the liver. It gives
to the bile its peculiar tint, and has, as we have remarked, the property of coloring
the tissues with which it comes in contact. Whenever the flow of bile is seriously
obstructed, the coloring matter is absorbed by the blood, and it can be readily detected
in the serum and in the urine. It also colors the skin and the conjunctiva. In the bile
it is liquid, but it may be coagulated and extracted by various processes. It does not
exist naturally in the form of pigmentary granulations.

This principle is precipitated from the bile by boiling with milk of lime. The filtered
residue is then decomposed with hydrochloric acid, which unites with the lime and leaves
a fatty residue, of an intense-green color. The fat is then removed by repeated washings
with ether, which is a very long and difficult process. The precipitate is then redissolved
in alcohol with ether added, which gives to the liquid a bluish-green color, and leaves,
after evaporation, a dark-green powder. This powder contains iron, but its proportion
has never been accurately estimated. The matter thus obtained is insoluble in water and
in chloroform, but it is soluble in ether, alcohol, sulphuric and hydrochloric acid.

It is unnecessary to follow out in detail all of the chemical investigations which have

TESTS FOR BILE. 449

been made into the ultimate composition and the modifications of this and the other col-
oring matters. Recent researches have shown that, in all probability, the coloring matter
called biliverdine is a mixture of several distinct coloring principles, and that these rapidly
change in contact with the oxygen of the air ; so that there is considerable uncertainty
with regard to the ultimate composition of these and other substances of the same class.

Tests for Bile. — It is frequently desired, particularly in pathological investigations,
to ascertain, by some easy test, the fact of the presence or absence of bile in various
of the fluids and solids of the body. It is, indeed, a most interesting physiological ques-
tion to determine the course and destination of the biliary salts after the bile has passed
into the intestinal canal ; and this can be done only by the application of appropriate
tests to the contents of the alimentary tract and the blood of the portal system. The
ingredients of the bile which it is important to detect are biliverdine, the biliary salts,
and cholesterine. The last-named substance can be detected most readily by applying
the method which we have just described for its extraction ; but several tests have been
proposed for the detection, on the one hand, of the coloring matter of the bile, and, on
the other, of the peculiar biliary salts.

Test for Biliverdine. — There is one test so simple and easy of application, that it alone
will suffice for the prompt detection of biliverdine. This is peculiarly applicable to the
urine, where the presence or absence of bile frequently becomes an important question.

We are led generally to suspect the presence of bile in the fluids of the body by their
peculiar color. If we spread out the suspected fluid in a thin stratum upon a white sur-
face, as a porcelain plate, and add a single drop of nitric acid, or, what is better, nitroso-
nitric acid, if the coloring matter of bile be present, a peculiar play of colors will be ob-
served at the circumference of the drop of acid as it diffuses itself. The color will rapidly
change from blue to red, orange, purple, and finally to yellow. This is due to the action
of the acid upon the biliverdine ; and this test does not indicate the presence of either cho-
lesterine or the biliary salts. It is used, therefore, only when we wish to determine the
presence of the coloring matter of the bile.

Test for the Biliary Salts. — The best, and, indeed, the only reliable test for the biliary
salts, was proposed many years ago by Pettenkofer, and this is now generally known as
Pettenkofer's test. This requires some care and practice.in its application, but it is entirely
reliable; and, although it has been objected that there are other substances, beside the
biliary salts, which produce similar reactions, they are not met with in the animal fluids
and consequently are not liable to produce confusion. If a considerable quantity of bile
be present in any fluid, and if there be not a large admixture of animal matters, the test
may be employed without any previous preparation ; but, in delicate examinations, it is
best to evaporate the suspected liquid, extract the residue with absolute alcohol, precipi-
tate with ether, and dissolve the ether-precipitate in distilled water. By this means a
clear solution is obtained, which will react distinctly, even when the biliary salts exist
in very small quantity. Pettenkofer's test is applicable to any of the biliary salts, what-
ever be their form, and the reaction is dependent upon the presence of cholic acid, which
enters into the composition of all the varieties of the biliary acids.

The following is one of the most common methods of employing Pettenkofer's test :
To the suspected solution we add a few drops of a strong solution of cane-sugar in
water. Sulphuric acid is then slowly added, to the extent of about two-thirds of the
bulk of the liquid. It is recommended to add the acid 'slowly, so that the temperature
shall be but little raised. If a large quantity of the biliary salts be present, a red color
shows itself almost immediately at the bottom of the test-tube, and this soon extends
through the entire liquid, rapidly deepening until it becomes of a dark-lake or purple.
If the biliary matters exist in very small proportion, it may be several minutes before any
red color makes its appearance, and the change to a purple is correspondingly slow, the
whole process occupying from fifteen to twenty minutes. Many organic matters may be
29

450 EXCRETION.

rendered dark by the action of the acid, and the sugar itself will be acted upon, even if
no bile be present, but the color due to the sugar alone is yellow. The peculiar play of
colors above described can easily be recognized after a little practice, and is observed
only in the presence of the biliary salts.

The ordinary modifications in the application of this test are unimportant. Some
recommend to add the sulphuric acid first, and then to add the solution of sugar; and
some, after adding to the liquid two-thirds of its volume of sulphuric acid, drop into the
mixture one or two lumps of cane-sugar. The reaction with the biliary salts is essen-
tially the same, whichever of these methods be employed.

Excretory Function of the Liver.

In 1862, in studying the properties and physiological relations of cholesterine, we
gave the first definite account of an excretory function of the liver. The experiments and
observations upon which we based our conclusions were extended and laborious, and, as
far as we know> they have not been repeated in detail by other observers; but the results
must be taken as positive, if the accuracy of the experiments be admitted, and they have
been adopted, to a greater or less extent, by scientific authorities. The details of these
experiments are too elaborate to be given in full, as contained in the original memoir.1

The few statements with regard to the function of cholesterine to be found in works
published before 1862 are very indefinite. In most treatises on physiology, this substance
is hardly mentioned, it being generally regarded as a curious principle, interesting only
to the physiological chemist. We have given, in the memoir referred to, extracts from
the works of Carpenter, Lehmann, Mialhe, and Dalton, which contain all that is said
with regard to the probable function of cholesterine ; and these quotations, which embody
about all that we could find on the subject, show that its office was not in the least
understood. Inasmuch as cholesterine is the only excrementitious principle as yet dis-
covered in the bile, bearing the same relation to this fluid that urea does to the urine, it is
evident that the ideas of physiologists, with regard to any excretory function of the liver,
must have been very indefinite before the relations of cholesterine had been determined.

The first question which arises is whether the liver has any excretory function. Some
authors have assumed that the bile is purely excrementitious and has no function as a
secretion. This question we have fully discussed in connection with the subject of diges-
tion. The confusion that has arisen with regard to this point has been due to the fact
that those who adopted the view that the bile was simply an excretion denied to it any
digestive properties ; while, on the other hand, those who believed it to be concerned in
digestion would not admit that it was an excretion. We have shown conclusively, in
treating of intestinal digestion, that the bile is so important in this process as to be essen-
tial to life ; but we have shown, at the same time, that the liver eliminates from the
blood one of the most important of the products of disassimilation. It will be found
important, as bearing upon the probable function of the bile, to apply to this fluid the
general law of the distinctions between secretions and excretions.

Cells of glandular epithelium are constantly manufacturing, out of materials furnished
by the blood, the elements of the true secretions ; but these elements do riot preexist in
the blood, they appear de novo in the secreting organ, and they never accumulate in the
system when the function of the secreting organ is disturbed. Again, the true secretions
ara not discharged from the body, but they have a function to perform in the economy,
and are poured out by the glands intermittently, at the times when this function is called
into action. As far as the biliary salts (the taurocholate and glycocholate of soda) are
concerned, the bile corresponds entirely to the true secretions. These principles are
manufactured by the liver, they do not preexist in the blood, and they do not accumu-

1 FLINT, Jr., Experimental Researches into a New Excretory Function of the Liver. — American Journal of
the Medical Sciences, Philadelphia, 1862, New Series, vol. xliv., p. 305, et seq. ; and, Reclierches efcperimentales sur
um, nouvelle fonction dufoie, Paris, 1868.

EXCRETORY FUNCTION OF THE LIVER. 451

late in tlie blood when their formation in the liver is disturbed. The research^- <»f
Bidder and Schmidt and others have shown that, although we cannot detect the biliary
salts in the blood or chyle coming from the intestine, these principles are not discharged
in the faeces. All of these facts point to an important function of the bile as a secretion.
It is true that it is discharged constantly, but, during digestion, its flow is very much
more abundant than at any other time. It is pretty well established that, during the
intervals of the flow of the secretions, the glands are manufacturing the materials of
secretion, which are washed out, as it were, in the great afflux of blood which takes
place during what has been called the functional activity of the gland. Now, if the liver,
in addition to its function as a secreting organ, be constantly forming bile for the purpose
of eliminating an excrementitious matter, it is to be expected that the bile would al-
ways contain a certain proportion of its elements of secretion.

The constant and invariable presence of cholesterine in the bile assimilates it in every
regard to the excretions, of which the urine may be taken as the type. Cholesterine
always exists in the blood and in certain of the tissues of the body. It is not produced
in the substance of the liver, but is merely separated from the blood by this organ. It
is constantly passed into the intestine, and is discharged, although in a modified form, in
the faeces. We know of no function which it has to perform in the economy, any more
than urea or any other of the excrementitious principles of the urine ; and we have
shown, in the memoir already referred to, that it accumulates in the blood in certain
cases of organic disease of the liver and gives rise to symptoms of blood-poisoning.

Origin of Cholesterine. — Cholesterine exists in largest quantity in the substance of
the brain and nerves. It is also found in the substance of the liver — probably in the
bile contained in this organ — the crystalline lens, and the spleen ; but, with these excep-
tions, it is found only in the nervous system and blood. Two views present themselves
with regard to its origin. It is either deposited in the nervous matter from the blood, or
it is formed in the brain and taken up by the blood. This is a question, however, which
can be settled experimentally, by analyzing the blood for cholesterine as it goes to the
brain by the carotid and as it comes from the brain by the internal jugular. The cho-
lesterine being found also in the nerves, and, of course, a large quantity of nervous mat-
ter existing in the extremities, it is desirable at the same time to make an analysis of the
venous blood from the general system.

With a view of determining this question, we made the following experiments :

Experiment I. — In this experiment, specimens of blood were taken from the carotid,
the internal jugular, the vena cava, hepatic veins, hepatic artery, and portal vein, in a liv-
ing animal (a dog about six months old). In addition, we took a specimen of bile from
the gall-bladder, and some of the substance of the brain. These were all carefully ex-
amined for cholesterine, and the following were the main results : In the brain, choles-
terine was found in large quantity. There was no cholesterine in the extract of the
blood from the carotid, examined three days after, and but a few crystals, eleven days
after. Cholestewne was almost immediately discovered in the extract of the blood from
the internal jugular, and the crystals were present in large numbers on the twelfth day.
In this experiment, the animal was etherized when the blood was taken, and the examina-
tions for cholesterine were not quantitative. In the succeeding experiments, the propor-
tion of cholesterine in the different specimens of blood was accurately estimated, and, in
most of them, no anaesthetic was used during the operative procedure.

Experiment II. — A medium-sized adult dog was put under the influence of etlur. ;u <1
the carotid artery, internal jugular, and femoral vein exposed. Specimens of blood wi-iv
drawn, first from the internal jugular, next from the carotid, and last from the femoral
vein. These specimens were received into carefully-weighed vessels, and weighed. They
were then analyzed for cholesterine by the process already described, with the follow-
ing results :

452 EXCKETION.

Quantity of blood. Cholesterine. Cholesterine per

grains. grains. 1,000 pts.

Carotid 179-462 0139 0'774

Internal jugular 134*780 O'lOS 0-801

Femoral vein 133-886 0'108 0'806

Percentage of increase in the blood from the jugular over the arterial blood 3 '488

Percentage of increase in the blood from the femoral vein over the arterial blood 4-134

This experiment shows an increase in the quantity of Cholesterine in the blood in its
passage through the brain, and an increase, even a little greater, in the blood passing
through the vessels of the posterior extremity. To facilitate the operation, however,
the animal was brought completely under the influence of ether, which, from its action
upon the brain, would not improbably produce some temporary disturbance in the nutri-
tion of that organ, and consequently might interfere with the experiment. For the pur-
pose of avoiding this difficulty, we performed the f olloAving experiments without adminis-
tering an anaesthetic :

Experiment III. — A small, young dog was secured to the operating-table, and the inter-
nal jugular and carotid were exposed upon the right side. Blood was taken, first from the
jugular, and afterward from the carotid. The femoral vein upon the same side was then
exposed, and a specimen of blood was taken from that vessel. The animal was very
quiet under the operation, although no anesthetic was used, so that the blood was drawn
without any difficulty and without the slightest admixture.

The three specimens were analyzed for cholesterine, with the following results :

Quantity of blood. Cholesterine. Cholesterine per

grains. grains. 1,000 pts.

Carotid 143'625 0'679 0'967

Internal jugular 29*956 0'046 1'545

Femoral vein 45-035 0'046 1*028

Percentage of increase in the blood from the jugular over the arterial blood 59*772

Percentage of increase in the blood from the femoral vein over the arterial blood 6-308

Experiment IV. — A large and powerful dog was secured to the operating-table, and
the carotid and internal jugular were exposed. Specimens of blood were taken from these
vessels, first from the jugular, and were carefully weighed and analyzed for cholesterine
in the usual way. The following results were obtained :

Quantity of blood. Cholesterine. Cholesterine per

grains. grains. 1,000 pts.

Carotid 140-847 0-108 0'768

Internal jugular 97-811 0'092 0'947

Percentage of increase in the blood passing through the brain 23-307

Experiment III. shows a very considerable increase in the quantity of cholesterine in
the blood passing through the brain, while the increase is comparatively slight in the
blood of the femoral vein. The proportion of cholesterine is also large in the arterial
blood, as compared with other observations.

Experiment IV. shows but a slight difference in the quantity of cholesterine in the
arterial blood in the two animals ; the proportion in the animal that was etherized being
0-774: per 1,000, and in the animal that was not etherized, 0'768 per 1,000, the difference
being but 0*006 ; but, as was suspected, the ether seemed to have an influence upon the
quantity of cholesterine absorbed by the blood in its passage through the brain. In the
first instance the increase was but 3*488 per cent., while in the latter it was 23-307 per
cent.

The natural conclusions to be drawn from these observations, with regard to the ori-
gin of cholesterine in the economy, are the following : It has been ascertained that the
brain and nerves contain a large quantity of this substance, which is found in hardly any

EXCRETORY FUNCTION OF THE LIVER. 453

other of the tissues of the body ; and the.se experiments, especially Experiments III. and
IV., show that the blood that comes from the brain contains a much larger quantity of
cholesterine than the blood supplied to this organ.

The conclusion is, then, that cholesterine is produced in the brain and is taken up by
the blood as it passes through this organ.

But the brain is not the only part where cholesterine is produced. It will be seen by
Experiment II. that there is 4'134 per cent., and in Experiment III., 6'308 per cent, of
increase in cholesterine in the passage of the blood through the inferior extremities,
and probably about the same in other parts of the muscular system. In examining these
tissues chemically, we find that the muscles contain no cholesterine, but that it is abun-
dant in the nerves ; and, as we have found that the proportion of cholesterine is immense-
ly increased in the passage of the blood through the great centre of the nervous system,
taken, as the specimens were, from the internal jugular, which collects the blood mainly
from the brain and very little from the muscular system, it is very probable that, in the
general venous system, the cholesterine which the blood contains is produced in the
substance of the nerves.

If the above conclusion be correct, and if cholesterine be one of the products of the
disassimilation of nervous tissue, its formation would be proportionate in activity to the
nutrition of the nerves; and any thing which interfered to any great extent with their
nutrition would diminish the quantity of cholesterine produced. In the production of
urea by the general system, which is analogous to the formation of cholesterine, mus-
cular activity increases the quantity, and inaction diminishes it, on account of their
influence upon nutrition. In cases of paralysis, we nave a diminution of the nutritive
forces in the parts affected, especially of the nervous system, which, after a time, becomes
so disorganized that, although the cause of the paralysis be removed, the nerves cannot
resume their functions. It is true that we have this disorganization taking place to a
certain extent in the muscles, but this is by no means so marked as it is in the nerves.
We should be able, then, to confirm the observations on animals by examining the
blood in cases of paralysis, when we should expect to find a very marked difference in
the quantity of cholesterine, between the venous blood coming from the paralyzed parts
and the blood from other parts of the body. With this point in view, we made analyses
of the blood from both arms, in three cases of hemiplegia :

Case I. — Sarah Rumsby, ret. 47, was affected with hemiplegia of the left side. Two
years ago she was attacked with apoplexy and was insensible for three days. When she
recovered consciousness, she found herself paralyzed on the left side. She said she had
epilepsy four or five years before the attack of apoplexy. Now she has entire paralysis
of motion of the affected side, with the exception of some slight power over the fingers,
but sensation is perfect. The speech is not affected. The general health is good.

Case II. — Anna Wilson, set. 23, Irish, was affected with hemiplegia of the right side.
Four months ago she was attacked with apoplexy, from which she recovered in one day,
with loss of motion and sensation of the right side. She is now improving and can use
the right arm slightly. The leg is not so much improved, because she will make no effort
to use it.

Case III. — Honora Sullivan, a3t. 40, Irish, was affected with hemiplegia of the right
side. About six months ago she was attacked with apoplexy and recovered consciousness
the next day, with paralysis. The leg was less affected than the arm, from the first.
The cause was supposed by Dr. Austin Flint, the attending physician, to be due to an
embolus. Her condition is now about the same as regards the arm, but the leg has
somewhat improved.

These cases all occurred at the Blackw ell's Island Hospital. The treatment in all
consisted of good diet, frictions, passive motion, and use of the paralyzed members as
much as possible.

A small quantity of blood was drawn from both arms in these three cases. It was

454

EXCRETION.

drawn from the paralyzed side, in each instance, with great difficulty, and but a small
quantity could be obtained.

The specimens were all examined for cholesterine, with the following results :

Table of Quantities of Cholesterine in Blood of Paralyzed and Sound Sides,
in Three Cases of Hemiplegia.

Blood.

Cholesterine.

Cholesterine per 1,000.

Grains.

Grains.

Case I. Paralyzed side.

55-458

• • • •

The watch - glass contained
0'031 of a grain of a granu-
lar substance, but the most
careful examination failed to

reveal a single crystal of cho-
lesterine.

Do. Sound side. . .

128-407

0-062

0-481.

Case II. Paralyzed side.
Do. Sound side...

18-381
66-396

0-062

Same as Case I.
0-808.

Case III. Paralyzed side.
Do. Sound side. . .

21-842
52-261

boil

Same as Case I.
0-5^9.

The result of these examinations is very interesting: not a single crystal of choleste-
rine was found in any of the three specimens of blood from the paralyzed side, while
about the normal quantity was found in the blood from the sound side. As the nutrition
of other tissues is interfered with in paralysis, it is impossible to say positively, from
these observations alone, that cholesterine is produced in the nervous system only.
But the nutrition of the nerves is undoubtedly most aifected ; and these observations,
taken in connection with the preceding experiments on animals, point very strongly to
such a conclusion.

Our experiments upon animals were so marked and invariable in their results, even
when performed under different conditions, that they leave hardly any doubt of the
fact that the blood, in passing through the brain, takes up cholesterine. It is more diffi-
cult to show, by actual demonstration, that the general system of nerves also gives up
cholesterine to the blood ; but the fact that the venous blood coming from the extremi-
ties contains more cholesterine than the arterial blood, taken in connection with the
fact that none of the tissues of the extremities contain cholesterine, except the nerves,
renders it more than probable that the nerves, as well as the brain, are the seat of the
formation of this principle.

Elimination of Cholesterine hy the Liner. — We attempted to demonstrate experimen-
tally the separation of cholesterine from the blood by the liver, in the same way that we
determined its passage into the blood circulating through the brain. In the first series
of experiments upon this subject, we endeavored to show, in the same animal, the origin
of cholesterine in certain parts, and the mechanism of its elimination. In these experi-
ments, which were only approximative, as we had not then succeeded in extracting the
cholesterine perfectly pure, we commenced with the arterial blood, examining it as it
went to the brain by the carotid, analyzing the substance of the brain, then analyzing
the blood as it came from the brain by the internal jugular, examining the blood as it
went to the liver by the hepatic artery and portal vein, examining the secretion of the
liver, then the blood as it came from the liver by the hepatic vein, examining, also,
the blood of the abdominal vena cava. The analyses of the blood from the carotid, inter-
nal jugular, and vena cava, have already been referred to in treating of the origin of

ELIMINATION OF CHOLESTERINE BY THE LIVER. 455

cholesterine. It will be remembered that there was a large quantity of this substance
in the internal jugular, and but a small quantity in the carotid, showing that it was
formed in the brain. We now give the conclusion of these observations, which bears
upon the separation of cholesterine from the blood :

Experiment I. — Specimens of blood were taken from the hepatic artery, portal vein,
and hepatic vein, and a small quantity of bile was taken from the gall-bladder. These
specimens were treated in the manner already indicated ; viz., evaporated and pulverized,
extracted with ether, the ether evaporated and the residue extracted with boiling alco-
hol, this evaporated, a solution of caustic potash added, and the specimen then subjected
to microscopical examination.

Microscopical examination of the extract from the portal vein showed quite a number
of crystals of cholesterine. These were observed after the fluid had nearly evaporated.

Microscopical examination of the extract from the hepatic artery, made after the fluid
had nearly evaporated, showed a considerable quantity of cholesterine, more than was
observed in the preceding specimen. There were also observed a few crystals of ster-
corine.

The first examination of the extract from the hepatic vein, which was made just
before the potash was added, showed a number of fatty masses, with some crystals of
stercorine. The solution of potash was then added, and, two days after, another careful
examination was made, revealing nothing but fatty globules and granules. The watch-
glass was then set aside and was examined eleven days after, when the fluid had entirely
evaporated. At this examination, a few crystals of cholesterine were observed for the
first time. There were also a number of crystals of margaric and stearic acid.

All the examinations of the extract from the bile showed cholesterine; and the pre-
cipitate consisted, indeed, of this substance in a nearly pure state.

Taking these experiments in connection with the first observations upon the carotid and
internal jugular, while the one series demonstrates pretty conclusively that cholesterine
is formed in the brain, the other shows that it disappears, in a measure, from the blood
in its passage through the liver, and is passed into the bile. In other words, it is formed
in the nervous tissue and is prevented from accumulating in the blood by its excretion
by the liver. This suggests an interesting series of inquiries ; and this fact, fully sub-
stantiated, would be as important to the pathologist as to the physiologist. But, in order
to settle this question, it is necessary to do something more than make an approximative
estimate of the quantity of cholesterine removed from the blood by the liver. The quan-
tity thus removed in the passage of the blood through this organ should be estimated, if
possible, as closely as the quantity which the blood gains in its passage through the brain.
This estimate, however, is more difficult. The operation for obtaining the specimens of
blood, in the first place, is much more serious than that for collecting blood from the carot-
id and internal jugular. It is very difficult to take the unmixed blood from the hepatic
vein ; and the exposure of the liver, if prolonged, may interfere with its eliminative func-
tion, in the same way that exposure of the kidneys arrests, in a few moments, the flow
from the ureters. It is probable, however, that the administration of ether does not
interfere with the elimination of cholesterine by the liver, as it does, apparently, with its
formation in the brain. Anesthetics, as we know, have a peculiar and special action upon
the brain, but they do not appear to interfere with the functions of vegetative life, such
as secretion or excretion ; and, we may suppose, they would not interfere with the depu-
rative function of the liver. It is fortunate that this is the case, for the operation of
taking blood from the abdominal vessels is immensely increased in difficulty by the strug-
gles of an animal that is not under the influence of an anaesthetic.

With the view of settling the question of the disappearance of a portion of the choles-
terine of the blood in its passage through the liver, by an accurate quantitative analysis,
we repeated the operation for drawing blood from the vessels which go into and emerge
from the liver. In the first trial, the blood was drawn so unsatisfactorily, and the oper-

456 EXCKETIOtf.

ation was so prolonged, that it was not thought worth while to complete the analysis,
and the experiment was abandoned. In the following experiment we were more suc-
cessful.

Experiment II. — A good-sized bitch (pregnant) was brought completely under the
influence of ether, the abdomen was laid freely open, and blood was drawn, first from the
hepatic vein, and next from the portal vein. The taking of the blood was entirely satis-
factory, the operation being done rapidly, and the blood collected without any admixture.
A specimen of blood was then taken from the carotid, to represent the blood from the
hepatic artery, assuming that the arterial blood is of uniform composition.

The three specimens of blood were then examined in the usual way for cholesterine,
with the following results

Quantity of blood. Cholesterine. Cholesterine per

grains. grains. 1,000 pts.

Arterial blood 159-537 0'200 1'257

Portal vein 168-257 0'170 T009

Hepatic vein. . 79'848 0'077 0'964

Percentage of loss in arterial blood in its passage through the liver 23-309

Percentage of loss in the blood of the portal vein 4*460

This experiment proves positively, what there was good ground for supposing from
Experiment L, that cholesterine is separated from the blood by the liver ; and here we
may note, in passing, a striking coincidence between the analysis in a previous experiment,
in which the blood was studied in its passage through the brain, and the one just men-
tioned, where the blood was examined after its passage through the liver. The gain of
the arterial blood in cholesterine in passing through the brain was 23-307 per cent., and
the loss of this substance in passing through the liver is 23-309 per cent. There must
be, of course, the same quantity separated by the liver as is produced by the nervous
system, it being formed, indeed, only to be separated by this organ, its formation being
continuous, and its removal necessarily the same, in order to prevent its accumulation in
the circulating fluid. The almost exact coincidence between these two quantities, in
specimens taken from different animals, though not at all necessary to prove the fact just
mentioned, is still very striking.

It is shown by Experiment II. that the portal blood, as it goes into the liver, contains
but a small percentage of cholesterine over the blood of the hepatic vein, while the per-
centage in the arterial blood is large. The arterial blood is the mixed blood of the entire
system ; and, as it probably passes through no organ which diminishes its cholesterine
before it gets to the liver, it contains a quantity of this substance which must be removed.
The portal blood, coming from a limited part of the system, contains less cholesterine,
although it gives up a certain quantity. In the circulation in the liver, the portal system
largely predominates and is necessary to other important functions of this organ, such as
the production of sugar ; but, soon after the portal vein enters the liver, its blood becomes
mixed with that from the hepatic artery, and from this mixture the cholesterine is sep-
arated. It is only necessary that blood, containing a certain quantity of cholesterine,
should come in contact with the bile- secreting cells, in order that this substance shall be
separated. The fact that it is eliminated by the liver is proven with much less difficulty
than that it is formed in the nervous system. In fact, its presence in the bile, and the
necessity of its constant removal from the blood, consequent on its constant formation
and absorption by this fluid, are almost sufficient in themselves to warrant the conclusion
that it is eliminated by the liver. This, however, is put beyond a doubt by the preceding
analyses of the blood going to and coining from this organ.

In treating of the composition of the faeces, we have considered so fully the changes
which the cholesterine of the bile undergoes, in its passage down the intestinal canal, that
it is not necessary to refer to this portion of the subject again. "We have made but one
examination of the quantity of stercorine contained in the daily fyecal evacuation, and,

ELIMINATION OF CIIOLESTERINE BY THE LIVER. 457

assuming that the amount of cholesterine excreted by the liver in twenty-four hours is
equal to the amount of stercorine found in the evacuations, the quantity is about ten and
a half grains. This corresponds with the estimates of the daily quantity of cholesterino
excreted, calculated from its proportion in the bile and the estimated daily amount of
bile produced by the liver.

To complete the chain of the evidence leading to the conclusion that cholesterine is
an excrementitious principle which is formed in certain of the tissues and eliminated by
the liver, it is only necessary to show that it is liable to accumulate in the blood when
the eliminating function of the liver is interrupted. It will be remembered that it was
only after extirpation of the kidneys, followed by accumulation of urea in the blood, that
Prevost and Dumas were able to demonstrate the preexistence of this principle in the cir-
culating fluid and to indicate the mechanism of its separation from the blood by the kid-
neys. This mode of study has been applied to certain of the elements of the bile, though
without success ; for Miiller, Kunde, Lehmann, and Moleschott, who extirpated the livers
from frogs, looked in the blood only for the biliary salts. We have not been able to
repeat these experiments upon frogs and analyze the blood for cholesterine, but we have
arrived at very positive results in the study of the blood in diseased conditions of the
liver, that are interesting alike to the physiologist and the pathologist.

It has long been recognized that cases of ordinary icterus are not of a grave character,
while there are instances in which the jaundice, though less marked as regards coloration
of the skin, is a very different condition. Chemists have analyzed the blood, in the hope
of explaining this difference by the presence, in the grave cases, of the taurocholate and
glycocholate of soda ; but their failure to detect these principles leaves the question still
uncertain. The real distinction, arguing from purely theoretical considerations, would lie
in the proposition that, in cases of simple jaundice, there is merely a resorption from the
biliary passages of the coloring matter of the bile, and, in grave cases — which are almost
invariably fatal — there is retention of cholesterine in the blood.

We have not been able, on account of the insolubility of cholesterine, to observe the
effects of injecting it into the blood-vessels, but we have had an opportunity of making
an examination of the blood of a patient in the last stages of cirrhosis of the liver, accom-
panied with jaundice, and we compared it with an examination of the blood of a patient
suffering from simple icterus. Both of these patients had decoloration of the faeces ; but
in the first the icterus was a grave symptom, accompanying the last stages of disorgani-
zation of the liver, while in the latter it was simply dependent on duodenitis, and the
prognosis was favorable and verified by the result. As icterus accompanying cirrhosis is
of very infrequent occurrence, we were fortunate in having an opportunity of comparing
the two cases.

Without giving in full the details of these cases and the examinations, which are con-
tained in our original memoir on cholesterine, it is sufficient here to state the main results
of the examinations of the blood and faeces.

In the case of simple jaundice from duodenitis, in which there was no great disturb-
ance of the system, a specimen of blood, taken from the arm, presented undoubted evi-
dences of the coloring matter of the bile, but the proportion of cholesterine was not
increased, being only 0'508 of a part per thousand. The faeces contained a large propor-
tion of saponifiable fat, but no cholesterine or stercorine.

In the case of cirrhosis with jaundice, there were ascites and great general prostra-
tion. This patient died a few days after the blood and fasces had been examined, and
the liver was found in a condition of cirrhosis, with the liver-cells shrunken, and the
gall-bladder contracted. In this case the blood contained T850 pt. of cholesterine per
thousand, more than double the largest quantity we had ever found in health. The faeces
contained a small quantity of stercorine.

Inasmuch as cases frequently present themselves in which there are evidences of cir-
rhosis of the liver, with little if any constitutional disturbance, while others are attended

458 SECRETION.

with grave nervous symptoms, it seemed an interesting question to determine whether it
be possible for cholesterine to accumulate in the blood without the ordinary evidence of
jaundice. We had an opportunity of examining the blood in two strongly-contrasted
cases of cirrhosis, in neither of which was there jaundice.

One of these patients had been tapped repeatedly (about thirty times), but the ascites
was the only troublesome symptom, and his general health was pretty good. In this case
the proportion of cholesterine in the blood was only 0-246 of a part per thousand, con-
siderably below the quantity that we had found in health.

The other patient had cirrhosis, but he was confined to the bed and was very feeble.
The proportion of cholesterine in the blood in this case was 0*922 of a part per thousand,
a little above the largest proportion we had found in health.

Like the examinations of the blood in the three cases of paralysis, these pathological
observations are not sufficient, in themselves, to establish the function of cholesterine ;
but, taken in connection with our other experiments, they fully confirm our views with
regard to the excretory function of the liver. It is pretty certain that organic disease of
the liver, accompanied with grave symptoms generally affecting the nervous system, does
not differ in its pathology from cases of simple jaundice in the fact of retention of the
biliary salts in the blood; but these grave symptoms, it is more than probable, are due
to a deficiency in the elimination of cholesterine — the true excrementitious principle of
the bile — and its consequent accumulation in the system. Like the accumulation of urea
in structural disease of the kidney, this produces blood-poisoning; and we have charac-
terized this condition by the name Cholesteraemia, a term expressing a pathological con-
dition, but at the same time indicating the physiological relations of cholesterine.

Since the firsfc publication of the preceding observations, numerous experiments have
been made upon the relations of cholesterine to nutrition and disassimilation ; but most of
those observations in which attempts were made to produce toxic effects by injecting cho-
lesterine into the blood have been unsuccessful. In 1873, Koloman Miiller ( Ueber Choles-
teramie. — Archivfiir experimentelle Pathologic und Pharmakologie, Leipzig, 1873, Bd. i.,
S. 213, et seq.} succeeded in injecting cholesterine without producing any bad effects by
mechanical obstruction of the blood-vessels. He made a preparation by rubbing choles-
terine with glycerine and mixing the mass with soap and water. He injected into the
veins of dogs, 2*16 fluidounces of this solution, containing about 69 grains of choles-
terine. In five experiments of this kind, he produced a complete representation of the
phenomena of "grave jaundice.1' Muller's experiments are in exact accordance with
our views concerning the physiological and pathological relations of cholesterine. Picot
(Journal de Vanatomie, Paris, 1872, tome viii., p. 246, el seq.} has reported a fatal case
of "grave jaundice," in which he determined a great increase in the proportion of choler-
terine in the blood, the quantity being 1-804 per 1,000.

In view of all of these facts, the missing link in our own chain of evidence having
been supplied by the experiments of Miiller, the excrementitious function of the liver,
consisting in the separation of cholesterine from the blood and its discharge in the faeces
in the form of stercorine, must, we think, be regarded as definitely established.

Production of Sugar in the Liver,

It was formerly supposed that the chief and the only important office of the liver was
to produce bile, and all physiological researches into the functions of this organ were
then directed to the question of the uses of the biliary secretion; but, in 1848, it wTas
announced by Bernard that he had discovered in the liver a new and important function,
and he proceeded to show, by an ingeniously-conceived series of experiments, that the
liver is constantly producing sugar of the variety that had long been recognized in the
urine of persons suffering from diabetes mellitus. The great physiological and pathologi-
cal importance of the discovery, attested, as it was, by experiments which seemed to be

PRODUCTION OF SUGAR IN THE LIVER. 459

positively conclusive in their results, excited the most profound scientific interest. Dur-
ing the present century, indeed, there have been few physiological questions that have
attracted so much attention ; and the observations of Bernard were soon repeated,
modified, and extended by experimentalists in different parts of the world. In 1857,
Bernard discovered a sugar-forming material in the liver, analogous in its composition
and properties to starch ; and this seemed to complete the history of glycogenesis.

Shortly after the publication of the glycogenic theory, it was found that other changes
were effected in the blood in its passage through the liver ; and physiologists then under-
stood, for the first time, how glandular organs might produce secretions and yet not dis-
charge them into excretory ducts. This, indeed, pointed the way to the explanation
of the function of the ductless glands. It is perfectly correct to say that the liver
secretes sugar ; but the secretion, in this instance, is carried away by the blood, and, from
this point of view, the liver is to be regarded as a ductless gland. It is evident, there-
fore, that, even after having studied fully the secretion and the physiological relations of
the bile, we have to consider other glandular functions of the liver which are hardly less
important.

Evidences of a Glycogenic Function in the Liver. — The proof of the glycogenic func-
tion of the liver rests upon the fact, experimentally demonstrated by Bernard, that, in
all animals, the blood coming from the liver by the hepatic veins contains sugar, and
that the presence of this principle here is not dependent upon the starch or sugar of
the food. Bernard assumes to have proven that, in carnivorous animals, never having
taken starch or sugar into the alimentary canal except in the milk, there is no sugar in
the blood of the portal vein as it passes into the liver ; but, under normal conditions, the
blood of the hepatic veins always contains sugar. Having examined the blood from vari-
ous parts of the body and made extracts of all the other tissues and organs, Bernard was
unable to find sugar in any other situations than in the liver and the blood coming from
the liver. As the blood from the liver is mixed in the vena cava with the blood from the
lower extremities, and in the right side of the heart, with the blood from the descending
cava, the amount of sugar is proportionately diminished in passing from the liver to the
heart. It was found that the sugar generally disappeared in the lungs and did not exist
in the blood of the arterial system. Assuming that these statements have been sustained
by experimental facts, there can be no doubt that the liver produces or secretes sugar,
that this secretion is taken up by the blood, and that the sugar is destroyed in its pas-
sage through the lungs.

The question of the production of sugar in the economy has given rise to a great deal
of discussion, and the experiments of Bernard have been repeated very extensively.
Many physiologists of high authority have been able to verify these observations in every
particular; but others have published accounts of experiments which seem to disprove
the whole theory.

There can be no doubt of the fact that sugar may, under certain conditions, be pro-
duced de now in the organism. Cases of diabetes, in which the discharge of sugar by the
urine continues, to a certain extent, when no starch or sugar is taken as food, are conclu-
sive evidence of this proposition. It is a fact equally well established, that the sugar
taken as food and resulting from the digestion of starch is consumed in the organism
and is never discharged. The fact with regard to diabetes shows, then, that it is not
impossible, when no sugar or starch is taken as food, that sugar should be produced in
the body ; and the failure to find the sugar of the food in the blood or excreta shows
that this principle is normally destroyed or consumed in the organism. It only remains,
therefore, to determine whether the production of sugar in diabetes bo a new pathologi-
cal process or merely the exaggeration of a physiological function.

We have so often repeated and verified the observations of Bernard, both in experi-
ments made for purposes of investigation and in public demonstrations, that we can.

460 SECRETION.

entertain no doubt with regard to the glycogenic function of the liver. "We have, how-
ever, made some late observations which have modified our views concerning the
mechanism of glycogenesis ; but the fact of the production of sugar in the healthy organ-
ism is not affected. Notwithstanding that it seems so easy to verify these experiments,
there is, particularly in Great Britain, a pretty wide-spread conviction, that the liver
does not produce sugar during life, and that the sugar found by Bernard and others is
due to post-mortem action. This view is based chiefly upon the observations of Dr. Pavy,
of Guy's Hospital ; but it has been adopted by some authorities in Germany and in
France. In this state of the question, it will not be sufficient to detail merely the experi-
ments that seem to demonstrate the glycogenic function, but it will be necessary to exam-
ine these observations critically and compare them with experiments which lead, appar-
ently, to opposite conclusions ; for it is but fair to admit that the observations of Pavy
seem to be as accurate, and, at the first blush, as conclusive as those of Bernard.

In the account of the discovery, given by Bernard, it appears that he first sought for
the situation in the body where the sugar derived from alimentary substances is destroyed.
With this end in view, he fed a dog for seven days with articles containing a large pro-
portion of sugar and starch. On analyzing the blood from the portal system, he found
a large proportion of sugar ; and he also found it in the blood of the hepatic veins. As a
counter-experiment, he fed a dog for seven days exclusively on meat and then looked for
sugar in the blood of the hepatic veins ; and, to his surprise, he found it in abundance.
This experiment he repeated frequently with the greatest care and always with the same
result ; and he concluded that sugar was formed in the liver and was contained in the
blood coming from this organ independently of the diet of the animal. He afterward
made extracts of the substance of the liver and of the other tissues, and he found that this
organ always contained sugar, while it was not to be detected in any other organ or tis-
sue in the economy. In subsequent experiments, it was demonstrated that the livers of
nearly all classes of animals contained sugar, and that it existed also in the human sub-
ject. He made observations, also, upon the mechanism of its production, its disappear-
ance in the blood circulating through the lungs, and the various influences which modify
the glycogenic function. These points will be considered in their appropriate place ;
and we shall now proceed, after examining the processes for the determination of sugar,
to take up, seriatim, the following questions :

1. The absence of sugar from the blood of the portal system in animals that have
taken neither starch nor sugar into the alimentary canal.

2. The presence of sugar in the blood as it comes directly from the liver by the
hepatic veins, independently of saccharine or amylaceous food.

3. The mechanism of the production of sugar by the liver.

Processes for the Determination of Sugar. — In Bernard's first observations upon the
liver, he applied the fermentation-test to a simple decoction of the hepatic substance and
obtained unmistakable evidences of sugar. In operating upon perfectly fresh and normal
blood, the addition of water and subsequent filtration frequently sufficed to procure a clear
solution, to which the ordinary copper-tests could be applied ; but the most satisfactory
method of making a clear extract was to boil the blood with water and an excess of sul-
phate of soda. By this means a clear extract can be obtained, containing, it is true, a
large quantity of sulphate of soda, but this salt, fortunately, does not interfere with
the tests. Later, Bernard decolorized his solutions and extracts by making the liquid
into a paste with animal charcoal and filtering. We have long been in the habit of
employing both of these methods; but, when we have simply desired to determine the
presence or absence of sugar, the process with the sulphate of soda has proved the more
convenient. In delicate examinations, however, we have generally used animal char-
coal. We have used both methods in decolorizing the decoction of the liver-substance,
as well as in operating upon the blood.

PRODUCTION OF SUGAR IN THE LIVEK. 461

In ordinary examinations, Trommer's test is sufficiently delicate ; but it is not so sen-
sitive or so convenient as some of the standard test-solutions. We have been in the
habit of using, for the determination of sugar in the urine, a modification of Fehling's
test, which is also very convenient for examinations of the blood and liver-extract. This
may be used as well for quantitative examinations ; but, like all of the standard solutions, it
presents the inconvenience of undergoing alteration by keeping, so that it is desirable to
use it freshly made for each series of examinations. We have succeeded in obviating
this difficulty, however, by the following modification in its preparation ; and, made in
this way, it is probably the most convenient test that can be used in the examination of
any of the animal fluids for sugar.

Fehling's Test for Sugar. — The modification in this test consists simply in preparing
three separate solutions, which are to be mixed just before using, as follows :

Solution of crystallized sulphate of copper, 94'73 grains in an ounce of distilled water.

Solution of neutral tartrate of potash, 378*91 grains in an ounce of distilled water.

Solution of caustic soda, specific gravity 1-12, or about 16|°, Baume"'s hydrometer.

These solutions are to be kept in separate bottles and used as follows :

Take half of a fluidrachm of the copper-solution, add half a fluidrachm of the tar-
trate of potash, and add the caustic soda, to make three fluidrachms. It is important to
measure the copper-solution with accuracy, in quantitative analyses, as the quantity of
copper decomposed indicates the amount of sugar.

To apply Fehling's test in ordinary qualitative analyses, heat a small portion of the
test-liquid to the boiling-point in a test-tube, and add the suspected fiuid, drop by drop.
If sugar be present in even a moderate quantity, a dense, yellowish precipitate of the sub-
oxide of copper will be produced after adding a few drops ; and, if the liquid be added to
about the same volume as the test, and the mixture be again raised to the boiling-point
without producing any deposit, it is certain that no sugar is present. The estimation of
the quantity of sugar in any liquid depends upon the fact that two hundred grains of the
test-liquid is decolorized by exactly one grain of glucose. To apply this test, measure oft',
in a glass specially graduated for the purpose, two hundred grains of the solution ; put
this into a flask, with about twice its volume of distilled water, and boil ; when boiling,
add the suspected solution, little by little, from a burette graduated in grains (raising the
mixture to the boiling-point each time and afterward allowing the precipitate to subside),
until the blue color is completely discharged ; by then reading off the number of grains
of the saccharine solution that has been added, the proportion of sugar may be readily
calculated. If the solution be suspected to contain a considerable quantity of sugar, the
estimate may be more accurately made by diluting it to a known degree, say with nine
parts of water, and adding this diluted mixture to the test-liquid.

Examination of the Blood of the Portal System for Sugar. — If starch or sugar be
taken into the alimentary canal, it is well known that sugar is always to be found, during
absorption, in the blood of the portal system ; but, in carnivorous animals, that have been
fed entirely upon meat, no sugar can be discovered in the portal blood. The statements of
Bernard are very definite upon this point, and he indicates a liability to error when the
operation of tying the portal vein has not been skilfully performed, and when blood, con-
taining sugar, is allowed to regurgitate from the substance of the liver. In taking the
blood just before it enters the liver, it is necessary to apply a ligature to the vessels as
they penetrate at the transverse fissure. This should be done quickly, and the opening
into the abdominal cavity should be small. Otherwise, as the vessels have no valves, we
are liable to have reflux of blood from the liver. We have frequently performed the
experiment, after the method described by Bernard, making a small opening in the linea
alba a little below the ensiform cartilage, just large enough to admit the forefinger of the
left hand ; introducing the finger, and feeling along the concave surface of the liver until
we are able to seize the vessels ; then passing in an aneurism-needle, and constricting
the vessels before the abdomen is widely opened, when a firm ligature is applied. When

462 SECRETION.

this step of the operation has been satisfactorily performed, we have never found a trace
of sugar in the extract from the blood of the portal system, in animals that have been
fed upon nitrogenized matter alone.

There can be no doubt that the blood carried to the liver by the portal vein does not
contain sugar, in animals fed solely upon nitrogenized matters. The quantity of blood
carried to the liver by the hepatic artery is insignificant ; and, although the arterial
blood may temporarily contain a trace of sugar, as we shall see farther on, this need not
complicate the question under consideration, as the presence of sugar in the blood of the
hepatic artery is exceptional, and its proportion, when it exists, is very minute.

Examination of the Blood of the Hepatic Veins for Sugar. — It is upon this question
that the whole doctrine of the sugar-producing function of the liver must rest. If it can
be proven that the blood, taken from the hepatic veins during life or immediately after
death, normally contains sugar, while the blood distributed to the liver contains neither
sugar nor any substance that can be immediately converted into sugar, the inevitable
conclusion is that the liver is a sugar-producing organ. We shall, consequently, examine
this part of the question with the care which its importance demands.

The proposition that the blood from the hepatic veins does not contain sugar during
life and health cannot be sustained by actual experiment. Observers may say that the
quantity is very slight, but its existence in this situation, independently of the kind of
food taken, cannot be denied. Dr. Pavy, who is the originator of the theory that the
sugar found in the liver and in the blood coming from the liver is due to a post-mortem
change, nowhere states that he has taken the blood from the hepatic veins and failed to
find sugar. He says that he has found the blood taken from the right side of the heart
by catheterization, in a living animal, " scarcely at all impregnated with saccharine mat-
ter," but he does not deny its presence in small quantity. In twelve examinations made
by Dr. M'Donnell, of Dublin, traces of sugar were found in five specimens of blood taken
from the right auricle by catheterization, in the living animal, and no sugar was detected
in seven. It must be remembered, in considering these experiments, that the blood of
the right side of the heart is the mixed blood from the entire body ; and, assuming that
the hepatic blood is constantly saccharine, the quantity in the blood of the right heart
would not be very great. In opposition to these experiments, which are only partially
negative, we have the following results of examinations of the blood of the hepatic veins
and of the right side of the heart, taken as nearly as possible under normal conditions.

To demonstrate the absence of sugar in the portal vein and its constant presence in
the hepatic veins in dogs fed exclusively upon meat, Bernard employed the following pro-
cess : The animal was killed instantly by section of the medulla oblongata. A small
opening was then made into the abdomen, just large enough to admit the finger and to
enable him to seize the portal vein as it enters at the transverse fissure and to apply a liga-
ture. The abdomen was then freely opened and a ligature was applied to the vena cava
just above the renal veins, to shut off the blood from the posterior extremities. The chest
was then opened, and a ligature was applied to the vena cava just above the opening of the
hepatic veins. Operating in this way, blood may be taken from the portal system before
it enters the liver, and from the hepatic veins as it passes out. In the blood from the
portal system no sugar is to be found, but its presence is unmistakable in the blood from
the hepatic veins. To avoid disturbing the circulation in the liver, and in order to col-
lect from the hepatic veins as large a quantity of blood as possible, Bernard modified the
experiment, in some instances, by introducing into the vena cava in the abdomen a
double sound, the extremity of which is provided with a bulb of India-rubber. This
was pushed into the vein above the diaphragm ; and, by inflating the bulb, the vein was
obstructed above the liver, and the blood could be collected through one of the canulao,
as it came directly from the hepatic vessels. Bernard never failed to determine the
presence of sugar in these specimens of blood, employing a number of different pro-
cesses, including the fermentation-test and even collecting the alcohol. To complete

PRODUCTION OF SUGAR IX THE LIVER.

463

the proof of the existence of sugar in the blood coming from the liver, Bernard demon-
strated its presence in blood taken from the right auricle in a living animal, which can
be readily done by introducing a catheter into the right side of the heart through
an opening in the external jugular __,. .-.^

vein. He also showed that, during
digestion, the whole mass of blood
contained sugar, but that the quantity
was greater in the right side of the
heart than in the arterial system.

It is unnecessary to cite all the
authorities that have confirmed the
observations of Bernard. Shortly
after these experiments were pub-
lished, Lehmann, Frerichs, and many
others verified their accuracy. Ber-
nard gives in full the experiments of
Poggiale and of Leconte, the results
of which were identical with his
own. He gives, also, in one of his
later works, the proportions of sugar
in the blood of the hepatic veins, ob-
tained by Lehmann, Schmidt, Pog-
giale, and Leconte, no sugar being
found in the blood of the portal sys-
tem. We have ourselves made a
number of experiments with a view
of harmonizing, if possible, the dis-
cordant observations of Bernard and
Pavy, and have examined the blood
from the hepatic veins for sugar, tak-
ing the specimens under what seemed
to be strictly physiological condi-
tions. In one of these published ex-
periments, blood was taken from the
hepatic veins of a large dog, fully-
grown and fed regularly every day
but not in digestion at the time of
the experiment, and the operation
lasted only seventy seconds. No
anesthetic was employed. The ex-
tract of this specimen of blood, treat-
ed with Fehling's test-liquid, pre-
sented a well-marked deposit of the
oxide of copper, revealing unequivo-
cally the presence of a small quan-
tity of sugar.1 This has been the in-
variable result in numerous experi-
ments and class-demonstrations made since 1858 ; and, since
the experiments just referred to were published, we have veri-
fied the observation with regard to the hepatic blood, keeping
the animal perfectly quiet before the operation, avoiding the
administration of an anaesthetic, and taking the blood so rap-

1 FLINT, Jr., K-rperi-iitentK undertaken for the Purpose of reconciling Rome of the, Itiscorflant

upon the Gl>(c»iji-iin> t-'uin-lion «f /: <• ///-,/•. .Y< /•• York Medical Journal, IH','.I, vol. viii.. p. 3S1. These expcri-

FIG. 137.— Catheter for the
right side of the heart.
(Bernard.)

E, extremity of the tube;
R, stop-cock, e, extrem-
ity to be introduced into
the right auricle.

The tube is introduced
through a small opening
into the external jugular
vein, the concavity of the
tube turned toward the
sternum, and the stop-
cock closed. When the
tube reaches the heart,
we feel the pulsations,
and the jet of blood,
when the stop-cock is
opened, is intermittent.

FIG. 138.— Double son HI?. 11*0 /
for collect in <j l,loo<l front th*
hepatic reins. (Bernard.)

0, £, 0', tube, with a stop-rock (;•).
u-=ed to intl:it<' the rubber
bulb (<";. //): 0. T. tube, with
an opening (" '. which re-
ceives the bloo.l from tile
hepatic veins, and is provided
with a stop-cock <K,.

464 SECRETION".

idly that no sugar could be formed by the liver post mortem. These experiments leave
no doubt of the fact that, during life and in health, the blood, as it passes through the
liver and is discharged by the hepatic veins into the vena cava, contains sugar, which is
formed by the liver, independently of the sugar and starch taken as food.

Does the Liner contain Sugar normally during Life f — This is the only question upon
which the results of reliable experiments have been entirely opposite. Bernard made
the greater part of his observations by analyzing the substance of the liver; and he
arrived at most of his conclusions with regard to the variations in the glycogenic function,
from estimates of the proportion of sugar in the liver under different conditions. For
many years we have been in the habit of repeating these experiments, with like results,
and we have never failed to find sugar under normal conditions of the system. We were
formerly in the habit of making the demonstrations of the formation of sugar in the liver
upon animals that had been etherized ; and then we always obtained a brilliant precipitate
from the clear extract of the substance of the liver boiled with the test-liquid. The
experiment was performed in this way before we had acquired sufficient dexterity to seize
the portal vein readily and to go through with the necessary manipulations with rapidity.
We subsequently made the operation by first suddenly breaking up the medulla oblon-
gata, then making a small incision into the abdominal cavity, seizing the portal vein
instantly, and following out the remaining steps of the experiment without delay. In this
way, although sugar was always found in the blood of the hepatic veins, we frequently
failed to obtain a distinct reaction in the extract of the liver ; and it appeared, indeed, that
the more accurately and rapidly the operation was performed, the more difficult was it
to detect sugar in the hepatic substance. It seems probable, in reflecting upon these
facts, that, inasmuch as no one has assumed that the actual quantity of sugar produced
by the liver is very considerable, and as a large quantity of blood (in which the sugar
is very soluble) is constantly passing through the liver, precisely as we pass water through
its vessels to remove the sugar, the sugar might be washed out by the blood as fast
as it is formed; and that really the liver might never contain sugar in its substance, as
a physiological condition, although it is constantly engaged in its production. We know
that the characteristic elements of the various secretions proper are produced in the
substance of the glands and are washed out at the proper time by liquid derived from
the blood, which circulates in their substance during their functional activity in very
much greater quantity than during the intervals of secretion. Now, the liver-sugar may
certainly be regarded as an element of secretion; and, possibly, it may be completely
washed out of the liver, as fast as it is formed, by the current of blood, the hepatic
vein, in this regard, serving as an excretory duct. To put this hypothesis to the test
of experiment, it was necessary to obtain and analyze a specimen of the liver in a condi-
tion as near as possible to that under which it exists in the living organism ; and, in
carrying out this idea, we instituted the following experiments :

Experiment I. — A medium-sized dog, full-grown, in good condition, and not in digestion,
was held upon the operating-table by two assistants, and the abdomen was widely opened
by a single sweep of the knife. A portion of the liver, weighing about two ounces, was
then excised and immediately cut into small pieces, which were allowed to fall into boil-
ing water. The time from the first incision until the liver was in the boiling water was
twenty-eight seconds. An excess of crystallized sulphate of soda was then added, and
the mixture was boiled for about five minutes. It was then thrown upon a filter, and the
clear fluid that passed through was tested for sugar by Trommer's test. The reaction
was doubtful and afforded no marked evidence of sugar.

Experiment II. — A medium-sized dog, in the same condition as the animal in the first
experiment, was held upon the table, and a portion of the liver was excised, as above

ments are the first on record, made with the view above indicated. The experiments by Dr. Lusk and by Dr. Dai-
ton were made later, with the view of confirming our original observations.

PRODUCTION OF SUGAR IN THE LIVER. 465

described. The whole operation occupied twenty -two seconds. Only ten seconds elapsed
from the time the portion of the liver was cut off until it was in the boiling water. It
was boiled for about fifteen minutes, made into a paste with animal charcoal, and thrown
upon a filter. The clear fluid that passed through was tested for sugar by Trommer's
test. There was no marked evidence of sugar.

Experiment III. — A large dog, full-grown and fed regularly every day, but not in diges-
tion at the time of the experiment, was held firmly upon the table. This dog had been
in the laboratory about a week and was in a perfectly normal condition. The abdominal
cavity was opened, and a piece of the liver was cut off and thrown into boiling water,
the time occupied in the process being ten seconds. Before the liver was cut up into the
boiling water, the blood was rinsed off in cold water. The liver was boiled for about
seventeen minutes, mixed with animal charcoal, and the whole was thrown upon a filter.

Immediately after cutting off a portion of the liver and throwing it into boiling water,
the medulla oblongata was broken up, a ligature was applied to the ascending vena cava
just above the renal veins, the chest was opened, and a ligature was applied to the vena
cava just above the opening of the hepatic veins. A specimen of blood was then taken
from the hepatic veins. This portion of the operation occupied not more than one minute.
A little water was added to the blood, which was boiled briskly, mixed with animal char-
coal, and thrown upon a filter. The liquid that passed through from both specimens was
perfectly clear.

While the filtration was going on, Fehling's test-liquid was made up, so as to be
perfectly fresh. Th« two liquids were then carefully tested for sugar. The extract of
the liver presented not the slightest trace of sugar. The extract from the blood of the
hepatic veins presented a well-marked deposit of the oxide of copper, revealing unequivo-
cally the presence of a small quantity of sugar.

Experiment IV. — This experiment was made upon a medium-sized dog, in full diges-
tion of meat. The medulla oblongata was broken up ; the portal vein was tied through
a small opening in the abdomen ; and the abdomen was then widely opened, and a por-
tion of the liver excised, rapidly rinsed, and cut up into boiling water. The length of
time that elapsed between breaking up the medulla and cutting up the specimen of liver
into the boiling water was one minute.

The vena cava was then tied above the renal veins, the chest opened, and the cava
again tied above the hepatic veins. Blood was then taken from the hepatic veins, about
an equal bulk of water was added, with an excess of the crystallized sulphate of soda, and
the mixture was boiled. A portion of the portal blood and the decoction of the liver
were then treated in the same way, and the three specimens were filtered.

The clear extracts were then tested with Fehling's liquid, with the following result :

There was no sugar in the portal blood.

There was no sugar in the extract of the liver.

There was a marked reaction in the extract of the blood from the hepatic veins, the
precipitate rendering the whole solution bright yellow and entirely opaque.

This experiment was made in the presence of the class at the Bellevue Hospital Med-
ical College, January 4, 1869.

The importance of the question under consideration and its present unsettled condi-
tion are, we hope, sufficient to justify the introduction of the details of the preceding
experiments. They were undertaken with the view of harmonizing, if possible, the facts
brought forward by different experimentalists.

It is difficult to imagine how any observer, so well known and accurate as Dr. Pavy,
could assert positively, as the result of personal examination, that the liver does not
contain sugar when examined immediately after its removal from the living body, when
Bernard and so many others have demonstrated its presence in this organ in large quantity.
Yet, such was the result of all the experiments of Pavy, arid the same conclusion was ar-
rived at by M'Donnell, and afterward by Meissner and Jaeger, and by Schiff. The ingenious
30

466 SECRETION.

experiment of Bernard, showing that sugar is formed in a liver removed from the body
and washed sugar-free by a stream of water passed through its vessels, demonstrated the
possibility of the production of sugar post mortem, so strongly claimed by Pavy as the
.only condition under which it is ever formed ; still, it does not seem possible to deny the
sugar-producing function of the liver, in view of the conclusive experimental proof of the
constant presence of glucose in the bloocj. of the hepatic veins.

From our own experiments, we have come to the conclusion that Dr. Pavy and those
who adopt his views cannot consistently deny that sugar is constantly formed in the liver
and discharged into the blood of the hepatic veins; nor can Bernard and his followers
ignore the fact that the liver does not contain sugar during life ; although, as has been
shown by Pavy, and more specifically by M'Donnell, sugar appears in the liver in great
abundance soon after death.

In the experiments that we have just detailed, which are simply typical examples of
numerous unrecorded observations, we attempted to verify the observations of Pavy
without losing sight of the facts observed by Bernard, and to verify the experiments of
Bernard in the face of the apparently contradictory statements of Pavy. "When an ani-
mal is in perfect health, has been kept quiet before the experiment, and a piece of the
liver is taken from him by two sweeps of the knife, the blood rinsed from it and the tis-
sue cut up into water already boiling, the whole operation occupying only ten seconds
(as was the case in Experiment III.), the liver is as nearly as possible in the condition in
which it exists in the living organism. As this was done repeatedly in animals during
digestion and in the intervals of digestion, and an extract was thoroughly made without
finding any sugar, we regarded the experiments of Pavy as entirely confirmed and the fact
demonstrated that the liver does not contain sugar during life. On the other hand, when
we made the experiment upon the liver as above described, and, in addition, took specimens
of the portal blood and the blood from the hepatic veins, under strictly physiological
conditions (as was done in Experiment IV.), and found no sugar in the portal blood or
in the substance of the liver, but an abundance in the blood of the hepatic veins, it was
impossible to avoid the conclusion that the sugar was formed in the liver and was washed
out in the blood as it passed through.

In treating of the mechanism of the formation of sugar in the liver, we shall describe
more fully the glycogenic matter ; but, taking into consideration the demonstration of
the presence of sugar in the blood of the hepatic veins by Bernard ; his discovery of the
post-mortem production of sugar in a liver washed sugar-free, probably from a substance
remaining in the liver and capable of being transformed into sugar ; the negative results
of the examinations of the liver for sugar by Pavy ; and, adding to this our own experi-
ments upon all of these points, we are justified in adopting the following conclusions :

1. A substance exists in the healthy liver, which is capable of being converted into
sugar ; and, inasmuch as this is formed into sugar during life, the sugar being washed
away by the blood passing through the liver, it is perfectly proper to call it glycogenic,
or sugar-forming matter.

2. The liver has a glycogenic function, which consists in the constant formation of
sugar out of the glycogenic matter, this being carried away by the blood of the hepatic
veins, which always contains sugar in a certain proportion. This production of sugar
takes place in the carnivora, as well as in those animals that take sugar and starch as
food ; and it is, essentially, independent of the kind of food taken.

3. During life, the liver contains the glycogenic matter only and no sugar, because
the great mass of blood which is constantly passing through this organ washes out the
sugar as fast as it is formed ; but, after death or when the circulation is interfered with,
the transformation of glycogenic matter into sugar goes on ; the sugar is not removed
under these conditions, and can then be detected in the substance of the liver.

Characters of the Liner- Sugar. — Very little is to be said regarding the chemical pe-

PRODUCTION OF SUGAR IN THE LIVER. 467

culiarities of liver-sugar. It resembles glucose, or the sugar resulting from the digestion
of starch, in its composition. This sugar, like glucose, responds promptly to all of the
copper-tests, and it undergoes transformation into melassic acid on being boiled with an
alkali. One of its most marked peculiarities is that it ferments more readily than any
other variety of sugar ; and another is that it is destroyed in the economy with extraor-
dinary facility. This fact has been illustrated by the following ingenious experiment :
Bernard injected under the skin of a rabbit a little more than seven grains of cane-
sugar dissolved in about an ounce of water, and he found sugar in the urine. Under
the same conditions, he found he could inject seven grains of milk-sugar, fourteen and
a half grains of glucose, twenty-one and a half grains of diabetic sugar, and nearly
thirty grains of liver-sugar, without finding any sugar in the urine ; showing that the
liver-sugar is consumed in the organism more rapidly and completely than any other sac-
charine principle.

Mechanism of the Production of Sugar in the Liver. — When Bernard first described
the glycogenic function of the liver, he thought that the sugar was produced from nitro-
genized principles, in some manner which he did not attempt to explain. Subsequent
discoveries, however, have led to conclusions entirely different.

In 1855, Bernard first published an account of his remarkable experiment showing
the post-mortem- production of sugar. After washing out the liver with water passed
through the vessels until it no longer contained a vestige of sugar, it was allowed to
remain at about the temperature of the body for a few hours and was then found to con-
tain sugar in abundance. This experiment we have already referred to, and it is one
that we have frequently verified. Bernard explained the phenomenon by the supposition,
subsequently shown to be correct, that the liver contains a peculiar principle, slightly
soluble in water and capable of transformation into sugar.

Glycogenic Matter. — In its composition, reactions, and particularly in the facility with
which it undergoes transformation into sugar, glycogenic matter bears a very close
resemblance to starch. It is described by Pavy under the name of amyloid matter, a
name which is applied to it, also, by Rouget. It is insoluble in water, and, by virtue
of this property, it may be extracted from the liver after the sugar has been washed
out. The following is the method for its extraction proposed by Bernard :

The liver of a small and young animal, like the rabbit, in full digestion, presents the
most favorable conditions for the extraction of the glycogenic matter. The liver is
taken from the animal immediately after it is killed, is cut into thin slices, and thrown
into boiling water. When the tissue is hardened, it is removed and ground into a pulp
in a mortar. It is then boiled a second time in the water of the first decoction, strained
through a cloth, and the opaline liquid which passes through is made into a thin
paste with animal charcoal. The paste is then put into a displacement-apparatus, the
end of which is loosely filled with shreds of moistened cotton. By successive wash-
ings, the paste is exhausted of its glycogenic matter, leaving behind the albuminoid
and coloring matters. The whitish liquid, as it flows, is received into a vessel of abso-
lute alcohol, when, as each drop falls, the glycogenic matter is precipitated in white
flakes. This is filtered and dried rapidly in a current of air. If the alcohol be not
allowed to become too dilute, the matter when dried is white and easily pulverized.
The substance thus obtained may be held in suspension in water, giving to the liquid a
strongly opaline appearance. It is neutral, without odor or taste, and presents nothing
characteristic under the microscope. It reacts strongly with iodine, which produces
a dark-violet or chestnut-brown color, but rarely a well-marked blue. It presents none
of the reactions of sugar and is entirely insoluble in alcohol. It is changed into sugar
by boiling for a long time with dilute acids, and this conversion is rapidly effected
by the saliva, the pancreatic juice, and a peculiar ferment found in the substance of

468

SECRETION.

ML.

the liver. Prepared in the way above indicated, and pulverized, it may be preserved

for an indefinite period.

The peculiar reaction of the glycogenic matter with
iodine has led to its recognition in the substance of the
liver-cells and in some other situations. Schiff found in
the liver-cells minute granulations, which presented the
peculiar color on the addition of iodine, characteristic of
glycogenic matter. Bernard, a few years after his dis-
covery of this principle in the liver, recognized it in cells
attached to the placenta. He believes that these cells
produce sugar during the early period of foetal life, before
the liver takes on this function, and that they disappear
during the later months, as the liver becomes fully devel-
oped.

Since the discovery of the glycogenic function of the
liver, anatomists have found amyloid corpuscles in various
of the tissues of the body. We do not propose, how-
ever, to discuss this question in all its bearings, but only
to consider the known relations of the amyloid substances
found in the body to the formation of sugar.

In the first place, there can be no doubt of the fact,
that the liver of a carnivorous animal that has been fed
exclusively on meat contains an amyloid substance readily
convertible into sugar. The question of the existence of
the same amyloid matter in other tissues and organs is
only pertinent in so far as it bears upon the production
of sugar or upon the formation of the glycogenic matter
in the liver. In no tissue or organ in the adult has it
been demonstrated that there is any formation of sugar,
except the ordinary transformation of starch into sugar
in the process of digestion.

If the liver taken from an animal recently killed be
simply kept at about the temperature of the body, after
it has been drained of blood or even after it has been
washed through the vessels, sugar will be rapidly formed
in its substance. This must be due to some ferment re-
maining in the tissue ; and Bernard has, indeed, been able
to isolate a principle which exerts this influence in a
marked degree. If an opaline decoction of the liver be
allowed to stand until it has become entirely clear, show-
ing that all the glycogenic matter has been transformed
into sugar, and alcohol be added to the liquid, the hepatic
ferment will be precipitated. This may be redissolved
in water, and it effects the transformation of starch into
sugar with great rapidity. From these facts, it is pretty

FIG. 139.— Apparatmfor the extrac- conclusively shown that the following is the mechanism

tion of glycogenic matter. (Ber-

nard.) of the production of sugar in the liver :

A B displacement apparatus in which The liver first produces a peculiar principle (analo-

the filtration takes place; C, animal

charcoal mixed with the decoction gous to starch in its composition and in many of its prop-
tion ; M/iamp-w^n^attoched' to erties, though it contains two atoms more of water) out
bonhrand fomfoj? auTaf^?uppar of which the sugar is to te formed. The name glycogenic
part of the apparatus; I, precipita- matter may properly be applied to this substance. It is.

ting-glass ; G. glyoogenic matter . , , . ,.

precipitated; V, alcohol. as far as is known, produced m all classes of animals,

VARIATIONS IN THE GLYCOGENIC FUNCTION. 469

carnivora and herbivora ; and, although its quantity may be modified by the kind of food,
its formation is essentially independent of the alimentary principles absorbed.

The glycogenic matter is not taken up by the blood as it passes through the liver, but
is gradually transformed, in the substance of the liver, into sugar, which is washed out
of the organ as fast as it is produced. Thus the blood of the hepatic veins always con-
tains sugar, although sugar is not contained in the substance of the liver during life.

Variations in the Glycoyenic Function.

In following out the relations of the glycogenic process to the various animal func-
tions, Bernard studied very closely its variations at different periods of life, with diges-
tion, the influence of the nervous system, and other modifying conditions. He made
some of his observations by examining the blood in living animals, and others, by esti-
mating the proportion of sugar in the liver. The latter method is to be considered, with
an appreciation of the fact that the liver does not normally contain sugar during life ;
but it represents, to a certain extent, the activity of the glycogenic function. Still, the
facts arrived at in this way must be taken with a certain degree of caution.

Glycogenesis in the Foetus. — In the early months of foetal life, many of the tissues
and fluids of the body were found by Bernard to be strongly saccharine ; but at this
time no sugar is to be found in the liver. Taking the observations upon foetal calves as
a criterion, sugar does not appear in the liver until toward the fourth or filth month of
intra-uterine life. Before this period, however, epithelial cells filled with glycogenic
matter are found in the placenta, and these produce sugar until the liver takes on its
functions. As the result of numerous observations by Bernard upon foetal calves, this
function of the placenta appears very early in foetal life, and, at the third or fourth
month, it has attained its maximum. At about this time, when glycogenic matter begins
to appear in the liver, the glycogenic organs of the placenta become atrophied, and they
disappear some time before birth.

Influence of Digestion and of Different Kinds of Food. — Activity of the digestive
organs has a marked influence upon the production of sugar in the liver. In a fasting
animal, sugar is always found in the blood of the hepatic veins and in the vessels between
the liver and the heart, but it never passes the lungs and does not exist in the arterial
system. During digestion, however, even when the diet is entirely nitrogenized, the
production of sugar is so much increased that a small quantity frequently escapes decom-
position in the lungs and passes into the arterial blood. Under these conditions, the
quantity in the arterial blood is sometimes so large that a trace may appear in the urine,
as a temporary and exceptional, but not an abnormal condition. This physiological fact
is well illustrated in certain cases of diabetes. There are instances, indeed, in which the
sugar appears in the urine only during digestion ; and, in almost all cases, the quantity
of sugar eliminated is largely increased after eating.

The influence of the kind of food upon the glycogenic function is a question of great
pathological as well as physiological importance. It is well known to pathologists that
certain cases of diabetes are relieved when the patient is confined strictly to a diet con-
taining neither saccharine nor amylaceous principles, and that, almost always, the quan-
tity of sugar discharged is very much diminished by such a course of treatment; but
there are instances in which the discharge of sugar continues, in spite of the most care-
fully-regulated diet. Bernard does not recognize fully the influence of different kinds of
food upon glycogenesis, and his experiments on this point are wanting in accuracy, from
the fact that the proportion of sugar in the liver is given, without indicating at what
period after death the examinations were made. In the observations upon this point by
Pavy, the examinations of the liver were made immediately after death, and the propor-
tion of glycogenic matter— not sugar — was estimated. His results are, consequently, much

470 SECRETIOK

more reliable and satisfactory. In a number of analyses of the livers of dogs confined
to different articles of diet, Pavy found a little over seven per cent, of glycogenic matter,
upon a diet of animal food ; over seventeen per cent., upon a diet of vegetable food ; and
fourteen and a half per cent., upon a diet of animal food and sugar. These results have
been confirmed by M'Donnell, who, in addition, found that hardly a trace of amyloid
substance could be detected in the liver upon a diet of fat, and none whatever upon a diet
of gelatine. Bernard had already observed that the amount of sugar produced by the
liver upon a diet of fat was the same as during total abstinence from food. These facts are
entirely in accordance with observations upon the effects of different -kinds of food in
diabetes, and they have an important bearing upon the dietetic measures to be employed
in this disease.

The effect of entire deprivation of food is to arrest the production of sugar in the
liver, three or four days before death. This arrest of the glycogenic function has gener-
ally been observed in cases of disease, except when death has occurred suddenly.

Influence of the Nervous System, etc. — Bernard has studied the influence of the ner-
vous system upon the production of sugar more satisfactorily than any other of the vari-
ations of the glycogenic function, for the reason that he has noted these
modifications by determining the sugar in the blood and in the urine.
Some of the points with regard to the nervous system we shall consider
again, and it is sufficient, in this connection, to mention the main results
of some of the most striking of the experiments upon this subject.

The most remarkable experiment upon the influence of the ner-
vous system on the liver is the one in which artificial diabetes is
produced by irritation of the floor of the fourth ventricle. This
operation is not difficult, and it is one that we have often repeated.
The instrument used is a delicate stilet, with a flat, cutting extremity,
and a small, projecting point about -fa of an inch long. In perform-
ing the operation upon a rabbit, the head of the animal is firmly
held in the left hand, and the skull is penetrated in the median
line, just behind the superior occipital protuberance. This can easily
be done by a few lateral movements of .the instrument. Once with-
in the cranium, the instrument is passed obliquely downward and for-
ward, so as to cross an imaginary line drawn between the two auditory
canals, until its point reaches the basilar process of the occipital bone.
The point then penetrates the medulla oblongata, between the roots of
the auditory nerves and the pneumogastrics, and, by its projection,
serves to protect the nervous centre from more serious injury from the
cutting edge. The instrument is then carefully withdrawn, and the
operation is completed. This experiment is almost painless, and it is
not desirable to administer an anaesthetic, as this, in itself, would dis-
turb the glycogenic process. The urine may be drawn before the oper-
ation, by pressing the lower part of the abdomen, taking care not to
allow the bladder to pass up above the point of pressure, and it will be
found turbid, alkaline, and without sugar. In one or two hours after
the operation, the urine will have become clear and acid, and it will react
FIG. i4o. — insiru- readily with any of the copper-tests. When this operation is performed
7natherfoo?Qf"th~e witnout injuring the adjacent organs, the presence of sugar in the urine
fourth ventricle, is only temporary, and the next day the secretion will have returned
to its normal condition. It is best, in performing this experiment, to
operate upon an animal in full digestion, when the production of sugar is at its maximum.
The production of diabetes in this way, in animals, is exceedingly interesting in its
relations to certain cases of the disease in the human subject, in which the affection is

VARIATIONS IN THE GLYCOGENIO FUNCTION. 471

traumatic and directly attributable to injury near the medulla. Its mechanism is dif-
ficult to explain. The irritation is not propagated through the pneumogastric nerves,
for the experiment succeeds after both of these nerves have been divided ; but the
influence of the pneumogastrics upon glycogenesis is curious and interesting. If both
of these nerves be divided in the neck, in a few hours or days, depending upon the
length of time that the animal survives the operation, no sugar is to be found in the liver,
and there is reason to believe that the glycogenic function has been arrested. After divi-
sion of the nerves in this situation, galvanization of their peripheral ends does not affect
the production of sugar; but, by galvanization of the central ends, an impression is con-
veyed to the nervous centre, which is reflected to the liver and produces a hypersecretion
of sugar. These questions will be referred to again, in connection with the physiology
of the nervous system.

FIG. 141. — Section of the head of a, rabbit, showing the operation of puncturing the floor of the fourth 'ventricle.

(Bernard.)

a, cerebellum ; &, origin of the seventh pair of nerves ; c, spinal cord ; d, origin of the pneumogastric; «, opening of
entrance of the instrument into the cranial cavity;/, instrument; g, fifth pair of nerves; h, auditory canal; *,
extremity of the instrument upon the spinal cord after having penetrated the cerebellum ; k, occipital venous
sinus ; I, tubercula quadrigemina ; m, cerebrum ; «., section of the atlas.

With regard to the influence of the sympathetic system upon the glycogenic function,
there have been few if any experiments which lead to conclusions of any great value.

It has been observed that the inhalation of anaesthetics and irritating vapors produces
temporary diabetes ; and this has been attributed to an irritation conveyed by the pneu-
mogastrics to the nerve-centre, and reflected, in the form of a stimulus, to the liver. It
is for this reason that we should avoid the administration of anaesthetics in all accurate
experiments on the glycogenic function.

Destination of Sugar. — Although sugar is constantly produced by the liver and taken
up by the circulation, it is exceptional to find it in the blood after it has passed through
the lungs. It is difficult to ascertain the precise mode of its destruction in the lungs, and,
indeed, the nutritive function of sugar in the economy is not thoroughly understood. All
that we can say of the destination of liver-sugar is, that it probably has the same office
in nutrition as the sugar taken as food and that resulting from the digestion of amylaceous
matters. The facts bearing upon this question will be reviewed under the head of nutri-
tion.

472 SECRETION".

Summary of the Functions of the Liver. — The liver seems to possess more varied
functions than any other glandular organ in the body. Under the head of digestion, we
have described the function of the bile in the small intestine, and have shown that,
although it is difficult to define precisely the action of this fluid, it undoubtedly assists in
the digestive process and its function is essential to life. Under the bead of excretion,
we have shown that the bile discharges an excrementitious substance, cholesterine, into
the small intestine, which, in its passage down the alimentary canal, is changed into ster-
corine and in this form is discharged in the fa3ces. When, from any cause, there is a
serious interference with the formation of bile, cholesterine has a tendency to accumu-
late in the blood, producing a condition called cholestersemia, which is recognizable by
certain toxic phenomena. It has also been shown that cholestera3mia may be artificially
produced in animals by the injection of cholesterine properly prepared into the circula-
tory system. We have just studied the function of the liver as a sugar-producing organ.
In this it acts as a ductless gland, producing a substance, by a process analogous to that
of secretion, which is not discharged by its excretory duct but is carried away by the
blood in the course of the circulation.

With regard to other functions which have been attributed to the liver, there is little
to say in the present state of our knowledge. Bernard held the opinion that the liver
was largely concerned in the formation of fat out of the saccharine and amylaceous ele-
ments of food ; but the examinations of the matters contained in the blood coming from
the liver, which were supposed by Bernard to be fatty, have not been sufficiently minute
and accurate to justify any positive conclusions with regard to their character or com-
position. While there can be no doubt concerning the actual production of fat in the
body independently of the fat taken as food, there is not sufficient ground for regard-
ing the liver as an organ specially concerned in its production. The observations of
Lehmann with regard to certain changes which he supposed to occur in the nitrogenized
elements of the blood in passing through the liver are not sufficiently clear and definite
to warrant any positive conclusions. The same remark applies to observations which
seem to show that the liver is concerned in the production of the white and red corpus-
cles of the blood.

CHAPTER XIV.

THE DUCTLESS GLANDS

Probable office of the ductless glands— Anatomy of the spleen— Fibrous structure of the spleen (trabeculae)— Malpi-
ghian bodies— Spleen-pulp— Vessels and nerves of the spleen— Some points in the chemical constitution of the
Bpleen — State of our knowledge concerning the functions of the spleen — Variations in the volume of the spleen
— Extirpation of the spleen — Anatomy of the suprarenal capsules— Cortical substance— Medullary substance
—Vessels and nerves— Chemical reactions of the suprarenal capsules— State of our knowledge concerning
the functions of the suprarenal capsules — Extirpation of the suprarenal capsules — Addison's disease — Anatomy
of the thyroid gland— State of our knowledge concerning the functions of the thyroid gland — Anatomy of the
thymus — Pituitary body and pineal gland.

CEETAIN organs in the body, with a structure resembling, in some regards, the true
glands, but without excretory ducts, have long been the subject of physiological specula-
tion; and the most extravagant notions concerning their functions have prevailed in the
early history of the science. The discovery of those functions of the liver which consist
in modifications in the composition of the blood passing through its substance dimly fore-
shadowed the probable office of the ductless glands ; for, as far as the production of sugar
is concerned, the liver belongs to this class. Indeed, the supposition that the ductless
glands effect some change in the blood is now regarded by physiologists as the most

ANATOMY OF THE SPLEEN. 473

reasonable of the many theories that have been entertained concerning their office in
the economy. Under this idea, these organs have been called blood-glands or vascular
glands; but, inasmuch as the supposition that these parts effect changes in the blood
or lymph is merely to supply the want of any definite idea of their function and rests
mainly upon analogy with certain of the functions of the liver, we shall retain the name
ductless glands, as indicating the most striking of their anatomical peculiarities.

As far as presenting any definite and important physiological information is concerned,
we might terminate here the history of the ductless glands. It is true that the largest
of them, the spleen, was extensively experimented upon by the earlier physiologists;
but, in point of fact, investigations have done little more than exhibit a want of knowl-
edge of the functions of these remarkable organs; and the literature of the subject is
mainly a collection of speculations and fruitless experiments. There are, however, some
interesting experimental facts with relation to the spleen and the suprarenal capsules,
although they are not very instructive, except that they indicate the extremely narrow
limits of our positive knowledge. These few facts, with a sketch of the anatomy of the
parts, will embrace all that we shall have to say concerning the ductless glands. Under
this head are classed, the spleen, the suprarenal capsules, the thyroid gland, the thymus,
and sometimes the pituitary body and the pineal gland. These parts have certain
anatomical points in common with each other, but, on account of our want of knowl-
edge of their functions, it is difficult to distinguish, as we have done in other organs,
their physiological anatomy.

Anatomy of the Spleen.

The spleen is situated in the left hypochondriac region, next the cardiac extremity of
the stomach. Its color is of a dark bluish-red, and its consistence is rather soft and fri-
able. It is shaped somewhat like the tongue of a dog, presenting above, a rather thick-
ened extremity, which is in relation with the diaphragm, and below, a pointed extremity,
in relation with the transverse colon. Its external surface is convex, and its internal
surface, concave, presenting a vertical fissure, the hilum, which gives passage to the ves-
sels and nerves. It is connected with the stomach by the gastro-splenic omentum and is
still farther fixed by a fold of the peritoneum passing to the diaphragm. It is about five
inches in length, three or four inches in breadth, and a little more than an inch in thick-
ness. Its weight is between six and seven ounces. In the adult it attains its maximum
of development, and it diminishes slightly in size and weight in old age. In early life it
bears about the same relation to the weight of the body as in the adult.

The external coat of the spleen is the peritoneum, which is very closely adherent to
the subjacent fibrous structure. The proper coat is dense and resisting; but, in the
human subjept, it is quite thin and somewhat translucent. It is composed of inelastic
fibrous tissue, mixed with numerous small fibres of elastic tissue and a few unstriped mus-
cular fibres.

At the hilum, the fibrous coat penetrates the substance of the spleen in the form of
sheaths for the vessels and nerves ; an arrangement analogous to the fibrous sheath of
the analogous structures in the liver. Th,e number of the sheaths in the spleen is equal
to the number of arteries that penetrate the organ. This membrane is sometimes called
the capsule of Malpighi. The fibrous sheaths are closely adherent to the surrounding
substance, but they are united to the vessels by a loose fibrous net-work. They follow
the vessels in their ramifications to the smallest branches and are lost in the spleen-pulp.
Between the sheath and the outer coat, are numerous bands, or trabeculre, presenting the
same structure as the fibrous coat. The presence of elastic fibres in these structures can
be easily demonstrated, and this kind of tissue is very abundant in the herbivora. In
the carnivora the muscular tissue is particularly abundant and can be readily demon-
strated; but in man this is not so easy, and the fibres are less numerous, some anatomists
denying the existence of any muscular structure. These peculiarities in the fibrous struct-

474

SECRETION.

ure are important in their relation to certain physiological changes in the size of the
spleen. Its contractility may be easily demonstrated in the dog by the application of a
galvanic current to the nerves as they enter at the hilum. This is followed by a prompt
and energetic contraction of the organ. Contractions may be produced, though they
are much more feeble, by applying the current directly to the spleen.

The substance of the spleen is soft and friable; and a portion of it, the spleen-pulp,
may be easily pressed out, or even washed away by a current of water. Aside from the
vessels and nerves, it presents for study: 1. An arrangement of fibrous bands, or tra-
beculse, by which it is divided into innumerable communicating cellular interspaces. 2.
Closed vesicles (Malpighian bodies), attached to the walls of the blood-vessels. 3. A soft,
reddish substance, containing numerous cells and free nuclei, called the spleen-pulp.

Fibrous Structure of the Spleen (Trabeculce). — From the internal face of the investing
membrane of the spleen and from the fibrous sheath of the vessels (capsule of Malpighi),
are numerous bands, or trabeculaa, which, by their interlacement, divide the substance
of the organ into irregularly-shaped, communicating cavities. These bands are from ^V
to -^ of an inch broad, and are composed, like the proper coat, of ordinary fibrous tissue
with elastic fibres and probably a few smooth muscular fibres. They pass off from the
capsule of Malpighi and the fibrous coat at right angles, very soon branch, interlace, and
unite with each other, becoming smaller and smaller, until they measure from -^ to -^
of an inch. As we should expect from the very variable size of the trabeculse, the dimen-
sions as well as the form of the cavities are exceedingly irregular. This fibrous net-work
serves as a skeleton or a support for the softer and more delicate parts.

Malpighian Bodies. — In the very elabo-
rate work on the spleen, by Malpighi, is a full
account of the closed follicles, which have
since been called the Malpighian bodies.
They are sometimes called the splenic cor-
puscles or glands. They are in the form of
rounded or slightly ovoid corpuscles, about
-jV of an inch in diameter, consisting of a deli-
cate membrane, generally homogeneous, but
sometimes faintly striated, with semifluid con-
tents. In their form, size, and structure,
they bear a close resemblance to the closed
follicles of the small intestine. The investing
membrane has no epithelial lining, and the
contents consist of an albuminoid liquid, with
numerous small, nucleated cells and a few
free nuclei. The cells measure from ^V^r to.
2-5*5-5- °f an in°h in diameter. Both the cells
and the free nuclei of the splenic corpuscles
bear a close resemblance to cells and nuclei
found in the spleen_pulp. The corpuscles are

surrounded by blood-vessels, which send
branches into the interior, to form a delicate
capillary plexus.

The number of the Malpighian corpuscles in a spleen of ordinary size has been esti-
mated by Sappey at about ten thousand. They are readily made out in the ox and
sheep but are frequently not to be discovered in the human subject. In about forty
examinations, in man, Sappey found them in only four; but in these they presented the
same characters as in the ox and the sheep, and resisted decomposition for twelve days,

FIG.

of the Q**» of the pig.

a, an artery, with its branches (b, fy ; c, c, c, Malpighian
bodies.

ANATOMY OF THE SPLEEN. 475

showing that it is not necessary to have recourse to perfectly fresh specimens to discover
them if they exist. Kolliker notes the fact that they are often absent in the human sub-
ject when death has taken place from disease or after long abstinence. He believes that
they are nearly always to be found in perfectly healthy persons. The occasional absence
of these bodies constitutes another point of resemblance to the solitary glands of the
small intestine.

The relations of the Malpighian bodies to the arterial branches distributed throughout
the spleen are peculiar. In specimens in which these corpuscles are easily made out, if a
thin section be made and the spleen- pulp be washed away by a stream of water, the cor-
puscles may be seen attached in some parts to the sides of the vessels, in others lying in
the notch formed by the branching of a vessel, and in others attached to an extremity of
an arterial twig, the vessel then breaking up into plexuses surrounding each corpuscle.
According to Sappey, the corpuscles are attached to arteries measuring from ^ to -^ of
an inch or less in diameter. When the artery is enclosed in its fibrous sheath, the cor-
puscles are applied to the sheath, but, in the smallest arteries, they are attached to the
walls of the vessels. The attachment of the Malpighian bodies to the vessels is very firm,
and they cannot be separated without laceration of the membranes.

Spleen-pulp. — "With regard to the constitution of the spleen-pulp, there is consider-
able diversity of opinion. While anatomists and physiologists are pretty generally agreed
concerning the structure and relations of the Malpighian bodies, some minutely describe
cells in the pulp, the existence of which is denied by others of equal authority. The
pulp, however, contains the essential elements of the spleen, and an accurate knowledge
of all the structures contained in it could hardly fail to throw some light on its function ;
but there is so little that is definitely known of either the anatomy or the physiology of
the spleen, that we shall refrain from discussing the views of different authors, referring
the reader for full information upon these points to elaborate works upon general anatomy.

The spleen-pulp is a dark, reddish, semifluid substance, its color varying in intensity in
different specimens. It is so soft that it may be washed by a stream of water from a thin
section, and it readily decomposes, becoming then nearly fluid. It is contained in the
cavities bounded by the fibrous trabecula3, and it contains itself numerous microscopic
bands of fibres arranged in the same way. It surrounds the Malpighian bodies, contains
the terminal branches of the blood-vessels, and probably the nerves and lymphatics.
Upon microscopical examination, it presents numerous free nuclei and cells like those
described in the Malpighian bodies ; but the nuclei are here relatively much more abun-
dant. In addition are found, blood-corpuscles (white and red) some natural in form and
size and others more or less altered, with pigmentary granules, both free and enclosed in
cells. Anatomists have attached a great deal of importance to large vesicles enclosing
what have been supposed by some to be blood-corpuscles, and by others to be pigmentary
corpuscles. The state of our knowledge upon these points, however, is very unsatisfac-
tory. Some authorities deny the existence of the so-called blood-corpuscle-containing
cells. We shall abstain from a discussion of these disputed questions, which are at present
of a character purely anatomical. All that we can say of the spleen-pulp is, that it con-
tains cells, nuclei, blood-corpuscles, and pigmentary granules, with a yellowish-red fluid,
and that it is intersected with microscopic trabeculas of fibrous and muscular tissue and a
delicate net-work of blood-vessels. It is difficult to determine whether the blood-cor-
puscles come from vessels that have been divided in making our preparations or are really
free in the pulp ; or whether the free nuclei are normal or come from cells that have
been artificially ruptured.

Vessels and Nerves of the Spleen. — The quantity of blood which the spleen receives
is very large in proportion to the size of the organ. The splenic artery is the larg-
est branch of the coeliac axis. It is a vessel of considerable length and is remarkable

476 SECKETION".

for its excessively tortuous course. In a man between forty and fifty years of age,
the vessel measured about five inches, without taking account of its deflections ; and a
thread placed on the vessel, so as to follow exactly all its windings, measured a little more
than eight inches. The large caliber of this vessel and its tortuous course are interesting
points in connection with the great variations in size and situation which the spleen is
liable to undergo in health and disease. The artery gives off several branches to the
adjacent viscera in its course, and, as it passes to the hilum, it divides into three or four
branches, which again divide so as to form from six to ten vessels. These penetrate the
substance of the spleen, with the veins, nerves, and lymphatics, enveloped in the fibrous
sheath, the capsule of Malpiglii. In the substance of the spleen, the arteries branch
rather peculiarly, giving off many small ramifications in their course, generally at right
angles to the parent trunk. These are accompanied by the veins until they are reduced
to from -gL to -sV of an inch in diameter. The two classes of vessels then separate, and
the arteries have attached to them the corpuscles of Malpighi. It is also a noticeable
fact that the distinct trunks passing in at the hilum have but few inosculations with each
other in the substance of the spleen, so that the organ is divided up into from six to ten
vascular compartments.

The veins join the fine branches of the arteries in the spleen-pulp and pass out of the
spleen in the same sheath. They anastomose quite freely in their larger as well as their
smaller branches. Their caliber is estimated by Sappey as about twice that of the arte-
ries. This author regards the estimates, which have put the caliber of the veins at four or
five times that of the arteries, as much exaggerated. The number of veins emerging
from the spleen is equal to the number of arteries of supply.

The lymphatics of the spleen are not numerous. By most anatomists, two sets of
vessels have been recognized, the superficial and the deep; but those who have studied
the subject practically have found it very difficult to demonstrate the superficial layer.
The deep lymphatics have been demonstrated in the capsule of Malpighi, attached to the
veins and emerging with them at the hilum. At the hilum, the deep vessels are joined
by a few from the surface of the spleen. The vessels, numbering five or six, then pass
into small lymphatic glands and empty into the thoracic duct opposite the eleventh or
twelfth dorsal vertebra. It was an old idea that the lymphatics were the excretory ducts
of the spleen ; but this is a speculation which does not demand discussion at the pres-
ent day.

The nerves of the spleen are derived from the solar plexus. They follow the vessels
in their distribution and are enclosed with them in the capsule of Malpighi. They are
distributed ultimately in the spleen-pulp, but nothing definite is known of their mode of
termination. We have already referred to the fact that, when these nerves are galvanized,
the non-striated muscles in the substance of the spleen are thrown into contraction.

Some Points in the Chemical Constitution of the Spleen. — Very little has been learned
with regard to the probable function of the spleen, from the numerous chemical analyses
that have been made of its substance. It will therefore be out of place to discuss its
chemical constitution very fully, and we shall only refer to certain principles, the exist-
ence of which, in the spleen-substance, may be considered as pretty well determined.
In the first place, cholesterine has been found to exist in the spleen constantly and in
considerable quantity, and the same may be said of uric acid. In addition, chemists
have extracted from the substance of the spleen, hypoxanthine, leucine, tyrosine, a
peculiar crystallizable substance called, by Scherer, lienine, crystals of haematoidine, lac-
tic acid, acetic acid, butyric acid, inosite, amyloid matter, and some indefinite fatty prin-
ciples. It is difficult, however, to say how far some of these principles are formed by
the processes employed for their extraction or are due to morbid action ; certainly, physi-
ologists have thus far been unable to connect them with any definite views with regard
to the probable function of the spleen.

FUNCTIONS OF THE SPLEEN. 477

State of our Knowledge concerning the Functions of the Spleen. — The spleen is al-
most universal in vertebrate animals ; it is an organ of considerable size, and is very
abundantly supplied with vessels and nerves ; it has a complex structure, unlike that of
any of the true glands ; its tissue presents a variety of proximate principles ; but it has
no excretory duct, and no opportunity is afforded for the study of its secretion, except
as it may be taken up by the current of blood. It must be admitted, also, that, up to
the present time, no definite physiological ideas have followed the elaborate microscopi-
cal and chemical examinations of the spleen. There have been only two methods of
inquiry, indeed, which have promised any such results : First, a comparison of the blood
and lymph going into and coming from the spleen, and an examination of the variations
in the volume of the organ during life ; and second, a study of the phenomena which fol-
low its extirpation in living animals. A review of the literature of the subject will show
that we have gained but little positive information from either of these methods of study.

The condition of the question of the influence of the spleen upon the composition of
the blood is well illustrated in the last edition of Longet's elaborate work upon physiology.
This author quotes opinions of the highest authorities, based chiefly upon microscopical
investigations, some in favor of the view that the blood-corpuscles are destroyed, and
others arguing that they are formed in the spleen, while he himself offers no opinion
upon the subject. Still, there are certain established points of difference between the
blood of the splenic artery and of the splenic vein. There can be little doubt of the fact
that the blood coming from the spleen contains a large excess of white corpuscles ; but
it can by no means be considered as settled that the function of the spleen is to form
white blood-corpuscles. In pathology, although great increase in the leucocytes of the
blood frequently attends hypertrophy of the spleen, this condition is also observed when
the spleen is perfectly healthy.

Diminution in the proportion of red corpuscles in the blood in passing through the
spleen, in a very marked degree, has been noted, and this gives color to the supposition
that the spleen is an organ for the destruction of the blood-corpuscles ; but we know
nothing of the importance or significance of this process, and it is not shown that the
corpuscles exist in undue quantity in animals after the spleen has been removed. We
learn nothing more definite from the fact that the blood of the splenic vein seems to contain
an unusual quantity of pigmentary matter. In connection with the marked diminution
in the proportion of blood-corpuscles, physiologists have observed a marked increase in
albuminoid matters in the blood of the splenic vein.

The significance of the facts just stated is so little understood, that it would seem
hardly necessary even to mention them, except as an illustration of the small amount of
definite information regarding the functions of the spleen that has resulted from an
examination of the blood coming from this organ. We know nothing of any changes
effected by the spleen in the constitution of the lymph.

Variations in the Volume of the Spleen. — One of the theories with regard to the
function of the spleen, which merits a certain amount of consideration, is that it serves
as a diverticulum for the blood, when there is a tendency to congestion of the other
abdominal viscera.

It has been shown that the spleen is greatly enlarged in dogs, from four to five hours
after feeding, that its enlargement is at its maximum at about the fifth hour, and that it
gradually diminishes to its original size during the succeeding twelve hours; but it is not
apparent how far these changes are important or essential to the proper performance of the
functions of digestion and absorption. Experiments have shown that animals may live,
digest, and absorb alimentary principles perfectly well after the spleen has been re-
moved, and this has even been observed in the human subject ; and, in view of these facts,
it is impossible to assume that the presence of the spleen, as a diverticulum for the blood,
is essential to the proper action of the other abdominal organs.

478 SECRETION.

Extirpation of the Spleen.— There is one experimental fact that has presented itself
in opposition to nearly every theory advanced with regard to the function of the spleen;
which is, that the organ may be removed from a living animal, and yet all the functions
of life go on apparently as before. The spleen is certainly not necessary to life, nor, as
far as we know, is it essential to any of the important general functions. It has been
removed over and over again from dogs, cats, and even from the human subject, and
its absence is attended with no constant and definite changes in the phenomena of life.
If it act as a diverticulum, this function is not essential to the proper operation of
the organs of digestion and absorption ; and, if its office be the destruction or the forma-
tion of the blood-corpuscles, the formation of leucocytes, of uric acid, of cholesterine, or
of any excrementitious matter, there are other organs which may perform these functions.
What renders this question even more obscure is the fact that we have no knowledge of
any constant modifications in the size or the functions of other organs as a consequence
of removal of the spleen. This is not surprising, however, when we reflect that one
kidney may accomplish the function of urinary excretion after the other has been removed,
and that the single organ which remains does not present enlargement of the Malphigian
bodies and the convoluted tubes.

There are certain phenomena that sometimes follow removal of the spleen from the
lower animals, which are curious and interesting, even if they do not afford much posi-
tive information. Extirpation of this organ is an old and a very common experiment.
In the works of Malpighi, published in 1687, we find an account of an experiment on a
dog, in which the spleen was destroyed, and the operation was followed by no serious
results. Since then it has been removed so often, and the experiments have been so
universally negative in their results, that it is hardly necessary to cite authorities upon the
subject. There are numerous instances, also, in which it has been in part or entirely
removed from the human subject, which it is unnecessary to refer to in detail ; but, in
nearly every case, when there was no diseased condition to complicate the observation,
the results have been the same as in experiments on the inferior animals.

One of the phenomena following extirpation of the spleen, to which we desire to
call attention, is a modification of the appetite. Great voracity in animals after removal
of the spleen was noted by the earlier experimenters, and this formed the basis of some
of their extravagant theories. Later experimenters have observed this change in the
appetite and have noted that digestion and assimilation do not appear to be disturbed,
the animals becoming unusually fat. Prof. Dalton has also observed that the animals,
particularly dogs, sometimes present a remarkable change in their disposition, becoming
unnaturally ferocious and aggressive. "We have frequently observed these phenomena
after removal of the spleen; and, in the following experiment, performed in 18G1, they
were particularly marked :

The spleen was removed from a young dog weighing twenty-two pounds, by tho
ordinary method ; viz., making an incision into the abdominal cavity in the linea alba,
drawing out the spleen, and exsecting it after tying the vessels. Before the operation
the dog presented nothing unusual, either in his appetite or disposition. The wound
healed rapidly, and, after recovery had taken place, the animal was fed moderately once
a day. It was noticed, however, that the appetite was excessively voracious; and the
dog became so irritable and ferocious that it was dangerous to approach him, and it
became necessary to separate him from the other animals in the laboratory. He would
eat refuse from the dissecting-room, the flesh of dogs, faeces, etc. On February 11, 1861,
about six weeks after the operation, having been well fed twenty-four hours before, the dog
was brought before the class at the New Orleans School of Medicine, and he ate a little
more than four pounds of beef-heart, nearly one fifth of his weight. This he digested
perfectly well, and the appetite was the same upon the following day. This dog had a
remarkably sleek and well-nourished appearance.

The above is a striking example of the change in the appetite and disposition of ani-

SUPRARENAL CAPSULES. 479

mals after extirpation of the spleen ; but these results are by no means invariable. "We
have often removed the spleen from dogs and kept the animals for months without
observing any thing unusual ; and, on the other hand, we have observed the change in
disposition and the development of an unnatural appetite, in animals after removal of
one kidney. These effects were also very well marked in an animal with biliary fistula,
that lived for thirty-eight days. In the latter instance, the voracity could be explained
by the disturbance in digestion and assimilation produced by shutting off the bile from
the intestine ; but these phenomena occurring after removal of one kidney, which ap-
peared to have no effect upon the ordinary functions, are not so readily understood. We
have observed both increase in the appetite and the development of extraordinary ferocity
after extirpation of one kidney almost invariably, since our attention has been directed
to this point ; and, in the experiments of which records were preserved, these effects
were very marked. In one, a dog lived for nearly two years with one kidney and was
finally killed. The appetite was voracious and depraved. He would eat dogs' flesh
greedily. In another, death took place in convulsions, forty-three days after removal of
one kidney, the animal having apparently recovered from the operation. This dog was
very ferocious, had an extraordinary appetite, and would eat faeces, putrid dogs' flesh, etc.,
which the other dogs in the laboratory would not touch. The other dog entirely recov-
ered from the operation of removing one kidney and presented the same phenomena.

In view of the above facts, it must be admitted that removal of the spleen in the
lower animals and the human subject has thus far demonstrated nothing, except that this
part is not essential to the proper performance of the vital functions. The voracity
which occasionally follows the operation in animals is one of the phenomena, like the
increase in the size of animals after castration, for which physiologists can offer no satis-
factory explanation.

It is evident from the foregoing considerations that, notwithstanding the great amount
of literature upon the anatomy and functions of the spleen, physiologists have no definite
knowledge of any important office performed by this organ. With this conclusion, we
pass to a consideration of the other ductless glands, the physiology of which is, unfortu-
nately, even more unsatisfactory.

Suprarenal Capsules.

The theories that have been advanced with regard to the function of the suprarenal
capsules have not, as a rule, been based upon anatomical investigations, but have taken
their origin from pathological observations and experiments upon living animals. This fact
detracts from the physiological interest attached to the structure of these bodies, and we
shall consequently treat of their anatomy very briefly.

The suprarenal capsules, as their name implies, are situated above the kidneys. They
are small, triangular, flattened bodies, situated behind the peritoneum, and capping the
kidneys at the anterior portion of their superior ends. The left capsule is a little larger
than the right, and is rather semilunar in form, the right being more nearly triangular.
Their size and weight are very variable in different individuals. Of the different esti-
mates given by anatomists, we may state, as an average, that each capsule weighs about
one hundred grains. They are about an inch and a half in length, a little less in width,
and a little less than one-fourth of an inch in thickness.

The weight of the capsules, in proportion to that of the kidney?, presents great vari-
ations at different periods of life ; and they are so much larger in the foetus than after
birth, that some physiologists, in the absence of any reasonable theory of their function in
the adult, have assumed that their office is chiefly important in intra-uterine life. Meckel
states that they are easily distinguished in the foetus of two months ; at the end of the
third month, they are a little larger and heavier than the kidneys ; they are equal in size
to the kidneys (though a little lighter) at four months ; and, at the beginning of the sixth
month, they are to the kidneys as two to five. In the foetus at term, the proportion is as

480 SECRETION.

one to three, and in the adult, as one to twenty-three. It was asserted by some of the
older writers, that the capsules are larger in the negro than in the white races, hut
Meckel states that, although he had observed this in a negress, he saw nothing of it in
dissecting a negro. This observation did not have much significance at that time ; but
since it has been supposed that the suprarenal capsules have some function in connection
with the formation of pigment, authors have quoted it as important.

The color of the capsules is whitish-yellow. They are completely covered by a thin,
fibrous coat, which penetrates their interior, in the form of trabeculaa. Upon section,
they present a cortical and a medullary substance. The cortex is yellowish, from fo to
T^ of an inch in thickness, surrounding the capsule entirely, and constituting about two-
thirds of its substance. The medullary substance is whitish, very vascular, and is
remarkably prone to decomposition, so that it is desirable to study the anatomy of these
bodies in specimens that are perfectly fresh.

/Structure of the Suprarenal Capsules.

Cortical Substance. — The cortical substance is divided into two layers. The external
is pale-yellow, and 4s composed of closed vesicles, rounded or ovoid in form, containing
an albuminoid fluid, cells, nuclei, and fatty globules. This layer is very thin. The greater
part of the cortical substance is of a reddish-brown color and is composed of closed tubes.
On making thin sections through the cortical substance previously hardened in chromic
acid and rendered clear by means of glycerine, numerous rows of cells are seen, arranged
with great regularity, and extending, apparently, from the investing membrane to the
medullary substance. On studying these sections with a high magnifying-power, it is
evident that the cells are enclosed in tubes measuring from T^V<y to ^^ of an inch in
diameter. The cells are granular, with a distinct nucleus and nucleolus, and a variable
number of oil-globules. They measure from TTYjy to J-^-Q of an inch in diameter. Be-
tween the tubes of the cortical substance, are bands of fibrous tissue, connected with the
covering of the capsule.

Medullary Substance. — The medullary substance is much paler and more transparent
than the cortex. In its centre are numerous openings, marking the passage of its venous
sinuses. It is penetrated in every direction by excessively delicate bands of fibrous tis-
sue, which enclose blood-vessels, nerves, and numerous elongated, closed vesicles, contain-
ing cells, nuclei, and granular matter. These vesicles, ¥V of an inch long and about -^-^
of an inch broad, have been demonstrated in the ox and in the human subject. The cells
in the human subject are from -p^ to T^Vo °f an mc^ m diameter. They are isolated
with difficulty and are very irregular in their form. The nuclei measure about ^Vs °f
an inch. The medullary substance is peculiarly rich in vessels and nerves.

Vessels and Nerves. — The blood-vessels going to the suprarenal capsules are very
numerous and are derived from the aorta, the phrenic artery, the cosliac axis, and the renal
artery. Sometimes as many as twenty distinct vessels penetrate each capsule. In the
cortical substance, the capillaries are arranged in elongated meshes, anastomosing freely,
and surrounding the tubes, but never penetrating them. In the medullary substance, the
meshes are more rounded, and here the vessels form a very rich capillary plexus. Two
large veins pass out, to empty, on the right side, into the vena cava, and on the left,
into the renal vein. Other smaller veins empty into the vena cava, the renal, and the
phrenic veins.

The nerves are very numerous and are derived from the semilunar ganglia, the renal
plexus, the pneumogastric, and the phrenic. Kolliker mentions that he has counted, in
the human subject, thirty -three nervous trunks entering the right suprarenal capsule.
The nerves probably pass directly to the medullary substance, but here their mode of dis-
tribution is unknown. In the medullary matter, however, are two ganglia, characterized
by nerve-cells of the ordinary form, and situated close to the central vein.

FUNCTIONS OF THE SUPRARENAL CAPSULES. 481

Nothing whatever is known of the lymphatics of the suprarenal capsules, and the
existence of these vessels, even, is doubtful.

Chemical Reactions of the Suprarenal Capsules. — A few years ago, M. Vulpian
discovered in the medullary portion of the suprarenal capsules a peculiar substance,
soluble in water and in alcohol, which gave a greenish reaction with the salts of iron and
a peculiar rose-tint on the addition of iodine. He could not determine the same reaction
with extracts from any other parts. Later, in conjunction with M. Cloez, he discovered
hippuric and taurocholic acid in the capsules of some of the herbivora. Other researches
have been made into the chemistry of these bodies, but without results of any great physi-
ological importance.

State of our Knowledge concerning the Functions of the Suprarenal

Capsules.

In 1855, the late Dr. Addison, of Guy's Hospital, published a remarkable memoir upon
a peculiar disease which he had found connected with disorganization of the suprarenal
capsules. This disease, sometimes called Addison's disease, is characterized by bronzing
of the skin and is accompanied by serious disorders in nutrition. It was supposed to be
invariably fatal. The peculiar discoloration of the surface, attended with disorganization
of the suprarenal capsules, led physiologists to suppose that, perhaps, these bodies had
some function connected with the formation of pigment ; and, following the publication
of Dr. Addison's memoir, we find quite a number of experiments upon animals, consisting
chiefly in extirpation of the capsules. Before this time, there had been no reasonable
theory, even, of the probable function of these bodies. As our first ideas of the rela-
tions of the suprarenal capsules to the formation of pigment were derived from cases of
disease, it may not be out of place to consider briefly whether there be any invariable
and positive connection between structural change in these organs and the affection
known under the name of bronzed skin.

In the memoir by Dr. Addison, are reported eleven cases of anaemia, accompanied
with bronzing of the skin, terminating fatally, and found, after death, to be attended
with extensive disorganization of the suprarenal capsules. The reports of these cases
attracted a great deal of attention among physiologists as well as pathologists. A year
later, Prof. I. E. Taylor, of Bellevue Hospital, reported seven cases of bronzed skin, in
two of which the diagnosis of disease of the suprarenal capsules was verified by post-
mortem examination. Attention now being directed to this peculiar condition of the
system, accompanied with discoloration of the skin, numerous cases were reported from,
time to time, but some of them did not fully carry out the views of Dr. Addison. Per-
haps the most extensive collection of cases taken from a great number of authorities is
given by Dr. Greenhow, in his work upon Addison's disease. Dr. Greenhow is appar-
ently convinced that the connection between the constitutional symptoms and discolora-
tion of the skin, described by Addison, and disorganization of the suprarenal capsules is
well established. He reports one hundred and ninety-six cases ; and, out of these, he
selects one hundred and twenty-eight, as fair representatives of Addison's disease. There
are several cases (ten) in which there was bronzing of the skin, the suprarenal capsules
being perfectly healthy ; but in only one of these were there any of the characteristic
constitutional symptoms. There are twenty-two cases cited of cancer of the suprarenal
capsules, not one of which presented the characteristic constitutional symptoms, only
seven presenting some slight discoloration of the skin. Without discussing this subject
more fully, it seems justifiable to adopt the opinion, entertained by many pathologists,
that there is a connection between bronzed skin accompanied with certain grave consti-
tutional symptoms, and disorganization of the suprarenal capsules, which is frequent but
not invariable ; but it is not established that the destruction of the capsules stands in a
31

482 SECRETION.

causative relation to the discoloration or to the constitutional disturbance. It is more
interesting to us, however, to know that the investigations into these diseased conditions
have developed little or nothing of importance concerning the physiology of the supra-
renal capsules.

Extirpation of the Suprarenal Capsules. — There are two important questions to be
settled by the removal of the suprarenal capsules from living animals. The first is,
whether or not these organs are essential to life ; and the second, to determine the con-
sequences of their removal, as exhibited in modifications of the animal functions.

Are the suprarenal capsules essential to life ? This question can be answered in a very
few words. Dr. Brown-Sequard, in his first experiments, removed sometimes one and
sometimes both capsules in rabbits, Guinea-pigs, dogs, and cats, and the animals died in
the course of two or three days. He also noted several peculiar results, such as turning,
and contraction of the pupil, when one capsule had been extirpated, and the development
of peculiar crystals in the blood. M. Gratiolet repeated these experiments and ascertained
that the left capsule could be removed with impunity, while extirpation of the right was
always fatal. M. Philipeaux added a number of observations, experimenting chiefly upon
rats and taking great care to disturb the adjacent organs as little as possible. As the result
of these experiments, he concluded that the capsules are not essential to life. Of four rats
operated upon in this way, three died, as Philipeaux supposed, of cold, the first in nine
days, the second in twenty-three days, and the third in thirty-four days. One was alive
and well when the report was made, although the capsules had been removed for forty-
nine days. In such a question as this, negative experiments are of little account ; and the
instances in which animals have recovered and lived perfectly well after removal of both
suprarenal capsules show conclusively that they are not essential to life. Death has prob-
ably been due, in most of the experiments, to injury of the semilunar ganglia, and it is
probably on account of the greater injury, from the situation of the capsule, produced
by operating on the right side, that the removal of the capsule of that side has been more
generally fatal. It is not necessary to take account, in this connection, of the contraction
of the pupil, "turning" and other symptoms referable to the nervous system, which have
sometimes followed these operations. These phenomena are undoubtedly due to injury
of adjacent parts, and not to extirpation of the capsules. The only remaining question to
determine is whether the capsules have any thing to do with the formation or change of
pigment. Notwithstanding the assertion of Dr. Brown-Sequard, that flakes of pigment
and blood-crystals differing from those developed in normal blood are found in animals
deprived of the suprarenal capsules, this view is adopted by a few physiological authori-
ties. In view of these facts, and in the absence of comparative examinations of the blood
going to the suprarenal capsules by the arteries and returned from them by the veins, it
is impossible to assign any definite function to these bodies, and it is certain that they
are not essential to life. Their greater relative size before birth has led to the supposi-
tion that they might have an important office in intra-uterine life, but this is a pure
hypothesis, based upon no positive knowledge.

Thyroid Gland.

The history of this gland belongs almost exclusively to descriptive anatomy, and its
only physiological interest is in the similarity of its structure to that of the other ductless
glands. It has no excretory duct. It is attached to the lower part of the larynx, follow-
ing it in its various movements. Its color is brownish-red. The anterior face is convex
and is covered by certain of the muscles of the neck. The posterior surface is concave
and is applied to the larynx and trachea. It is formed of two lateral lobes, with a
rounded, thickened base below, and a long, pointed extremity extending upward, con-
nected by an isthmus. Each of these lobes is about two inches in length, three-quarters
of an inch in breadth, and about the same in thickness at its thickest portion. The isth-

THYMUS GLAND. 483

mus connects the lower portion of the lateral lohes. It covers the second and third
tracheal rings and is about half an inch wide and one-third of an inch thick. From the
left side of the isthmus, and sometimes from the left lobe, is a portion projecting upward,
called the pyramid. The weight of the thyroid gland, according to Sappey, is from three
hundred and fifty to three hundred and eighty grains. It is usually stated by anatomical
writers that it is relatively larger in the foetus and in early life than in the adult; but
Sappey, from his own researches, is disposed to believe that its weight, in proportion to
the weight of the adjacent organs, does not vary with age. It is a little larger and more
prominent in the female than in the male.

Structure ofth* Thyroid Gland. — The thyroid gland is covered with a thin but resisting
coat of ordinary fibrous tissue, which is loosely connected with the surrounding parts. From
the internal surface of this membrane, are numerous fibrous bands, or trabeculae, giving
off, as they pass through the gland, secondary trabeculoe, and then subdividing until they
become of microscopic size. By this arrangement, the gland is divided up into communi-
cating cells, like a sponge. These bands are mingled with numerous small elastic fibres.
Throughout the substance of the gland, lodged in the meshes of the trabeculse, are numer-
ous rounded or ovoid closed vesicles, measuring from -$^ to ^-$ of an inch. These are
formed of a structureless membrane, and they are lined by a single layer of pale, granular,
nucleated cells, from ^V? to FOIJTF °f an inc^ in diameter. The layer of cells sometimes
lines the vesicle completely, sometimes it is incomplete, and sometimes it is wanting.
The contents of the vesicles are a clear, yellowish, slightly viscid, albuminoid fluid, with
a few granules, pale cells, and nuclei. Robin has described in these vesicles curiously-
shaped, translucent, feebly-refracting, colorless bodies which he has called sympexions;
but there is little known of their constitution or properties. The vesicles are arranged
in little collections or lobes, with the great veins passing between them.

Vessels and Nerves. — The blood-vessels of the thyroid gland are very numerous, this
organ being supplied by the superior and inferior thyroid arteries and sometimes by a
branch of the innominata. The arteries break up into a close capillary plexus, surround-
ing the vesicles with a rich net-work, but never penetrating their interior. The veins
are large, and, like the hepatic veins, they are so closely adherent to the surrounding
tissue that they do not collapse when cut across. The veins emerging from the gland
form a plexus over its surface and the surface of the trachea, and they then go to form
the superior, middle, and inferior thyroid veins. The nerves are derived from the pneu-
mogastric and the cervical sympathetic ganglia. The lymphatics are numerous but are
difficult to inject. The exact distribution of the nerves and the origin of the lymphatics
are not well understood.

State of our Knowledge concerning the Functions of the Thyroid Gland. — It is gen-
erally admitted that the thyroid gland may be removed from animals without interfering
with any of the vital functions ; and this, taken in connection with the fact that it is so
often diseased in the human subject without producing any general disturbance, shows
that its function cannot be very important. Nothing of importance has been learned
from a chemical analysis of its substance. The blood of the thyroid veins has been ana-
lyzed, but the changes in its composition in passing through the gland are slight and
indefinite. An instance is quoted by Longet of periodical enlargement of the gland in a
female during menstruation, but there is no evidence that this is of constant occurrence.

Thy mus Gland.

The anatomy of the thymus assimilates it to the ductless glands, but its function,
whatever it may be, is confined to early life. In the adult the organ is wanting, traces,
only, of fibrous tissue, with a little fat, existing after puberty in the situation previously
occupied by this gland. As there never has been a plausible theory, even, of the func-

484

SECRETION.

tion of this organ, the existence of which is confined to the first two or three years of
life, we shall abstain from all discussions with regard to minute points in its anatomy,
and give a simple sketch of its structure, as compared with the ductless glands already
considered.

The thymus appears at about the third month of foetal life, and it gradually increases in
size until about the end of the second year. It then undergoes atrophy, and it disappears
almost entirely at the age of puberty. It is situated partly in the thorax and partly in
the neck. The thoracic portion is in the anterior mediastinum, resting upon the pericar-
dium, extending as low as the fourth costal cartilage. The cervical portion extends
upward as far as the lower border of the thyroid gland. The whole gland is about two
inches in length, one and a half inch broad at its lower portion, and about one-quarter
of an inch thick. Its color is grayish, with a slightly rosy tint. It is usually in the form of
two lateral lobes lying in apposition in the median line, although sometimes there exists
but a single lobe. It is composed of numerous lobules held together by fibrous tissue.

The proper coat of the thymus is a delicate fibrous
membrane, sending processes into the interior of the
organ. Its fibrous structure, however, is loose, so that
the lobules can be separated with little difficulty. Por-
tions of the gland may be, as it were, unravelled, by
loosening the interstitial fibrous tissue. In this way it
will be found to be composed of numerous little lobular
masses attached to a continuous cord. This arrange-
ment is more distinct in the inferior animals of large

FIG. 143. — Unravelled thymus from the calf;

natural size. (Koll'iker.)
a, a, cord of the thymus ; 6, 6, 6, lobules ; c,
small nodules attached to the cord.

FIG. 144. — Half of the human thymits, laid open in
its 'lower portion. (Kolliker )

size than in man. The lobules are composed of rounded vesicles, from ten to fifteen in num-
ber, and from -^ to -fa of an inch in diameter. The walls of these vesicles are thin,
finely granular, and excessively fragile. The vesicles contain a small quantity of an
albuminoid fluid, with cells and free nuclei. The cells are small and transparent, and the
nuclei, spherical, relatively large, and containing from one to three nucleoli. The free
nuclei are also rounded and contain several distinct nucleoli. These vesicles are easily

PITUITARY BODY AND PINEAL GLAND. 485

ruptured, when their contents exude in the form of an opalescent fluid, sometimes called
the thymic juice.

Anatomists are somewhat divided in their opinions with regard to the structure
of the central cord and the lobules. Some adopt the view advanced by Sir Astley
Cooper, that the cord has a central canal connected with cavities in the lobules ; while
others believe that the cavities thus described are produced artificially, by the processes
employed in anatomical investigation. The latter opinion is the latest and is probably
correct.

The blood-vessels of the thymus are numerous, but their caliber is small, and the gland
is not very vascular. They are derived chiefly from the internal mammary artery, a few
coming from the inferior thyroid, the superior diaphragmatic, or the pericardial. They
pass between the lobules, surround and penetrate the vesicles, and form a capillary plexus
in their interior. The vesicles, in this respect, bear a certain resemblance to the closed
follicles of the intestine. The veins are also numerous, but they do not follow the course
of the arteries. The principal vein emerges at about the centre of the gland posteriorly,
and it empties into the left brachio-cephalic. Other small veins empty into the internal
mammary, the superior diaphragmatic, and the pericardial. A few nervous filaments
from the sympathetic system surround the principal thymic artery and penetrate the
gland. Their ultimate distribution is uncertain. The lymphatics are very numerous.

Inasmuch as the thymus is peculiar to early life, one of the most interesting points in
its anatomical history relates to its mode of development. This, however, does not pre-
sent any great physiological importance and is fully treated of in works upon anatomy.

Pituitary Body and Pineal Gland.

These little bodies, situated at the base of the brain, are quite vascular, contain closed
vesicles and but few nervous elements, and are sometimes classed with the ductless glands.
Physiologists have no idea of their function.

The pituitary body is of an ovoid form, a reddish-gray color, weighs from five to ten
grains, and is situated on the sella turcica of the sphenoid bone. It is said to be larger in
the foetus than in the adult, and in fo3tal life it has a cavity communicating with the third
ventricle. This little body has been studied by M. Grandry, in connection with the
suprarenal capsules. He regards it as essentially composed of closed vesicles, with fibres
of connective tissue and blood-vessels. The vesicles measure from ^jr to -^ of an inch
in diameter. They are formed of a transparent membrane, containing irregularly po-
lygonal, nucleated cells, and free nuclei. The cells are from -^J^ to yyV^ of an inch in
diameter. The nuclei are distinct, with a well-marked nucleolus, and measure about
-5-5*^ of an inoh. Capillary vessels surround these vesicles without penetrating them.
M. Grandry did not observe either nerve-cells or fibres between the vesicles. In old
subjects he found the peculiar concretions (sympexions) already described as existing in
the thyroid gland.

The pineal gland is situated just behind the posterior commissure of the brain, between
the nates, and is enclosed in the velum interpositum. It is of a conical shape, one-third
of an inch in length, and of nearly the color of the pituitary body. It is connected with
the base of the brain by several delicate commissural peduncles. It presents a small
cavity at its base, and frequently it contains in its substance little calcareous masses, com-
posed of phosphate and carbonate of lime, phosphate of magnesia and ammonia, and a
small quantity of organic matter. It is covered with a fibrous envelope, which sends
processes into its interior. As the result of the researches of M. Grandry, it has been
found to present a cortical substance, entirely analogous in its structure to the pituitary
body, and a central portion, composed of the ordinary nervous elements found in the gray
matter of the brain. Its structure is regarded by Grandry as very like that of the medul-
lary portion of the suprarenal capsules.

486 NUTRITION".

It is difficult to classify organs, of the function of which we are entirely ignorant; but
the structure of the little bodies just described certainly resembles that of the ductless
glands. "We have indicated their anatomy merely to show that their function is probably
analogous to that of other organs of the same class.

CHAPTER XV.

NUTRITION— ANIMAL HEAT.

Nature of the forces involved in nutrition— Definition of vital properties — Life, as represented in development and
nutrition— Principles which pass through the organism— Principles consumed in the organism— Development of
power and endurance by exercise (training) — Formation and deposition of fat — Conditions under which fat exists
in the organism^Physiological anatomy of adipose tissue — Conditions which influence nutrition — Products of
disassimilation— Animal heat — Limits of variation in the normal temperature in man — Variations with external
temperature — Variations in different parts of the body — Variations at different periods of life — Diurnal variations
— Eelations of animal heat to digestion — Influence of defective nutrition and inanition — Influence of exercise,
mental exertion, and the nervous system, upon the heat of the body — Sources of animal heat — Connection of the
production of heat with nutrition — Seat of the production of animal heat — Eelatiocs of animal heat to the different
processes of nutrition— Relations of animal heat to respiration— Exaggeration of the animal temperature in par-
ticular parts after division of the sympathetic nerve and in inflammation — Intimate nature of the calorific pro-
cesses— Equalization of the animal temperature.

• NUTRITION proper, in the light in which we propose to consider it in this chapter,
is the process by which the physiological decay of the tissues and fluids of the body is
compensated by the appropriation of new matter. All of the physiological processes
that we have thus far studied, including circulation, respiration, alimentation, digestion,
absorption, and secretion, are to be regarded as means directed to a single end ; and
the great function, to which all the others are subservient, is the general process of
nutrition.

The nature of the main forces involved in nutrition, be it in a highly-organized part,
like the brain or muscles, or in a tissue called extra- vascular, like the cartilages or nails, is
unknown. The phenomena attending the general process, however, have been studied
most carefully, and certain important positive results have been attained ; but we really
find no more satisfactory explanation of the nature of the causative force of nutrition in
the doctrines of to-day than in the speculative theories of the ancients.

We can hardly realize the vast extent of the problem of nutrition from a review of the
functions which we have already considered. We have seen that the blood contains all
the elements that enter into the composition of the tissues and secretions, either identical
with them in form and composition, as is the case with the inorganic principles, or in a
condition which allows of their transformation into the characteristic principles of the
tissues, as we see in the organic substances proper. These materials are supplied to
the tissues, in the required quantity, through the' circulatory apparatus; and oxygen,
which is immediately indispensable to all the operations of life, is introduced by respira-
tion. The great nutritive fluid, being constantly drawn upon by the tissues for materials
for their regeneration, is kept at the proper standard by the introduction of new matter
into the system in alimentation, its elaborate preparation by digestion, and its appropria-
tion by the fluids by absorption. Many of these processes require the action of cer-
tain secretions. 'The introduction of new matter, so essential to the continuance of the
phenomena of life, is demanded, on account of the change of the substance of the tissues
into what we call effete matter ; and this is discharged from the animal organism, to be
appropriated by vegetables, and thus maintain the equilibrium between these two great
kingdoms in Nature.

What is it that causes the parts of a living animal organism to undergo change into

GENERAL CONSIDERATIONS. 487

effete matter, incapable of any further animal functions ; and what is it that gives to
these parts the power of self-regeneration, when new matter is presented under proper
conditions ?

These questions are the physiological ignis fatuus, which, it is to be feared, will forever
elude the grasp of scientific inquiry. They constitute one of the great mysteries ever
present in the mind of the student of Nature, and one, the grandeur of which is so
immense that it is a problem with which our intelligence can scarcely grapple. Its
greatness is commensurate with that of the question of the soul, and its relations to the
finite and the infinite ; a question which philosophers have been constrained either to
admit upon the faith of revelation or to hopelessly abandon. Little if any real progress
is to be made by endeavoring to cover the inscrutable problem of life with a simplicity
entirely artificial. This will always be attractive, and, to a certain extent, satisfactory to
the minds of those unacquainted with the details of natural laws or willing to admit
speculative theories upon subjects concerning which it is impossible, in the present con-
dition of science, to have any positive information ; and, if generally admitted by biologi-
cal students, it would carry our science back to the dark periods in its history, when the
study of Nature was confined to speculation, and there existed no knowledge based upon
the direct observation of phenomena. A new name, arbitrarily applied to organic matter,
without any addition to its physiological history, does not advance our definite knowledge.
For example, it has long been known that certain nitrogenized constituents of the organ-
ism, classed collectively as organic principles, seem to give to the tissues their property
of self-regeneration and development. It may seem to those not engaged in scientific
inquiry that a recital of the wonderful properties of " protoplasm " affords some additional
information concerning the phenomena observed in organized bodies ; but the true defi-
nition of the term leads us back to our former ideas of the so-called vital properties of
organic matters.

It is a well-established fact that, while nearly all of the tissues undergo disassimila-
tion, or conversion into effete matter, during their physiological decay in the living or-
ganism, others, like the epidermis and its appendages, are gradually desquamated, and,
when once formed, do not pass through any farther changes. The whole question of the
essence and nature of the nutritive property or force resolves itself into vitality. Life is
always attended with what we know as the phenomena of nutrition, and nutrition does
not exist except in living organisms. When we can state positively what is life, we shall
know something of nutrition. At present, physiologists have been able to define life
only by a recital of certain of its invariable and characteristic attendant conditions ; and
yet there are few, if any, definitions of life — regarding' it as the sum of the phenomena
peculiar to living organisms — that are not open to grave objections.

If we regard life as a principle, it stands in the relation of a cause to the vital phe-
nomena ; if we regard it as the totality of these phenomena, it is an effect.

If we study the development of a fecundated ovum, life seems to be a principle, giv-
ing the wonderful property of appropriating matter from without, until the germ
becomes changed, from a globule of microscopic size and an apparently simple structure,
into a complete organism with highly-elaborated parts. This organism has a definite
form and size, a definite period of existence, and it produces, at a certain time, generative
elements, capable of perpetuating its life in new beings. "We may say that an organism
dies physiologically because the vital principle, if we admit the existence of such a prin-
ciple, has a limited term of existence. But, on the other hand, the fully-developed living
organism, which we call an animal, presents numerous distinct parts, each endowed with
an independent property called vital, that property recognized by Haller in various tis-
sues, under the name of irritability ; and it is the coordinated sum of these vitalities that
constitutes the perfect being. These are more or less distinct ; and we do not commonly
observe a sudden and simultaneous arrest of the vital properties in all the tissues, m
what we call death. For example, the nerves may die before the muscles, or the mus-

488 NUTRITION.

cles, before the nerves. It is also found that vital properties, apparently lost or destroyed,
may be made to return ; as in resuscitation after asphyxia, or in the restoration of mus-
cular or nervous irritability by injection of blood.

The life of a fecundated ovum is the property which enables it to undergo a certain
development when placed under favorable conditions; and, by the surrounding condi-
tions, its development may be arrested, suspended, or modified. The life of a non-fecun-
dated ovum is like that of any ordinary anatomical element.

The life of an anatomical element or tissue in process of development is the property
by virtue of which it arrives at its perfection of organization and performs certain
defined functions, as far as its organization will permit. This can also be destroyed,
suspended, or modified by surrounding conditions.

The life of a perfect anatomical element or tissue is the property which enables it to
regenerate itself and perform its functions, subject, also, to modifications from surround-
ing conditions.

The life of a perfect animal organism is the sum of the vitalities of its constituent
parts; but a being may live with the vitality of certain parts abolished or seriously
modified, as a man exists and preserves his identity with a limb amputated. Life may
continue for a long time without consciousness, or with organs paralyzed or their func-
tion destroyed ; but certain functions, such as respiration and circulation, are indispensa-
ble to the nutrition of all parts, and the vitality of the different tissues is speedily lost
when these processes are arrested, and the being then ceases to exist.

These considerations make it evident that it is difficult, if not impossible, to give a
single, comprehensive definition of life, a study of the varied phenomena of which con-
stitutes the science of physiology.

The general process of nutrition begins with the introduction of matter from with-
out, called food. It is carried on by the appropriation of this matter by the organ-
ism. It is attended with the production of excrementitious principles and the develop-
ment of certain phenomena that we have not yet studied, the most important of which is
the production of heat. We shall have little to say about food, beyond what we have
already considered under the head of alimentation, except to classify the alimentary
principles with reference to their relations to the general process of nutrition.

Principles which pass through the Organism.

All of the inorganic principles taken in with the food pass out of the organism, gen-
erally in the form in which they enter, in the fa3ces, urine, and perspiration ; but it must
not be inferred from this fact that they are not useful as constituent parts of the body.
Some of these principles, such as water and the chlorides, have very important functions
of a purely physical nature. It is necessary, for example, that the blood should contain
a certain proportion of the chloride of sodium, this substance modifying and regulating
the processes of absorption and probably of assimilation. In addition, however, we find
the chlorides as constituent parts of every tissue and organ of the body, and they are so
closely united with the nitrogenized principles that they cannot be completely separated
without incineration. Those inorganic matters, the function of which is so marked in their
passage through the body, are found largely as constituents of the fluids and are less
abundant in the solids. They are contained in quantity, also, in the liquid excretions ;
and any excess over the amount actually required by the system is thrown off in this
way. Other inorganic matters are especially important as constituent parts of the tissues,
and they are more abundant in the solids than in the fluids. Examples of principles of
this class are the salts of lime, particularly the phosphates. These are also in a condition
of intimate union with organic matter, and they accompany these principles in all of their
so-called vital acts.

If we except certain simple chemical changes, such as the decomposition of the bicar-

INORGANIC PRINCIPLES. 439

bonates, the inorganic elements of food do not necessarily undergo any modification in
the process of digestion. They are generally introduced already in combination with
organic matter, and they accompany it in the changes which it passes through in digestion,
assimilation by the blood, deposition in the tissues, and the final transformations that
result in the various excrementitious matters ; so that we find the inorganic principles
united with the organic matter of the food as it enters the body, and what seem to be
the same principles in connection with the organic excrementitious matters. Between
these two extremes, however, are the various operations of assimilation and disassimila-
tion, from which inorganic matter is never absent. As we have not yet taken up fully
the connection of the various inorganic matters with nutrition, it will be convenient here
to give a brief review of the different individual principles of this class.

Inorganic Principles.

The number of these principles now well established as existing in the human body
is about twenty-one. All substances which at any time exist in the body are proximate
principles ; but some are found in small quantities, are not always present, and apparent-
ly have no very important function. These will be passed over rapidly, as well as
those which are so intimately connected with some important function as to render their
full consideration in connection with that function indispensable. The following is a
list of the most important inorganic principles, excluding those which are excrementi-
tious and one or two which are not yet well established :

Table of Inorganic Principles.

Proximate Principles. Where found.

I Oxygen. Lungs and blood.

Hydrogen. Gases of stomach and colon, and blood.

Nitrogen. Lungs, intestinal gases, and blood.

Carburetted hydrogen. Lungs (expired air), intestines.

Sulphuretted hydrogen. Lungs (expired air), intestines.

Water. Universal.

Chloride of sodium. Universal, except the enamel.

Chloride of potassium. Muscles, liver, milk, chyle, blood, mucus, saliva, bile, gas-
tric juice, cephalo-rachidian fluid, and urine.

Phosphate of lime (basic). Universal.

Carbonate of lime. Bones, teeth, cartilage, internal ear, blood, sebaceous mat-
ter, and sometimes the urine.

Carbonate of soda. Blood, bone, saliva, lymph, cephalo-rachidian fluid, and

urine.

Carbonate of potassa. Blood, bone, lymph, and urine.

Phosphate of magnesia. Universal.

Phosphate of soda (neutral). Universal.

Phosphate of potassa. Universal.

Sulphate of soda. Universal, except milk, bile, and gastric juice.

Sulphate of potassa. Same as sulphate of soda.

Sulphate of lime. Blood and faeces.

Hydrochlorate of ammonia. Gastric juice, saliva, tears, and urine.

Carbonate of magnesia. A trace in the blood and sebaceous matter.

Bicarbonate of soda. Blood (Liebig).

Gases.— The gases (oxygen, hydrogen, nitrogen, carburetted hydrogen, and sulphuretted
hydrogen) exist both in a gaseous state and in solution in some of the fluids of the body.
Oxygen plays a most important part in the function of respiration ; but the office of the

490 NUTRITION.

other gases is by no means so essential. Nitrogen seems to be formed by the system in
small quantity and is taken up by the blood and exhaled by the lungs, except during inani-
tion, when the blood absorbs a little from the inspired air. It exists in greatest quantity
m the intestinal canal. Oarburetted and sulphuretted hydrogen, with pure hydrogen,
are found in minute quantities in the expired air and are also found in a gaseous state in
the alimentary canal. From the offensive nature of the contents of the large intestine,
we should suspect the presence of sulphuretted hydrogen in considerable quantity; but
actual analysis has shown that the gas contained in the stomach and intestines, large as
well as small, is composed chiefly of nitrogen, with hydrogen and carburetted hydrogen
in about equal proportions (five to eleven parts per hundred), and but a trace of sulphu-
retted hydrogen. With the exception, then, of oxygen and carbonic acid, the latter being
an excretion, the gases do not hold an important place among the proximate principles.
At all events, their function, whether it be important or not, is but little understood.

Water. — This principle exists in all parts of the body ; in the fluids, some of which,
as the lachrymal fluid and perspiration, contain little else, and in the hardest structures,
as the bones and the enamel of the teeth. In the solids and semisolids it does not exist as
water, but it enters into their structure, assuming the consistence by which the tissues are
characterized. For example, we have water in the bones, teeth, and even in the enamel,
not contained in the interstices of their structure as in a sponge, but incorporated into
the substance of the tissue. In these situations, it is essentially water of composition.
During the process of nutrition, water is deposited in the tissues with the other nutritive
principles, as we have it incorporated in the substance of certain inorganic compounds in
the process of crystallization, when it is known in chemistry as water of crystallization.
In the interior of the body, water is thus incorporated in the substance of organic mat-
ters, which are of indefinite chemical composition and non-crystallizable, and the water
enters into their composition, within certain limits, in indefinite proportions, assuming
the consistence of the organic substance. As physiologists, studying the organism not
from a purely chemical point of view, we must consider water as an integral constituent
of the tissues and not as merely absorbed by them.

All the organized structures contain a certain proportion of water, and this is neces-
sary to the performance of all or any of their functions. If a normal muscle be consid-
ered as a contracting organ, and a nerve, as a conducting organ, or albumen, as a nutri-
tious element, we must consider water as one of their constituents. It is necessary to
the proper form, consistence, and function of these and of all organized structures. In
analyses of organic matters, when water is lost or driven off in our manipulations, the
principle is not brought near a state of chemical purity, but it is essentially and radically
changed.

The quantity of water which each organic substance contains is important ; and it is
provided that this quantity, though indefinite, shall not exceed or fall below certain lim-
its. The truth of this proposition is made evident from the following facts : In the first
place, all organs and tissues must contain a tolerably definite quantity of water to give
them proper consistence. The evils of too great a proportion of water in the system,
and consequently a diminution of solid elements, are well known to the practical physi-
cian. General muscular debility, loss of appetite, dropsies, and various other indications
of imperfect nutrition, are among the results of such a condition ; while a deficiency of
Avater is immediately made known by the sensation of thirst, which leads to its introduc-
tion from without.

The fact that water never exists in any of the fluids, semisolids, or solids, without
being combined with inorganic salts, and especially chloride of sodium, is one reason why
its proportion in various situations is to a certain extent constant. The presence of these
salts influences, in the semisolids at least, the quantity of water entering into their com-
position, and consequently it regulates their consistence. A very simple experiment shows

INORGANIC PRINCIPLES.

491

this with reference to the chloride of sodium. If a piece of muscle be placed in a strong
solution of common salt, as in salting meat, it becomes harder and loses a portion of its
water of composition ; but, if it be exposed to the action of pure water, it absorbs a cer-
tain quantity and becomes softer. The nutrient fluid of the muscles during life contains
water with just enough saline matter to preserve the normal consistence of the parts.
This action of saline matters is even more apparent in the case of the blood-corpuscles.
If pure water be added to the blood, these bodies swell up and are finally dissolved ;
while, if we add a strong solution of salt, they lose water and become shrunken and cor-
rugated. Their natural form and consistence can be restored, however, even after they
have been completely dried, by adding water containing about the proportion of salt
which exists in the blood-plasma. It seems clear, then, that water is a necessary ele-
ment of all tissues and is especially important to the proper constitution of organic m'tro-
genized substances ; that it enters into the constitution of these substances, not as pure
water, but always in connection with certain inorganic salts ; that its proportion is con-
fined within certain limits ; and that the quantity in which it exists, in organic nitrogen-
ized substances particularly, is regulated by the quantity of salts which enter, with it,
into the constitution of these substances.

The quantities of water which can be driven off by a moderate temperature (212°
Fahr.) from the different fluids and tissues of the body vary of course very consider-
ably, according to the consistence of the parts. The following is a list of the quantities
in the most important fluids and solids :

Table of Quantities of Water.

Parts per 1,000.

In Enamel of the teeth 2

" Epithelial desquamation 37

" Teeth 100

" Bones 130

" Tendons (Burdach) 500

12 ] " Articular cartilages 550

" Skin (Weinholt) 575

" Liver (Frommherz and Gugert) 618

" Muscles of man (Bibra) ; 725

" Ligaments (Chevreul) 768

" Mean of blood of man (Becquerel and Rodier) 780

" Milk of human female (Simon) 887

" Chyle of man (Rees) 904

" Biie 905

" Urine 933

" Human lymph (Tiedemann and Gmelin) 960

" Human saliva (Mitscherlich) 983

" Gastric juice 984

" Perspiration 986

" Tears 990

" Pulmonary vapor 997

Function of Water. — After what has been stated respecting the condition in which
water exists in the body, there remains but little to say concerning its function. As a
constituent of organized tissues, it gives to cartilage its elasticity, to tendons their plia-
bility and toughness; it is necessary to the peculiar power of resistance of the bones;
and, as we have already seen, it is essential to the proper consistence of all parts of the
body. It has other important functions as a solvent. Soluble articles of food are intro-
duced in solution in water. The excrementitious matters, which are generally soluble in
water, are dissolved by it in the blood, are carried to the organs of excretion, and are dis-
charged in a watery solution from the body.

492 NUTRITION.

Origin and Discharge of Water. — It is evident that a great proportion of the water in
the organism is introduced from without, in the fluids and in the watery constituents of
all kinds of food ; hut the views of some physiologists with regard to the action of oxy-
gen upon the hydro-carbons in the organism have led to the supposition that water is
also formed in the body by a direct union of oxygen and hydrogen. The true way of
determining thio point is to estimate all the water introduced into the organism and to
compare this quantity with that which is discharged. In 1878, we instituted a series of
observations bearing upon this point, which will be considered again in connection with
animal heat. In one set of experiments, no food was taken for thirty-three and a quarter
hours. The observations were begun nine and a quarter hours after the last meal and
were continued for twenty-four hours. During the twenty-four hours, there was a loss
of weight of 56 ounces; the water taken was 20 ounces; the urine was collected and
analyzed, and the quantity of carbon eliminated in the form of carbonic acid was esti-
mated from standard authorities. An estimate of the heat-value of the urinary nitrogen
and of the carbon discharged, compared with an estimate of the total heat produced by
the body in the twenty-four hours, showed a deficiency in the former of more than one-
third. This result rendered it probable that heat had been generated in the body by a
direct union of oxygen and hydrogen. In another set of experiments, made some years
before, the water of the food and drink and the water discharged from the body were
carefully estimated for five days, and the subject of the experiment was weighed at the
beginning and at the close of the observations. The result showed a probable daily
excess of water discharged over the water ingested of about 12£ ounces. In the discharge
of water by the kidneys and skin, it has long been observed that, in point of activity,
these two emunctories bear a certain relation to each other. When the skin is inactive,
as in cold weather, the kidneys discharge a large quantity of water; and when the skin
is active, the quantity of water discharged by the kidneys is diminished.

Chloride of Sodium. — Chloride of sodium is next in importance, as an inorganic
proximate principle, to water. It is found in the body at all periods of life, existing
even in the ovum. It exists in all the fluids and solids of the body, with the single ex-
ception of the enamel of the teeth. The exact quantity of chloride of sodium in the
entire body has never been ascertained ; nor, indeed, has any accurate estimate been
made of the quantity contained in the various tissues, for all the chlorides are generally
estimated together. It exists in greatest proportion in the fluids, giving to some of them,
as the tears and perspiration, a distinctly saline taste. The following table gives the
quantities found in some of the most important of the fluids and solids :

Table of Quantities of Chloride of Sodium.

Parts per 1,000.

In Blood, human (Lehmann) 4-210

" Chyle (Lehmann) 5-310

" Lymph (Nasse) 4-120

" Milk, human (Lehmann) 0'870

" Saliva, human (Lehmann) 1 '530

" Perspiration, human (mean of three analyses, Piutti) 3'433

" Urine (maximum) } C 7'280

" " (mean) > Valentin. •< 4-610

" " (minimum)) ( 2'400

" Faecal matters (Berzelius) 3-010

Function of Chloride of Sodium. — The function of this principle is undoubtedly im-
portant, but it is not yet fully understood. It does not seem to enter into the substance
of the organized solids and semisolids as an important and essential element, but apparent-

INORGANIC PRINCIPLES. 493

ly it exercises its chief function in the fluids. It certainly determines, to a great extent,
the quantities of exudations, regulates absorption, and serves to maintain the albuminoids,
especially those contained in the blood, in a state of fluidity. Albumen is coagulated by
heat with much greater difficulty in a solution of chloride of sodium than when mixed
with pure water. A strong solution of common salt is capable of dissolving caseine or
of preventing the formation of fibrin. We have already alluded to the fact that it is
the chloride of sodium particularly which regulates the quantity of water entering into
the composition of the blood-corpuscles, thereby preserving their form and consistence ;
and that it seems to perform an analogous function with regard to the other semi-
solids of the body. As to the general function of this substance, the following proposi-
tion of Liebig is adopted by Robin and Verdeil, and a little reflection will show that it
is sustained, as far as we know, by the facts :

" Common salt is intermediate in certain general processes, and does not participate
by its elements in the formation of organs."

In the first place, the fluids of the body are generally intermediate in their functions,
containing nutritious elements, which are destined to be appropriated by the tissues and
organs, and worn-out elements, which are to be separated from the body. In the blood
and chyle, chloride of sodium is found in greatest abundance. As the nutrition of organs
occurs, which consists in the fixation of new proximate principles, chloride of sodium is
not deposited in any considerably quantity, but it seems to regulate the general process, at
least to a certain extent. In all civilized countries, salt is used extensively as a condi-
ment, and it undoubtedly facilitates digestion by rendering the food more savory and
increasing the flow of the digestive fluids ; here, likewise, acting simply as an interme-
diate agent. There is nothing more general among men and animals than this desire for
common salt. The carnivora crave it and obtain it in the blood of animals ; the her-
bivora frequent " salt licks " and places where it is found, and relish it when mixed with
their food ; and by man its use is almost universal. In the domestic herbivora, the
effect of a deprivation of this article is very marked and has been made the subject of
some very interesting experiments, by Boussingault. This observer experimented upon
two lots of bullocks, of three each, all of them, at the time the observations were com-
menced, being perfectly healthy and in fine condition. One of these lots he deprived
entirely of salt, except what was contained in their fodder, while the other was sup-
plied with the usual quantity. No marked difference in the two lots was noticed until
between five and six months, when the difference in general appearance was very distinct.
The animals receiving salt retained their fine appearance, while the others, though not
diminished in flesh, were not so sleek and fine. At the end of a year the difference was
very marked. The hides of those which had been deprived of salt were rough and ragged,
and their appearance, listless and inanimate, contrasting strongly with the sleek appearance
and vivacious disposition of the others. The experiments of Boussingault are the most
conclusive that have ever been instituted with regard to the influence of chloride of sodium
upon nutrition. They indicate a certain deficiency in the nutrition of animals deprived
of it, but not any considerable loss of weight. Before these observations were made,
Dailly made analogous experiments upon twenty sheep, which were continued for three
months. At the end of that time, the lot which received salt presented a considerable
excess of weight (about 22f Ibs.) over the others.

It is a significant fact that the quantity of chloride of sodium existing in the
blood is not subject to variation, but that an excess introduced with the food is thrown
off by the kidneys. The quantity in the urine, then, bears a relation to the amounf
introduced as food, but the proportion in the blood is constant. This is anothei
fact in favor of the view that the presence of a definite quantity of common salt in
the circulating fluid is essential to the proper performance of the general function of
nutrition.

Origin and Discharge of Chloride of Sodium.— This substance is always introduced

494 NUTRITION.

with food in the condition in which it is found in the body. It is contained in the sub-
stance of all kinds of food, animal and vegetable ; but, in the herbivora and in man, this
source is not sufficient to supply the wants of the system, and it is introduced, therefore,
as salt. The quantity which is discharged from the body has been estimated by Barral
to be somewhat less than the quantity introduced, about one-fifth disappearing ; but
these estimates are not exactly accurate, for the amount thrown off* in the perspiration has
never been directly ascertained. It exists in the blood in connection with the phosphate
of potassa, and a certain amount is lost in a double decomposition which takes place
between these two salts, resulting in the formation of chloride of potassium and phos-
phate of soda. It also is supposed to furnish the soda to all the salts which have a soda
base, and a certain quantity, therefore, disappears in this way.

Existing, as it does, in all the solids and fluids of the body, chloride of sodium is
discharged in all the excretions, being thrown off in the urine, faeces, perspiration,
and mucus.

Chloride of Potassium. — Chloride of potassium, although neither so important a proxi-
mate principle as the chloride of sodium nor so generally distributed in the economy,
seems to have an analogous function. It is found in the muscles, liver, milk, chyle, blood,
mucus, saliva, bile, gastric juice, cephalo-rachidian fluid, and urine. It is exceedingly
soluble, and in these situations it exists in solution in the fluids. Its quantity in these
situations has not been accurately ascertained, as it has generally been estimated in
connection with the chloride of sodium. In the muscles, it exists, however, in a larger
proportion than common salt. In cow's milk, Berzelius has found 1'7 part per 1,000;
Pfaff and Schwartz, 1-35 per 1,000 in cow's milk, and 0'3 per 1,000 in human milk.
Of the function of this principle, little remains to be said after what has been stated
with regard to the chloride of sodium. The functions of these two principles are prob-
ably identical, although the latter, from its greater quantity in the fluids and its univer-
sal distribution, is by far the more important.

Origin and Discharge of Chloride of Potassium. — This substance has two sources ;
one in the food, existing, as it does, in muscular tissue, milk, etc., and the other in a
chemical reaction between the phosphate of potassa and the chloride of sodium, forming
the chloride of potassium and the phosphate of soda. That this decomposition takes
place in the body, is evident from the fact that the ingestion of a considerable quantity
of common salt has been found, in the sheep, to increase the quantity of chloride
of potassium in the urine, without having any influence upon the amount of chloride
of sodium. The chloride of potassium is discharged from the body in the urine and
mucus.

Phosphate of Lime.— This salt is found in all the solids and fluids of the body. As it
is always united, in the solids, with organic substances as an important element of consti-
tution, it is hardly second in importance to water. It differs in its functions so essen-
tially from the chlorides of sodium and potassium, that they are hardly to be compared.
It is insoluble in water, but is held in solution in the fluids of the body by virtue of free
carbonic acid, the bicarbonate^, and the chloride of sodium. In the solids and semi'
solids, the condition of its existence is the same as that of water ; i. e. it is incorporated,
particle to particle, with the organic substance characteristic of the tissue and is one
of its essential elements of composition, and cannot be completely separated without
incineration. Nothing need be added here with regard to this mode of union in the
body of organic and inorganic substances, after what has been said under the head of
water.

The following table gives the relative quantities of phosphate of lime in various situa-
tions :

INORGANIC PRINCIPLES. 495

Table of Quantities of Phosphate of Lime.

Parts per 1,000.

In Arterial blood, )p}aleandMarcha]< 0-79

" Venous blood, f ( 0'76

" Milk, human (Pfaff and Schwartz) 2*50

" Saliva (Wright) 0-60

" Urine, proportion to weight of ash (Fleitmann) 25'70

" Excrements (Berzelius) 40'00

" Bone (Lassaigne) 400-00

" Vertebra of a rachitic patient (Bostock) 136-00

" Teeth of an infant one day old -\ r 510-00

" Teeth of adult I . I 610-00

"Teeth, at eighty-one years.. | ] 660-00

" Enamel of the teeth J I 885*00

By this table it is seen that the phosphate of lime exists in very small quantity in the
fluids but is abundant in the solids. In the latter, the quantity is in proportion to the
hardness of the structure, the quantity in enamel being, for example, more than twice
that in bone. The variations in quantity with age are very considerable. In the teeth
of an infant one day old, Lassaigne found 510 parts per 1,000 ; in the teeth of an adult,
610 parts; and in the teeth of an old man of eighty-one years, 660 parts. This increase
in the calcareous elements of the bones, teeth, etc., in old age is very marked ; and in
extreme old age they are deposited in considerable quantity in situations where there
existed but a small proportion in adult life. The system seems to gradually lose the
property of appropriating to itself organic matters ; and, although articles of food are
digested as well as ever, the power of assimilation by the tissues is diminished. The bones
become brittle, and fractures, therefore, are common at this period of life, when disloca-
tions are almost unknown. Inasmuch as the real efficiency of organs depends upon organic
matters, the system actually wears out, and this progressive change finally unfits the
various parts for the performance of their functions. An individual, if he escape acci-
dents and die, as we term it, of old age, passes away thus by a simple wearing out of his
organism.

Function of Phosphate of Lime. — This substance, as before remarked, enters largely
into the constitution of the solids of the body. In the bones its function is most appar-
ent. Its existence, in suitable proportion, is necessary to the mechanical office of these
parts, giving them their power of resistance, without rendering them too brittle. It is
more abundant in the bones of the lower extremities, which have to sustain the weight
of the body, than in those of the upper extremities ; and in the ribs, which are elastic
rather than resisting, it exists in less quantity than in the bones of the arm.

The necessity of a proper proportion of phosphate of lime in the bones is made evi-
dent by cases of disease. In rachitis, where, as is seen by the table, its quantity is very
much diminished, the bones are unable to sustain the weight of the body, and they become
deformed ; and finally, when the phosphate of lime is deposited, they retain their distorted
shape. The phosphate of lime may be extracted from the bones by maceration in dilute
hydrochloric acid, which dissolves it, leaving only the organic substance. Bones treated
in this way, although they retain their form, become very pliable ; and a long slender
bone, like the fibula, may be actually tied into a knot.

Origin and Discharge of Phosphate of Lime. — The origin of this principle is exclu-
sively from the external world. It enters into the constitution of our food and is dis-
charged in the faeces, urine, and other matters thrown off by the body. Its quantity
in the urine is exceedingly variable. Lecann found from 0'437 to 29-250 grains thrown
off by the kidneys during the twenty-four hours.

Carbonate of Lime. — This principle exists in the bones, teeth, cartilage, internal ear,

496 NUTRITION.

blood, sebaceous matter, and sometimes in the urine. It exists as a normal constituent in
the urine of some herbivora, but not in the carnivora or in man. It is most appro-
priately considered immediately after the phosphate of lime, because it is the salt next
in importance in the constitution of the bones and teeth. In these structures it exists
intimately combined with the organic matter, under the same conditions as the phos-
phates, and it has analogous functions. In the fluids it exists in small quantity and is held
in solution by virtue of free carbonic acid and the chloride of potassium.

The carbonate of lime is the only example of an inorganic proximate principle exist-
ing uncombined and in a crystalline form in the body. In the internal ear it is found in
this form and has some function connected with audition.

Table of Quantities of Carbonate of Lime.

Parts per 1,000.

In Bone, human (Berzelius). 1 13'00

" " " (Marchand) 102-00

" " " (Lassaigne) 76'00

" Teeth of an infant one day old \ ( 140'00

" Teeth of an adult V Lassaigne < 100-00

" Teeth of an old man, eighty-one years i ' lO'OO

" Urine of the horse (Boussingault) 10*82

Origin and Discharge of Carbonate of Lime. — Carbonate of lime is introduced into
the body with our food, held in solution in water by the carbonic acid which is always
present in small quantity. It is also formed in the body, particularly in the herbivora,
by a decomposition of the tartrates, malates, citrates, and acetates of lime contained in
the food. These salts, meeting with carbonic acid, are decomposed, and the carbonate
of lime is formed. It is probable that, in the human subject, some of it is changed into
the phosphate of lime, and in this form is discharged in the urine ; but when and how
this change takes place has not been definitely ascertained.

Carbonate of Soda. — This salt is found in the blood and saliva, giving to these fluids
their alkalinity ; in the urine of the human subject, when it is alkaline without being
ammoniacal ; in the urine of the herbivora ; and in the lymph, cephalo-rachidian fluid, and
in bone. The analyses of chemists with regard to this substance are very contradictory, on
account of its formation during the process of incineration ; but there is no doubt that it
is found in the above situations. The following table gives the quantities which have
been found in some of the fluids and solids :

Table of Quantities of Carbonate of Soda.

Parts per 1,000.

In Blood of the ox (Marcet) 1'62

" Lymph (Nasse) 0'56

" Cephalo-rachidian fluid (Lassaigne) 0'60

" Compact tissue of the tibia in a male of 38 years (Valentin) 2*00

" Spongy tissue of the same (Valentin) 0-70

Function of Carbonate of Soda. — This substance has a tendency to maintain the
fluidity of the albuminoid constituents of the blood, and it assists in preserving the form
and consistence of the blood-corpuscles. Its function in nutrition is rather accessory,
like that of chloride of sodium, than essential, like the phosphate of lime, in the con-
stitution of certain structures.

Origin and Discharge of Carbonate of Soda. — This substance is not introduced into
the body as carbonate of soda, but it is formed, as is the carbonate of lime in part, by a
decomposition of the malates, tartrates, etc., which exist in fruits. It is discharged occa-
sionally in the urine of the human subject, and a great part of it is decomposed hi the

INORGANIC PRINCIPLES. 497

lungs by the action of pneumic acid, setting free carbonic acid, which is discharged in
the expired air.

Carbonate of Potassa. — This salt exists particularly in herbivorous animals. It is
found in the human subject when subjected to a vegetable diet. Under the heads of func-
tion, origin, and discharge, what has been said with regard to the carbonate of soda will
apply to the carbonate of potassa.

Carbonate of Magnesia . and Bicarbonate of Soda. — It is most convenient to take up
these two salts in connection with the other carbonates, though they are put at the end
of the list of inorganic substances as the least important. We know very little about
them, chemically or physiologically. Traces of carbonate of magnesia have been found
in the blood of man, and it exists normally in considerable quantity in the urine of
herbivora. In the human subject it is discharged in the sebaceous matter.

Liebig has merely indicated the presence of bicarbonate of soda in the blood.

Phosphate of Magnesia, Phosphate of Soda (neutral), and Phosphate of Potassa. — These
salts are found in all the fluids and solids of the body, though not existing in a very large
proportion, as compared with the phosphate of lime, which we have already considered.
In their relations to organized structures, they are analogous to the phosphate of lime,
entering into the composition of the tissues, and existing there in a state of intimate
combination. They are all taken into the body with food, especially by the carnivora, in
the fluids of which they are found in much greater abundance than the carbonates;
which latter, as we have already seen, are in great part the result of the decomposition
by carbonic acid of the malates, tartrates, oxalates, etc. With respect to their functions,
we can only say that, with the phosphate of lime, they go to form the organized struct-
ures of which they are necessary constituents. They are discharged from the body in
the urine and faeces.

Sulphate of Soda, Sulphate of Potassa, and Sulphate of Lime. — The sulphate of soda
and the sulphate of potassa are identical in their situation, and apparently in their func-
tions. They are found in all the fluids and solids of the body, except in the milk, bile, and
gastric juice. Their origin in the body is from the food, in which they are contained in
small quantity, and they are discharged in the urine. Their chief function appears to be
in the blood, where they tend to preserve the fluidity of the albuminoid matters and the
form and consistence of the blood-corpuscles. The sulphate of lime is found in the blood
and faeces. It is introduced into the body in solution in the water which is used as drink,
and it is discharged in the faeces. Its function is not understood and is probably not very
important.

Hydrochlorate of Ammonia. — This substance has simply been indicated by chemists
as existing in the gastric juice of ruminants, the saliva, tears, and urine. Some chemists
make a rearrangement of its atoms, calling it chloride of ammonium; It is discharged in
the urine, in which it exists, according to Simon, in the proportion of 0'41 part per 1,000.
Its origin and function are unknown. Various combinations of bases with organic acids
taken as food, as the acetates, tartrates, etc., found in fruits, undergo decomposition in
the body and are transformed into carbonates. In this form they behave precisely like
the other inorganic salts.

Principles consumed by the Organism.

All of the assimilable organic matter taken as food is consumed in the organism, and
none is ever discharged from the body, in health, in the form under which it was intro-
duced. The principles thus consumed in nutrition have been divided into nitrogenized
32

498 NOTETTIOH.

and non-nitrogenized ; and, although they both disappear in the organism, they possess
certain marked differences in their properties, and probably, also, in their relations to
nutrition.

Nitrogenized Principles. — The nitrogenized principles, having for their basis, carbon,
hydrogen, nitrogen, and oxygen, undergo, in the process of digestion and absorp-
tion, remarkable changes ; but these are more marked as regards their properties than
their ultimate chemical composition. They are all converted into the nitrogenized ele-
ments of the blood, which, in their turn, are transformed into the characteristic nitro-
genized principles of the different tissues, and are appropriated by these tissues, to sup-
ply the place of worn-out matter. With the intimate nature of this series of transfor-
mations, we are entirely unacquainted ; but we know that the deposition of new
nitrogenized matter in the tissues, constituting one of the most important of the acts of
nutrition, is attended with a corresponding loss of matter that has become changed into
the nitrogenized elements of excretion. It is the intermediate series of phenomena that
is so obscure.

The nutrition of the nitrogenized elements of the tissues may be greatly modified by
the supply of new matter. For example, a diet composed of niti ogenized matter in a
readily assimilable form will undoubtedly affect favorably the development of the corre-
sponding tissues of the body ; and, on the other hand, a deficiency in the supply will pro-
duce a corresponding diminution in power and development. The modifications in nutri-
tion due to supply have, however, certain well-defined limits. An excess taken as food
is not discharged in the fasces, nor does it pass out in the form in which it entered, in
the urine ; but it apparently undergoes digestion, becomes absorbed by the blood, and
increases the quantity of nitrogenized excrementitious matter discharged, particularly
the urea. This fact is shown by the great increase in the elimination of urea produced
by an excess of nitrogenized food. "Whether the nitrogenized matter that is not actually
needed in nutrition be changed into urea in the blood, or whether it be appropriated by
the tissues, increasing the activity of their disassimilation, is a question difficult to deter-
mine experimentally. Certain it is, however, that an excess of nitrogenized food is
thrown off in nearly the same way as an excess of inorganic matter; the difference being
that the latter passes out in the form in which it has entered, and the former is discharged
in the form of nitrogenized excrementitious matter.

Development of Power and Endurance ly Exercise and Diet (Training). — The nutrition
of the nitrogenized elements of the body is greatly influenced by functional exercise.
This is partly local and partly general in its effects. For example, by the persistent
exercise of particular muscles, their development can be carried to a high degree of per-
fection, the rest of the muscular system undergoing no change ; or the entire muscular
system may, by appropriate general exercise, be made to increase considerably in volume,
and a person may become capable of great endurance, under an ordinary diet. It is sur-
prising, sometimes, to see how" small an amount of well-regulated exercise will accomplish
this end. But, if it be desired to attain the maximum of strength and endurance, it is
necessary to carefully regulate the diet as well as the exercise. Those who are in the
habit of "training" men, particularly for pugilistic encounters, have long-since demon-
strated practically certain facts which physiologists have been rather slow to appreciate.
By carefully regulating the diet, confining it chiefly to nitrogenized articles, eliminating
fat entirely, and reducing the starchy elements to the minimum ; by regulating the exer-
cise so as to increase the nutritive activity of all the muscles to the greatest possible
extent ; by increasing the respiratory activity by running, etc., and removing from the
body all the unnecessary adipose tissue ; by all these means, which favor nutritive assimi-
lation by the nitrogenized elements of the organism, a man may be " trained " so as to be
capable of immense muscular effort and endurance.

PRINCIPLES CONSUMED BY THE ORGANISM. 499

The process of training, skilfully carried out, is in accordance with what are now
admitted as physiological laws ; although it has been practised for years by ignorant
persons, and its rules are entirely empirical. It is stated that the athletes of ancient
times, while vigorously exercising the muscles, favored by their diet the development of
fat, so as to be better able to resist the blows of their antagonists. However this may
be, since the English prize-ring has been regularly organized, or since about the middle
of the last century, the system of training has been entirely different, and fat has been,
as far as possible, removed from every part of the body. Fat is regarded by trainers as
inert matter; and they recognize, practically at least, the fact that the characteristic
functions of parts depend for their activity upon their nitrogenized constituents. The
contraction of a muscle, for example, is powerful in proportion to the amount and condi-
tion of its -musculine ; and it has been ascertained by experience that the muscular sys-
tem can be most thoroughly developed by carefully-graduated exercise and a diet com-
posed largely of nitrogenized matter. In the regular system of training, starch, sugar, fat,
and liquids are avoided ; and the diet is confined almost entirely to rare meats, eggs, and
stale bread or toast, with oatmeal-gruel. The oatmeal has been used from time immemo-
rial, and it is supposed to be useful in keeping the bowels in good condition. A very
small amount of alcohol and of other nervous stimulants, chiefly in the form of home-
brewed ale, sherry wine, and tea, is allowed. Sexual intercourse and all unusual nervous
excitement are interdicted.

Those who adopt absolutely the classification of food into plastic, or tissue-forming,
and calorific, or respiratory, would regard this course of diet as eminently plastic ; but,
during the severe habitual exercise, which is most rigid after the man has been " trained
down " so that his fat is reduced to the minimum, the respiratory power and the exhala-
tion of carbonic acid are immensely increased, while the proportion of hydro-carbons in
the food is very small.

We do not propose to discuss from a scientific point of view all of the minutia}
of training. Many of its traditional rules are trivial and unimportant ; but it is certainly
a question of great physiological interest to study the processes by which the muscular
strength and endurance of a man may be brought to the highest possible point of
development.

One of the most remarkable of the results of thorough training is the development of
immense endurance and " wind." This is accomplished by running and prolonged exer-
cise, not so violent as to be exhausting, and always followed by ablutions and frictions,
so as to secure a full reaction. The surprising faculty of endurance thus developed must
be due in a great measure to nervous power as well as to a gradual, careful, and perfectly
physiological development of the muscular system. A man may be brought into the ring
in what would appear to be perfect condition ; but, if he be trained down too much or
too rapidly, he is liable to give out after comparatively slight exertion. A man who docs
not possess the required constitutional stamina and nervous power is likely to break down
in training, and he cannot be brought to proper condition. On the other hand, a man in
perfect condition is capable of the maximum of muscular exertion for an hour, or can
easily walk a hundred miles in a day.

It is a question of great importance, in connection with the subject of nutrition, to
determine whether the extraordinary muscular power developed by severe training be,
in the end, beneficial or deleterious. This can be answered very easily upon practical as
well as theoretical grounds. A fully-grown, well-developed man, in perfect health, may
be trained so as to be brought to what is technically called fine condition, and he will
present at that time all the animal functions in their perfection. He is then a model of a
physical man ; and the only consequences that can result from such a course are beneficial.
The argument that professional pugilists are short-lived is fallacious ; for it is well known
that almost all of them, after training for and passing through an encounter, immediately
relapse into a course of life in which all physiological laws are habitually violated.

500 NUTRITION".

During training, even of the most severe character, not only is great attention paid to
diet and exercise, but all of the functions are scrupulously watched. Tranquillity of
mind, avoidance of exhaustion, of artificial excitement, stimulants, tobacco, etc., are
strictly enjoined ; and the process is always very gradual, especially at its commencement,
and is continued for several months. The cases in which training has been followed by
bad effects are entirely different. Undeveloped boys are frequently trained for boating,
in the most reckless manner, until they break down. An attempt is made to accomplish
in a few weeks what can only be done physiologically in several months ; and the result
is, that some of the vital organs, particularly the heart, are liable to become permanently
injured. To improve the " wind " and endurance, a person undergoes the most violent
exercise, which is followed by great exhaustion, intense respiratory distress, and disturb-
ance of the action of the heart, these parts being suddenly forced far beyond their func-
tional capacity. This cannot be done without danger of permanent disturbances of the
system, such as have been frequently observed ; and it is all the more liable to be followed
by bad results, from the fact that amateurs are trained together, five or six under one
man, and are more or less independent, while the professional athlete is never out of the
sight of his trainer for months, and during that time is under complete control. There
is, it seems, every physiological reason to believe that it is beneficial to the general sys-
tem to bring it to the highest point of functional activity by training ; but, if this be not
done with great caution and judgment, it is liable to be followed by serious results.

Non-Nitrogenized Principles. — The non-nitrogenized principles present a marked
contrast to the alimentary substances we have just considered. In the first place, they
are not indispensable to the nutrition of all animals. The carnivora, for example, may be
well nourished upon a diet composed exclusively of nitrogenized matter ; and the remarks
we have just made upon training show that the human subject may be brought to a high
condition of physical development, when starch, sugar, and fat are almost entirely elimi-
nated from the food. This shows conclusively that the division of the food into plastic
and calorific elements is not absolute, and that the animal temperature may be maintained
without the hydro-carbons. The nitrogenized principles are probably the only class of
alimentary substances capable of forming muscular tissue ; but, by certain transformations,
with the exact nature of which we are imperfectly acquainted, this class of substances is
capable of producing heat and of furnishing the carbonic acid eliminated in respiration.
The non-nitrogenized principles are incapable in themselves of meeting the nutritive
demands of the system, and they are either consumed without forming part of the tis-
sues or are deposited in the form of fat. These questions we have already considered
under the head of alimentation ; and it will be remembered that, with a few exceptions,
fat always exists in the body uncombined, either in the form of adipose tissue or of fatty
granulations in the substance of other tissues.

The non-nitrogenized elements taken up by the blood may be divided into two varie-
ties : one, the sugars, composed of carbon with hydrogen and oxygen in the proportions
to form water, constituting the true hydro-carbons; and the other, the fats, in which the
hydrogen and oxygen do not exist in the proportion to form water. We speak of the sugars
only, because starch and all varieties of sugar taken as food are transformed into glucose.

In connection with the study of alimentation and glycogenesis, we have already
referred to the destination of the true hydro-carbons in the organism. They are taken
as food to a considerable extent, particularly in the form of starch, and are formed con-
stantly by the liver in all classes of animals. Sugar is never discharged from the body
in health, nor is it deposited in any part of the organism, even as a temporary condition.
It generally disappears in the passage of the blood through the lungs. In studying the
changes which sugar is capable of undergoing, it has been found that it may be converted
into lactic acid or be changed into carbonic acid and water ; but precisely to what extent
the sugars undergo these changes, or how they are acted upon by the inspired oxygen, it

PRINCIPLES CONSUMED BY THE ORGANISM. 501

has been impossible thus far to determine. "We must be content to say that the exact
changes which the sugars undergo in nutrition are unknown. They seem to be very
important in development, being abundant in the food and formed largely in the system
in early life. They certainly do not enter into the composition of the tissues ; and it
would seem that they must be important in the two remaining phenomena of nutrition,
namely, the formation of fat and the development of animal heat. The relations of sugar
to these two processes will be taken up under their appropriate heads.

The fats taken as food are either consumed in the organism or are deposited in the
form of adipose tissue. That the fats are consumed, there can be no doubt; for, in the
normal alimentation of man, fat is a constant article, and it is never discharged from the
body. We are forced to admit, however, that the changes which fat undergoes in its
process of .destruction are not thoroughly understood. All that we positively know is,
that the fatty principles of the food are formed into a fine emulsion in the small intestine,
and are taken up, chiefly by the lacteals, and discharged into the venous system. For a
time, during absorption, fat may exist in certain quantity in the blood; but it soon disap-
pears and is either destroyed directly in the circulatory system or is deposited in the
form of adipose tissue to supply a certain amount of this substance consumed. That it
may be destroyed directly is proven by the consumption of fat in instances where the
amount of adipose matter is insignificant ; and that the adipose tissue of the organism
may be consumed is shown by its rapid disappearance in starvation.

The question of the relations of fat to nutrition is important but somewhat obscure.
It does not take part in the nutrition of the parts that are endowed to an eminent
degree with the so-called vital functions ; and, when these tissues are brought to their
highest point of development, the fat is entirely removed from their substance. If
fat be not a plastic material, it would seem to have no function remaining but that of
keeping up, by its oxidation, the animal temperature. But jt is not proven that the fats, or
fats and sugar, are the sole principles concerned in the production of carbonic acid and
the generation of heat; for both of these phenomena occur in the carnivora, and in man,
when fat and sugar are eliminated from the food and the fat in the body has been
reduced to the minimum. Fat is undoubtedly destroyed in the organism, and probably
it assists in the formation of the carbonic acid eliminated ; it is also taken in much larger
proportion in cold than in temperate or warm climates; but we cannot, with our present
information, say without reserve that fats and sugar are oxidized directly, by a process
with which we are familiar under the name of combustion, and that their exclusive func-
tion is the production of animal heat.

It is a curious fact that fat is generally deposited in tissues during their retrograde
processes. The muscular fibres of the uterus, during the involution of this organ after
parturition, become the seat of a deposit of fatty granulations. Long disuse of any part
will produce such changes in its power of appropriating nitrogenized matter for its regen-
eration, that it soon becomes atrophied and altered. Instead of the normal nitrogenized
elements of the tissue, we have, under these circumstances, a deposition of fatty matter.
The fat is here inert, and it takes the place of the substance that gives to the part its char-
acteristic functions. These phenomena are strikingly apparent in muscles that have been
long disused or paralyzed and in nerves that have lost their functional activity. If the
change be not too extensive, the fat may be made to disappear, and the part will return
to its normal constitution, with appropriate exercise ; but frequently the alteration has
proceeded so far as to be irremediable and permanent.

Accurate observations have shown that, in young animals rapidly fattened, all the
adipose matter in the body cannot be accounted for by what is taken in as food; and it
is certain that fat may be produced de novo in the organism.

Formation and Deposition of Fat. — The question of the generation of fat in the econo-
my is one of great importance. "Whatever the exact nature of the changes accompanying

502 NUTRITION".

the destruction of non-nitrogenized matters may be, it is certain that the fat stored up in
the body is consumed, when there is a deficiency in any of the elements of food, as well
as that which is taken into the alimentary canal. It is rendered probable, indeed, by the
few experiments that have been made upon the subject, that obesity increases the power
of resistance to inanition. At all events, in starvation, the fatty constituents of the body
are the first to be consumed, and they almost entirely disappear before death. As we
have already seen, sugar is never deposited in any part of the organism, and it is merely a
temporary constituent of the blood. If the sugars and fats have, in certain regards, simi-
lar functions in nutrition, and if, in addition to the mechanical functions of fat, it may
be retained in the organism for use under extraordinary conditions, it becomes very
important to ascertain the mechanism of its production and deposition.

The production of fatty matter by certain insects, in excess of the fat supplied with
the food, was established long ago by the researches of Huber ; and analogous observa-
tions have been made upon birds and mammals by Boussingault. Some of the experi-
ments of Boussingault are peculiarly interesting, as they were made upon pigs, in which
the digestive apparatus closely resembles that of the human subject. They showed con-
clusively that, under certain circumstances, more fat exists in the bodies of animals than
can be accounted for by the total amount of fat taken as food added to the fat existing
at birth. In some very interesting experiments with reference to the influence of different
kinds of food upon the development of fat, it was ascertained that fat could be produced
in animals upon a regimen, sufficiently nitrogenized, but deprived of fatty matters ; but
the fact should be recognized that " the nutriment which produces the most rapid and
pronounced fattening is precisely that which joins to the proper proportion of albuminoid
substances the greatest proportion of fatty principles."

Animals cannot be fattened without a certain variety in the regimen. We have
already discussed the necessity of a varied diet and have shown that an animal will die
of starvation when confined exclusively to one class of principles, even if this be of the
most nutritious character ; and it is not necessary to refer again to the experiments which
have demonstrated that a diet confined exclusively to starch, sugar, or fat, or even pure
albumen or fibrin, cannot sustain life, much less fatten an animal. We are prepared,
then, to understand why, in the pigs experimented upon by Boussingault, a regimen con-
fined to potatoes did not prove to be fattening, notwithstanding the large proportion of
starch, and that fat was produced in abundance only when the food presented the proper
variety of principles.

Very little is known concerning the precise mechanism of the production of fat. The
experiments of Boussingault seem to leave no doubt that it may be formed from any kind
of food, even when the alimentation is exclusively nitrogenized ; but it is, nevertheless, a
matter of common observation that certain articles of diet are more favorable to its
deposition than others ; and it is also true that the herbivora are fattened much more
readily, as a rule, than the carnivora.

Theoretical considerations would immediately point to starch and sugar as the ele-
ments of food most easily convertible into fat, as they contain the same elements, though
in different proportions ; and it is more than probable that this view is correct. It is said
that, in sugar-growing sections, during the period of grinding the cane, the laborers be-
come excessively fat, from eating large quantities of the saccharine matter. We cannot
refer to any exact scientific observations upon this point, but the fact is pretty generally
admitted by physiologists. Again, it has been frequently a matter of individual experience
that sugar and starch are favorable to the deposition of fat, especially when there is a
constitutional tendency to obesity. A most remarkable example of this, and one which
has met with considerable notoriety, is worthy of mention, though not reported by a
scientific observer. We refer to the letter on corpulence, by Mr. Banting. The writer
of this curious pamphlet, in 1862, was sixty-six years old, five feet and five inches in
height, and weighed two hundred and two pounds. Under the advice of Mr. William

PRINCIPLES CONSUMED BY THE ORGANISM. 503

Harvey, F. R. C. S., of London, he confined himself to a diet containing no sugar and as
little starch and fat as possible. Continuing this regimen for one year, he gradually lost
weight, at the rate of about one pound each week, until he was reduced to one hundred
and fifty-six pounds. At the time the last edition of the pamphlet was published, in
1864, he enjoyed perfect health and weighed one hundred and fifty pounds, his weight
varying only to the extent of one pound, more or less, in the course of a month. This
little tract is very interesting, both from the importance of its physiological deductions and
its quaint literary style. It has had an immense circulation, and many persons suffering
from excessive adipose development have adopted the system here advised, with results
more or less favorable. A study of the course of diet here prescribed shows it to be a
pretty rigid training system, with the exception of succulent vegetables and liquids,
which are allowed without restriction. It is proper to remark, however, that some
enthusiastic advocates of the plan have exceeded the limits prescribed and have neglected
the caution of the author always to employ it under the advice of a physician ; and its too
rigid enforcement has been followed by serious disturbances in general nutrition. Others,
however, have verified the favorable results obtained by Mr. Banting.

It is difficult to explain the remarkable constitutional tendency to obesity observed in
some individuals, which is very often hereditary. Such persons will become very fat
upon a comparatively low diet, while others deposit but little adipose matter, even when
the regimen is abundant. It is to be noted, however, that the former are generally
addicted to the use of starchy, saccharine, and fatty elements of food, while the latter con-
sume a greater proportion of nitrogenized matter.

It is not an uncommon remark that the habit of taking large quantities of liquids
favors the formation of fat ; but it is not easy to find any scientific basis for such an
opinion. * As to the formation of fat by any particular organ or organs in the body, no
positive scientific view has been advanced, except the proposition by Bernard, that the
liver had this function, in addition to its glycogenic office. This we have already dis-
cussed and have shown that such a function is far from being positively established.

Condition under which Fat exists in the Organism. — It is said that fat combined with
phosphorus is united with nitrogenized matter in the substance of the nervous tissue ; but
its condition here is not well understood, as we shall see when we come to treat of the
nervous system. A small quantity of fat is contained in the blood-corpuscles, and a little
is held in solution in the bile; but, with these exceptions, fat always exists in the body
isolated and uncombined with nitrogenized matter, in the form of granules or globules
and of adipose tissue. The three varieties of fat are here combined in variable propor-
tions, which is the cause of the differences in its consistence in different situations. The
ultimate elements of fat are, carbon, hydrogen, and
oxygen, the two latter in unequal proportions.

Physiological Anatomy of Adipose Tissue. — Adipose
tissue is found in abundance in the interstices of the
subcutaneous areolar tissue, where it is sometimes
known as the panniculus adiposus. It is not, how-
ever, to be confounded with the so-called cellular or ^u^_AfHpo,e ^,MM . ma(mifie(l
areolar tissue, and is simply associated with it without 350 <//</>/>< >/<'/*.

being one of its essential parts; for the areolar tissue * bnS ™at3 JiTc th?'

is abundant in certain situations, as the evelids and by which the fat is dissolved, the

empty vesicles remaining.

scrotum, where there is no adipose matter, and adipose

tissue exists sometimes, as in the marrow of the bones, without any areolar tissue.

Adipose tissue is widely distributed in the body and has important mechanical func-
tions. Its anatomical element is a vesicle, from -^ to ^7 of an inch in diameter, com-
posed of a delicate, structureless membrane, ^^ of an incn tm>ckj enclosing fluid con-

504 NUTKITION".

tents. The form of the vesicles is naturally rounded or ovoid; but in microscopical
preparations they are generally compressed so as to become irregularly polyhedrical.
The membrane sometimes presents a small nucleus attached to its inner surface. The
contents are, a minute quantity of an albuminoid fluid moistening the internal surface of
the membrane, and a mixture of oleine, margarine, and stearine, liquid at the temper-
ature of the body, but becoming harder on cooling. Little rosettes of acicular crystals of
margarine are frequently observed in the fat-vesicles at a low temperature. The amount
of fat in a man of ordinary development, according to Carpenter, equals about one-
twentieth of the weight of the body.

The adipose vesicles are collected into little lobules, from ^ to £ of an inch in diame-
ter, which are surrounded by a rather wide net-work of capillary blood-vessels. Close
examination of these vessels shows that they frequently surround individual fat-cells, in
the form of single loops. There is no distribution of nerves or lymphatics to the ele-
ments of adipose tissue. It is seen by this sketch of the structure of adipose tissue, that
there is no anatomical reason for classing these vesicles with the ductless glands, as is
done by some physiologists. They undoubtedly, under certain conditions, have the
power of filling themselves with fat ; but it would be no more appropriate to call fat
a secretion than to apply this term to the development and nutrition of the muscular
substance within the sarcolemma.

Conditions which influence Nutrition. — We know more concerning the conditions
that influence the general process of nutrition than about the nature of the process itself.
It will be seen, for example, when we come to study the nervous system, that there are
nerves which regulate, to a certain extent, the nutritive forces. We do not mean to
imply that nutrition is effected through the influence of the nerves, but it is the fact that
certain nerves, by regulating the supply of blood, and perhaps by other influences, are
capable of modifying the nutrition of parts to a very considerable extent.

In discussing the influence of exercise upon the development of parts, we have shown
that this is not only desirable but indispensable ; and the proper performance of the func-
tions of nearly all parts involves the action of the nervous system. It is true that the sep-
arate parts of the organism and the organism as a whole have a limited existence ; but it is
not true that the change of nitrogenized, living substance into effete matter, a process that
is increased in activity by physiological exercise, consumes, so to speak, a definite amount
of the limited life of the parts. Physiological exercise increases disassimilation, but it also
increases the activity of nutrition and favors development. It is a favorite sophism to
assert that bodily or mental effort is made always at the expense of a definite amount of
vitality and matter consumed. This is partly true, but mainly false. Work involves
change into effete matter ; but, when restricted within physiological limits, it engenders
a corresponding activity of nutrition, assuming, of course, that the supply from without
be sufficient. Other things being equal, a man will live longer under a system of physio-
logical exercise of every part, than if he made the least effort possible. It is, indeed,
only by such use of parts that they can undergo proper development and become the seat
of normal nutrition. But, notwithstanding all these facts, life is self-limited. Unless
subjected to some process which arrests all changes, such as cold, the action of preserva-
tive fluids, etc., organic substances are constantly undergoing transformation. In the
living body, their disassimilation and nutrition are unceasing ; and, after they are re-
moved from what are termed vital conditions, they change, first losing irritability, or
becoming incapable of performing their functions, and afterward decomposing into mat-
ters which, like the results of their disassimilation, are destined to be appropriated by
the vegetable kingdom. Nutrition sufficient to supply the physiological decay of parts
cannot continue indefinitely. The wonderful forces in the fecundated ovum lead it
through a process of development that requires, in the human subject, more than twenty
years for its completion ; and, when development ceases, no one can say why it becomes
arrested, nor can we give any sufficient reason why, with a sufficient and appropriate

PRINCIPLES CONSUMED BY THE ORGANISM. 5Q5

supply of material, a man should not grow indefinitely. After the being is fully devel-
oped, and during what is known as the adult period, the supply seems to be about equal
to the waste. But, after this, nutrition gradually becomes deficient, and the deposition of
new matter in progressive old age becomes more and more inadequate to supply the place
of the living nitrogenized substance. We may at this time, as an exception, have a con-
siderable deposition of fat, but the nitrogenized matter is always deficient, and the pro-
portion of inert, inorganic matter combined with it is increased.

There can be little if any doubt that the forces which induce the regeneration or
nutrition of parts reside in the organic nitrogenized substance, and that these give to the
parts their characteristic functions, which we call vital; the inorganic matter being
passive, or having, at the most, purely physical functions. If, therefore, as age advances,
the organic matter be gradually losing the power of completely regenerating its sub-
stance, and if its proportion be progressively diminishing while the inorganic matter is
increasing in quantity, a time will come when some of the organs necessary to life will
be unable to perform their office. When this occurs we have death from old age, or
physiological dissolution. This may be a gradual failure of the general process of nutri-
tion, or it may attack some one organ or system.

Animal Heat.

The process of nutrition in animals is always attended with the development of heat
which is more or less independent of external conditions. This is true in the lowest
as well as the highest organizations ; and analogous phenomena have even been observed
in plants. In cold-blooded animals, nutrition may be suspended by a diminished external
temperature, and certain of the functions become temporarily arrested, to be resumed
when the animal is exposed to a greater heat. This is true, to some extent, in certain
warm-blooded animals that periodically pass into a condition of stupor, called hiberna-
tion ; but in man and most warm-blooded animals, the general temperature of the body
can undergo but slight variations. The animal heat is nearly the same in cold and in
hot climates ; and if, from any cause, the body become incapable of keeping up its tem-
perature when exposed to cold, or of moderating it when exposed to heat, death is the
inevitable result. The study of the temperature in different classes of animals presents
very great interest, but the limits of a work upon human physiology restrict us to the
phenomena as observed in man and in animals in which the processes of nutrition are
essentially the same.

Estimated Quantity of Heat produced ly the Body. — As the result of experiments
made by Senator upon dogs, in. 1872, and observations made later in the same year by
Prof. J. 0. Draper, upon his own person, it may be stated, in general terms, that the body
produces about four heat-units per pound weight per hour, the heat-unit representing the
raising of one pound of water one degree Fahrenheit. According to this, a man weighing
one hundred and forty pounds would generate 13,440 heat-units in twenty-four hours.

Limits of Variation in the Normal Temperature in Man. — A great number of obser-
vations have been made upon the normal temperature in the human subject under differ-
ent conditions; but we shall cite those only in which all sources of error in thermometry
seem to have been avoided, and in which the results present noticeable peculiarities.
One of the most common methods of taking the general temperature has been to intro-
duce a delicate thermometer into the axilla, reading off the degrees after the mercury has
become absolutely stationary. Nearly all observations made in this way agree with the
results obtained by Gavarret, who estimated that the temperature in the axilla, in a per-
fectly healthy adult man, in a temperate climate, ranges between 97'7° and 99'5° Fahr.
Dr. Davy, from a large number of observations upon the temperature under the tongue,

506 NUTRITION.

fixes the standard, in a temperate climate, at 98°. When we examine the temperature of
the hlood in the deeper vessels and note the variations in different parts, we shall see
that the axilla and the tongue, being more or less exposed to external influences, do not
exactly represent the general heat of the organism ; but these are the situations, particu-
larly the axilla, in which the temperature is most frequently taken, both in physiological
and pathological examinations. As a standard for comparison, we may assume that the
most common temperature in these situations is 98°, subject to variations, within the lim-
its of health, of about 0'5° below and 1-5° above.

Variations with External Temperature. — The general temperature of the body varies,
though within very restricted limits, with extreme changes in climate. The results ob-
tained by Davy, in a large number of observations in temperate and hot climates, show
an elevation in the tropics of from 0'5° to 3°. It is well known, also, that the human
body, the surface being properly protected, is capable of enduring for some minutes a
heat much greater than that of boiling water. Under these conditions, the animal tem-
perature is raised but slightly, as compared with the intense heat of the surrounding
atmosphere. According to the observations of Dr. Dobson, the temperature was raised
to 99*5° in one instance, 101 '5° in another, and 102° in a third, when the body was ex-
posed to a heat of more than 212°. MM. Delaroche and Berger, however, found that
the temperature in the mouth could be increased by from 3° to 9°, after sixteen minutes'
exposure to intense heat. This was for the external parts only ; but it is not at all prob-
able that the temperature of the internal organs ever undergoes such wide variations.

It is very difficult to estimate the temperature in persons exposed to intense cold, as
in Arctic explorations, because the greatest care is always taken to protect the surface of
the body as completely as possible; but experiments have shown that the animal heat
may be considerably reduced, as a temporary condition, without producing death. In
the latter part of the last century, Dr. Currie caused the temperature in a man to fall
15° by immersion in a cold bath ; but he could not bring it below 83°. This extreme
depression, however, lasted only two or three minutes, and the temperature afterward
returned to within a few degrees of the normal standard. The results of experiments
show that, while the normal variations in the temperature in the human subject, even
when exposed to great climatic changes, are very slight, generally not ranging beyond
two degrees, the body may be exposed for a time to excessive heat or cold, and the ex-
treme limits, consistent with the preservation of life, may be reached. As far as has been
ascertained by direct experiment, these limits are about 83° and 107°.

Variations in Different Parts of the Body.—li is to be expected that the temperature
of the internal organs should be higher and more constant than that of parts, like the
axilla or mouth, more or less exposed to loss of heat by evaporation and contact with
the cool air ; and the differences observed in the blood in certain parts, as in the two
sides of the heart, have important bearings, as we shall hereafter show, upon the various
theories of animal heat. We shall here note the variations observed in the blood in dif-
ferent situations and confine ourselves to recent observations which have been made
with apparatus much more reliable and delicate than that which was formerly employed.

It is universally admitted that the blood becomes slightly lowered in its temperature
in passing through the general capillary circulation ; but the amount of difference is ordi-
narily not more than a fraction of a degree. This fact is not at all opposed to the prop-
osition that the animal heat is generated in greatest part in the general capillary system,
as one of the results of nutritive action ; for the blood circulates with such rapidity that
the heat acquired in the capillaries of the internal organs, where little or none is lost, is
but slightly diminished before the fluid passes into the arteries, even in circulating through
the lungs ; and cutaneous evaporation simply moderates the heat acquired in the tissues
and keeps it at the proper standard.

ANIMAL HEAT. 507

The investigations of Bernard have demonstrated that the hlood is, as a rule, from
0'36° to 1'8° warmer in the hepatic veins than in the aorta. The temperature in the he-
patic veins is from 0'18° to 1'44° higher than in the portal veins. These figures are the
result of many experiments made upon dogs. Compared with the aorta, the temperature
in the portal vein was generally found to be higher (maximum of difference, 0'9°) ; but, in
a few instances (five out of fifteen), it was a very little lower, which is explained by Ber-
nard upon the supposition that the intestinal canal is not entirely removed from external
modifying influences. These results show that the blood coming from the liver is warmer
than in any other part of the body. In a series of experiments by Breschet and Becquerel,
who were among the first to employ thermo-electric apparatus in the study of animal
heat, it was found that the cellular tissue was from 2'5° to 3'3° cooler than the muscles.

A most interesting question, in this connection, relates to the comparative tempera-
ture of the blood in the two sides of the heart. Upon this point there have been several
conflicting observations, the results favoring two opposite theories of calorification. By
some it has been thought that the blood gains heat in passing through the lungs, and this
is explained by the theory of the direct union, in these organs, of oxygen with the
hydro-carbons. Others suppose that the blood is slightly refrigerated in the air-cells.

It is evident that, when the chest is opened, the external refrigerating influences
might act differently upon the two sides of the heart, particularly as the right ventricle
is much thinner than the left. It would not be improper, indeed, to exclude all observa-
tions made in this way, and to depend entirely upon experiments in which the physiological
conditions are not so palpably violated. Magendie and Bernard introduced delicate ther-
mometers into the two sides of the heart, through the vessels in the neck, without opening
the chest. These experiments were made upon a horse, and the right heart was always
found considerably warmer than the left. Bering introduced a thermometer into the cavi-
ties of the heart in a living calf affected with cardiac ectopia. The temperature of the
right side was 102'74:0, and the left side, 101'79°. Georg von Liebig illustrated one of
the sources of error in all examinations made after opening the chest, by filling the cavi-
ties of the heart of a dog with warm water, placing the organ in a water-bath, and bring-
ing the two sides to precisely the same temperature. After five minutes' exposure to the
air, the temperature in the right ventricle was sensibly lower than in the left, whirh
was undoubtedly due to the difference in the thickness of the ventricular walls. The
observations made by Bernard upon dogs and sheep are very conclusive, as far as
these animals are concerned. In dogs he found a difference of from 0*1° to 0'2°,
always in favor of the right side; and the results in sheep were nearly the same.
These experiments are only indirectly applicable to the human subject ; and if it be
proven that, in animals, the conditions vary with " the state of the skin, the digestive
apparatus, and the muscular system " (Colin), it is impossible, in the absence of positive
demonstration, to say what change in temperature, if any, takes place in the blood in its
passage through the lungs. The only reliable observations upon this point in man are
those made by Prof. J. S. Lombard, who used a very ingenious and delicate thermo-
electric apparatus capable of indicating a difference of ^Vfr °f a degree cent. With this
instrument, he was able to determine very slight variations in the temperature of the
blood in the arterial system, by simply placing the conductors over any of the superficial
vessels, like the radial. Of course it is impossible to note the actual temperature in the
two sides of the heart in the human subject during life ; but Prof. Lombard endeavored
to arrive at the same end, by calculating that, if all the sources of refrigeration in the
lungs were artificially removed, the blood in the arteries should gain about the same
amount of heat that would be lost under ordinary conditions. To effect this object, ho
breathed air saturated with moisture and of the same temperature as the circulating
blood. " If, then, when respiration takes place under ordinary circumstances, the blood
is cooled one-third of a degree (cent.) in passing through the lungs, the temperature
nhould be raised so much ; that is to say, one-third of a degree, when we respire air at the

508 NUTRITION.

temperature of the blood and saturated with the vapor of water, all loss of heat then
being impossible." In a number of experiments performed upon this principle, Prof.
Lombard failed to observe a sufficiently marked elevation of temperature to justify the
conclusion that the blood is cooled in passing through the lungs. These experiments can-
not be so positive as those made by introducing thermometers into the heart in living ani-
mals without opening the chest or disturbing the circulation; but they are important, in
connection with such observations, as failing to prove that the blood is either cooled or
heated in the lungs. From these facts it appears that there is no positive evidence of
any change in the temperature of the blood in passing through the lungs in the human
subject. In animals there probably exist no constant differences in temperature in the
two sides of the heart. When the loss of heat by the general surface is active, as in ani-
mals with a slight covering of hair, the blood is generally cooler in the right cavities ;
but, in animals with a thick covering, that probably lose a great deal of heat by the pulmo-
nary surface, the blood is cooler upon the left side. Undoubtedly there are refrigerating
influences in the lungs, both from the low temperature of the inspired air and from evap-
oration ; but these are equalized and sometimes overcome by processes in the blood itself.

Variations at Different Periods of Life. — The most important variations in the tem-
perature of the body at different periods of life are observed in infants just after birth.
Aside from one or two observations, which are admitted to be exceptional, the body of
the infant and of young mammalia, removed from the mother, presents a diminution in
temperature of from one to four degrees. In infancy the ability to resist cold is less than
in later years ; but after a few days the temperature of the child nearly reaches the stand-
ard in the adult, and the variations produced by external conditions are not so great.

The experiments of W. F. Edwards have an important bearing upon our ideas of nu-
trition during the first periods of extra-uterine life. He found that, in certain animals,
particularly dogs and cats, that are born with the eyes closed and in which the foramen
ovale remains open for a few days, the temperature rapidly diminished when they were
removed from the bod.y of the mother, and that they then become reduced to a condition
approximating that of cold-blooded animals; but, after about fifteen days, this change in
temperature could not be effected. In dogs just born, the temperature fell after three or
four hours' separation from the mother to a point but a few degrees above that of the
surrounding atmosphere. The views advanced by Edwards are well illustrated in in-
stances of premature birth, when the animal heat is much more variable than in infants
at term, and in cases of persistence of the foramen ovale.

In adult life there does not appear to be any marked and constant variation in the
normal temperature; but, in old age, while the actual temperature of the body is not
notably reduced, the power of resisting refrigerating influences is diminished very con-
siderably. There are no positive observations showing any constant differences in the
temperature of the body in the sexes; and it may be assumed that, in the female, the
animal heat is modified by the same influences and in the same way as in the male.

Diurnal and other Variations in the Heat of the Body. — Although the limits of varia-
tion in the animal temperature are not very extended, certain fluctuations are observed,
depending upon repose or activity, digestion, sleep, etc., .which it is necessary to take
into account. These conditions, which are of a perfectly normal character, may induce
changes in the temperature amounting to from one to three degrees. It has been ascer-
tained that there are two well-marked periods in the day when the heat is at its maxi-
mum. These, according to the most recent observations in Germany, are at eleven A. M.
and four p. M. ; and it is a curious fact, that, while all observations agree upon this point,
the very elaborate experiments of Lichtenfels and Frohlich show that these periods are
well marked, even when no food is taken. Barensprung and Ladame farther show that
the fall in temperature during the night takes place sleeping or waking ; and that when

ANIMAL HEAT. 509

sleep is taken during the day it does not disturb the period of the maximum, which
occurs at about four P. M. According to these experiments, at eleven in the morning,
the animal heat is at one of its periods of maximum ; it gradually diminishes for two or
three hours and is raised again to the maximum at about four in the afternoon, when it
again undergoes diminution until the next morning. The variations amount to from
about 1° to 2- 10°. The minimum is always during the night.

The influence of defective nutrition or inanition upon the heat of the body is very
marked. John Hunter, in his experiments upon animal heat, made a few observations
upon this point and noted a decided fall in temperature in a mouse kept fasting. The
same phenomena were also observed by Collard de Martigny ; and Chossat noted the
effects of deprivation of food upon the power of maintaining the animal temperature, in
the most exact and satisfactory manner. In pigeons, the extreme diurnal variation hi
temperature, under normal conditions, was found by Chossat to be 1*3°. During the
progress of inanition, the daily variation was increased to 5'9°, with a slight diminution
in the absolute temperature, and the periods of minimum temperature were unusually
prolonged. Immediately preceding death from starvation, the diminution in temperature
became very rapid, the rate being from 7° to 11° per hour. Death usually occurred when
the diminution had amounted to about 30°.

When tiie surrounding conditions call for the development of an unusual amount of
heat, the diet is always modified, both as regards the quantity and kind of food; but
when food is taken in sufficient quantity and is of a kind capable of maintaining proper
nutrition, its composition does not affect the general temperature. The temperature
of the body, indeed, seems to be uniform in the same climate, even in persons living
upon entirely different kinds of food. The observations of Dr. Davy are very conclu-
sive upon this point: "The similarity of temperature in different races of men is the
more remarkable, since between several of them whose temperatures agreed, there was
nothing in common but the air they breathed — some feeding on animal food almost
entirely, as the Vaida — others chiefly on vegetable diet, as the priests of Boodho— and
others, as Europeans and Africans, on neither exclusively, but on a mixture of both."
Nevertheless, the conditions of external temperature have a remarkable influence upon
the diet. It is well known that, in the heat of summer, the amount of meats and fat
taken is relatively small, and of the succulent fresh vegetables and fruits, large, as com-
pared with the diet in the winter. But although the proportion of starchy matters
in many of the fresh vegetables used during a short season of the year is not great, these
articles are equally deficient in nitrogenized matter. During the winter, the ordinary
diet, composed of meat, fat, bread, potatoes, etc., contains a large amount of nitrogenized
substance, as well as a considerable proportion of the hydro-carbons; and, in the sum-
mer, we instinctively reduce the proportion of both of these varieties of principles, the
more succulent articles taking their place. This is even more strikingly illustrated by a
comparison of the diet in the torrid or temperate and in the frigid zone. Under the head
of alimentation, we have already noted the prodigious quantities of food consumed in the
Arctic regions and the effect of the continued cold upon the habits of diet of persons
accustomed to a temperate climate. It is stated that the daily ration of the Esquimaux is
from twelve to fifteen pounds of meat, about one-third of which is fat. Dr. Hayes, the
Arctic explorer, noted that, with a temperature ranging from —60° to —70°, there was
a continual craving for a strong, animal diet, particularly fatty substances. Some of the
members of the party, indeed, drank the contents of the oil-kettle with evident relish.

The influence of alcoholic beverages upon the animal temperature has been studied
chiefly with reference to the question of their use in enabling the system to resist exces-
sive cold. We have already discussed somewhat fully the physiological effects of alcohol,
and we have seen that its use does not enable men to endure a very low temperature for
a great length of time. This is the universal testimony of scientific Arctic explorers.

As a rule, when the respiratory activity is physiologically increased, as it is by exer-

510 NUTRITION.

else, bodily or mental, ingestion of food, or by diminished external temperature, the gen-
eration of heat in the body is correspondingly augmented ; and, on the other hand, it is
diminished by conditions which physiologically decrease the absorption of oxygen and the
exhalation of carbonic acid. The relations of animal heat to the general process of nutri-
tion are most intimate. Any condition that increases the activity of nutrition and of
disassimilation, or even any thing that increases disassimilation alone, will increase the
production of heat. The reverse of this proposition is equally true.

Influence of Exercise, etc., upon the Heat of the Body. — The influence of muscular
activity upon animal heat is interesting in connection with the theories of calorification,
from the fact that the muscular system constitutes the greatest part of the organism ;
and a muscle taken from a living animal is not only capable of contraction upon the
application of a stimulus, but it will perform for a time certain acts of nutrition and
disassimilation, such as the appropriation of oxygen and the exhalation of carbonic
acid.

The most complete repose of the muscular system is observed during sleep, when
hardly any of the muscles are brought into action, except those concerned in tranquil
respiration. There is always a notable diminution in the general temperature at this
time. In the diurnal variations in the heat of the body, the minimum is always during
the night ; and, as we have already seen, this is not entirely dependent upon sleep, for a
depression in temperature is always observed at that time, even when sleep is avoided.

It is a matter of common observation, that one of the most efficient methods of resist-
ing the depressing influence of cold is to constantly exercise the muscles ; and it is well
known that, after long exposure to intense cold, the tendency to sleep, which becomes
almost irresistible, if yielded to, is followed by a very rapid loss of heat and almost cer-
tain death. In some animals, the amount of increase in the temperature during muscular
activity is very great, and this is notably marked in the class of insects. In the experi-
ments of Newport, upon bees and other insects, a difference of about 27° was noted
between the conditions of complete repose and great muscular activity. These facts are
interesting, as showing the very great elevation of temperature that can be produced in
the lower order of beings during violent excitement; but, in man, the differences, although
distinct, are never very considerable, for the reason that violent muscular exertion is gen-
erally attended with greatly-increased action of the skin, which keeps the heat of the body
within very restricted limits. In the experiments of Newport, the loss of heat from the
surface was arrested by confining the insects in small glass bottles.

The elevation in temperature that attends muscular action is produced directly in the
substance of the muscle. This important fact was settled by the very interesting and
ingenious experiments of Becquerel and Breschet. Introducing a thermo-electric needle
into the biceps of a man who used the arm in sawing wood for five minutes, these physi-
ologists noted an elevation of temperature of one degree centigrade (nearly two degrees
Fahr.). The production of heat in the muscular tissue was even more strikingly illus-
trated by Matteucci, in experiments with portions of muscle from the frog. Not only did
he observe absorption of oxygen and exhalation of carbonic acid after the muscle had
been removed from the body of the animal, but he noted an elevation in temperature of
about one degree Fahr., following contractions artificially excited.

Observations upon the influence of mental exertion on the temperature of the body
have not been so numerous, but they are, apparently, no less exact in their results. Dr.
Davy was the first to make any extended experiments upon this point, and he noted a
slight but constant elevation during " excited and sustained attention." The same line
of observation has been followed by Prof. Lombard, who employed much more exact
methods of investigation. Prof. Lombard noted an elevation of temperature in the head
during mental exertion of various kinds, but it was slight, the highest rise not exceeding
one-twentieth of a degree. It is stated, also, by Burdach, that the temperature of the body

ANIMAL HEAT. 511

is increased by the emotions of hope, joy, anger, and all exciting passions, while it is
diminished by fear, fright, and mental distress.

It is evident that, if animal heat be one of the necessary attendant phenomena of
nutrition, it must be greatly influenced by conditions of the circulation. It has been a
question, indeed, whether the modifications in temperature produced by operating upon
the sympathetic system of nerves be not due entirely to changes in the supply of blood.
It is certain that whatever determines an increased supply of blood to any part raises
the temperature; and, whenever the quantity of blood in any organ or part is consider-
ably diminished, the temperature is reduced. This fact is constantly illustrated in opera-
tions for the deligation of large arteries. It is well known that, after tying a large vessel,
the utmost care is necessary to keep up the temperature of the part to which its branches
are distributed, until the anastomosing vessels become enlarged sufficiently to supply the
amount of blood necessary for healthy nutrition.

Sources of Animal Heat.

The most interesting question connected with calorification relates to the sources of
heat in the living organism ; and a careful estimate of the physiological value of all the
facts that have been positively established with reference to this point places the follow-
ing proposition beyond any reasonable doubt :

The generation of heat in the living animal organism is connected, more or less inti-
mately, with all of the processes of nutrition and disassimilation, including, of course, the
consumption of oxygen and the production of carbonic acid and probably of water; and
this function is modified, to a greater or less degree, by conditions that influence general
nutrition or the operation of the nutritive forces in particular parts.

This proposition is not contradicted by any well-settled physiological facts or princi-
ples. All the functions of the body bear more or less closely upon nutrition ; and all the
physiological modifications of the various functions, without exception, affect the process
of calorification. We must bear in mind the fact that, in man and in the warm-blooded
animals generally, the maintenance of the temperature of the organism at a nearly fixed
standard is a necessity of life; and that, while heat is generated in the organism with an
activity that is constantly varying, it is counterbalanced by physiological loss of heat
from the cutaneous and the respiratory surface. Variations in the activity of calorifica-
tion are not to be measured by corresponding changes in the temperature of the body,
but are to be estimated by calculating the amount of heat lost. The ability of the human
race to live in all climates is explained by the adaptability of man to different conditions
of diet and exercise, and by the power of regulating loss of heat from the surface by
appropriate clothing. Eegarding calorification, then, as connected with all of the varied
processes of nutrition, it remains for us to consider the following questions:

1. In what part or parts of the organism is heat generated?

2. What is the relative importance in calorification, as regards the amount of heat
generated, of the different processes of nutrition, as we can study them separately ?

3. What are the principles invariably and of necessity consumed and produced in the
organism in calorification ; and what is the relative importance of the different principles
thus consumed and the various products thus generated and thrown off?

4. How far have we been able to follow those material transformations in the organ-
ism which involve the consumption of certain principles, the production of new com-
pounds, and the generation of heat ?

Seat of the Production of Animal Heat.—$w if any physiologists at the present
day hold to the opinion that there is any part or organ in the body specially and exclu-
sively concerned in the production of heat. In the early history of the oxidation-theory
of Lavoisier, it was thought by some that the inspired oxygen combined with the hydro-

512 NUTRITION.

carbons of the blood in the lungs, and that the heat of the body was generated almost
exclusively in these organs ; but this idea has long since been abandoned.

It is only necessary to refer back to the pages treating of the variations in the tem-
perature of the blood in different parts, to show that heat is produced in the general
.system and not in any particular organ or in the blood as it circulates. The experiments
of Matteucci, showing an elevation of temperature in a muscle excited to contraction
after it had been removed from the body, and the observations of Becquered and Bres-
chet, showing increased development of heat by muscular contraction, are sufficient
evidence of the production of heat in the muscular system ; and, inasmuch as the muscles
constitute by far the greatest part of the weight of the body, they are a most important
source of animal heat.

It has been demonstrated, by the experiments of Bernard, that the blood becomes
notably warmer in passing through the abdominal viscera. This is particularly marked
in the liver, and it shows that the large and highly-organized viscera are also important
sources of caloric.

As far as it is possible to determine by experimental demonstration, not only is there
no particular part or organ in* the body endowed with the special function of calorifica-
tion, but every part in which the nutritive forces are in operation produces a certain
amount of heat; and this is probably true of the blood-corpuscles and other anatomical
elements of this class. The production of heat in the body is general and is one of the
necessary consequences of the process of nutrition; but, with nutrition, it is subject to
local variations, as is strikingly illustrated in the effects of operations upon the sympa-
thetic system of nerves and in the phenomena of inflammation.

Relation of Animal Heat to Nutrition. — Nutrition and disassimilation involve the
appropriation of matters taken into the body and the production and discharge of effete
substances. In its widest signification, this includes the consumption of oxygen and the
elimination of carbonic acid; and, consequently, we may strictly regard respiration as a
nutritive act. All of the nutritive processes go on together, and they all involve, in most
warm-blooded animals at least, a nearly uniform temperature. During the first periods
of embryonic life, the heat derived from the mother is undoubtedly necessary to the
development of tissue by a change of substance, analogous to nutrition and even superior
to it in activity. During adult life, animal heat and the nutritive force are coexistent.
It now becomes a question to determine whether there be any class of nutritive prin-
ciples specially concerned in calorification, or any of the nutritive acts, that we have been
able to study by themselves, which are exclusively or specially directed to the mainte-
nance of the normal temperature of the body.

The supply of the waste of tissue being effected by a metamorphosis of nutritive mat-
ters— a process the exact nature of which we have not been able to determine — it has
thus far been possible, only, to divide the food into different classes. Of these, leaving
out oxygen and the inorganic salts, we shall consider, in this connection, the organic
matters, divided into nitrogenized and non-nitrogenized.

What is the relation to calorification of those processes of nutrition which involve the
consumption of nitrogenized matter and the production of the nitrogenized excrementi-
tious principles ?

We cannot study the phenomena of calorification alone, isolated from the other acts
of nutrition. We may confine an animal to a purely nitrogenized diet, and the heat of the
body will be maintained at the proper standard ; but at all times there is a certain quan-
tity of non-nitrogenized matter (sugar and perhaps fat) produced in the system, which is
formed only to be consumed. We may starve an animal, and the temperature will not fall
to any very great extent until a short time before death. Here we may suppose that the
process of deposition of nutritive matter in the tissues from the blood is inconsiderable,
as compared with the transformation of the substance of these tissues into effete matter ;

ANIMAL HEAT. 513

and it is almost certain that non-nitrogenized matter is not produced in the organism in
quantity sufficient to account, by its destruction in the lungs, for the carbonic acid exhaled.
It seems beyond question that there must be heat evolved in the body by oxidation of
nitrogenized matter. When the daily amount of food is largely increased for the purpose
of generating the immense amount of heat required in excessively cold climates, the nitro-
genized matters are taken in greater quantity, as well as the fats, although their increase
is not in the same proportion. From these facts, and from other considerations that have
already been fully discussed, it is evident that the physiological metamorphoses of ni-
trogenized matter bear a certain share in the production of animal heat.

What is the relation of the consumption of non-nitrogenized matter to the production
of animal heat ?

It has been pretty clearly shown that both sugar and fat are actually produced in the
organism, even when the diet is strictly nitrogenized in its character ; but we shall con-
sider only the relations of the non-nitrogenized elements introduced into the body, assum-
ing that the principles of this class appearing de now in the organism are the result of
a transformation of nitrogenized substances.

As far as the destination of the amylaceous, saccharine, and fatty elements of food is
concerned, we only know that they are incapable, of themselves, of repairing muscular
tissue, and that they cannot sustain life. They are never discharged from the body in
health in the form under which they enter ; but they are in part or completely destroyed
in nutrition. They are completely destroyed in persons who, from habitual muscular ex-
ercise, have very little adipose tissue. When their quantity in the food is large, they are
not of necessity entirely consumed, but they may be deposited in the form of adipose
tissue.

There can be no doubt that the non-nitrogenized class of alimentary principles is
craved by the system in long-continued exposure to extreme cold. This is particularly
marked with regard to the fats. In all cold climates, fat is a most important element of
food ; and, in excessively cold regions, while the nitrogenized elements are largely in-
creased, there is a very much larger proportional increase in the quantity of fat. These
facts are very significant. If the non-nitrogenized elements of food do not form tissue,
are riot discharged from the body, and are consumed in some of the processes of nutri-
tion, it would seem that their change must involve the production of carbonic acid, per-
haps also of water, and the evolution of heat.

Although we may assume that the non-nitrogenized elements of food are particularly
important in the production of animal heat, and that they are not concerned in the repair
of tissue, it must be remembered that the animal temperature may be kept at the proper
standard upon an exclusively nitrogenized diet; and we cannot, indeed, connect calorifi-
cation exclusively with the consumption of any single class of principles or with any sin-
gle one of the acts of nutrition.

Relations of Calorification to Respiration. — Respiration is one of the nutritive pro-
cesses that can be closely studied by itself, as it involves the appropriation by the system
of a single principle (oxygen), which is carried to the tissues by the blood. There can be
no doubt that, of all the nutritive acts, respiration in the substance of the tissues is, far
more than any other, intimately connected with calorification. As far as the general pro-
cess is concerned, the production of heat is usually in direct ratio to the consumption of
oxygen and the exhalation of carbonic acid. In the animal scale, wherever we have the
largest amount of heat produced, we observe the greatest respiratory activity. In man,
whatever increases the generation of heat increases as well the consumption of oxygi-n
and the elimination of carbonic acid. The production of heat in warm-blooded animals
is constant, and it cannot be interrupted, even for a few minutes. The same is true of
respiration. The tissues may waste for want of nourishment, but the heat of the body
must be kept near a certain standard, which is almost always much higher than that of
33

514 NUTRITION.

the surrounding atmosphere; and there is no other nutritive act so constant and so
immediately necessary to existence as the appropriation of oxygen.

The physiological history of respiration and of animal heat dates from the same series
of discoveries. In the latter part of the last century, th4 great chemist, Lavoisier, discov-
ered the intimate nature of the respiratory process and applied the theory of the con-
sumption of oxygen and the evolution of carbonic acid to calorification. Like nearly all
of the great advances in physiological science, the distinctly-enunciated idea was fore-
shadowed by earlier writers. It will not be necessary to treat, from a purely historical
point of view, of the discoveries made by Lavoisier. He undoubtedly went as far in his
explanations of the phenomena of animal heat as was possible in the condition of the
science at the time his investigations were made ; and, although he inevitably fell into
some errors in his calculations and deductions, he must forever be regarded as the author
of the first reasonable theory of the generation of heat by animals.

The Consumption of Oxygen and Production of Carbonic Acid and Water in Connec-
tion with the Evolution of Heat. — As far as it has been possible to determine by actual
experiment, all animals, even those lowest in the scale, appropriate oxygen and eliminate
carbonic acid. This is equally true of all living tissues ; and, since it has been ascertained
that oxygen is taken up, as oxygen, by the arterial blood, that it disappears in part or
entirely in the capillary circulation, that carbonic acid is taken up by the venous blood
to be discharged in the lungs, and that the tissues themselves have the property of appro-
priating oxygen and exhaling carbonic acid, those who adopt the theory of Lavoisier have
simply changed the seat of oxidation from the lungs to the general system.

It has been proven beyond question that oxygen, of all the principles introduced from
without, is the one most immediately necessary to nutrition ; and carbonic acid is to be
regarded as an element of excretion, like urea, creatine, etc., differing from them only in
the immediate necessity for its elimination. As the comparatively slow excretion of
urea and other nitrogenized matters is connected with the ingestion of ordinary aliment-
ary substances that are slowly appropriated by the tissues, so the rapid elimination of
carbonic acid is connected with the equally rapid appropriation of oxygen. There is no
reason why we should not regard carbonic acid, like other effete substances, as an excre-
tion, the result of disassimilation of the tissues generally ; but, more closely than any, it
is connected with the rapid and constant evolution of heat.

Experiments on the influence of the sympathetic nerves upon the temperature of par-
ticular parts have completed the chain of evidence in favor of the localization of the
heat-producing function in the tissues. It is not our purpose to discuss the relations of
the sympathetic system to nutrition, deferring this subject until we come to treat spe-
cially of the nervous system; but the facts bearing on calorification are briefly as follows:

If the sympathetic nerve be divided in the neck of a rabbit or any other warm-blooded
animal, the side of the head supplied by this nerve will become from five to eight or ten
degrees warmer than the opposite side. This observation we have repeatedly verified.
The conditions under which this local exaggeration of the animal heat is manifested are,
dilatation of the arteries of supply of the part, so that it receives very much more blood
than before, and increased activity in the general process of nutrition.

It is evident that, in normal nutrition by food, the heat of the body must be main-
tained by changes which take place, either directly in the blood or indirectly in the tis-
sues, in the alimentary matters, and that these changes involve oxidation to a very con-
siderable extent. Under ordinary conditions of nutrition, it is assumed that the food
furnishes all the material for maintaining the heat of the body and for the development
of force in work, such as the muscular work of respiration and circulation and general
muscular effort. If no food be taken for a certain time, the heat of the body must be
maintained and the work must be accomplished at the expense of the substance of the
body itself; and the individual loses weight. To furnish a positive scientific basis for

ANIMAL HEAT. 515

this view, physiologists have burned various articles of food in oxygen and have calcu-
lated their heat- value. This has heen expressed in what are called heat-units, the Eng-
lish value of a heat-unit heing the amount of heat required to raise one pound of water
one degree Fahrenheit. It is also calculated that one heat-unit converted into force
will raise 772 pounds one foot high, or is equal to 772 foot-pounds. The theory of the
heat-value and the force-value of food, based upon these premises, is the following:

The heat-value of food may be expressed in a definite number of heat-units. A cer-
tain proportion of these heat-units serves to maintain the standard animal temperature.
A certain proportion is converted into the force used in the muscular work of respira-
tion and circulation. A certain proportion is used in ordinary muscular work. If the
supply of food be in excess of these various requirements, a certain part of it is not used
and the body may gain in weight. If the supply of food, however, be below the de-
mands of the system, a part of the tissues of the body itself is consumed, and there
must be a loss of weight.

Following the observations made by Fick and Wislicenus, in 1866, by which these
observers attempted to show that nearly all the force resulting from muscular action is
due to the oxidation of non-nitrogenized matters, physiologists have estimated the heat-
value and the force-value of different articles of food. They have reasoned that the
food, by its oxidation in the body, is capable of producing a certain amount of heat and
that a part of this heat is converted into force. A method now employed to calculate
the heat produced is to subtract the daily mechanical force expended from the total
force-value of the food, the result giving the daily formation of heat. Foster estimates
in this way that " between one-fifth and one-sixth of the total income is expended as
muscular labor, the remaining four-fifths or five-sixths leaving the body in the form of
heat." The reduction of heat-units to units of force is made in accordance with Joule's
formula, already referred to, that one heat-unit is equal to 772 foot-pounds, or will raise
772 pounds one foot high. -

In 1860, Franldand made a number of calculations of the heat-units and the estimated
force-value of various articles of food, which are now accepted and used by most writers
upon subjects connected with the theories of animal heat and the source of muscular
power. As regards the heat produced by the oxidation of these substances in the body,
if it be assumed that the same quantity of heat is produced by the oxidation, under all
circumstances, of a definite amount of oxidizable matter, it is necessary simply to deduct
from the heat-value of articles of food the heat-value remaining in certain parts of the
food which pass out of the body in an unoxidized state. It was in this way that Frank-
land arrived at a determination of the heat-value of articles of food oxidized in the body.
As we have already stated, according to the observations of Senator and of Draper, the
actual heat produced by the body is equal to about four heat-units per pound weight
per hour. We shall assume that this estimate, as well as the determinations made by
Frankland of the heat-value of certain articles of food, are reasonably accurate, and we
shall treat them as definite propositions in discussing the following observations :

Observation 1. — In 1870, we had occasion to note the work, the quantity of food
taken, and various other conditions in a healthy man for several consecutive days. The
observations were made at that time with another object in view, but the data obtained
will serve in the present argument. "We shall here make use of the estimates made for
five consecutive days, during which the subject of the observations walked 317^ miles.
In these calculations, we estimate the heat-value of the loss of weight of the body ao
well as that of the food. The nkrogenizsd food and loss of body-weight gave 13,416-64
heat-units, and tho non-nitrogenized food, 19,521-41 heat-units, making a total of 32,-
938-05. The heat actually produced by the body, at four heat-units per pound per hour,
was estimated at 55,440-00 heat-units. This leaves 22,501 '25 heat-units not accounted
for, or about fort: Per cent., not taking into consideration the heat-units converted into
force expended in circulation and respiration and in walking 317i miles.

516 NUTRITION".

Observation 2.— November 22, 1878, we made an experiment, fasting for twenty-four
hours, beginning the observations for the twenty-four hours nine and one-quarter hours
after the last meal. In this experiment, the urine of the twenty-four hours was collected
and analyzed, and we drank during this period twenty ounces of water. The loss of
weight of the body was fifty-six ounces. The calculations of the sources of heat, exclud-
ing the possible generation of heat by the union of oxygen with hydrogen, were made by
estimating the heat-value of the carbonic acid eliminated by the lungs and of the urin-
ary nitrogen. Estimated in this way, the total heat represented by the nitrogen elimi-
nated in the urine and by the carbonic acid was equivalent to 12,436-79 heat-units. The
estimated heat produced by the body for the same period was equivalent to 17,904*00 heat-
units, leaving 5, 467*21 heat-units, or about one-third of the heat produced, unaccounted for.

Observation 3. — November 30, 1878, we made another experiment in which the heat-
value of the food taken for twenty-four hours was estimated, the weight of the body
remaining stationary. In this observation, the total heat-value of the food was equivalent
to 14,979'! 5 heat-units, and the heat produced by the body was equal to 17,880-00 heat-
units, leaving 2,900'85 heat-units, or about one-sixth of the heat produced by the body,
unaccounted for by the food.

The results of these observations naturally led to a consideration of the theory first
proposed by Lavoisier and Laplace, that oxygen may unite with hydrogen in the body
to form water and produce heat. Thus far, however, there has been no experimental
demonstration of the actual production of water in the animal economy. In the ex-
periment in which we fasted for thirty-three hours, during twenty-four hours of which
no food was taken after the digestion of articles taken about nine hours before had
been completed, it was estimated that about thirty-two ounces of water were discharged
by the lungs and skin, and thirty-four ounces of water were actually eliminated by
the kidneys, making a total discharge of water of sixty-six ounces. During this period,
twenty ounces of water were taken, leaving about forty-six ounces over and above the
quantity ingested. The loss of weight was fifty-six ounces, of which we may estimate
a loss of about ten ounces in solid matters in the urine and in carbon by the lungs.
The question now is whether this loss of forty six ounces of water was simply a dis-
charge of water already formed, from the blood and the watery parts of the tissues, or
whether it is to be attributed in part to water actually formed in the body by a union of
oxygen and hydrogen. If the watery parts of the body be actually deficient in quantity,
there is usually a sensation of thirst. There was no suffering from thirst, and, indeed,
we drank rather more water than was desired. Recent experiments by Valentin, Panum,
Colin, and others, have shown, in opposition to the previously-received opinions, that
abstinence from food has very little effect in diminishing the volume of the blood. This
fact, taken in connection with the absence of thirst during the twenty-fours of fasting, is
favorable to the view that all of the excess of water discharged did not come directly
from the blood.

If water be actually produced in the economy by a union of oxygen and hydrogen, what
is the probable source of these two elements? There is no deficiency of hydrogen in the
body, and, if it be used to form water which is discharged, there would be loss of weight
when no food is taken, and it would be supplied by the food under ordinary conditions of
nutrition. There is no deficiency of oxygen in the body itself, and the oxygen discharged
in urea represents only about one-third of the proportion of oxygen contained in the
nitrogenized constituents of the body. Of the oxygen taken into the lungs, about eighty-
six per cent, only is returned in combination with carbon to form carbonic acid, leaving
fourteen per cent, to form some other combination in the body, possibly a union with
hydrogen. There is, indeed, little oi' no difficulty in accounting for the elements to form
water in the body, if it can be shown that more water is discharged from the organism
than is taken with the ingesta, and that the excess thus discharged does not come simply
from the watery parts, producing an actual deficiency of water in the body.

ANIMAL HEAT. 517

The actual demonstration that more water is ever discharged from the body than can
be accounted for by the water of the ingesta, or by water simply withdrawn from the
blood rendering this fluid more dense, presents very considerable but not insurmountable
difficulties. A process that would be open to few objections, provided all of the elements
used in the calculations were accurate, is the one which we have attempted to employ in
cases of loss of weight. This process is the following :

Take the weight of a man at the beginning of the experiment, calculate accurately
the weight of the ingesta for a certain period, and add this latter to the weight of the
body. This forms a sum total from which the following quantities are to be deducted:
Take the weight of the urine and feeces passed during the time of the experiment; add to
this the weight of the carbon contained in the carbonic acid exhaled, which' carbon car-
ries with it a portion of the inspired oxygen ; add both of these to the weight of the body
taken at the close of the experiment; the difference will give the amount of water dis-
charged by the lungs and skin. Having thus the quantity of water discharged by the
lungs and skin, to ascertain the total quantity of water discharged from the body, we
have to add the water contained in the urine and fasces. We then carefully estimate the
amount of water contained in the ingesta and can compare the amount of water dis-
charged with the quantity taken. In Pettenkofer's chamber, in which a man may be
confined and all of the excreta be estimated, these calculations could be made with suf-
ficient accuracy, and the only uncertain element in the problem would be as to whether
or not the blood became modified in density or volume. In the following calculation, we
were forced to estimate the amount of carbon eliminated, but we endeavored to correct
this estimate by an indirect method.1 The subject of the experiment was the person
mentioned in Observation 1, and the investigations described were continued for five days,
during which period he walked 317i miles. The following is a summary of the results:

Observation upon the Ingress and Egress of Water.

Ounces.

Body-weight at the beginning of the observation 1,907-20

Weight of the ingesta for five days 857'34

Total 2,764-54

Weight of the urine and faeces for five days 220-47

Carbon eliminated for five days, estimated at 10 ounces per day. . . . 50*00
Body-weight at tae end of the five days (showing a loss of 55*2 ounces) 1,852*00

2,122-47

Water eliminated by the lungs and skin 642*07

Water contained in the urine and faeces. 208*89

Total water discharged 850*96

The water of the food and drink taken for the five days was carefully estimated, and
it amounted to 788*18 ounces. This deducted from the total quantity of water discharged
gives an excess of 62*78 ounces discharged for five days, or a daily excess of 12*56 ounces.

The heat- value of the hydrogen required to form one ounce of water is equal to 432-5

1 As stated in the text, we were forced to estimate the amount of carbon discharged, bnt preferred to put it too
high rather than too low. Ten ounces per day is a very high estimate for a man weighing 115$ pounds. The follow-
ing indirect calculation of the probable sources of carbon shows that this estimate is certainly not too low. We
<• ii ulate the total carbon of the food as amounting to about twenty-five ounces. To this we add the carbon of forty-
eight ounces of muscular tissue consumed (5-23 ounces), and of 7*2 ounces of fat, both loss of weight (5-69 ounces).
This gives about thirty-six ounces of carbon for five days. From this we deduct nine ounces of carbon discharged in
the urea, wtiidi loaves twenty-seven ounces for five days, or 5'4 ounces per day. If we calculated that the entire
toss of weight of 55-2 ounces should be estimated as fat— which is very improbable from the condition of the subject
on beginning the walk and the discharge of a considerable quantity of nitrogen from the body over and above the
nitrogen of food -we should have about fifty-nine ounces of carbon for five days, or 11*3 ounces per day. The last-
named quantity would make very little difference in the results given above.

518 NUTRITION.

heat-units. The heat-value, then, represented by the formation of 12-56 ounces of water
would be 5,432-2 heat-units.

During these five days, the subject of this experiment walked 317i miles and lost 55'2
ounces in weight. We calculated for these five days the total heat produced by the body,
and the heat-units used in maintaining circulation and respiration and in walking 317-J
miles. We then calculated the heat-value of the food and of the loss of body-weight,
the latter estimated as muscular tissue, taking no account of the hydrogen. According
to this, there remained 38,926-52 heat-units unaccounted for. If we take in addition the
heat-value represented by the excess of water discharged for tbe five days, which is equal
to 27,161-00 heat-units, we have 11,765-52 heat-units unaccounted for, which is about
sixteen per cent, of the heat-units expended, instead of fifty-five per cent. However, in
estimating the heat-units used in respiration, circulation, and walking 317& miles, we
took calculations that we regard as grossly erroneous and use them for sake of argument
and without any confidence in their accuracy. The percentage of sixteen is probably
not more than the error in the computation of the heat-units converted into force ex-
pended in maintaining circulation and respiration and in walking 317$ miles.

One of the observations, in which we calculated the amount of water discharged as
compared with the quantity ingested, was for twenty-four hours of abstinence from food.
The other was for a person who lost considerable weight as the result of excessive mus-
cular exertion. Even when no food is taken, a certain amount of heat must be produced,
and the standard animal temperature must be maintained. The heat thus produced can-
not be accounted for by the carbon discharged in carbonic acid, but it can be accounted
for by the hydrogen discharged in water, and it seems reasonably certain that water is
actually formed in the body. Under excessive exercise attended with loss of weight, it
seems certain that water is produced in the body by a union of hydrogen and oxygen.
Animal heat is undoubtedly produced very largely by oxidation; and it has been shown
that muscular work, while it has a tendency to raise the animal temperature, very con-
siderably increases the elimination of water.1 The chemical products of this oxidation
are represented mainly by urea, as far as nitrogen is concerned, and by carbonic acid
and water. There are thus three elements with which the oxygen combines; viz., nitro-
gen, carbon, and hydrogen. We cannot account for the total amount of heat produced
in the body by the urea and carbonic acid discharged, but this can be accounted for by
supposing that a certain quantity of hydrogen is oxidized in the body to form water.

We do not pretend to assert that the oxygen absorbed by the blood in its passage
through the lungs forms a direct and immediate union with carbon and hydrogen to form
carbonic acid and water. If such a union take place, carbonic acid and water are the
final products resulting from a series of /nolecular changes, the various steps of which we
are unable to follow ; but it is probably true that, if a union of oxygen with carbon and
hydrogen will produce a definite amount of heat, the quantity of heat is the same
whether the combination be slow or rapid. As regards the oxidation of carbon and hy-
drogen, -all that it is necessary to show is that carbonic acid and water are actually pro-
duced in the body, as a part of the final results of the intricate molecular changes involved
in nutrition and disassimilation. There is no good reason to suppose that the processes
of physiological wear or disassimilation are radically changed in their character during a
short period of abstinence from food, or during exercise which for a time wastes the tis-
sues more rapidly than they can be repaired. When the appropriation of nutritive mat-
ters produces an equilibrium between the physiological waste and repair, it is logical to
conclude that the waste of the tissues, which involves the oxidation of a certain quantity
of carbon, nitrogen, and possibly hydrogen, is repaired by the food, the nature of the

1 Pettenkofer and Yoit, as one of the conclusions arrived at by experiments upon a man twenty-eight years of age,
kept for twenty-four hours in their large respiration-apparatus, make the following statement : " The elimination of
water is very much increased by work, and the increase continues during the ensuing hours of sleep." (Journal of
Anatomy and Physiology, Cambridge and London, 1868, vol. ii., p. 181.)

ANIMAL HEAT. 519

processes involved in the waste being the same as during a period of abstinence from
food. As regards the oxidation of hydrogen, we may suppose that the hydrogen of the
non-nitrogenized parts is used, and that the matter thus consumed is supplied again to the
tissues in order to maintain the physiological status of the organism.

The supposition that water may be actually formed within the organism under certain
conditions not only completes the oxidation-theory of the production of animal heat, but
it enables us to understand certain physiological phenomena that have heretofore been
obscure. It is well known, for example, that a proper system of physical training will
reduce the fat of the body to a minimum consistent with health and strength. This
involves a diet containing a relatively small proportion of fat and liquids, and regular
muscular exercise attended with profuse sweating. We have seen that muscular work
increases the elimination of water, while it also exaggerates for the time the calorific
processes. The muscular exercise undoubtedly favors the consumption of the non-nitro-
genized parts of the body, and a diminution of the supply of hydro-carbons, carbo-hydrates,
and water in the food prevents, to a certain extent, the new formation of fat. By taking
an unnecessary quantity of liquids, we do not increase the calorific processes or promote
activity of the circulation, and the excess of water is usually discharged by the kidneys.
When, however, we exert the muscular system excessively, we increase the production of
water and the circulation becomes more active. The volume of blood then circulating
in the skin and passing through the lungs in a given time is relatively increased, and
there is an increased discharge of water from these surfaces. The same condition that
produces an increased quantity of water in the body and has a tendency to exaggerate the
process of calorification seems to produce also an increased evaporation from the surface,
which serves to equalize the animal temperature.

We shall restrict the conclusions to be drawn from the experiments just described to
points connected with the production of animal heat. It is undoubtedly true that, com-
puting all of the force produced in the body as heat-units, more heat is generated than
is absolutely necessary to maintain the normal animal temperature, and that a certain
amount of this excess is manifested as force used in the work of respiration and circula-
tion and general muscular effort. The computation of the force thus used is always made
in accordance with the formula that one heat-unit is equivalent to 772 foot-pounds. The
reduction of the force of the heart and the force exerted by the respiratory muscles to
units of foot-pounds is so excessively difficult and uncertain that the estimates given by
writers ar«, in our opinion, almost worthless. The same remark applies to the reduction
of ordinary muscular work to definite units. Without some such method of reduction,
however, the force exerted by muscles cannot be expressed in definite quantities. All
that we can do is to show, if possible, that more heat-units are produced in the body
than are required to maintain the heat of the body, and that a part of the excess is con-
verted into force. We do not conceive that the simple experiment, which shows that
one pound in falling 772 feet will produce heat enough to raise the temperature of one
pound of water one degree Fahrenheit, proves absolutely that one heat-unit produced
by burning food in oxygen, when the same food is oxidized in the body, making allow-
ance for that which escapes such oxidation, can be converted into muscular force equal
to 772 foot-pounds. From our own experiments upon the subject under consideration,
we may legitimately draw, however, the following conclusions:

1. It is probable that nearly all the animal heat is produced by oxidation, in the
body, of certain elements, which are chiefly nitrogen, carbon, and hydrogen.

2. It is probable that this oxidation takes place chiefly in the substance of the various
tissues, and that it is connected with the general processes of nutrition and disassimila-
tion. Heat is thus generated, and the final products of the chemical actions involved are
mainly urea, carbonic acid, and water. It must be remembered, however, that the
oxidation is not necessarily a process identical with combustion out of the body, but
that it is probably connected with a series of intricate molecular changes, which

520 NUTRITION.

cease with the life of the tissues, and of which we are able to recognize only the final
results.

3. Recognizing the products, urea, carbonic acid, and water, as representing probably
the evolution of a certain amount of heat, we cannot account for the heat actually pro-

.duced in the body by the amount represented by the urea and carbonic acid discharged.
If we admit that hydrogen is oxidized in the body, resulting in the evolution of heat and
the production of water, this will enable us to account for all the heat actually manifested
as heat,, leaving an excess which may be converted into force.

4. Our experiments show pretty clearly that, when no food is taken and when, food
being taken, muscular work is performed so that there is loss of body- weight, water is
actually produced in the body. This, and this only, enables us to account for all the heat
evolved under these conditions. There is no reason to suppose that the processes in-
volved in the production of heat are radically changed in their character when enough
food and water are taken to maintain a uniform body-weight.

5. Animal heat is produced mainly by oxidation of the nitrogen, carbon, and hydrogen
of the tissues, the waste of these elements being supplied by food. Probably the oxida-
tion of carbon and hydrogen is a more important factor in calorification than the oxida-
tion of nitrogen ; at least it is certain that the heat- value of the oxidation of carbon and
hydrogen is greater than that of the oxidation of nitrogen, and the quantity of heat thus
produced is much larger. Of the two elements, carbon and hydrogen, the oxidation
of which produces animal heat, the heat-value of the hydrogen is by far the greater.

6. It is probable that there is always a certain amount of oxidation of hydrogen in the
body, and that this is necessary to maintain the animal temperature ; and it is almost cer-
tain that this occurs during prolonged abstinence from food and when the production of
heat is much increased by violent and protracted muscular exertion. It may be, also,
that there is an active and unusual oxidation of hydrogen as well as of carbon in fevers.

Alcohol, which is so extensively used as a measure of sustaining treatment in fevers,
is now almost universally recognized as an element consumed in the body and not dis-
charged to any considerable extent as alcohol. According to Brande, Cognac brandy
contains 46 per cent, of absolute alcohol. With a specific gravity of 0-930, one ounce of
brandy weighs 406-875 grains and contains 187'1625 grains of alcohol. The alcohol, with
a composition of C^eOa, contains 12 -9 per cent, of hydrogen, or 24-14 grains, and 52*65
per cent, of carbon, or 98'54 grains. . The heat-value of 24*14 grains of hydrogen equals
214*77 heat-units. The heat-value of 98-54 grains of carbon equals 182-44 heat-units.
Taking, then, the total heat-value of the hydrogen and carbon contained in one ounce of
brandy, it amounts to 397-21 heat-units. If we assume that a man produces four heat-
units per pound weight of the body per hour, the amount of heat normally produced in
twenty-four hours by a man weighing 140 pounds is equal to 13,440 heat-units. The
quantity of brandy required to supply this amount of heat, according to the calculations
just made, would be a little less than thirty-four ounces. Theoretically, then, it is easy
to see how alcohol may furnish material to supply heat and save waste of tissue in fevers ;
and it is not very unusual, in certain stages of fever, to administer from sixteen to
thirty-two ounces of brandy in twenty-four hours.1

"We conclude this subject with the following query, which has occurred to mind in
connection with reflections upon the question of the oxidation of hydrogen as one of the
sources of animal heat :

If the excessive heat produced in essential fevers be due in part to an excessive oxi-
dation of hydrogen, why would not the exhaustion and rapid emaciation which attend
the progress of fever be more or less moderated by supplying hydrogen to the system
in the form of fatty matters, starchy matters, sugar and alcohol, until the fever has

1 For a more complete account of the experiments given above, the reader is referred to an article by the author,
entitled Experiments and Reflections upon Animal Heat. — American Journal of the Medical Sciences, Phila-
delphia, April, 1879, p. 338, et seq.

ANIMAL HEAT. 521

ran its course ; and might not this supply, to a certain extent, the abnormal waste of
tissue ?

Equalization of the Animal Temperature. — A study of the phenomena of calorification
in the human subject has shown that, under all conditions of climate, the general heat of
the body is equalized. There is always more or less loss of heat by evaporation from the
general surface, and, when the surrounding atmosphere is very cold, it becomes desira-
ble to reduce this loss to the minimum. This is done by appropriate clothing, which
must certainly be regarded as a physiological necessity. Clothing protects from excessive
heat as well as from cold. Thin, porous articles moderate the heat of the sun, equalize
evaporation, and afford great protection in hot climates. In excessive cold, clothing is
of the greatest importance in preventing the escape of heat from the body. When the
body is not exposed to currents of air, the garments are useful chiefly as non-conductors,
imprisoning many layers of air, which are warmed by contact with the person. It is
farther very important to protect the body from the wind, which increases so greatly the
loss of heat by evaporation.

When from any cause there is a tendency to undue elevation of the heat of the body,
cutaneous transpiration is increased, and the temperature is kept at the proper standard.
We have already considered this question in treating of the action of the skin, and we have
noted facts showing that men can work when exposed to a heat much higher than that
of the body itself. The amount of vapor that is lost under these conditions is sometimes
enormous, amounting to from two to four pounds in an hour. We have ourselves often
noted a loss of between two and three pounds after exposure for less than an hour in a
steam-bath of from 110° to 116°; and a much greater elevation of temperature, in dry
nir, can be tolerated with impunity. We have alluded to some of the observations upon
t::e temperatures that could be borne without bad results, in connection with the ques-
tion of variations in the heat of the body. In the experiments of Delaroche and Berger,
the temperature was considerably under 200°. Tillet recorded an instance of a young
girl who remained in an oven for ten minutes without inconvenience, at a temperature
of 130° Reaumur, or 324-5° Fahr. Dr. Blagden, in his noted experiments in a heated
room, made in connection with Drs. Banks, Solander, Fordyce, and others, .found, in one
series of observations, that a temperature of 211° could be easily borne; and, at another
time, the heat was raised to 260°. Chabert, who exhibited in this country and in Eu-
rope under the name of the " fire-king," is said to have entered ovens at from 400° to
600°. Under these extraordinary external conditions, the body is protected from the
radiated heat by clothing, the air is perfectly dry, and the animal temperature is kept
down by excessive evaporation from the surface.

It is a curious fact, that, after exposure of the body to an intense dry heat or to a
heated vapor, as in the Turkish or Russian baths, when the general temperature is
somewhat raised and the surface is bathed in perspiration, a cold plunge, which checks
the action of the skin almost immediately, is not injurious and is decidedly agreeable.
This presents a striking contrast to the effects of sudden cold upon a system heated and
exhausted by long-continued exertion. In the latter instance, when the perspiration is
suddenly checked, serious disorders of nutrition, inflammations, etc., are very liable to
occur. The explanation of this, as far as we can present any, seems to be the following:
When the skin acts to keep down the temperature of the body in simple exposure to
external heat, there is no modification in nutrition, and the tendency to an elevation of
the animal temperature comes from causes entirely external. It is a practical observa-
tion that no bad effects are produced, under these circumstances, by suddenly changing
the external conditions ; but, when the animal temperature is raised by a modification
of the internal nutritive processes, as in prolonged muscular effort, these changes should
not be suddenly arrested ; and a suppression of the compensative action of the skin is
apt to produce disturbances in nutrition, very often resulting in inflammations.

522 MOVEMENTS.

CHAPTER XYI.

MOVEMENTS— VOICE AND SPEECH.

Amorphous contractile substance— Ciliary movements— Movements due to elasticity— Varieties of elastic tissue-
Muscular movements— Physiological anatomy of the involuntary muscles— Mode of contraction of the invol-
untary muscular tissue — Physiological anatomy of the voluntary muscles — Fibrous and adipose tissue in the
voluntary muscles — Connective tissue — Blood-vessels and lymphatics of the muscular tissue — Connection of
the muscles with the tendons — Chemical composition of the muscles — Physiological properties of the mus-
cles—Muscular contractility, or irritability— Muscular contraction— Changes in the form of the muscular
fibres during contraction — /Secousse, Ziickung, or -spasm — Mechanism of prolonged muscular contraction —
Tetanus— Electric phenomena in the muscles — Muscular effort— Passive organs of locomotion — Physiological
anatomy of the bones— Marrow of the bones— Medullocells— Myeloplaxes— Periosteum— Physiological anatomy
of cartilage — Fibro-cartilage — Voice and speech— Sketch of the physiological anatomy of the vocal organs —
Vocal chords — Muscles of the larynx — Mechanism of the production of the voice — Appearance of the glottis
during ordinary respiration— Movements of the glottis during phonation— Variations in the quality of the
voice, depending upon differences- in the size and form of the larynx and the vocal chords- -Action of the
intrinsic muscles of the larynx in phonation — Action of the accessory vocal organs — Mechanism of the differ-
ent vocal registers— Mechanism of speech— The phonograph.

THE organic, or vegetative functions of animals involve certain movements; and
almost all animals possess, in addition, the power of locomotion. Very many of these
movements have, of necessity, been considered in connection with the different functions ;
as the action of the heart and vessels in the circulation, the uses of the muscles in respi-
ration, the ciliary movements in the air-passages, the muscular acts in deglutition, the
peristaltic movements, and the mechanism of defalcation and urination. There remain,
however, certain general facts with regard to various kinds of movement and the mode
of action of the different varieties of muscular tissue, that will demand more or less
extended consideration. As regards the exceedingly varied and complex acts concerned
in locomotion, it is difficult to fix the limits between anatomy and physiology. A full
comprehension of such movements must be preceded by a complete descriptive anatomi-
cal account of the passive and active organs of locomotion ; and special treatises on
anatomy almost invariably give the uses and actions, as well as the structure and rela-
tions of these parts.

Amorphous Contractile Substance and Amoeboid Movements. — In some of the very
lowest orders of beings, in which hardly any thing but amorphous matter and a few gran-
ules can be recognized by the microscope, certain movements of elongation and retrac-
tion of their amorphous substance have been
observed. In the higher animals, similar
movements have been noticed in certain of
their structures, such as the leucocytes, the
contents of the ovum, epithelial cells, and
connective-tissue cells. These movements
are generally simple changes in the form
of the cell, nucleus, or whatever it may be.
FIG. UG.-Am<*i>a diffluens, changing in form and They are supposed to depend upon an organic

moving in the direction indicated by the arrow, principle Called sarcode Or protoplasm ; but

it is not known that such movements are

characteristic of any one definite proximate principle, nor is it easy to determine their
cause and their physiological importance. In the anatomical elements of adult animals
of the higher classes, the sarcodic movements usually appear slow and gradual, even
when viewed with high magnifying powers ; but, in some of the very lowest orders of
beings, these movements serve as the means of progression and are more rapid. Such
movements are sometimes called amoeboid.

It does not seem possible, in the present condition of our knowledge, to explain the

CILIARY MOVEMENTS. 523

nature and cause of the movements of homogeneous contractile substance ; and it must
be excessively difficult, if not impossible, to observe directly the effects of different stim-
uli, in the manner in which we study the movements of muscles. As far as we can
judge, they are analogous to the ciliary movements, the cause of which is equally obscure.

Ciliary Movements. — The epithelium covering certain of the mucous membranes is pro-
vided with little hair-like processes upon the free portion of the cells, called cilia. These
are in constant motion, from the beginning to the end of life, and they produce currents
upon the surfaces of the membranes to which they are attached, the direction being gener-
ally from within outward. In many of the infusoria, the ciliary motion serves as a means
of progression, effects the introduction of nutriment into the alimentary canal, and, indeed,
is almost the sole agent in the performance of the functions involving movement. Even
in higher classes, as the mollusca, the movements of the cilia are of great importance.
In man and in the warm-blooded animals generally, the ciliated or vibratile epithelium is
of the variety called columnar, conoidal, or prismoidal. The cilia are attached to the
thick ends of the cells, and they form on the surface of the membrane a continuous sheet
of vibrating processes.

It is unnecessary to describe in detail the size and form of the cells provided with
cilia, as their variations in different situations have been and will be considered in con-
nection with the physiological anatomy of different parts. In general structure, the ciliary
processes are entirely homogeneous, and they gradually taper from their attachment to
the cell to an extremity of excessive tenuity. Although anatomists, from time to time,
have described striaa at the bases of the cilia and have attempted to explain their mo-
tion by a kind of muscular action, no well-defined structure has ever been actually
demonstrated in their substance.

The presence of cilia has been demonstrated upon the following surfaces : The respira-
tory passages, including the nasal fossae, the pituitary membrane, the summit of the
larynx, the bronchial tubes, the superior surface of the velum palati, and the Eustachian
tubes ; the. sinuses about the head ; the lachrymal sac and the internal surface of the
eyelids ; the genital passages of the female, from the middle of the neck of the uterus
to the extremities of the Fallopian tubes ; and the ventricles of the brain. They prob-
ably exist, also, at the neck of the capsule of Muller, in the cortical substance of the kid-
ney. In these situations, to each cell of
conoidal epithelium are attached from six to
twelve prolongations, about 3-5^-5^ °f an ^nc^
in thickness at their base, and from -g-^Vfr to
a-gVff °f an mcn in length. The appearance
of the cilia in detached cells is represented
in Fig. 147. When seen in situ, they ap-
pear regularly disposed upon the surface, are
of nearly equal length, and are generally
slightly inclined in the direction of the open-
ing of the cavity lined by the membrane.

The ciliary motion is one of the most
beautiful physiological demonstrations that
can be made with the microscope. By scrap-
ing the roof of the mouth of a living frog,
the mucous membranes of the respiratory
passages in a warm - blooded animal just
killed, the beard of the oyster or clam, and FlGt
placing the preparation, moistened with a
little serum, under a magnifying power of about two hundred and fifty diameters, the
currents produced in the liquid will be strikingly exhibited. The movements may be

524 MOVEMENTS.

studied in detached cells, in the human subject, by introducing a feather into the nose, by
which a few cells may be removed with the mucus and can be observed in the same way.
This demonstration serves to show the similarity between the movements in man and in
the lower orders of animals. When the movements are seen in a large number of cells
in situ, the appearance is very graphically illustrated by the apt comparison of Henle to
the undulations of a field of wheat agitated by the wind. In watching this movement,
it is usually seen to gradually diminish in rapidity, until what at first appeared simply as
a current, produced by movements too rapid to be studied in detail, becomes revealed as
distinct undulations, in which the action of individual cilia can be readily studied. Sev-
eral kinds of movement have been described, but the most common is a bending of the
cilia, simultaneously or in regular succession, in one direction, followed by an undulating
return to the perpendicular. The other movements, such as the infundibuliform, in
which the point describes a circle around the base, the pendulum-movement, etc., are
not common and are unimportant.

The combined action of the cilia upon the surface of a mucous membrane, moving as
they do in one direction, is to produce currents of considerable power. This may be
illustrated under the microscope by covering the surface with a liquid holding little solid
particles in suspension. In this case, the granules are tossed from one portion of the
field to another; with considerable force. It is not difficult, indeed, to measure in this
way the rapidity of the ciliary currents. In the frog it has been estimated at from -gfa
to T|T of an inch per second, the number of vibratile movements being from seventy -five
to one hundred and fifty per minute. In the fresh-water polyp the movements are more
rapid, being from two hundred and fifty to three hundred per minute. There is no reli-
able estimate of the rapidity of the ciliary currents in man, but they are probably more
active than in animals low in the scale.

The movements of cilia, like those observed in fully-developed spermatozoids, seem
to be entirely independent of nervous influence, and they are affected only by purely local
conditions. They will continue, under favorable circumstances, for more than twenty-
four hours after death and can be seen in cells entirely detached from the body when
they are moistened with proper fluids. "When the cells are moistened with pure water,
the activity of the movement is at first increased ; but it soon disappears as the cells
become swollen. Acids arrest the movement, but it may be excited by feeble alkaline
solutions. All abnormal conditions have a tendency either to retard or to abridge the
duration of the ciliary motion. It is true that, when the movement is becoming feeble,
it may be temporarily restored by very dilute alkaline solutions, but the ordinary stimuli,
such as are capable of exciting muscular contraction, are without effect. Purkinje and
Valentin, Sharpey, and others, have attempted to excite the movements of cilia by gal-
vanic stimulus, but without success. Anesthetics and narcotics, which have such a
decided effect upon muscular action, have no influence upon the cilia.

It is useless to follow the speculations that have been advanced to account for the move-
ment of cilia. There is no muscular structure in the cilia, no connection with the nervous
system, and there seems to be no possibility of explaining the movement except by a bare
statement of the fact that the cilia have the property of moving in a certain way so long
as they are under normal conditions. As regards the physiological uses of these move-
ments, it is sufficient to refer to the physiology of the parts in which cilia are found,
where the peculiarities of their action are considered more in detail. In the lungs and
the air-passages generally and in the genital passages of the female, the currents are of
considerable importance ; but it is difficult to imagine the use of these movements in
certain other situations, as the ventricles of the brain.

Movements due to Elasticity. — There are certain important movements in the body
that are due simply to the action of elastic ligaments or membranes. These are entirely
distinct from muscular movements, and are not even to be classed with the movements

MOVEMENTS DUE TO ELASTICITY.

525

produced by the resiliency of muscular tissue, in which that curious property, called
muscular tonicity, is more or less involved. Movements of this kind are never excited
by nervous, galvanic, or other stimulus, but they consist simply in the return of movable
parts to a certain position after they have been displaced by muscular action, and the
reaction of tubes after forcible distention, as in the walls of the large arteries.

Elastic Tissue. — Most writers of the present day adopt the division of the elements of
elastic tissue into three varieties. This division relates to the size of the fibres ; and all
varieties are found to possess essentially the same chemical composition and general
properties, including the elasticity for which they are so remarkable. On account of the
yellow color of this tissue, presenting, as it does, a strong contrast to the white, glisten-
ing appearance of the inelastic fibres, it is frequently called the yellow elastic tissue.

The first variety of elastic tissue is composed of small fibres, generally intermingled

Fia. 148. — Small elastic fibres, from the peritoneum ;
magnified 350 diameters. (Kolliker.)

FIG. 149.— Larger elastic fibres. (Robin.)

with fibres of the ordinary inelastic tissue. These are sometimes called, by the French,
dartoic fibres. They possess all the chemical and physical characters of the larger fibres,
but are excessively minute, measuring from ^-^nj- to ^^ or -^^ of an inch in diameter.
If we add acetic acid to a preparation of ordinary connective tissue, the inelastic fibres
are rendered semitransparent, but the elastic fibres are unaffected and become very dis-
tinct. They are then seen isolated, that is, never arranged in bundles, generally with a
dark, double contour, branching, brittle, and when broken, their extremities curled and
presenting a sharp fracture, like a piece of India-rubber. These fibres pursue a wavy
course between the bundles of inelastic fibres in the areolar tissue and in most of the ordi-
nary fibrous membranes, and here they exist as an accessory anatomical element. They
are found in greater or less abundance in the situations just mentioned ; also, in the liga-
ments (but not the tendons) ; in the layers of involuntary muscular tissue ; the true skin ;
the true vocal cords ; the trachea, bronchial tubes, and largely in the parenchyma of the
lungs ; the external layer of the large arteries ; and, in brief, in nearly all situations in
which the ordinary connective tissue exists.

The second variety of elastic tissue is composed of fibrei, larger than the first, ribbon-
shaped, with well-defined outlines, anastomosing, undulating or curved in the form of the
letter S, presenting the same curled ends and sharp fracture as the smaller fibres. These
measure from -^Vff to ToVff of an m°h m diameter. Their type is found in the ligamenta
subflava and the ligamcntum nuchee. They are also found in some of the ligaments of
the larynx, the stylo-hyoid ligament, and the suspensory ligament of the penis. The
form and arrangement of these fibres may be very strikingly demonstrated by tearing
off a portion of the ligamentuni nucha9 and lacerating it with needles in a drop of acetic

526 MOVEMENTS.

acid. The action of the acetic acid renders the accessory structures of the ligament

transparent, and the elastic fibres become very distinct. The same may be accomplished

by boiling the tissue for a short time in caustic soda.

The third variety of elastic tissue can hardly be said to consist of fibres, as their branches

are so short and their anastomoses so frequent. This kind of structure is found forming
the middle coat of the large arteries, and it has already been de-
scribed in connection with the vascular system. The fibres are
very large, flat, with numerous short branches, " which unite
again with the trunk from which they originate or with adja-
cent fibres. In certain situations, the interstices are considera-
ble, in proportion to the diameter of the fibres, and the anasto-
mosing branches are given off at acute angles, so that they
follow pretty closely the direction of the trunks, and the anas-
tomoses do not disturb the longitudinal direction and parallelism

of the fibres. Indeed, the anastomoses are so numerous, and the
Fre. 150 —Large elastic fibres . , , ,, ,, ,, », ,. . , ,,

(fenestrated membrane), intervals so small, proportionally to the fibres, that we should

u^carotid^flLTotsf; Believe we had under observation a reticulated membrane, pre-

maonified 350 diameters, senting openings, rounded and oval, some large and others
small." (Henle.) These anastomosing fibres, forming the so-
called fenestrated membranes, are arranged in layers, and the structure is sometimes
called the lamellar elastic tissue. ,

The great resistance which the elastic tissue presents to chemical action serves to
distinguish it from nearly every other structure in the body. We have already seen that
it is not affected by acetic acid or by boiling with caustic soda. It is not softened
by prolonged boiling in water, but it is slowly dissolved, without decomposition, by
sulphuric, nitric, or hydrochloric acid, the solution not being precipitable by potash. Its
organic base is a nitrogenized substance called elasticine, containing carbon, hydrogen,
oxygen, and nitrogen, without sulphur. This is supposed to be identical with the sarco-
lemma of the muscular tissue.

The purely physical property of elasticity plays an important part in many of the
animal functions. We have already had an example of this in the action of the large
arteries in the circulation and in the resiliency of the parenchyma of the lungs ; and we
shall have occasion, in treating of the functions of other parts, to refer again to the uses
of elastic membranes and ligaments. The ligamenta subflava and the ligamentum nucha3
are important in aiding to maintain the erect position of the body and head, and to restore
this position when flexion has been produced by muscular action. Still, the contraction
of muscles is also necessary to keep the body in a vertical position.

Muscular Movements.

Muscular movements are observed only in the higher classes of animals. Low in the
scale of animal life, we have the contractions of amorphous substance and ciliary motion ;
and, in some vegetables, movements, even attended with locomotion, have been observed.
These facts make the absolute distinction between the two kingdoms a question of some
difficulty ; but in animals only, do we have a distinct muscular system.

The muscular movements capable of being excited by stimulus of various kinds are
divided into voluntary and involuntary ; and generally there is a corresponding division
of the muscles as regards their minute anatomy. The latter, however, is not absolute ;
for there are certain involuntary functions, like the action of the heart or the movements
of deglutition, that require the rapid, vigorous contraction characteristic of the voluntary
muscular tissue, and here we do not find the structure characteristic of the involuntary
muscles. With a few exceptions, however, the anatomical division of the muscular tissue
into voluntary and involuntary is sufficiently distinct.

STRUCTURE OF THE INVOLUNTARY MUSCLES.

527

Physiological Anatomy of the Involuntary Muscles. — We have so often described this
tissue, as it is found in the vascular system, the digestive organs, the skin, and in other
situations, that it will not be necessary, in this connection, to give more than a sketch
of its structure and mode of action.

The involuntary muscular system presents a striking contrast to the voluntary mus-
cles, not only in its minute anatomy and mode of action, but in the arrangement of its
fibres. While the voluntary muscles are almost invariably attached by their two extrem-
ities to movable parts, the involuntary muscles form sheets or membranes in the walls of
hollow organs, and, by their contraction, they simply modify the capacity of the cavities
which they enclose. Various names have been given to this tissue to denote its distribu-
tion, mode of action, or structure. The name involuntary muscle indicates that its contrac-
tion is not under the control of the will ; and this is the fact, these muscles being chiefly
animated by the sympathetic system of nerves, while the voluntary muscles are supplied
mainly from the cerebro-spinal system. On account of the peculiar structure of these
fibres, they have been called muscular fibre-cells, smooth muscular fibres, pale fibres,
non-striated fibres, fusif6rm fibres, and contractile cells. The distribution of these fibres
to parts concerned in the organic or vegetative functions, as the alimentary canal, has
given them the name of organic muscular fibres, or fibres of organic, or vegetative life.
It is difficult to isolate the individual fibres of this tissue in microscopical preparations;
and, when seen in situ, their borders are faint, and we can make out their arrangement

Fio. 151. — Muscular fibres from
the urinary I/ladder of the
htvman subject; magnified
200 diameters. (Sappey.)

1, 1, 1, nuclei ; 2, 2, 2, borders of
some of the fibres ; 3, 3, iso-
lated fibres; 4, 4, two fibres
joined together at (5).

FIG. 152.— Mwcular fibre* from
the aorta of the calf; magni-
fied 200 diameters. (Sappey.)

1, 1, fibres joined with each other ;
2, 2, 2, isolated fibres.

FIG. 153.— Muscular fibres from the uterus
of a woman who died at the ninth
month of utero-gestation ; magnified
850 diameters. (Sappey.)

1, 1, 2, short, wide fibres; 8, 4, 5, 5, lon-rer
and narrower fibres: 6, 6, two fibres
united at (T) ; 8, small fibres in process
of development.

best by the appearance of their nuclei. Robin recommends soaking of the tissue for a few
days in a mixture of one part of ordinary nitric acid to ten of water. This renders the
fibres dark and granular, makes their borders very distinct, and frequently some of them
become entirely isolated. The nuclei, however, are obscured. In their natural condi-
tion, the fibres are excessively pale, very finely granular, flattened, and of an elongated
spindle-shape, with a very long, narrow, almost linear nucleus in the centre. The nu-
cleus generally has no nucleolus, and it is sometimes curved or shaped like the letter S.

528 , MOVEMENTS.

The ordinary length of these fibres is about -yfo, and their breadth about ^Vs- °f an inch.
In the gravid uterus they undergo remarkable hypertrophy, measuring here from -fa
to ^ of an inch in length, and ^Vo °f an inc^ ^n breadth. The peculiarities of their
structure in the uterus will be fully considered under the head of generation.

In the contractile sheets formed of involuntary muscular tissue, the fibres are arranged
side by side, are closely adherent, and their extremities are, as it were, dove-tailed into ead-
other. Generally the borders of the fibres are regular and their extremities are simple ;
but sometimes the ends are forked, and the borders present one or more little projections.
It is very seldom that we see the fibres in a single layer, except in the very smallest arte-
rioles. Usually the layers are multiple, being superimposed in regular order. The action
of acetic acid is to render the fibres pale, so that their outlines become almost indistin-
guishable, and to bring out the nuclei more strongly. If we have an indistinct sheet of
this tissue in the field of view, the addition of acetic acid, by bringing out the long, nar-
row, and curved nuclei arranged in regular order, and by rendering the fibrous and other
structures more transparent, will often enable us to recognize its character.

Contraction of the Involuntary Muscular Tissue. — The mode of contraction of the
involuntary muscles is peculiar. It does not take place immediately upon the reception
of a stimulus, applied either directly or through the nerves, but it is gradual, enduring for
a time and then followed by slow and gradual relaxation. A description of the peristaltic
movements of the intestines gives a perfect idea of the mode of contraction of these
fibres, with the gradual propagation of the stimulus along the alimentary canal, as the
food makes its impression upon the mucous membrane. An equally striking illustration
is afforded by labor-pains. These are due to the muscular contractions of the uterus,
and they last from a few seconds to one or two minutes. Their gradual access, continua-
tion for a certain period, and gradual disappearance coincide exactly with the history of
the contractions of the involuntary muscular fibres.

The contraction of the involuntary muscular tissue is slow, and the fibres return
slowly to a condition of repose. The movements are always involuntary. Peristaltic
action is the rule, and the contraction takes place progressively and without oscillations.
Contractility persists for a long time after death. Arrest of function is followed by little
or no atrophy, and hypertrophy is very marked as the result of exaggerated action. Ex-
citation of the nerves has less influence upon contraction of these fibres than direct exci-
tation of the muscles. The involuntary muscular tissue is regenerated very rapidly, while
the structure of the voluntary muscles is restored with great difficulty after destruction
or division. (Legros and Onimus.)

Physiological Anatomy of the Voluntary Muscles. — A voluntary muscle is the most
highly organized and is possessed of the most varied endowments of all living structures.
It contains, in addition t<3 its own peculiar contractile substance, fibres of inelastic and
elastic tissue, adipose tissue, numerous blood-vessels, nerves, and lymphatics, with certain
nuclear and cellular anatomical elements. The muscular system in a well-proportioned
man equals, according to Sappey, about two-fifths of the weight of the body. Its nutri-
tion consumes a large proportion of the reparative material of the blood, while its disas-
similation furnishes a corresponding quantity of excrementitious matter. The condition
of the muscular system, indeed, is an almost unfailing evidence of the general state of
the body, allowing, of course, for peculiarities in different individuals. Among the
characteristic properties of the muscles are, elasticity, a constant and insensible tendency
to contraction, called tonicity, the power of contracting forcibly on the reception of a
proper stimulus, called irritability, a peculiar kind of sensibility, and the faculty of gen-
erating galvanic currents. The relations of particular muscles, as taught by descriptive
anatomy, involve special functions; but the most interesting physiological points con-
nected with this system relate to the general properties and functions of the muscles, and
must necessarily be prefaced with a sketch of their general anatomy.

STRUCTURE OF THE VOLUNTARY MUSCLES.

529

It has been demonstrated by minute dissection that all of the red, or voluntary mus-
cles are made up of a great number of microscopic fibres, known as the primitive muscular
fasciculi. These are called red, striated, or voluntary fibres, or the fibres of animal life.
Their structure is complex, and they may be subdivided longitudinally into fibrillae, and
transversely into disks, so that it is somewhat doubtful as to what is, strictly speaking,
the ultimate anatomical element of the muscular tissue.

A primitive muscular fasciculus runs the entire length of the muscle, and is enclosed
in its own sheath, without branching or inosculation. This sheath contains the true
muscular substance only, and it is not penetrated by blood-vessels, nerves, or lymphatics.
If we examine with the microscope a thin, transverse section of a muscle, the divided ends
of the fibres will present an irregularly polygonal form, with rounded corners. They
seem to be cylindrical, however, when viewed in their length and isolated. Their color
by transmitted light is a delicate ambe'r, resembling somewhat the color of the blood-
corpuscles.

FIG. 154.— Striated muscular fibres, from the mouse ; magnified 500 diameters. (From a photograph taken ct

the United States Army Medical Museum.)
The injected capillaries are seen, somewhat out of focus.

The primitive fasciculi vary very much in size in different individuals, in the same
individual under different conditions, and in different muscles. As a rule, they are smaller
in young persons and in females than in adult males. They are comparatively small in
persons of slight muscular development. In persons of great muscular vigor, or when
the general muscular system or particular muscles have been increased in size and power
by exercise, the fasciculi are relatively larger. It is probable that the physiological
increase in the size of a muscle from exercise is due to an increase in the size of the pre-
existing fasciculi, and not to the formation of any new elements. In young persons, the
34

530

MOVEMENTS.

fasciculi are from ^'-5- to T^-Q- of an inch in diameter. In the adult, they measure from

Tfo to -STV of an inch-

The appearance of the primitive muscular fasciculi under the microscope is character-
tic and unmistakable. They present regular, transverse striae, formed of alternating dark
and clear bands about ^yforr °f an mc^ wide. These are generally very distinct in healthy
muscles. In addition, we frequently observe longitudinal striae, not so distinct, and quite
difficult to follow to any extent in the length of the fasciculus, but tolerably well marked,
particularly in muscles that are habitually exercised. The muscular substance, present-
ing this peculiar striated appearance, is enclosed in an excessively thin but elastic and
resisting tubular membrane, called the sarcolemma or myolemma, which is probably
composed of the same substance as the elastic tissue. This envelope cannot be seen in
ordinary preparations of the muscular tissue ; but it frequently happens that the con-
tractile muscular substance is broken, leaving the sarcolemma intact, which gives a good
view of the membrane and conveys an idea of its strength and elasticity. Attached to
the inner surface of the sarcolemma, are numerous small, elongated nuclei with their
long diameter in the direction of the fasciculi. These are usually not well seen in the
unaltered muscle, but the addition of acetic acid renders the muscular substance pale and
destroys the striae, when the nuclei become very distinct.

"Water, after a time, acts upon the muscular tissue, rendering the fasciculi somewhat
paler and larger. Acetic acid and alkaline solutions efface the stria3, and the fibres
become semitransparent. In fasciculi that are slightly decomposed, there is frequently a
separation at the extremity into numerous smaller fibres, called fibrillse. These, when
isolated, present the same striated appearance as the primitive fasciculus ; viz., alternate
dark and light portions. They measure about ^1-^ of an inch in diameter, and their
number, in the largest primitive fibres, is estimated by Kolliker at about two thousand.
The structure of the fibrillse is probably uniform, the appearance of alternate dark and
light segments being due to differences in thickness. In fact, it is well known that water,
by its simple mechanical action, swells the fibrillae and causes the stria3 to disappear.

Late researches have shown that the interior of each primitive fasciculus is pene-
trated by an excessively delicate membrane, closely surrounding the fibrillae. This

arrangement may be distinctly seen in a
thin section of a fibre treated with a solu-
tion of salt in water in the proportion of
five parts per thousand. The arrangement
of this membrane, which is nothing more
nor less than a series of tubular sheaths
for the fibrillae, is a strong argument in
favor of the view that the fibrilla is the ana-
tomical element of the muscular tissue.

When we come to the question of the
real anatomical element of the muscular tis-
sue, there are only two reasonable views
that present themselves. One is that any
subdivision of the primitive fasciculus is arti-
ficial, and that it, with its investing mem-
brane, the sarcolemma, is the true element.
An argument in favor of this opinion is that
the tissue is most readily separated into fas-
ciculi, each enclosed in its own membrane
and not penetrated by vessels, nerves, or
lymphatics ; while the fibrillse are situated
in a reticulum of canals, from which they cannot readily be isolated. The other opinion,
that the fibrillae are the ultimate elements, is based upon the fact that these little fibres

FIG. 155. — Voluntary muscular fibres; magnified
250 diameters. (Sappey.)

A, transverse strise and nuclei of a primitive fasciculus ;
B, longitudinal striae and fibrillae of a primitive fas-
ciculus in which the sarcolemma has been lacerated
at one point by pressure.

STEUCTURE OF THE VOLUNTARY MUSCLES. 531

present the striae and all the anatomical characteristics of the primitive fasciculi, and that
by far the most natural and easy mode of separation of these fasciculi is in a longi-
tudinal direction. The question of adopting one or the other of these views is not of
very great physiological importance. *

Fibrous and Adipose Tissue in the Voluntary Muscles. — The structure of the mus-
cles strikingly illustrates the relations between the principal and the accessory anatomi-
cal elements of tissues. The characteristic, or principal element is, of course, the mus-
cular fibre or fibrilla ; but we also find in the substance of the muscles certain anatomi-
cal elements, not peculiar to the muscles, and merely accessory in their function, but
none the less necessary to their proper constitution. For example, every muscle is com-
posed of a number of primitive fasciculi ; but these are gathered into secondary bundles,
which in turn are collected into bundles of greater and greater size, until, finally, the
whole muscle is enveloped in its sheath and is penetrated by a fibrous connective sub-
stance. We find, probably, in the muscles, the best illustration of the structure of what
is known as the connective tissue.

Connective Tissue. — We have already had occasion to refer to certain of the elements
of connective tissue, more especially the inelastic and elastic fibres. In this connection,
we shall treat specially of the connective tissue of the muscles ; but our description will
answer for almost all situations in which fibrous tissue exists merely for the purpose of
holding parts together. In the muscles, we have a membrane holding a number of the
primitive fasciculi into secondary bundles. This is known as the perimysium. The
fibrous membranes that connect together these secondary bundles with their contents
are enclosed in a sheath enveloping the whole muscle, sometimes called the external
perimysium. The peculiarity of these membranes, and their distinction from the sar-
colemma, are that they have a fibrous structure and are connected together throughout the
muscle, while the tubes forming the sarcolemma are structureless, and each one is dis-
tinct.

FIG. 15G.— Fibres of tendon of the human subject. (Rollett.)

The name now most generally adopted for the tissue under consideration is connec-
tive tissue. It has been called cellular, areolar, or fibrous, but most of these names were
given to it without a clear idea of its structure. Its principal anatomical element is a
fibre of excessive, almost immeasurable, tenuity, wavy, and with a single contour. These
fibres are connected into bundles of very variable size and are held together by an
adhesive amorphous substance. The wavy lines that mark the bundles of fibres give
them a very characteristic appearance.

The direction and arrangement of the fibres in the various tissues present marked

532

MOVEMENTS.

differences. In the loose areolar tissue beneath the skin and between the muscles, and
in the loose structure surrounding some of the glands and connecting the sheaths of
blood-vessels and nerves to the adjacent parts, the bundles of fibres form a large net-
work and are very wavy in their course. In the strong, dense membranes, as the
aponeuroses, the proper coats of many glands, the periosteum and perichondrium, and
the serous membranes, the waves of the fibres are shorter, and the fibres themselves
interlace much more closely. In the ligaments and tendons, the fibres are more nearly
straight and are all arranged longitudinally.

On the addition of acetic acid, the bundles of inelastic fibres swell up, become semi-
transparent, and the nuclei and elastic fibres are brought out. The proportion of elastic
fibres differs very much in different situations, but they are all of the smallest variety, and
they present a striking contrast to the inelastic fibres in their form and size. Although
they are still very small, they always present a double contour.

FIG. 157.— Loose net-work of connective tissue from the human subject, showing the fibres and cells. (Eollett.)

a, a, a capillary blood-vessel

Certain cellular and nuclear elements are always found in the connective tissue. The
cells have been described under the name of connective-tissue cells. They are very
irregular in size and form, some of them being spindle-shaped or caudate, and others,
star-shaped. They possess one, and sometimes two or three clear, ovoid nuclei, with
distinct nucleoli. On the addition of acetic acid the cells disappear, but the nuclei are
unaffected. These are the fibro-plastic elements of Lebert, and the embryo-plastic ele-
ments of Robin. It is impossible to give any accurate measurements of the cells, on
account of their great variations in size. The length of the nuclei is from ^Vo to ^Vs
of an inch, and their diameter, from -^^ to ^-5- of an inch. The appearance of the
connective tissue, with a few cells and nuclei, is represented in Fig. 157.

Between the muscles, and in the substance of the muscles between the bundles of
fibres, there always exists a greater or less quantity of adipose tissue in the meshes of
the fibrous structure.

Blood-vessels and Lymphatics. — The muscles are abundantly supplied with blood-ves-
sels, generally by a number of small arteries with two satellite veins. The capillary

PHYSIOLOGICAL PROPEETIES OF THE MUSCLES. 533

arrangement in this tissue is peculiar. From the smallest arterioles, capillary vessels are
given off, arranged in a net- work with tolerably regular, oblong, rectangular meshes,
their long diameter following the direction of the fibres. These envelop each primitive
fasciculus, enclosing it completely, the artery and vein being upon the same side. The
capillaries are smaller than in any other part of the vascular system. When distended
with blood they are from ^V^ to -^^ of an inch in diameter ; and when empty their
diameter is from -^V^ to inrViy °f an inch.

The arrangement of the lymphatics in the muscles has never been definitely ascer-
tained. There are numerous lymphatics surrounding the large vascular trunks of the
extremities and of the abdominal and thoracic walls, which, it would appear, must come
from the substance of the muscles ; but they have never been traced to their origin.
Sappey has succeeded in injecting lymphatics upon the surface of some of the larger
muscles, but he has not been able to follow them into the muscular substance.

Connection of the Muscles with the Tendons. — It is now generally admitted that the
primitive muscular fasciculi terminate in little conical extremities, which are received
into corresponding depressions in the bundles of fibres composing the tendons; but this
union is so close, that the muscle or the tendon may be ruptured without a separation at
the point of union. In the penniform muscles this arrangement is quite uniform and
elegant. In other muscles it is essentially the same, but the perimysium seems to be con-
tinuous with the loose areolar tissue enveloping the corresponding tendinous bundles.

Chemical Composition of the Muscles. — We are as yet so little acquainted with the
exact constitution of the nitrogenized constituents of the body, that we cannot appreciate
the nature of all the proximate principles that exist in the muscular substance. The
most important of these is musculine. This resembles fibrin, but it presents certain points
of difference in its behavior to reagents, by which it may be readily distinguished. One
of its peculiar properties is that it is dissolved at an ordinary temperature by a mixture
of one part of hydrochloric acid and ten of water.

The muscular substance is permeated by a fluid, called the muscular juice, which con-
tains a peculiar coagulable principle called myosine.

Combined with the organic principles, we find a great variety of mineral salts in the
muscular substance, that cannot be separated without incineration. Certain excremen-
titious matters have also been found in the muscles ; and probably nearly all of those
eliminated by the kidneys exist here, although they are taken up by the blood as fast as
they are produced and are consequently detected with difficulty. The muscles also con-
tain inosite, inosic acid, lactic acid, and certain other acids of fatty origin. During life,
the muscular fluid is slightly alkaline, but it becomes acid soon after death. The muscle
itself, during contraction, has an acid reaction. The muscular juice is alkaline or neutral
after moderate exercise, as well as during complete repose ; but, when a muscle is made
to undergo excessive exercise, the lactic acid exists in greater quantity, and the reaction
becomes acid.

Physiological Properties of the Muscles.

The general properties of the striated muscles, as distinguished from all other tissues
except the involuntary muscles, are as follows: 1. Elasticity; 2. Tonicity; 3. Sensi-
bility of a peculiar kind ; 4. Contractility, or irritability. These are all necessary to the
physiological action of the muscles. Their elasticity is brought into play in opposing
muscles or sets of muscles ; one set acting to move a part and to extend the antagonistic
muscles, which, by virtue of their elasticity, retract when the extending force is removed.
Their tonicity is an insensible and a more or less constant contraction, by which the
action of opposing muscles is balanced when both are in the condition of what we call
repose. Their sensibility is peculiar and is expressed chiefly in the sense of fatigue and

534 MOVEMENTS.

in the appreciation of weight and of resistance to contraction. Their contractility or
irritability is the property which enables them to contract and exert a certain amount of
mechanical force under the proper stimulus. All of these general properties strictly
belong to physiology, as do some special acts that are not neceisarily involved in the
study of ordinary descriptive anatomy.

Elasticity of Muscles. — The true muscular substance contained in the sarcolemma is
eminently contractile; and, although it may possess a certain degree of elasticity, this
property is most strongly marked in the accessory anatomical elements. The interstitial
fibrous tissue is loose and possesses a certain number of elastic fibres, and, as we have
seen, the sarcolemma is very elastic. It is probably the sarcolemraa that gives to the
muscles their retractile power after simple extension.

It is unnecessary to follow out in detail all of the numerous experiments that have
been made upon the elasticity of muscles. There is a certain limit, of course, to their
perfect elasticity (understanding by this the degree of extension that is followed by com-
plete retraction), and this cannot be exceeded in the human subject without dislocation
of parts. It has been found by Marey, that the gastrocnemius muscle of a frog, detached
from the body, can be extended about one-fiftieth of an inch by a weight of a little more
than three hundred grains. This weight, however, did not extend the muscle beyond
the limit of perfect elasticity. The muscle of a frog of ordinary size was extended beyond
the possibility of complete restoration, by a weight of about seven hundred and fifty
grains. Marey also showed that fatigue of the muscles increased their extensibility and
diminished their power of subsequent retraction. This fact has an application to the
physiological action of muscles; for it is well known that they are unusually relaxed
during fatigue after excessive exertion, and, as we should expect, they are at that time
more than ordinarily extensible.

Muscular Tonicity. — The muscles, under normal conditions, have an insensible and
a constant tendency to contract, which is more or less dependent upon the action of the
motor nerves. If, for example, a muscle be cut across in a surgical operation, the divided
extremities become permanently retracted ; or, if the muscles of one side of the face be
paralyzed, the muscles upon the opposite side insensibly distort the features. It is diffi-
cult to explain these phenomena by assuming that tonicity is due to reflex action, for
there is no evidence that the contraction takes place as the consequence of a stimulus.
All that we can say is, that a muscle, not excessively fatigued, and with its nervous
connections intact, is constantly in a state of insensible contraction, more or less marked,
and that this is an inherent property of all of the contractile tissues.

Sensibility of the Muscles. — The muscles possess to an eminent degree that kind of
sensibility which enables us to appreciate the power of resistance, immobility, and elas-
ticity of substances that are grasped, on which we tread, or which, by their weight, are
opposed to the exertion of muscular power. It is by the appreciation of weight and
resistance that we regulate the amount of force required to accomplish muscular acts.
These properties refer chiefly to simple muscular efforts. After long-continued exertion
we appreciate a sense of fatigue that is peculiar to the muscles. It is difficult to separate
this entirely from the sense of nervous exhaustion, but it seems to be, to a certain extent,
distinct; for, when suffering from the fatigue that follows over-exertion, it seems as
though we could send a nervous stimulus to the muscles, to which they are, for the time,
unable to respond. When we come to consider fully the subjects of muscular and ner-
vous irritability, we shall see that these two properties are entirely distinct, and that we
may exhaust or destroy the one without necessarily affecting the other.

When the muscles are thrown into spasm or tetanic contraction, a peculiar sensation
is produced, entirely different from painful impressions made upon the ordinary sensitive

PHYSIOLOGICAL PROPERTIES OF THE MUSCLES. 535

nerves. In the cramps of cholera, tetanus, or the convulsions from strychnine, these
distressing sensations are very marked. The so-called recurrent sensibility of the anterior
roots of the spinal nerves is probably due in part to the tetanic contractions produced by
galvanizing these filaments. This question, however, will be taken up again in connection
with the nervous system.

If the muscles possess any general sensibility, it is very faint. A muscle may be
lacerated or irritated in any way without producing actual pain, although we always can
appreciate the contraction produced by irritants and the sense of tension when the mus-
cles are drawn upon.

Muscular Contractility, or Irritability. — Physiologists now regard muscular irrita-
bility as synonymous with contractility; and, perhaps, the latter term more nearly
expresses the fact, although the term irritability, applied to the nerves, and even of late
years to the glands, is one very generally used.

By irritability we understand a property belonging to highly-organized parts, which
enables them to perform certain peculiar and characteristic functions in obedience to a
proper stimulus. In the sense in which the terra is generally received, it is proper to apply
it to any tissue or organ that performs its vital function, so called, under a natural or an
artificial stimulus. The nerves receive impressions and carry a stimulus to the muscles,
causing them to contract. This property, which is always present during life, under normal
conditions, and which persists for a certain period after death, is called nervous irritability.
It has lately been shown that the application of a proper stimulus will induce secretion by
the glands; and Bernard has called this glandular irritability. The application of a stim-
ulus to the muscular tissue causes the fibres to contract ; and this is muscular irritability.
As it always involves contraction and is extinct only when the muscles can no longer act,
it is equally proper to call this property contractility. No property, such as we under-
stand by this definition of irritability, is manifested by tissues or organs that have purely
passive or mechanical functions, such as bones, cartilages, and fibrous or elastic mem-
branes. The term irritability can only be applied properly to nerves or nerve-centres,
to contractile structures, and to glands.

During life and under normal conditions, the muscles will always contract in obe-
dience to a proper stimulus applied either directly or through the nerves. In the natural
action of the organism, this contraction is induced by nervous influence through reflex
action or volition. Still, a muscle may be living and yet have lost its contractility.
For example, after a muscle has been for a long time paralyzed and disused, the applica-
tion of the most powerful galvanic excitation will fail to induce contraction. But, when
we examine such a muscle with the microscope, it is found that the nutrition has become
profoundly affected, and that the contractile substance has disappeared, giving place to
inert fatty matter. Muscular contractility persists for a certain time after death and in
muscles separated from the body; and this fact has been taken advantage of by physiolo-
gists in the study of the so-called vital properties of the muscular tissue. We have
already seen that a muscle detached from the living body continues for a time to respire,
and probably it undergoes some of the changes of disassimilation observed in the organ-
ism. So long as these changes are restricted to the limits of physical and chemical integ-
rity of the fibre, contractility remains. As these processes are very slow in the cold-
blooded animals, the irritability of all the parts persists for a considerable time after
death. We have repeatedly demonstrated muscular contractility, several days after
death, in alligators and turtles.

In the human subject and the warm-blooded animals, the muscles cease to respond to
excitation a few hours after death, although the time of disappearance of irritability is
very variable. Xysten, in a number of experiments upon the disappearance of contrac-
tility in the human subject after decapitation, found that different parts lost their con-
tractility at different periods, but that generally this depended upon exposure to the air.

536

MOVEMENTS.

With the exception of the right auricle of the heart, the muscles of the voluntary sys-
tem were the last to lose their irritability. In one instance, certain of the voluntary
muscles that had not been exposed retained their contractility seven hours and fifty min-
utes after death. The observations of Longet and Masson show that a galvanic shock,
sufficiently powerful to produce death, instantly destroys the irritability of the muscular
tissue and of the motor nerves.

One of the most important questions to determine with regard to muscular irritability
is whether it be a property inherent in the muscular tissue or derived from the nervous
system. The fact that muscles can be excited to more powerful and regular contractions
by stimulating the motor nerves than by operating directly upon their substance, and the
great difficulty in tracing the nerves to their termination in the muscles, have led to the
view that muscular contractility is dependent upon nervous influence, and consequently
that the muscles have no irritability or contractility, as a property inherent in their own
substance. This doctrine, however, cannot be sustained.

The experiments of Longet, published in 1841, presented almost conclusive proof
of the independence of muscular irritability. He resected the facial nerve and found
that it ceased to respond to mechanical and galvanic stimulus, or, in other words, lost
its irritability, after the fourth day. Operating, however, upon the muscles supplied
exclusively with filaments from this nerve, he found that they responded promptly to
mechanical and galvanic irritation, and that they continued to contract, under stimu-
lation, for more than twelve weeks. In some farther experiments it was shown that,
while the contractility of the muscles could be seriously influenced through the ner-
vous system, this was effected only by modifications in their nutrition. When the
mixed nerves were divided, the nutrition of the muscles was generally disturbed ; and,

although muscular irritability persisted for some time
after the nervous irritability had disappeared, it be-
came very much diminished at the end of six weeks.
These experiments are very striking and satisfactory;
but the whole question was definitively settled by the
observations of Bernard upon the peculiar influence of
the woorara-poison and the sulphocyanide of potas-
sium. As the result of these experiments, it was
ascertained that some varieties of woorara destroy
the irritability of the motor nerves, leaving the sen-
sitive filaments intact. If a frog be poisoned by intro-
ducing a little of this agent under the skin, irritation,
galvanic or mechanical, applied to an exposed nerve,
fails to produce the slightest muscular contraction ; but,
if the stimulus be applied directly to the muscles, they
will contract vigorously. In this way the nerves are,
as it were, dissected out from the muscles ; and the dis-
covery of an agent that will paralyze the nerves with-
out affecting the muscles affords conclusive proof that
the irritability of these two systems is entirely distinct.
If a frog be poisoned with sulphocyanide of potassium,
precisely the contrary effect will be observed ; that is,
the muscles will become insensible to excitation, while
the nervous system is unaffected. This fact may be
demonstrated by applying a tight ligature around the
body in the lumbar region, involving all the parts ex-
cept the lumbar nerves. If the poison be now intro-
duced beneath the skin of the parts above the ligature, the anterior parts only are affect-
ed, because the vascular communication with the posterior extremities is cut off. If the

FIG. 158. — Frog's legs prepared so as to
show the, effects of woorara. (Bernard.)

Galvanization of the nerves in this animal,
which has been poisoned with woorara,
has no effect ; while galvanization applied
directly to the muscles (see dotted lii
produces contraction.

Ines)

PHYSIOLOGICAL PROPERTIES OF THE MUSCLES. 537

exposed nerves be now galvanized, the muscles of the legs are thrown into contraction,
showing that the nervous irritability remains. Reflex movements in the posterior
extremities may also be produced by irritation of the parts above the ligature. These
experiments, most of which we have frequently repeated, taken in connection with the
observations of Longet, leave no doubt of the existence of an inherent and independent
irritability in the muscular tissue. Contractions of muscles, it is true, are normally
excited through the nervous system, and artificial stimulation of a motor or mixed nerve
is the most efficient method of producing the simultaneous action of all the fibres of a
muscle or of a set of muscles ; but galvanic, mechanical, or chemical irritation of the
muscles themselves will produce contraction, after the nervous irritability has been
abolished.

The conditions under which muscular irritability exists are simply those of normal
nutrition of the muscular tissue. When the muscles have become profoundly affected
in their nutrition, as the result of section of the mixed nerves or after prolonged paraly-
sis, the irritability disappears and cannot be restored. The determination of the pres-
ence or absence of muscular contractility, in cases of paralysis, is one of the methods of
ascertaining whether treatment directed to the restoration of the nervous power will be
likely to be followed by favorable results. If the muscular irritability have entirely dis-
appeared, it is almost useless to attempt to restore the functions of the part.

A great many experiments have been made with regard to the influence of the circu-
lation upon muscular irritability, chiefly with reference to the effects of tying large vessels.
Among the most recent are those of Longet. He tied the abdominal aorta in five dogs and
found that voluntary motion ceased in about a quarter of an hour, and that the muscular
irritability was extinct in two hours and a quarter. When the blood was restored, after
three or four hours, by removing the ligature, the irritability and finally voluntary move-
ment returned. These experiments show that the circulation of the blood is necessary
to the contractility of the muscles. Tying the vena cava did not affect the irritability of
the muscles. In dogs in which this experiment was performed, the lower extremities
preserved their contractility, and the voluntary movements were unaffected up to the
time of death, which took place in twenty-six hours.

The relations of muscular irritability to the circulation have been farther illustrated,
in some very curious and interesting experiments, by Dr. Brown-Sequard. The first
observations were made upon two men executed by decapitation. Thirteen hours and
ten minutes after death, when the muscular irritability had entirely disappeared and was
succeeded by cadaveric rigidity, a quantity of fresh, defibrinated venous blood, from the
human subject, was injected into the arteries of one hand and was returned by the veins.
It was afterward reinjected several times during a period of thirty-five minutes. The
whole time occupied in the different injections was from ten to fifteen minutes. Ten
minutes after the last injection, and about fourteen hours after death, the irritability was
found to have returned, in a marked degree, in twelve muscles of the hand. There were
only two muscles out of the nineteen, in which the irritability could not be demonstrated.
Three hours after, the irritability still existed, but it disappeared a quarter of an hour
later. The second observation was essentially the same, except that defibrinated blood
from the dog was used, and the experiments were made upon the muscles of the arm.
The irritability was restored in all of the muscles, and it persisted, the cadaveric rigidity
having disappeared, twenty hours after decapitation. These experiments are exceedingly
interesting, as showing the dependence of irritability upon certain of the processes
of nutrition, which are probably restored, though temporarily and imperfectly, by the
injection of fresh blood. They are also important in connection with the study of
cadaveric rigidity of muscles, a condition which follows the loss of their so-called vital
properties. The subject of cadaveric rigidity will be fully discussed as one of the phe-
nomena of death.

538

MOVEMENTS.

Muscular Contraction.

The stimulus of the will, conveyed through the conductors of motor influences from
the brain to a muscle or set of muscles, produces an impression upon the muscular fibres
and causes them to contract. In parts where the muscles have been exercised and edu-
cated, this action is regulated with exquisite nicety, so that the most delicate and rapid,
as well as powerful contractions may be produced. Certain movements, not under the
control of the will, are produced as the result of unconscious reflection from a nervous
centre, along the motor conductors, of an impression made upon sensitive nerves. During
this action, certain important phenomena are observed in the muscles themselves. They
change in form, consistence, and, to a certain extent, in their constitution ; the different
periods of their stimulation, contraction, and relaxation are positive and well-marked ;
their nutrition is for the time modified ; they develop galvanic currents ; and, in short,
they present a number of general phenomena, distinct from the results of their action,
that are more or less interesting and important to the physiologist.

The most striking of the phenomena accompanying muscular action is shortening and
hardening of the fibres. It is only necessary to observe the action of any well-developed
muscle to appreciate these changes. The active shortening is shown by the approxima-
tion of the points of attachment, and the hardening is sufficiently palpable. The latter

phenomenon is marked in proportion to
the development of the true muscular
tissue and its freedom from inert mat-
ter, such as fat. We have already seen
that it is the muscular substance alone
which has the property of contraction ;
and we have shown that this action in-
creases the consumption of oxygen and
probably of other matters, the produc-
tion of carbonic acid and some other
excrernentitious principles, and that it
develops heat.

Notwithstanding the marked and
constant changes in the form and con-
sistence of the muscles during contrac-
tion, their actual volume is unchanged,
or it undergoes modifications so slight
that they may practically be disre-
garded. Experiments upon this point
have been so uniform in their results,
that it is hardly necessary to refer to
them in detail. All modern observers
accept the results of the older experi-
ments, in which muscles have been made
to contract in a vessel of water con-
nected with a small upright tube, show-
ing that, when the muscles are in active
contraction as the result of a galvanic
stimulus, the elevation of the liquid in
the tube is unchanged. It is evident,
therefore, that a muscle, while it hard-
ens and changes in form during contraction, does not sensibly change in its actual volume.

Changes in the Form of the Muscular Fibres during Contraction. — It has been found
exceedingly difficult to determine a question apparently so simple as that of the change

to show that muxcles do not increase
in volume during contraction. (Marey.)
A, vessel of water, provided with a tube (C) ; B, galvanic ap-
paratus ; D, nerve, to which the stimulus is applied.

MUSCULAR CONTRACTION-. 539

in form which the muscular fibres undergo during contraction ; and it is only of late
years that this single point has been definitively settled. The idea that the fibres
do not shorten, but that they assume a zigzag arrangement during contraction, is not
adopted by any modern writers. All are now agreed that in muscular contraction
there is an increase in the thickness of the fibre, exactly compensating its diminution in
length. This has been repeatedly observed in microscopical examinations, and the only
points now to determine are the exact mechanism of this transverse enlargement, its
duration, the means by which it may be excited, and its physiological modifications.
These questions, within the last few years, have been made the subjects of elaborate
investigations by Helmholtz, Du Bois-Reymond, Aeby, Marey, and others ; and, although
it is hardly necessary to follow these experimenters through all of their investigations,
many points have been developed, particularly by the system of registering the muscular
movements, that possess considerable physiological importance.

One essential condition in the study of the mechanism of muscular contraction is to
imitate, in a muscle or a part of a muscle that can be subjected to direct observation, the
force that naturally excites it to contraction. The application of electricity to the nerve
is beyond all question the most perfect method that can be employed for this purpose.
We can in this way excite a single contraction, or, by employing a rapid succession of
currents, we can excite either continuous or tetanic action. While the electric current is
not identical with the nervous force, it is the best substitute we can employ in experi-
ments upon muscular contractility, and it has the advantage of not affecting the physical
and chemical integrity of the nervous and muscular tissue. In studying this subject, we
shall first follow some of the experiments upon muscular contraction excited artificially,
and then apply them, as far as possible, to the strictly physiological actions of muscles.

There are two classes of phenomena that may be produced by electrical excitation of
motor nerves : 1. When the stimulus is applied in the form of a single discharge, it is fol-
lowed by a single muscular contraction. 2. Under a rapid succession of discharges, the
muscle is thrown into a state of permanent, or tetanic contraction. It will greatly facilitate
our comprehension of the subject to study these phenomena separately and successively.

The muscular contraction produced by a single stimulus applied to the nerve is called
by the French, secousse (shock), and by the Germans, ZucTcung (convulsion). It will be
convenient for us to employ some term that will express this sudden action of the mus-
cular fibres, as distinguished from the contraction that takes place on repeated stimula-
tion or in continued muscular effort ; and we shall designate a single muscular contraction,
then, as spasm, Applying the term tetanus, to continued action.

Spasm produced ~by Artificial Excitation. — If an electric discharge, even very feeble,
be applied to a motor nerve connected with a fresh muscle, it is followed by a sudden
contraction, which is succeeded by a rapid relaxation. Under this stimulation, the muscle
shortens by about three-tenths of its entire length. The form of the contraction, as
registered by the apparatus of Helmholtz, Marey, and others who have applied the
so-called graphic method to the study of muscular action, presents certain interesting
peculiarities. We shall give, however, only the general characters of this action, with-
out discussing in detail the complicated apparatus employed.

According to Helmholtz, the whole period of a single contraction and relaxation of
the gastrocnemius muscle of a frog is a little less then one-third of a second. The mus-
cles of mammals and birds contract more rapidly, but, with this exception, the essential
characters of the contraction are the same. The following are the periods occupied by
these different phenomena :

Interval between stimulation and contraction 0"'020

Contraction 0"'180

Relaxation 0"'105

0"'305

540 MOVEMENTS.

The duration of the electric current applied to the nerve is only 0"-0008. Contrac-
tion, however, does not follow immediately, there being an interval, called pose, of about
one-fiftieth of a second. The contraction then follows, which is succeeded by gradual
relaxation, the former being a little longer than the latter. This description represents
the contraction of an entire muscle, but it does not indicate the changes in form of the
individual fibres, a point much more difficult to determine satisfactorily. It is pretty
well established, however, that a single fibre, with its irritability unimpaired, becomes
contracted and swollen at the point where the stimulation is applied. Now, the question
is whether, in normal contraction of the fibres in obedience to the natural nervous stimu-
lus, there be a uniform shortening of the whole fibre, a shortening of those portions only
that are the seat of the terminations of the motor nerves, or a peristaltic shortening and
swelling, rapidly running the length of the fibre.

The recent experiments of Aeby, which have been repeated and extended by Marey,
demonstrate beyond a doubt that, when one extremity of a muscle is excited, a contrac-
tion occurs at that point and is propagated along the muscle in the form of a wave, ex-
actly like the peristaltic action of the intestines, except that it is more rapid. Both Aeby
and Marey have succeeded in measuring the rapidity of the wave, and they find it to be
about forty inches per second. Applying this principle to the physiological action of
muscles, Aeby advances the theory that shortening of the fibres takes place wherever a

stimulus is received, and that
this is propagated in the form of
a wave, which meets in its course
another wave starting from a dif-
ferent point of stimulation. As
we know that the motor nerves
terminate at different points by
becoming fused, as it were, with
the sarcolemma, we can readily
comprehend, under this theory,
how the simultaneous contrac-
tion of all the fibres of a muscle
is produced by stimulation of its
motor nerve. This idea is ex-
pressed in the accompanying dia-
FIG. 160.— Diagram of the muscular wave. (Aeby.) gram. Although this view of the

physiological action of the mus-
cular fibres is extremely probable, it cannot be assumed that it has been absolutely
demonstrated ; but it is certainly more satisfactory and better sustained by experimental
facts than any theory that has hitherto been advanced.

Mechanism of prolonged Muscular Contraction. — By a voluntary effort we are able
to produce a muscular contraction of a certain duration, and of a power, within certain
limits, proportionated the amount of force we may desire to produce ; but, after a cer-
tain time, the muscle becomes fatigued, and it may become exhausted to the extent that
it will not respond to the normal stimulus. This is the kind of muscular action most
interesting to us as physiologists.

The experiments of Marey seem to show precisely how far the nervous action that
gives rise to a powerful and continuous muscular contraction can be imitated by elec-
tricity. Calling the movement produced by a single electric discharge, secousse, which
we have translated by the word spasm, he calls the persistent contraction, tetanus. We
shall adopt this name to distinguish persistent muscular action from the single contrac-
tion that we have just described.

It is a curious fact that a continued current of galvanic electricity passed through a

MUSCULAE CONTRACTION. 541

nerve or a muscle does not induce muscular contraction ; and it is only when the cur-
rent is closed or broken, that any action is observed. But if we employ statical elec-
tricity, a muscular spasm occurs at every discharge, proportionate, in some degree, to
the power of the excitation. If the discharges be very frequently repeated, or if a gal-
vanic current be applied, broken by an interrupting apparatus, the spasms follow each
other in quick succession. In experimenting upon the muscles of the frog, with a regis-
tering apparatus, Marey has found that, with a gradual increase in the rapidity of the
electric shocks, the individual muscular spasms become less and less distinct, and that
finally the contraction is permanent. His diagrams show well-marked spasms under
ten excitations per second, a more complete fusion of the different acts with twenty
per second, and a complete fusion, or tetanus, with twenty-seven per second. When
the contraction had become continuous, there was an elevation in the line, showing
increased power, as the excitations became more and more frequent. This is precisely
the kind of contraction that occurs in the physiological action of muscles. Although
the nervous force is not by any means identical with electricity, either the interrupted
galvanic current or a succession of statical discharges is capable of producing a muscular
action very like that which is involved in voluntary movements. The observations
of Marey, showing that the intensity of what he terms artificial tetanic contraction
is in proportion to the rapidity with which the electric discharges succeed each other,
are exceedingly interesting in their practical applications ; and an important question at
once arises regarding the nervous force that excites voluntary motion. Is this a series of
discharges, as it were, producing a power of muscular contraction in exact proportion to
their rapidity ? In view of the experiments just cited, this theory is very probable ; and
it is certain that the effect of a rapid succession of electric discharges almost exactly simu-
lates the normal action of muscles. That vibrations, more or less regular, actually occur
in muscular contraction, has been settled beyond a doubt by the researches of Wollaston,
Haughton, and more lately by Helmholtz, the latter having recognized a musical tone in
contracting muscles, exactly corresponding with the number of impressions per second
made upon the nerve. He farther devised an ingenious method of recognizing the tone,
by filling the ears with wax and contracting the temporal and masseter muscles. Marey
has found, in repeating this experiment, that the tone may be changed by modifying the
intensity of the muscular action. With the jaws feebly contracted, a grave sound is
produced, and this can be raised one-fifth, by contracting the muscles as forcibly as
possible.

The nerves are not capable of conducting an artificial stimulus for an indefinite period,
nor are the muscles able to contract for more than a limited time upon the reception of
^such an excitation. The electric current may be made to destroy for a time both the
nervous and muscular irritability ; and these properties become gradually extinguished, the
parts becoming fatigued before they are completely exhausted. Precisely the same phe-
nomena are observed in the physiological action of muscles. When a muscle is fatigued
artificially, a tetanic condition is excited more and more easily, but the intensity of the
contraction proportionally diminishes. Muscles contracting in obedience to an effort of
the will pass through the same stages of action. It is probable that constant contraction
is excited more and more easily as the muscles become fatigued, because the nervous
force gradually diminishes in intensity. It is certain that the vigor of contraction at the
same time progressively diminishes.

Electric Phenomena in the Muscles. — It was ascertained a number of years ago, by
Matteucci. that all living muscles are the seat of electric currents, which are not very
powerful, it is true, but still are sufficiently marked to be detected by ordinary galvanome-
ters. It is difficult, in the present state of our knowledge, to appreciate the physiological
significance of this fact, and we shall therefore merely allude to the chief electric phe-
nomena that are ordinarily observed, without attempting to follow out the elaborate and

542

MOVEMENTS.

curious experiments since made by Du Bois-Reymond and others. One of the most sim-
ple methods of demonstrating this current is to prepare the leg of a frog with the crural
nerve attached, and to apply one portion of the nerve to the deep parts of an incised

muscle and the other to the
surface. As soon as the con-
nection is made, a contraction
of the leg takes place. The
same fact may be demonstrated
with an ordinary galvanometer ;
but the evidence obtained by
the frog's leg, when the experi-
ment is properly performed, is
sufficiently conclusive.

Matteucci constructed out of
the fresh muscles from the thigh
of the frog, what is sometimes
called a frog-battery; which ex-
hibits these currents in the most
striking manner, their intensity
being in direct ratio to the num-
ber of elements in the pile. To
do this, he takes the muscles
of the lower half of the thigh
from several frogs, removing
the bones, and arranges them in
a series, each with its conical
extremity inserted into the cen-
tral cavity of the one below.
In this way the external sur-
face of each thigh except the
last is in contact with the in-
ternal surface of the one below.
If the two extremities of the
pile be now connected with a galvanometer, quite a powerful current from the internal
to the external surface of the muscle may be demonstrated. In a pile formed of ten ele-
ments, the needle of a galvanometer was deviated to from 30° to 40°.

Electric currents are observed in all living muscles, but they are most marked in the,
mammalia and warm-blooded animals. They exist, also, for a certain time after death.
Artificial tetanus of the muscles, however, instead of intensifying the current, causes the
galvanometer to recede. If, for example, the needle of the instrument show a deviation
of 30° during repose, when the muscle is excited to tetanic contraction, it will return so
as to mark only 10° or 15°. This phenomenon is observed only during a continued mus-
cular contraction, and it does not attend a single spasm.

Muscular Effort. — The mere voluntary movement of parts of the body, when there
is no obstacle to be overcome or no great amount of force is required, is very different
from a muscular effort. For example, in ordinary progression there is simply a move-
ment produced by the action of the proper muscles, almost without our consciousness,
and this is unattended with any modification in the circulation or respiration ; but, if we
attempt to lift a heavy weight, to jump, to strike a powerful blow, or to make any vigor-
ous effort, the action is very different. In the latter instance, we prepare for the mus-
cular action by inflating the lungs, closing the glottis, and contracting more or less forci-
bly the expiratory muscles, so as to render the thorax rigid and unyielding ; and, by

FIG. 1 61 . —Muscular curren t in the frog. (Bernard.)

Fig. 1, portion of the thigh, with the skin removed ; «, surface of the
muscles ; &, section ; the direction of the current is indicated by the
arrow.

Fig. 2. the nerve of a frog's leg (the leg enclosed in a glass tube) is ap-
plied to the section and the surface of the muscle. There is no contrac-
tion, because it is necessary that a portion of the nerve should be
raised up.

Fig. 3. a portion of the nerve is raised with a glass rod. The contraction
of the galvanoscopic leg occurs at the making of the circuit, because
the current follows the course of the nerve, or is direct.

Fig. 4, the contraction here occurs at the breaking of the circuit, because
the direction of the current is opposite the course of the nerve, or is
Inverse.

PASSIVE ORGANS OF LOCOMOTIOK 543

a concentrated effort of the will, the proper muscles are then brought into action.
This remarkable action of the muscles of the thorax and abdomen, due to simple
effort and independent of the particular muscular act that is to be accomplished, com-
presses the contents of the rectum and bladder and obstructs very materially the venous
circulation in the large vessels. It is well known that hernia is frequently produced in
this way ; the veins of the face and neck become turgid ; the conjunctiva may become
ecchymosed; and sometimes aneurismal sacs are ruptured. An effort of this kind is
generally of short duration, and it cannot, indeed, be prolonged beyond the time during
which respiration can be conveniently arrested. At its conclusion there is commonly a
prolonged expiration, which is audible and somewhat violent at its commencement.

There are degrees of effort which are not attended with this powerful action of the
muscles of the chest and abdomen, and in which the glottis is not completely closed ;
and an opening into the trachea or larynx, rendering immobility of the thorax impossi-
ble, does not interfere with certain acts that require considerable muscular power. If
we examine a dog with the glottis exposed, when he makes violent efforts to escape, we
can see that the opening is firmly closed. This fact we have often observed in vivisec-
tions ; but Longet has shown that dogs with an opening into the trachea are frequently
able to run and leap with u astonishing agility." He also saw a horse, with a large
canula in the trachea, that performed severe labor and drew heavily -loaded wagons in
the streets of Paris.

Passive Organs of Locomotion.

It would be out of place to describe fully and in detail all of the varied and complex
movements produced by muscular action. Many of these, such as the movements of
deglutition and of respiration, are necessarily considered in connection with the func-
tions of which they form a part ; but others are purely anatomical questions. Associ-
ated and antagonistic movements, automatic and reflex movements, etc., belong to the
history of the motor nerves and will be fully considered under the head of the nervous
system.

The study of locomotion involves a knowledge of the physiological anatomy of cer-
tain passive organs, the bones, cartilages, and ligaments. Although a complete history
of the structure of these parts trenches somewhat upon the domain of anatomy, we are
tempted to give a brief description of their histology, as it will complete our account of
the tissues of the body, with the exception of the nervous system and the organs of
generation, which will be taken up hereafter.

Locomotion is effected by the muscles acting upon certain passive, movable parts.
These are the bones, cartilages, ligaments, aponeuroses, and tendons. We have already
described the fibrous structures, and it only remains for us to study the bones and car-
tilages.

Physiological Anatomy of the Bones. — The number, classification, and relations of the
bones are questions belonging to descriptive anatomy ; and the only points we propose to
consider refer to their general, or microscopical structure.

Every bone, be it long or short, is composed of what is called the fundamental sub-
stance, marked by microscopic cavities and canals of peculiar form. The cavities con-
tain corpuscular bodies, called bone-corpuscles. The canals of larger size serve for the
passage of blood-vessels, while the smaller canals (canaliculi) connect the cavities with
each other and finally with the vascular tubes. Many of the bones present a medullary
cavity, filled with a peculiar structure, called marrow. In almost all bones there are two
distinct portions ; one, which is exceedingly compact, and the other, more or less spongy
or cancellated. The bones are also invested with a membrane, containing vessels an<?
nerves, called the periosteum.

The method usually employed in the study of the bones is by thin sections made in

544

MOVEMENTS.

various directions and examined either in their natural condition or with the calcareous
matter removed by maceration in weak acid solutions. By the first method, we can
make out the relations of the fundamental substance, the direction and relations of the
vascular canals, and the form, size, relations, and connections of the bone-cavities and
small canals. By the latter method, we can isolate and study the organic and corpuscular
elements.

Fundamental Substance. — This constitutes the true bony substance, the medullary
contents, vessels, nerves, etc., being simply accessory. It is composed of a peculiar
organic matter, called osteine, combined with various inorganic salts, in which the phos-
phate of lime largely predominates. In addition to the phosphate of lime, the bones
contain carbonate of lime, fluoride of calcium, phosphate of magnesia and of soda, and
chloride of sodium. The relative proportions of the organic and inorganic matters are
somewhat variable ; but the average is about one-third of the former to two-thirds of
salts. This proportion is necessary to the proper consistence and toughness of the bones.

FIG. 162. — Vascular canals and lacunae, seen in a lon-
gitudinal section of the humerus ; magnified 200
diameters. (Sappey.)

FIG. 163. — Longitudinal section of "bone, from the
^ aft of tit e human femur; 'magnified 180 di-

ameters. (From a photograph taken at the United
a, a, a, vascular canals ; 5, 6, 6, lacunas and canaliculi in Btates Army Medical Museum.)

the fundamental substance.

This figure is introduced for the reason that it is a copy
of a photograph of the actual structure.

Anatomically, the fundamental substance of the bones is arranged in the form of regu-
lar, concentric lamellae, about g-^Ys- of an inch in thickness. This matter is of an indefinite-
ly and faintly striated appearance, but it cannot be reduced to distinct fibres. In the long
bones, the arrangement of the lamellae is quite regular, surrounding the Haversian canals,
and forming what are sometimes called the Haversian rods, following in their direction
the length of the bone. In the short, thick bones the lamella} are more irregular, fre-
quently radiating from the central portion to the periphery. These peculiarities in the
disposition of the fundamental substance will be more readily understood after a descrip-
tion of the Haversian canals.

The Haversian canals exist in the compact bony structure. They are either absent or
very rare in the spongy and reticulated portions. Their form is rounded or ovoid, the larger

PASSIVE ORGANS OF LOCOMOTION.

545

canals being sometimes quite irregular. In the long bones their direction is generally lon-
gitudinal, although they anastomose by lateral branches. Each one of these canals con-
tains a blood-vessel, and their disposition constitutes the vascular arrangement of the bones.
They are all connected with the openings on the surface of the bones, by which the arte-
ries penetrate and the veins emerge. Their size, of course, is variable. According to
Sappey, the largest are about ^ an^ tne smallest, ^^ of an inch in diameter. Their
average size is from ^-5- to ^^ of an inch. In a transverse section of a long bone, the
Haversian canals may be seen cut across and surrounded by from twelve to fifteen
lamelhe. In a longitudinal section the course and anastomoses may be studied.

Lacunae. — The fundamental substance is everywhere marked by irregular, micro-
scopic excavations, of a peculiar form, called lacunae or osteoplasts. These were at one
time supposed to be corpuscles of calcareous matter and were known as the bone-cor-
puscles; but it has since been ascertained that this appearance is due to the imperfect
methods of preparation of the thin sections of bone. They are connected with numer-
ous little canals, giving them a stellate appearance. These are most numerous at the
sides. The lacunas measure from -^^ to F^ of an inch in their long diameter, by about
yij^ °f an mcn m width. They contain the true bone-corpuscles, which we shall pres-
ently describe.

Canaliculi, — These are little wavy canals, connecting the lacunae with each other
and presenting a communication between the first series of lacuna and the Haversian

FIG. 164.— Vascular canals and lacunae, seen in a transverse section of the humerus; magnified 200 diameters.

(Sappey.)

1, 1, 1, section of the Haversian canals ; 2, section of a longitudinal canal divided at the point of its anastomosis with
a transverse canal. Around the canals, cut across perpendicularly, are seen the lacunae (with their canaliculi),
forming concentric rings.

canals. Each osteoplast presents from eighteen to twenty canaliculi radiating from its
borders. Their length is from ¥i-g- to -$^ of an inch, and their diameter, about ssloo °f
an inch. The arrangement of the Haversian canals, lacuna, and canaliculi is shown in
Fig. 1G4.

Bone-cells or Corpuscles. — By treating perfectly fresh specimens of bone with weak
acid solutions, Virchow has demonstrated the presence of stellate cells or corpuscles,
exactly filling up the lacunae and sending prolongations into the canaliculi. These
structures have since been studied by Rouget, who has succeeded in demonstrating them
in fresh bones from the foetus, without using any reagent. They are stellate, granular,
with a large nucleus and several nucleoli, and are of exactly the size and form of the
35

546

MOVEMENTS.

lacunse. They send out prolongations into the canaliculi, but it has been impossible to

ascertain positively whether or not they form membranes lining the canaliculi through-
out their entire length.

Marrow of the Bones.— 1}iQ peculiar
structure called marrow is found in the me-
dullary cavities of the long bones, filling
them completely and moulded to all the
irregularities of their surface. It is also
found filling the cells of the spongy portion.
In other words, with the exception of the
vascular canals, lacunse, and canaliculi, the
marrow fills all the spaces in the fundament-
al substance. We know very little of the
functions of the marrow, and we shall there-
fore pass it over with a brief description.

It is now settled that the cavities of the
bones are not lined with a membrane corre-
sponding to the periosteum, and that the
marrow is applied directly to the bony sub-
stance. In the foetus and in very young
children, the marrow is red and very vascu-
lar. In the adult it is yellow in some bones
and gray or gelatiniform in others. It con-
tains certain peculiar cells and nuclei, with

amorphous matter, adipose vesicles, connective tissue, blood-vessels, and nerves.

Medullocells. — Robin has described little bodies, existing both in the form of cells

and free nuclei, called inednllocells. These are found in greater or less number in the

FIG. 165.— Transverse section of bone, from the shaft
of the human humerus ; magnified 180 diameters.
(From a photograph taken at the United States Army
Medical Museum.)

This figure is introduced for the reason that it is a copy
of a photograph of the actual structure.

FIG. 166.— Bone-corpuscles, witk their prolongations. (Eollett.)

bones at all ages, but they are more abundant in proportion as the amorphous matter and
fat-cells are deficient. The nuclei are spherical, with borders sometimes irregular, gen-
erally without nucleoli, finely granular, and from -5-^ to ^Vo °f an mcn m diameter.

PASSIVE ORGANS OF LOCOMOTION. 547

They are insoluble in acetic acid. The cells are less numerous than the free nuclei. They
are spherical or slightly polyhedric, contain a few pale granulations, are rendered pale
but are not dissolved by acetic acid, and they measure about yyV^ of an inch in diameter.

Myeloplaxes. — These are irregular, nucleated patches, also described by Robin, more
abundant in the spongy portions of the bones than in the medullary canals, and are
applied to the internal surfaces of the bones. They are exceedingly irregular in size and
form (measuring from y^^ to ?%-$ of an inch in diameter), are finely granular, and present
from two to twenty or thirty nuclei. The nuclei are clear, ovoid, generally with a nucle-
olus, and are from ^-^ to ^Vo °* an mc^ l°ng> by -j-oVcr or ^^ of an inch broad. The
myeloplaxes are rendered pale by acetic acid, and the nuclei are then brought out more
distinctly.

In addition to the anatomical elements just described, the marrow contains a few very
delicate bundles of connective tissue, most of which accompany the blood-vessels. In
the foetus, the adipose vesicles are few or may be absent ; but in the adult they are quite
numerous, and in some bones they aeern to constitute the whole mass of the marrow.
They do not differ materially from the fat-cells in other situations. Holding these different
structures together, is a variable quantity of semitransparent, amorphous, or slightly
granular matter.

The nutrient artery of the bones sends branches to the marrow, generally two in
number for the long bones, which are distributed between the various anatomical elements
and finally surround the fatty lobules and the fat-vesicles with a delicate capillary plexus.
The veins correspond to the arteries in their distribution. The nerves follow the arteries
and are lost when these vessels no longer present a muscular coat. Nothing is known
of the presence of lymphatics in any part of the bones or in the periosteum.

The only point of physiological interest connected with the marrow is, that it has
been found to possess, in common with the periosteum but in a less degree, the property
of generating true bony substances. We shall see farther on, that the periosteum is not
only very important to the nutrition of the bones, but that it will generate bone when
transplanted into vascular parts. M. Oilier, who has made a very extended series of
experiments upon the physiological properties of the periosteum, endeavored to produce
bone by transplanting portions of marrow, but was unsuccessful. M. Goujon, however,
has lately been more fortunate. He has found that frequently, but not always, marrow
transplanted into the muscular tissue will generate bone, particularly the marrow taken
from young bones, but the bony tissue thus formed is soon absorbed.

Periosteum. — In most of the bones the periosteum presents a single layer of fibrous
tissue, but in some of the long bones two or three layers may be demonstrated. This
membrane adheres to the bone but can generally be separated without much difficulty.
It covers the bones completely, except at the articular surfaces, where its place is supplied
by cartilaginous incrustation. It is composed mainly of fibres of the white inelastic variety,
with numerous small elastic fibres, blood-vessels, nerves, and a few adipose vesicles.

The arterial branches ramifying in the periosteum are quite numerous, forming a close,
anastomosing plexus, which sends numerous small branches into the bony substance.
There is nothing peculiar in the arrangement of the veins. The distribution of the veins
in the bony substance has been very little studied.

The nerves of the periosteum are very abundant and form in its substance quite a
close plexus.

The adipose tissue is very variable in quantity. In some parts it forms a continuous
sheet, and in others the vesicles are scattered here and there in the substance of the
membrane.

The importance of the periosteum to the nutrition of the bones is very great. Instances
are on record where bones have been removed, leaving the periosteum, and in which the
entire bone has been regenerated. The importance of the periosteum has been still

548

MOVEMENTS.

farther illustrated by the remarkable experiments of M. Oilier, upon transplantation of
this membrane in the different tissues of living animals.

Physiological Anatomy of Cartilage. — In this connection, the structure of the articu-
lar cartilages presents the chief physiological interest. The articular surfaces of all the
bones are encrusted with a layer of cartilage, varying in thickness from -^ to -fa of an
inch. The cartilaginous substance is white, opaline, and semitransparent when examined
in thin sections. It is not covered with a membrane, but in the non-articular carti-
lages it has an investment analogous to the periosteum.

Examined in thin sections, cartilage is found to consist of a homogeneous fundamental
substance, marked with numerous excavations, called cartilage-cavities, or chondroplf.FtF.
The intervening substance has a peculiar
organic base, called cartilagine. By pro-
longed boiling this is changed into a new
substance, called chondrine. The organic
matter is united with a certain proportion
of inorganic salts. This fundamental sub-
stance is elastic and resisting. The car-
tilages are closely united to the subjacent
bony tissue. The free articular surface
has already been described in connection
with the synovial membranes.

Cartilage- Cavities. — These cavities are

FIG. 167.— Section of cartilage from the rib of the ox,
showing the homogeneous fundamental substance,
cartilage-cavities, and cartilage-cells ; magnified
870 diameters. (From a photograph taken at the
United States Army Medical Museum.)

FIG. 168. — Perpendicular section of a diaithrodial
cartilage. (Sappey.)

1,1, osseous tissue; 2,2, superficial layer of osseous
tissue treated with hydrochloric acid ; 3. 3, cavities
and cells of the deep layer of cartilage ; 4. 4, cavities
and cells of the middle layer ; 5, 5, cavities and cells
of the superficial layer.

rounded or ovoid, measuring from T^ to ^ of an inch in diameter. They are gener-
ally smaller in the articular cartilages than in other situations, as in the costal cartilages.
They are simple excavations in the fundamental substance, have no lining membrane,
and contain a small quantity of a viscid liquid, with one or more cells. They are entirely
analogous to the lacunas of the bones.

Cartilage- Cells. — Near the surface of the articular cartilages, the cavities contain each
a single cell ; but in the deeper portions the cavities are long and contain from two to
twenty cells arranged longitudinally. The cells are of about the size of the smallest
cavities. They are ovoid, with a large, granular nucleus. They often contain a few
small globules of oil. In the costal cartilages the cavities are not numerous but are

PASSIVE ORGANS OF LOCOMOTION.

549

rounded and quite large. The cells contain generally a certain amount of fatty matter.
The appearance of the ordinary articular cartilage is represented in Fig. 168.

The ordinary cartilages have neither blood-vessels, lymphatics, nor nerves, and are
nourished exclusively by imbibition from the surrounding parts. Their function has
already been sufficiently considered in treating of the synovial membranes. In the devel-
opment of the body, the anatomy of the cartilaginous tissue possesses peculiar interest,
from the fact that the deposition of cartilage precedes the formation of bone ; but we
have here only to do with the permanent cartilages.

Fibro- Cartilage. — This variety of cartilage presents certain important peculiarities
in the structure of its fundamental substance. It exists in the synchondroses, the car-
tilages of the ear, of the Eustachian tubes, the interarticular disks, the intervertebral
cartilages, the cartilages of Santorini and of Wrisberg, and the epiglottis. Its structure
has been very closely and successfully studied by Sappey, who has arrived at results dif-
fering considerably from those obtained by other observers.

According to Sappey, nbro-cartilage is composed of true fibrous tissue, with a great
predominance of elastic fibres, fusiform, nucleated fibres, a certain number of adipose

FIG. 16.1.— Section of the cartilage of the ear of the human subject. (Eollett.)
«, fibro-cartilage ; &, connective tissue. In this preparation, the cartilage had been boiled and dried.

vesicles, cartilage-cells, and numerous blood-vessels and nerves. The presence of cartilage-
cells assimilates this tissue to the ordinary cartilage, although its structure is very much
more complex. The fibrous elements above mentioned take the place of the homogeneous
fundamental substance of the true cartilage. The most important peculiarity in the
structure of this tissue is that it is abundantly supplied with blood-vessels and nerves.

The reader is referred to works upon anatomy for a history of the action of the muscles.
In some works upon physiology, will be found descriptions of the acts of walking, running,
leaping, swimming, etc. ; but we have thought it better to omit these subjects, rather than
to enter as minutely as would be necessary into anatomical details and to give elaborate
d3scriptions of movements which are simple and familiar.

Voice and Speech.

There are few subjects connected with human physiology of greater interest than the
mechanism of voice and speech. In common with most of the higher classes of animals,
man is endowed with voice ; but, in addition, he is able to express by speed) the ideas
that are the result of the working of the brain. In this regard there is a difference be-
tween man and all other animals. It is the remarkable development and the peculiar

550

VOICE AND SPEECH.

properties of the brain that enable him to acquire the series of movements that constitute
articulate language ; and this faculty is nearly always impaired paripassu with deficiency
in the intellectual endowment. Language is one of the chief expressions of intelligence ;
and its study, in itself, constitutes almost a distinct science, inseparably connected with
psychology. In connection with the study of movements, therefore, it is not necessary
to discuss the origin and construction of language, but simply to indicate the mechanism,
first, of the formation of the voice, and afterward, the manner in which the voice is
modified in the production of articulate sounds.

The voice in the human subject, presenting, as it does, a variety of characters as
regards intensity, pitch, and quality, and being susceptible of great modifications by habit
and cultivation, affords a very extended field for physiological study. Of late years, this
has been the subject of careful investigation by the most eminent pbysicists and physiolo-
gists of the day ; but to follow it out to its extreme
limits requires a knowledge of the physics of sound
and the theory of music, a full consideration of which
would be inconsistent with the scope and objects of
this work. We shall content ourselves, therefore, with
a sketch of the physiological anatomy of the parts con-
cerned in the formation of the voice, and the mechanism
by which sounds are produced in the larynx, without
treating fully of their varied modifications in quality.
It will not be necessary to treat of the different the-
ories of the voice that have been presented from time
to time, except in so far as they have been confirmed
by recent and complete observations, particularly
those in which the vocal organs have been studied in
action by means of the laryngoscope.

/Sketch of the Physiological Anatomy of the Vocal
Organs. — The principal organ concerned in the pro-
duction of the voice is the larynx. The accessory or-
gans are the lungs, trachea, and expiratory muscles,
and the mouth and resonant cavities about the face.
The lungs furnish the air by which the vocal chords
are thrown into vibration, and the mechanism of this
action is merely a modification of the process of expira-
tion. By the action of the expiratory muscles the
intensity of vocal sounds is regulated. The trachea
not only conducts the air to the larynx, but, by cer-
tain variations in its length and caliber, it may assist
in modifying the pitch of the voice. Most of the varia-
tions in the tone and quality, however, are effected by
the action of the larynx itself and of the parts situated
above it.

It is impossible to give a complete account of the
structure of the larynx, without going more fully than

FIG. 170.— Longitudinal section of the hu-
man larynx, showing the vocal chords.
(Sappey.)

1, ventricle of the larynx ; 2, superior vocal
chord ; 3, inferior vocal chord ; 4, aryte-
noid cartilape ; 5, section of the arytenoid
muscle: 6. 6, inferior portion of the cav-
ity of the larynx ; 7, section of the pos-
terior portion of the cricoid cartilage ; 8,
section of the anterior portion of the cri-
coid cartilage ; 9, superior border of the
cricoid cartilape ; 10, section of the thy-

roid cartilage ; it. ii, superior portion of

'» desirable into purely anatomical details. Some an-
i9S8i9;2o8trache!i0n °f the hyOid bone' atomical points have already been referred to under

the head of respiration, in connection with the respi-

ratory movements of the glottis ; and we propose here only to refer to the situation of
the vocal chords, and to indicate the modifications that they can be made to undergo in
their relations and tension by the action of certain muscles.

The vocal chords are stretched across the superior opening of the larynx from before

ANATOMY OF THE VOCAL ORGANS. 551

backward. They consist of two pairs. The superior, called the false vocal chords, are
not concerned hi the production of the voice. They are less prominent than the inferior
chords, although they have nearly the same direction. They are covered by an excessively
thin mucous membrane, which is closely adherent to the subjacent tissue. The chords
themselves are composed of fibres of the white inelastic variety, mixed with a few
elastic fibres.

The true vocal chords are situated just below the superior chords. Their anterior
attachments are near together, at the middle of the thyroid cartilage, and are immovable.
Posteriorly they are attached to the movable ary tenoid cartilages ; and, by the action of
certain muscles, their tension may be modified, and the chink of the glottis may be opened
or closed. These ligaments are much larger than the false vocal chords, and they con-
tain a very great number of elastic fibres. Like the superior ligaments, they are covered
with an excessively thin and closely adherent mucous membrane. The mucous mem-
brane over the borders of the chords is covered with pavement-epithelium without
cilia. There are no mucous glands in the membrane covering either the superior or
the inferior chords.

It has been conclusively shown that the inferior vocal chords alone are concerned
in the production of the voice. Longet, who has made numerous experiments upon
phonation, has demonstrated, by operations upon dogs, that the epiglottis, the superior
vocal chords, and the ventricles of the larynx, may be injured, without producing any
serious alteration in the voice, but that phonation becomes impossible after serious
lesion of the inferior chords. This being the fact, as far as the mere production of the
voice in the larynx is concerned, we have only to study the mechanism of the action of
the inferior ligaments and the muscles by which their tension and relations are modified.

Muscles of the Larynx. — Anatomists usually divide the muscles of the larynx into
extrinsic and intrinsic. The extrinsic muscles are attached to the outer surface of the
larynx and to adjacent organs, such as the hyoid bone and the sternum. They are con-
cerned chiefly in the movements of elevation and depression of the larynx. The intrinsic
muscles are attached to the different parts of the larynx itself, and, by their action upon
the articulating cartilages, are capable of modifying the condition of the vocal chords.
The number of the intrinsic muscles is nine, consisting of four pairs and a single muscle.
In studying the situation and attachments of these. muscles, it will be useful at the same
time to note their mode of action.

Bearing in mind the relations and attachments of the vocal chords, we can understand
precisely how they can be rendered tense or loose by muscular action. Their fixed point
is in front, where their extremities, attached to the thyroid cartilage, are nearly or quite
in contact with each other. The arytenoid cartilages, to which they are attached poste-
riorly, present a movable articulation with the cricoid cartilage ; and the cricoid, which is
narrow in front, and is wide behind, wjiere the arytenoid cartilages are attached, presents a
movable articulation with the thyroid cartilage. It is evident, therefore, that muscles act-
ing upon the cricoid cartilage can cause it to swing upon its two points of articulation with
the inferior cornuaof the thyroid, raising the anterior portion and approximating it to the
lower edge of the thyroid ; and, as a consequence, the posterior portion, which carries
the arytenoid cartilages and the posterior attachments of the vocal chords, is depressed.
This action would, of course, increase the distance between the arytenoid cartilages and
the anterior portion of the thyroid, elongate the vocal chords, and subject them to a cer-
tain degree of tension. Experiments have shown that such an effect is produced by the
contraction of the crico-thyroid muscles.

The articulations of the different parts of the larynx are such that the arytenoid car-
tilages may be approximated to each other posteriorly, though perhaps only to a slight
extent, thus diminishing the interval between the posterior attachments of the vocal
chords. This action can be effected by contraction of the single muscle of the larynx
(the arytenoid) and also by the lateral crico-ary tenoid muscles. The thyro-ary tenoid mus-

552

VOICE AND SPEECH.

cles, the most complicated of all the intrinsic muscles in their attachments and the direc-
tion of their fibres, give rigidity and increased capacity of vibration to the vocal chords.

The posterior crico-arytenoid muscles, arising from each lateral half of the posterior
surface of the cricoid cartilage and passing upward and outward to be inserted into the
outer angle of the inferior portion of the arytenoid cartilages, rotate these cartilages
outward, separate them, and act as dilators of the chink of the glottis. These muscles
are chiefly concerned in the respiratory movements during inspiration.

The muscles mainly concerned in the modifications of the voice, by their action upon

FIG. ill.— Posterior view of the muscles of the larynx.
(Sappey.)

FIG. 172. — Lateral view cf the muscles of the larynx.
(Sappey.)

1, posterior crico-arytenoid muscle ; 2. 8, 4, different fas- 1, body of the hyoid bone ; 2, vertical section of the thy-
ciculi of the arytenoid muscle; 5, aryteno-epiglot- roid cartilage; 3, horizontal section of the thyroid

tidean muscle. cartilage turned downward to show the deep attach-

ment of the crico-thyroid muscle ; 4, facet of articu-
lation of the small cornu of the thyroid cartilage with
the cricoid cartilage ; 5, facet on the cricoid cartilage ;

6, superior attachment of the crico-thyroid muscle ;

7, posterior crico-arytenoid muscle; 8, 10, arytenoid
muscle; 9, thyro-arytenoid muscle ; 11, aryteno-epi-
glottidean muscle; 12, middle thyro-hyoid ligament;
13, lateral thyro-hyoid ligament.

the vocal chords, are the crico-thyroids, the arytenoid, the lateral crico-arytenoids,
and the thyro-arytenoids. The following is a sketch of their attachments and mode of
action :

Crico-thyroid Muscles. — These muscles are situated on the outside of the larynx at
the anterior and lateral portions of the cricoid cartilage. Each muscle is of a triangular
form, the base of the triangle looking posteriorly. It arises from the anterior and lateral
portions of the cricoid cartilage, and its fibres diverge to be inserted into the inferior
border of the thyroid cartilage, extending from the middle of this border posteriorly, as
far back as the inferior cornua. Longet, after dividing the nervous filaments distributed
to these muscles, noted hoarseness of the voice due to relaxation of the vocal chords;
and, by imitating their action mechanically, he approximated the cricoid and thyroid car-
tilages in front, carried back the arytenoid cartilages, and rendered the chords tense.

Arytenoid Muscle. — This single muscle fills up the space between the two arytenoid
cartilages and is attached to their posterior surface and borders. Its action evidently is to
approximate the posterior extremities of the chords and to constrict the glottis, as far as

MECHANISM OF THE PRODUCTION OF THE VOICE. 553

the articulations of the arytenoid cartilages with the cricoid will permit. In any event,
this muscle is important in phonation, as it serves to fix the posterior attachments of the
vocal chords and to increase the efficiency of certain of the other intrinsic muscles.

Lateral Crico-arytenoid Muscles. — These muscles are situated in the interior of the
larynx. They arise from the sides and superior borders of the cricoid cartilage, pass
upward and backward, and are attached to the base of the arytenoid cartilages. By
dividing all of the filaments of the recurrent laryngeal nerves, except those distributed to
these muscles, and then galvanizing the nerves, Longet has shown that they act to ap-
proximate the vocal chords, and to constrict the glottis, particularly in its interligamentous
portion. These muscles, with the arytenoid, act as constrictors of the larynx.

Thyro-arytenoid Muscles. — It is sufficiently easy to indicate the relations and attach-
ments of these muscles, but their mode of action is more complex and difficult of compre-
hension. When we come to study the conditions of the vocal chords involved in certain
modifications of the voice, we shall refer more in detail to the action of different fasciculi
of these muscles. In this connection, we shall only describe very briefly their situation
and attachments and the general results of their contraction.

The thyro-arytenoid muscles are situated within the larynx. They are broad and flat,
and they arise in front from the upper part of the crico-thyroid membrane and the lower
half of the thyroid cartilage. From this line of origin, each muscle passes backward in two
fasciculi, both of which are attached to the anterior surface and the outer borders of the
arytenoid cartilages. The application of galvanism to the nervous filaments distributed to
these muscles has the effect of rendering the vocal chords rigid, increasing the inten-
sity of their vibrations. The great variations that may be produced in the pitch and
quality of the voice by the action of muscles operating directly or indirectly upon the vocal
chords render the problem of determining the precise mode of action of the intrinsic
muscles of the larynx exceedingly complicated and difficult. It is certain, however, that,
in these muscular acts, the thyro-arytenoids play an important part. Their contraction
regulates the thickness and rigidity of the vocal chords, while at the same time it modi-
fies their tension. The swelling of the chords, which may be rendered regular and pro-
gressive under the influence of the will, is one of the most important agents in the forma-
tion of the timbre of the voice.

Mechanism of the Production of the Voice.

It will save much unprofitable discussion to dismiss quite briefly most of the theories
that have been advanced to explain the production of the voice, and to avoid compari-
sons of the larynx with different kinds of musical instruments. Before the larynx had
been studied in action by means of the laryngoscope, physiologists, having the anatomical
structure of the parts for their only guide, presented various speculations with regard to
the mechanism of phonation, which were frequently entirely opposed to each other in
principle. The vocal apparatus was compared to wind or brass instruments, to reed-
instruments, to string-instruments, to the flute, etc., and some even refused to the vocal
chords any share in the sonorous vibrations. An apparatus was devised to imitate the
vocal organs, experiments were made with the larynx removed from the body, and every
thing seemed to be done, indeed, except to observe the organs in actual function. A short
time, however, after the laryngoscope came into use, the larynx was examined during the
production of vocal sounds. The true value of previous theories was then positively
demonstrated ; and, while it has not been possible to settle all disputed points with regard
to the precise mode of action of certain muscles, the appearances of the larynx itself dur-
ing phonation and the results of the action of certain of the intrinsic muscles have been
quite accurately described.

Appearance of the Glottis during Ordinary Respiration. — If the glottis be examined
with the laryngoscope during ordinary respiration, the wide opening of the chink during

554

VOICE AND SPEECH.

inspiration, due to the action of the crico-arytenoid muscles, can be observed without
difficulty. This action is effected by a separation of the posterior points of attachment
of the vocal chords to the arytenoid cartilages. During ordinary expiration, none of the
intrinsic muscles seem to act, and the larynx is entirely passive, while the air is gently
forced out by the elasticity of the lungs and of the thoracic walls. But, as soon as an
effort is made to produce a vocal sound, the appearance of the glottis undergoes a re-
markable change, and it becomes modified in the most varied and interesting manner with
the different changes in pitch and intensity that the voice can be made to assume. Al-
though it is sufficiently evident that a sound may be produced, and even that words may
be articulated, with the act of inspiration, true and normal phonation is effected during
expiration only. It is evident, also, that the inferior vocal chords alone are concerned
in this act. The changes in the position and tension of the chords we shall study, first
with reference to the general act of phonation, and afterward, as the chords act in the
varied modifications of the voice as regards intensity, pitch, and quality.

Movements of the Glottis during Phonation. — It is somewhat difficult to observe with
the laryngoscope all of the vocal phenomena, on account of the epiglottis, which hides a
considerable portion of the vocal chords anteriorly, especially during the production of
certain tones; but the patience and skill of Garcia enabled him to overcome most of
these difficulties, and to settle, by autolaryngoscopy, the most important questions with
regard to the movements of the larynx in singing. It is fortunate that these observa-
tions, which are models of scientific accuracy and the result of most persevering study,
were made by one profoundly versed, theoretically and practically, in the knowledge of
music, and possessed of great control over the vocal organs.1

Garcia, after having observed the respiratory movements of the larynx, as we have
briefly described them, noted that, as soon as any vocal effort was made, the arytenoid
cartilages were approximated, so that the glottis appeared as a narrow slit formed by
two chords of equal length, firmly attached posteriorly as well as anteriorly. The glottis
thus undergoes a marked change. A nearly passive organ, opening widely for the pas-
sage of air into the lungs (because the inspiratory act has a tendency to draw its edges
^ ± ^ together) and entirely passive in expiration, has now be-

come a sort of musical instrument, presenting a slit with
borders capable of accurate vibration.

The approximation of the posterior extremities of the
vocal chords and their tension by the action of certain of
the intrinsic muscles are accomplished just before the vocal
effort is actually made. The glottis being thus prepared
for the emission of a particular sound, the expiratory mus-
cles force air through the larynx with the required power.
It seems wonderful how a carefully-trained voice can be
modulated and varied in all its qualities, including the in-
ryngoscope during the emission tensity of vibration, which is so completely under control ;

tSSKS^tSSSS^ but' when we consider the changes hl its quality' we must

5. 6, pharynx; 7, arytenoid car- remember, in explanation, the varying conditions of ten-

tilages; 8, opening between the . , . ,. 1. ,, ' , , ,, ,.,3, . ,,

true vocal chords; fl, aryteno-epi- sion and length of the vocal chords, the differences in the
8ize of the la'Tnx, trachea, and vocal passages generally,

FIG. VIZ.— Glottis seen with the la-

12, superior vocal chords; 13, in- and the different relations that the accessory vocal organs

ferior vocal chords.

can be made to assume. The power of the voice is simply
due to the force of the expiratory act, which is regulated chiefly by the antagonistic rela-

1 Manuel Garcia, the author of these observations, Is the son of Garcia, the great composer and singer, and the
brother of Mme. Malibran. He now enjoys a great reputation in London, as a singing-master; and his experiments
were made with a view, if possible, of reducing the art of singing, which had always been taught according to purely
empirical methods, to scientific accuracy. It is evident that this could be accomplished only through an exact
knowledge of the mechanism of the production of vocal sounds.

MECHANISM OF THE PRODUCTION OF THE VOICE. 555

tions of the diaphragm and the abdominal muscles. From the fact that the diaphragm,
as an active inspiratory muscle, is exactly opposed to the muscles which have a tendency
to push the abdominal organs, with the diaphragm over them, into the thoracic cavity,
and thus to diminish the pulmonary capacity, the expiratory and inspiratory acts may
be balanced so nicely that the most delicate vocal vibrations can be produced. The
glottis, thus closed as a preparation to a vocal act, presents a certain amount of resist-
ance to the egress of air. This is overcome by the action of the expiratory muscles,
and, with the passage of air through the chink, the edges of the opening, which are formed
by the true vocal chords, are thrown into vibration. Many of the different qualities
that are recognized in the human voice are due to differences in the length, breadth, and
thickness of the vibrating ribbons ; but, aside from what is technically known as quality,
the pitch is dependent chiefly upon the length of the opening through which the air is
made to pass and the degree of tension of the chords. The mechanism of these changes
in the pitch of vocal sounds is well illustrated by Garcia in the following passage, which
relates to what is known as the chest-voice :

" If we emit veiled and feeble sounds, the larynx opens at the notes r^y« ] H"iq,
and we see the glottis agitated by large and loose vibrations through- pE~ rt~
out its entire extent. Its lips comprehended in their length the do> re> mL

anterior apophyses of the arytenoid cartilages and the vocal chords ; but, I repeat it,
there remains no triangular space.

" As the sounds ascend, the apophyses, which are slightly rounded on their internal
side, by a gradual apposition commencing at the back, encroach on the length of the glottis ;

and as soon as we reach the sounds r~&~ [ they finish by touching each other

throughout their whole extent ; pfe"11— |— I | but their summits are only solidly
fixed one against the other at i) -&--+- the notes [ J} izuj. In some

organs these summits are a little va- <», do. cillating -((T) 1—- J when they

form the posterior end of the glottis, and two or three half-tones tJ i*1 which are

formed show a certain want of purity and strength, which is do, re. very well

known to singers. From ri$:~ ^qthe vibrations, having become rounder and

purer, are accomplished by p^ pzz|EE| the vocal ligaments alone, up to the end of

the register. ^T~|J- **

" The glottis at this do, re. moment presents the aspect of a line swelled

toward its middle, the length of which diminishes still more as the voice ascends. We
shall also see that the cavity of the larynx has become very small, and that the superior
ligaments have contracted the extent of the ellipse to less than one-half."

These observations have been in the main confirmed by Battaille, Emma Seiler, and
all who have applied the laryngoscope to the study of the voice in singing. On several
occasions we have had opportunities of observing, by means of the laryngoscope, the
changes in the form of the glottis during the production of vocal sounds of different de-
grees of pitch ; and the various points to which we have alluded can be illustrated by
autolaryngoscopy in the most marked manner. Nothing can be more striking than the
changes thus observed in the form of the glottis in a transition from low to high notes.
We have also frequently noted the general appearance of the glottis in phonation in ex-
periments upon animals in which the glottis has been exposed to view, although the
phenomena are much less striking than they are in the human subject.

Variations in the Quality of the Voice, depending upon Differences in the Size and
Form of the Larynx and the Vocal Chords.— We are all sufficiently familiar with the char-
acters of the male as distinguished from the female voice, and with what are known as the
different vocal registers. In childhood, the general characters of the voice are essentially
the same in both sexes. The larynx is smaller than in the adult, and the vocal muscles
are evidently more feeble ; but the quality of the vocal sounds at this period of life is
peculiarly pure and penetrating. While there are certain characters that distinguish the
voices of boys before the age of puberty, they present, as in the female, the different qualities

556 VOICE AND SPEECH.

of the soprano and contralto. At this age the voices of boys are capable of considerable
cultivation, and their peculiar quality is sometimes highly prized in church-music. After
the age of puberty, the female voice does not commonly undergo any very marked
change, except in the development of additional strength and increased compass, the
quality remaining the same ; but in the male there is a rapid change at this time in the
development of the larynx, and the voice assumes an entirely different quality of tone.
This change does not usually take place if castration be performed in early life ; and this
operation was frequently resorted to in the seventeenth century, for the purpose of pre-
serving the qualities of the soprano and contralto, particularly for church -music. It
is only of late years, indeed, that this practice has fallen into disuse in Italy.

The ordinary range of all varieties of the human voice is given by Miiller as equal to
nearly four octaves; but it is rare that any single voice has a compass of more than two
and a half octaves. There are examples, however, in which singers have acquired a
compass of three octaves and even more. The celebrated singer, Mme. Parepa-Kosa,
had a compass of voice that touches three full octaves, from sola to sols. In music, the
notes are written the same for the male as for the female voice, but the actual value of
the female notes, as reckoned by the number of vibrations in a second, is always an
octave higher than the male.

In both sexes there are differences, both in the range and the quality of the voice,
which it is impossible for a cultivated musical ear to mistake. In the male, we have the
bass and the tenor, with an intermediate voice, called the barytone. In the female, we
have the contralto and the soprano, with the intermediate, or mezzo-soprano. In the
bass and barytone, the lower and middle notes are the most natural and perfect ; and,
while the higher notes may be acquired by cultivation, they are not easy and do not pos-
sess the same quality as the corresponding notes of the tenor. The same remarks apply
to the contralto and soprano. The mezzo-soprano is regarded by many as an artificial
division.

The following scale, proposed by Millier, gives the ordinary rnnges of the different
kinds of voice ; but it must be remembered that there are individual instances in which
these limits are very much exceeded :

r

CONTRALTO

mi fa sol la si do re mi fa sol la si do re mi fa sol la si do re mi fa sol la si do
1111122 22 2223383 333 44 44 4445

la si d(

There is really no great difference in the mechanism of the different kinds of voice,
and the differences in pitch are due chiefly to the greater length of the vocal chords in
the low-pitched voices and to their shortness in the higher voices. The differences in
quality are due to peculiarities in the conformation of the larynx, to differences in its
size, and to variations in the size and form of the auxiliary resonant cavities. Great
changes in the quality of the voice may be effected by practice. A cultivated note, for
example, has an entirely different sound from a harsh, irregular vibration ; and, by prac-
tice, a tenor may imitate the quality of the bass, and vice versa, although the effort is
unnatural. It is not at all unusual to hear male singers imitate very closely the notes of
the female, and the contralto will sometimes imitate the voice of the tenor in a sur-
prisingly natural manner. These facts have a somewhat important bearing upon certain
disputed points with regard to the mechanism of the different vocal registers, which will
be considered farther on.

Action of the Intrinsic Muscles of the Larynx in Phonation. — It is much more diffi-

MECHANISM OF THE PRODUCTION" OF THE VOICE. 557

cult to find an entirely satisfactory explanation of the different tones produced by the
human larynx in the action of the intrinsic muscles than to describe the changes in the
tension and relations of the vocal chords. These muscles are concealed from view, and
the only idea that we can have of their action is by reasoning from a knowledge of their
points of attachment, and by operations upon the dead larynx, either imitating the con-
traction of special muscles or galvanizing the nerves in animals recently killed. In this
way, as we have seen, some of the muscular acts have been studied very satisfactorily ;
but the precise effect of the contraction of certain of the muscles, particularly the thyro-
arytenoids, is still a matter of discussion.

In the production of low chest-tones, in which the vocal chords are elongated and are at
the mininum of tension that will allow of regular vibrations, the crico-thyroid muscles are
undoubtedly brought into action, and these are assisted by the arytenoid and the lateral
crico-arytenoids, which combine to fix the posterior attachments of the vibrating liga-
ments. It will be remembered that the crico-thyroids, by approximating the cricoid and
thyroid cartilages in front, have a tendency to remove the arytenoid cartilages from the
anterior attachment of the chords.

As the tones produced by the larynx become higher in pitch, the posterior attach-
ments of the chords are approximated more firmly, and at this time the lateral crico-
arytenoids are probably brought into vigorous action.

The function of the thyro-arytenoids is more complex ; and it is probably in great
part by the action of these muscles that the varied and delicate modifications in the
rigidity of the vocal chords are produced.

The remarkable differences in singers as regards the purity of their tones are undoubt-
edly due in greatest part to the unswerving accuracy with which some put the vocal chords
upon the stretch ; while, in those in whom the tones are of inferior quality, the action of
the muscles is more or less vacillating, and the tension is frequently incorrect. The fact
that some celebrated singers can make the voice heard above the combined sounds from a
large chorus and orchestra is not due entirely to the intensity of the sound, but in a great
measure to the absolute mathematical equality of the sonorous vibrations and the com-
parative absence of discordant waves. Musicians who have heard the voice of the cele-
brated basso, Lablache, all bear testimony to the remarkable quality of his voice, which
could be heard at times above a powerful chorus and orchestra. A grand illustration of
this occurred at the musical festival at Boston, in 18G9. In some of the solos by Mme.
Parepa-Rosa, accompanied by a chorus of nearly twelve thousand, with an orchestra of
more than a thousand and largely composed of brass instruments, we distinctly heard the
pure and just notes of this remarkable soprano, standing alone, as it were, against the
entire choral and instrumental force ; and this in an immense building containing an
audience of forty thousand persons. The absolute accuracy of the tone was undoubtedly
an important element in its remarkably penetrating quality. In the same way we explain
the fact that the flute, clarinet, or the sound from a Cremona violin, may be heard soaring
above the chords of a full orchestra.

Action of Accessory Vocal Organs. — A correct use of the accessory organs of the
voice is of the greatest importance in singing ; but the manner in which these parts per-
form their function is exceedingly simple and does not require a very extended descrip-
tion. The human vocal organs, indeed, consist of a vibrating instrument, the larynx,
and of certain tubes and cavities by which the sound is reenforced and modified.

The trachea serves, not only to conduct air to the larynx, but to reenforce the sound
to a certain extent by the vibrations of the column of air in its interior. When a power-
ful vocal effort is made, it is easy to feel, with the finger upon the trachea, that the air
contained in it is thrown into vibration. The structure of this tube is such that it may
be elongated and shortened at will. In the production of low notes, the trachea is
shortened and its caliber is increased, the reverse obtaining in the higher notes of the
scale:

558 VOICE AND SPEECH.

Coming to the larynx itself, we find that the capacity of its cavity is capable of certain
variations. In fact, both the vertical and the bilateral diameters are diminished in high
notes and are increased in low notes. The vertical diameter may be modified slightly
by ascent and descent of the true vocal chords, and the lateral diameter may be reduced
by the inferior constrictors of the pharynx, acting upon the sides of the thyroid cartilage.

The epiglottis, the superior vocal chords, and the ventricles, are by no means indis-
pensable to the production of vocal sounds. In the formation of high notes, the epiglottis
is somewhat depressed, and the superior chords are brought nearer together ; but this
only affects the character of the resonant cavity above the glottis. In low notes the
superior chords are separated. It was before the use of the laryngoscope in the study of
vocal phenomena that the epiglottis and the ventricles were thought to be so important
in phonation. Undoubtedly the epiglottis has something to do with the character of the
voice ; but its function in this regard is not absolutely necessary, or even very important,
as has been clearly shown in experiments of excising the part in living animals.

The most important modifications of the laryngeal sounds are produced by the reso-
nance of air in the pharynx, mouth, and nasal fossse. This resonance is indispensable to
the production of the natural human voice. Under ordinary conditions, in the production
of low notes the velum palati is fixed by the action of its muscular fibres, so that there is
a reverberation of the bucco-pharyngeal and naso-pharyngeal cavities; that is, the velum is
in such a position that neither the opening into the nose nor into the mouth is closed, and
all of the cavities resound. As the notes are raised, the isthmus contracts, the part imme-
diately above the glottis is also constricted, the resonant cavity of the pharynx and mouth
is reduced in size, until finally, in the highest notes of the chest-register, the communica-
tion between the pharynx and the nasal fossae is closed, and the sound is reenforced
entirely by the pharynx and month. At the same time the tongue, a very important
organ to singers, particularly in the production of high notes, is drawn back into the
mouth. The point being curved downward, its base projects upward posteriorly and
assists in diminishing the capacity of the cavity. In the changes which the pharynx thus
undergoes in the production of different notes, the uvula acts with the velum and assists
in the closure of the different openings. In singing up the scale, this is the mechanism,
as far as the chest-notes extend. When, however, we pass into what is known as the
head-voice, the velum palati is drawn forward instead of backward, and the resonance
takes place chiefly in the naso-pharyngeal cavity.

Mechanism of the different Vocal Registers. — There has been a great deal of discus-
sion, even among those who have studied the voice with the laryngoscope, with regard
to the exact mechanism of the different vocal registers. It is now pretty well settled
how the ordinary notes of what is known as the chest-register are produced ; but, with
regard to the falsetto, the difficulties in the way of direct observation are so great, that
the question of its mechanism cannot be said to be definitively established.

The following are the vocal registers now recognized by most physiologists :

1. The chest-register, most powerful in male voices and in contraltos, and, indeed,
almost characteristic of the male.

2. The falsetto register, which is the most natural voice of the soprano ; though this
voice is capable of chest-notes, not so full, however, as in the contralto or in the male.
In the female this is known as the middle register.

3. The head-register, produced by a peculiar action of the glottis and the resonant
cavities above the larynx. This is cultivated particularly in tenors and in the female.

Aside from the three registers, which belong to every voice, a practised ear can find
no difficulty in distinguishing the different voices in nearly any part of the scale, both in
the male and the female, by the following peculiarities : In the bass, the low notes are
full, natural, and powerful, and the higher notes nearly always seem more or less artifi-
cial. In singing, the passage from the natural to the artificial notes in the scale is gen-
erally more or less apparent. In the tenor the full, natural notes are higher in the scale,

VOCAL REGISTERS. 559

the lower notes being almost always feeble and wanting in roundness. Corresponding
peculiarities enable us to distinguish between the contralto and the soprano.

Chest- Register. — "We shall simply recapitulate briefly the mechanism of the chest-
notes, to enable us to study more easily the transitions to the different upper registers.
This is the voice commonly used in speaking, and it is the most natural, the vocal liga-
ments vibrating according to their tension, as the air is forced through the larynx from
the chest, and the air in the pharynx, mouth, and nasal fossas producing a resonance
without any artificial division of the different cavities. As the notes are elevated, the
vocal chords are simply rendered more tense, and the parts above the larynx are more
or less constricted, without any other change in the mechanism of the sound. But the
chest-voice in the male cannot pass certain well-defined limits ; and in the very highest
notes it must be merged either into the head-voice or the falsetto. The falsetto, how-
ever, is now but little cultivated, although some tenor singers, after long practice, succeed
in making the change from one register to the other so nicely that it is hardly perceptible,
even to a cultivated ear. The head-voice has essentially the same mechanism in the
male as in the female, and this will be considered after we have discussed the falsetto,
which is the natural voice of soprano singers.

Falsetto Register. — The difference of opinion among laryngoscopists with regard to
the mechanism of the falsetto is probably in great part due to the fact that, when these
notes are produced, the isthmus of the fauces is so powerfully contracted that it becomes
exceedingly difficult to study the action of the vocal chords. There is no reason for sup-
posing that the mechanism of this register does not involve vibration of the true vocal
chords, as in the chest-voice, the difference being in the tension and in the extent of the
vibrating portion. According to the observations of Fournie, in the falsetto the tongue
is pressed strongly backward and the epiglottis is forced over the larynx. Mrs. Emma
Seller, from an extended series of autolaryngoscopic observations, has arrived at the con-
clusion that this voice involves vibrations of the fine, thin edges of the chords only, a
greater width vibrating in the production of the chest-voice. She is particularly careful
to insist upon the distinction between the falsetto and the head-register, the latter being
produced by an entirely different mechanism. On the whole, this explanation seems to
be the most satisfactory.

It must be remembered that the distinction between the chest-register or the head-
register and the falsetto, as far as pitch is concerned, is not absolute. Certain of the high
notes of the chest or the head-voice, for example, may be produced in the falsetto. In
the cultivation of the female voice, Mrs. Seiler considers that it is exceedingly important
not to strain the chest-voice to its highest point, but to use each register in its normal
place in the scale, taking care, by practice, to render the transition from one to the other
natural and agreeable. We have heard male singers, probably endowed with peculiar
vocal powers, who were able, by the use of the falsetto, to imitate almost exactly the
soprano voice, though without the sweetness and purity of tone characteristic of the per*
feet female organ. In the same way, by straining the chest-voice beyond its normal
limits, some females, particularly contraltos, are able to produce a very good imitation
of the tenor quality.

Head- Register. — This voice is highly cultivated, particularly in tenors and in the best
female singers. It is not to be confounded, however, with the falsetto, as was done by
some physiologists before the invention of the laryngoscope. Head-notes may be pro-
duced by cultivated male singers, bass and barytone, as well as tenor ; but the former
seldom have occasion for any but the chest-notes. Still, there are musical passages in
which the sotto-voce head-notes of the bass have an exquisite softness and are used with
great effect. We have already stated that, in the transition to the head-voice, the velum
palati is applied to the base of the tongue, and the sound is reenforced by resonance
from the naso-pharyngeal cavity. If this be its mechanism, its study with the laryngo-
scope must be exceedingly difficult.

560 VOICE AND SPEECH.

The most important theory of the mechanism of the head-voice has been proposed by
Mrs. Seiler. After long and patient effort, she was able to expose the glottis during the
production of these notes, when it was found that the vocal chords were firmly approxi-
mated posteriorly, leaving an oval opening, with vibrating edges, involving only one-half
or one-third of the vocal ligaments. This orifice contracted progressively with the higher
notes. This peculiar division of the vocal ligaments is due, according to Mrs. Seiler, to
the action of a muscular bundle, called the internal thyro-arytenoid, upon little cartilages
(the cuneiform) extending forward from the arytenoid cartilage, in the substance of the
vocal ligaments, as far as the middle of the glottis.

With proper cultivation, the transition from the middle register to the head-voice in
the female may be effected almost imperceptibly, thereby increasing the compass from
three to six notes, and even more ; and in the male the same may be accomplished with-
out difficulty, particularly in tenors. There can be hardly any doubt of the fact that the
naso-pharyngeal space is chiefly concerned in the resonance that takes place in head-
notes, though its actual demonstration is very difficult. The distinction between the
head and the chest notes is fully as marked in the male as in the female ; but it must be
remembered that one of the great ends to be accomplished in the cultivation of the human
voice is to make the three registers pass into each other so that they shall appear as one.

Mechanism of Speech.

Articulate language consists in a conventional series of sounds made for the purpose
of conveying certain ideas. There being no universal language, we must confine our
description of the faculty of speech to the mode of production of the language in which
this work is written. Language, as it is naturally acquired, is purely imitative and does
not involve of necessity the construction of an alphabet, with its combinations into
syllables, words, and sentences ; but, as civilization has advanced, we have been taught
to associate certain differences in the accuracy and elegance with which ideas are
expressed, with the degree of development and cultivation of the intellectual faculties.
Philologists have long since established a certain standard — varying, to some extent, it is
true, with usage and the advance of knowledge, but still sufficiently definite — by which
the correctness of modes of expression is measured. We do not propose to discuss the
science of language, or to consider, in this connection, at least, the peculiar mental opera-
tions concerned in the expression of ideas, but to take our own tongue as we find it, and
describe briefly the mechanism of the production of the most important articulate sounds.

Almost every language is imperfect, as far as an exact correspondence between its
sounds and written characters is concerned. Our own language is full of incongruities
in spelling, such as silent letters and arbitrary and unmeaning variations in pronuncia-
tion ; but these do not belong to the subject of physiology. There are, however, certain
natural divisions of the sounds as expressed by the letters of the alphabet.

Vowels. — Certain articulate sounds are called vowel, or vocal, from the fact that they
are produced by the vocal chords and are but slightly modified as they pass out of the
mouth. The true vowels, a, e, i, o, w, can all be sounded alone and may be prolonged
in expiration. These are the sounds chiefly employed in singing. The differences in
their characters are produced by changes in the position of the tongue, mouth, and lips.
The vowel-sounds are necessary to the formation of a syllable, and, although they are
generally modified in speech by consonants, each one may, of itself, form a syllable or a
word. In the construction of syllables and words, the vowels have many different quali-
ties, the chief differences being as they are made long or short. In addition to the modi-
fications in the vowel-sounds by consonants, two or three may be combined so as to be
pronounced by a single vocal effort, when they are called respectively, diphthongs and
triphthongs. In the proper diphthongs, as oi, in voice, the two vowels are sounded. In

MECHANISM OF SPEECH. 561

the improper diphthongs, as ea, in heat, and in the Latin diphthongs, as ce, in Csesar, one
of the vowels is silent. In triphthongs, as eau, in beauty, only one vowel is sounded.
F, at the beginning of words, is usually pronounced as a consonant ; but in other situa-
tions it is pronounced as e or i.

A very curious and interesting inquiry relates to the differences, with which we are
all familiar, in the quality of the different vowel-sounds when pronounced with equal
pitch and intensity. The cause of these differences was studied very closely in the latter
part of the last century, but it has lately been rendered very clear by the elaborate and
convincing researches of Helrnholtz. In this connection, it will be sufficient to indi-
cate the results of modern investigations very briefly. When we come to study the
physics of sound in connection with the sense of hearing, we shall see that nearly all
sounds, even when produced by a single vibrating body, are compound. Helmholtz, by
means of his resonators, has succeeded in analyzing the apparently simple sounds into dif-
ferent component parts, and he has shown that the quality of such sounds may be modified
by reenforcing certain of the overtones, as they are called, such as the third, fifth, or
octave. For those who are familiar with the physics of sound, the explanation which we
shall give of the mechanism of the production of vowel-sounds will be readily compre-
hensible. The reader is referred, however, to our remarks upon overtones in another part
of this work, under the head of audition, for a more thorough exposition of this subject.
This should be read in connection with what we shall say here of vowel-sounds, when
the whole subject will be sufficiently clear. We may pronounce the different vowel-
sounds with the same pitch and intensity, but the sound in each is different, on account
of variations in the resonant cavities of the accessory vocal organs, especially the mouth.
It has been ascertained experimentally that the overtones in each instance are different,
as they are reenforced by the vibrations of air in the accessory vocal organs, in some
instances the third, in others, the fifth, etc., being increased in intensity. We cannot
illustrate this better than by the following quotation from Tyndall, in which modern
researches have been applied to the vowel-sounds of our own language:

" For the production of the sound U (o o in hoop), I must push my lips forward so as
to make the cavity of the mouth as deep as possible, at the same time making the orifice
of the mouth small. This arrangement corresponds to the deepest resonance of which
the mouth is capable. The fundamental tone of the vocal chords is here reenforced, while
the higher tones are thrown into the shade. The U is rendered a little more perfect
when a feeble third tone is added to the fundamental.

" The vowel 0 is pronounced when the mouth is so far opened that the fundamental
tone is accompanied by its strong higher octave. A very feeble accompaniment of the
third and fourth is advantageous, but not necessary.

" The vowel A derives its character from the third tone, to strengthen which by
resonance the orifice of the mouth must be wider, and the volume of air within it smaller
than in the last instance. The second tone ought to be added in moderate strength, whilst
weak fourth and fifth tones may also be included with advantage.

" To produce E the fundamental tone must be weak, the second tone comparatively
strong, the third very feeble, but the fourth, which is characteristic of this vowel, must
be intense. A moderate fifth tone may be added. ISTo essential change, however, occurs
in the character of the sound when the third and fifth tones are omitted. In order to
exalt the higher tones which characterize the vowel-sound E, the resonant cavity of the
mouth must be small.

"In the production of the sound ah! the higher overtones come principally into
play; the second tone may be entirely neglected ; the third rendered feebly ; the higher
tones, particularly the fifth and seventh, being added strongly.

"These examples sufficiently illustrate the subject of vowel-sounds. We may blend
in various ways the elementary tints of the solar spectrum, producing innumerable com-
posite colors by their admixture. Out of violet and red we produce purple, and out of
36

562 VOICE AND SPEECH.

yellow and blue we produce white. Tims also may elementary sounds be blended so as
to produce all possible varieties of clang-tint. After having resolved the human voice
into its constituent tones, Helmholtz was able to imitate these tones by tuning-forks, and,
by combining them appropriately together, to produce the clang-tints of all the vowels."

Consonants. — Some of the consonants have no sound in themselves and serve merely to
modify vowel-sounds. These are called mutes. They are 5, d, &, p, t, and c and g hard.
Their office in the formation of syllables is sufficiently apparent.

The consonants known as semivowels are,/, £, m, n, r, s, and c and g soft. These
have an imperfect sound of themselves, approaching in character the true vowel-sounds.
Some of these, Z, m, n, and r, from the facility with which they flow into other sounds,
are called liquids. Orthoepists have farther divided the consonants with reference to the
mechanism of their pronunciation : d, j, «, t, z, and g soft, being pronounced with the
tongue against the teeth, are called dentals; d, g, j, &, Z, ??, and q are called palatals; &,
j»,/, 0, and m are called labials ; m, 72, and ng are called nasals; and &, §-, and c and g
hard are called gutturals. After the description we have given of the voice, it is not
necessary to discuss farther the mechanism of these simple acts of articulation.

For the easy and proper production of articulate sounds, absolute integrity of the
mouth, teeth, lips, tongue, and palate is required. We are all acquainted with the modi-
fications in articulation, in persons in whom the nasal cavities resound unnaturally, from
imperfection of the palate ; and the slight peculiarities observed after loss of the teeth
and in hare-lip are sufficiently familiar. The tongue is generally regarded, also, as an
important organ of speech, and this is the fact in the great majority of cases ; but
instances are on record in which distinct articulation has been preserved after complete
destruction of this organ. These cases, however, are unusual, and they do not invalidate
the great importance of the tongue in ordinary speech.

It is thus seen that speech consists essentially in a modification of the vocal sounds
by the accessory organs, or by parts situated above the larynx ; the latter being the true
vocal instrument. While the peculiarities of pronunciation in different persons and the
difficulty of acquiring foreign languages after the habits of speech have been formed show
that the organs of articulation must perform their function with great accuracy, their
movements are simple, and they vary with the peculiarities of different languages.

The Phonograph. — In 1877, a remarkable invention was made in this country by Mr.
Thomas A. Edison, which possesses considerable physiological interest. Mr. Edison con-
structed a very simple instrument, called the phonograph, which will repeat, with a cer-
tain degree of accuracy, the peculiar characters of the human voice both in speaking and
singing, as well as the pitch and quality of musical instruments. This demonstrates con-
clusively the fact that the qualities of vocal sounds depend upon the form of the sono-
rous vibrations. The following are the main features in the construction of this remark-
able and almost miraculous instrument: It consists of a cylinder of iron provided with
very fine, shallow grooves in the form of an exceedingly close spiral. Upon this cylin-
der, a sheet of tin-foil is accurately fitted. Bearing upon the tin-foil, is a steel-point
connected with a vibrating plate of mica or of thin iron. The vibrating plate is
connected with a mo.uth-piece which receives the vibrations of the voice or of a
musical instrument. The cylinder is turned with a crank, and, at the same time, the
plate is thrown into vibration by speaking into the mouth-piece. As the disk vibrates in
consonance with the voice, the vibrations are marked by little indentations upon the tin-
foil. When this has been done, the cylinder is moved back to the starting point and is
turned again at the same rate as before. As the steel point passes over the indentations
in the tin-foil, the plate is thrown into vibration, and the sound of the voice is actually
repeated, although much diminished in intensity and distinctness.

GENERAL CONSIDERATIONS. 563

CHAPTER XVII.

PHYSIOLOGICAL DIVISIONS, STRUCTURE, AND GENERAL PROPERTIES OF THE

NERVOUS SYSTEM.

General considerations— Divisions of the nervous system— Physiological anatomy of the nervous tissue — Anatomical
divisions of the nervous tissue— JVIedullated nerve-fibres— Simple, or non-medullated nerve-fibres — Gelatinous
nerve-fibres (fibres of Remak)— Accessory anatomical elements of the nerves— Branching and course of the nerves
— Termination of the nerves in the muscular tissue — Termination of the nerves in glands — Terminations of the
sensory nerves — Corpuscles of Pacini, or of Vater — Tactile corpuscles — Terminal bulbs— Structure of the nerve-
centres— Nerve-cells— Connection of the cells with the fibres and with each other— Accessory anatomical elements
of the nerve-centres— Composition of the nervous substance— Regeneration of the nervous tissue — Reunion of
nerve-fibres — Motor and sensory nerves — Distinct seat of the motor and sensory properties of the spinal nerves-
Experiments of Magendie upon the roots of the spinal nerves — Properties of the posterior roots of the spinal nerves
— Properties of the anterior roots of the spinal nerves — Recurrent sensibility— Mode of action of the motor nerves
— Associated movements — Mode of action of the sensory nerves — Sensation in amputated members — General prop-
erties of the nerves — Nervous irritability— Different means employed for exciting the nerves — Disappearance of
the irritability of the motor and sensory nerves after exsection — Nerve-force — Rapidity of nervous conduction —
—Estimation of the duration of acts involving the nerve-centres— Action of electricity upon the nerves— Induced
muscular contraction — Galvanic current from the exterior to the cut surface of a nerve — Effects of a constant gal-
vanic current upon the nervous irritability— Electrotonus, anelectrotonus, and catelectrotonus— Neutral point-
Negative variation.

THE nervous system is anatomically distinct in all animals except those lowest in the
scale of being. It is useless to speculate upon the question of the existence of matter
endowed with properties analogous to those observed in the nervous system of the higher
animals, in beings so low in their organization as to present no divisions into anatomical
elements ; for the present condition of physiological science does not admit of the recog-
nition of functions without organs. All animals that present any thing like nervous
functions present also an anatomically distinct nervous system. Within certain limits,
the perfection of the animal organization depends upon the general development of the
nervous system.

High in the animal scale, as in the warm-blooded animals, the general development of
the nervous system presents little if any variation ;' but special attributes are coexistent
with the development of special organs. The development in this way of particular por-
tions of the nervous system is in accordance with the peculiar conditions of existence of
different animals ; it is a necessary part of their organization, and is not dependent upon
education or intelligence. Examples of this are in the extraordinary development of the
sense of sight, hearing, or smell, in different animals. There are animals in which these
special senses possess a delicacy of perception to which man, even with the greatest
amount of intelligent education, can never attain ; but man, possessing a nervous organi-
zation not superior to that of other warm-blooded animals in its general development,
and inferior to many in the development of special organs, stands immeasurably above
all other beings, by virtue of the immense preponderance of what is known as the
encephalic portion of the nervous system.

These brief general considerations will convey some idea of the physiological impor-
tance of the nervous system ; of the care which should be exercised in its study ; and of
the great interest attached to it, from the fact that the most complex and important of
its functions belong to human physiology, and to human physiology alone.

We can best define what is to be included under the head of the nervous system, by
citing certain of its prominent and well-established properties and functions :

1. The nervous system is anatomically and physiologically distinct from all other sys-
tems and organs in the body. It receives impressions made upon the terminal branches of
its sensory portion and it conveys stimulus to parts, determining and regulating the opera-
tion of their functions; but its physiological properties are inherent, and it gives to no

564 NERVOUS SYSTEM.

tissue or organ its special "irritability" or the power of performing its particular func-
tion.

2. The nervous system connects into a coordinated organism all parts and organs of
.the body. It is the medium through which all iinpressioDS are received. It animates
or regulates all movements, voluntary and involuntary. It regulates the functions of
secretion, nutrition, calorification, and all the processes of organic life.

In addition to its functions as a medium of conduction and communication, the ner-
vous system, in certain of its parts, is capable of receiving impressions and of generating
a stimulating influence, or force, peculiar to itself. As there can be no physiological
connection or coordination of different parts of the organism, having an active function,
without nerves, there can be no unconscious reception of impressions giving rise to invol-
untary movements, no appreciation of impressions, general, as in ordinary sensation, or
special, as in sight, smell, taste, or hearing, no instinct, volition, thought, or even knowl-
edge of existence, without nerve-centres.

Possessing, as it does, these varied properties and functions, it is evidently of the
greatest physiological importance that the anatomical characters of the nervous sys-
tem should be most carefully studied, with a view of connecting, if possible, certain of
the nervous properties with peculiarities in structure. It is also important to subdivide
the system, as regards general properties and functions, as well as with reference to the
special office of particular parts. With this end in view, we shall point out first, the
great anatomico-physiological divisions common to nervous matter wherever it exists,
and afterward, the subdivisions of the system as regards special functions.

Divisions of the JVervous /System.

Nervous matter, whatever may be its special function, presents two great divisions,
each with distinct anatomical as well as physiological differences. One of these divisions
presents the form of fibres or tubes. This kind of nervous matter is incapable of gener-
ating a force or stimulus, and it serves only as a conductor. The other division is in the
form of cells, and this kind of nervous matter alone is capable of generating the so-called
nervous force.

The nervous matter is divided into two great systems, as follows :

1. The cerebro-spinal system, composed of the brain and spinal cord with the nerves
directly connected with these centres. This system is specially connected with the func-
tions of relation, or of animal life. The centres preside over general sensation, the spe-
cial senses, voluntary and some involuntary movements, intellection, and, in short, all
of the functions that characterize the animal. The nerves serve as the conductors of
impressions known as general or special sensations, and of the stimulus that gives rise to
voluntary and certain involuntary movements, the latter being the automatic movements
connected with animal life.

2. The sympathetic, or organic system. This system is specially connected with the
functions relating to nutrition, operations which have their analogue in the vegetable
kingdom and are sometimes called the functions of vegetative life. Although this sys-
tem presides over functions entirely distinct from those characteristic of and peculiar to
animals, the centres of this system all have an anatomical and physiological connection
with the cerebro-spinal nerves.

The cerebro-spinal system is subdivided into centres presiding over movements and
ordinary sensation, and centres capable of receiving impressions connected with the special
senses, such as sight, audition, olfaction, and gustation. The nerves which receive these
special impressions and convey them to the appropriate centres are more or less insen-
sible to ordinary impressions. The organs to which these special nerves are distributed
are generally of a complex and peculiar structure, and they present numerous accessory
parts which are important and essential in the transmission of the special impressions to
the terminal branches of the nerves.

PHYSIOLOGICAL ANATOMY OF THE NERVOUS TISSUE. 565

In treating of the nervous system, we shall consider first the physiological anatomy
of the nervous tissue ; next, the general properties of the cerebro-spinal system ; next,
the functions of different portions of this system connected with motion, ordinary sensi-
bility, intellection, etc. ; next, the functions of the sympathetic, or organic system of
nerves ; and finally, the special senses, with the physiological anatomy and mechanism
of the accessory parts.

Physiological Anatomy of the Nervous Tissue.

The physiological anatomy of the nervous system naturally divides itself into two
sections ; one embracing what is called the general anatomy of the nervous tissue, and
the other, the arrangement of this tissue in special organs, as far as this is connected
with their functions.

The intimate structure of the different portions of the nervous system may now be
regarded as tolerably well understood, at least so far as those anatomical points bearing
upon physiology are concerned. The connection between the nerve-cells and the fibres
and the modes of termination of the motor filaments in the muscles are points nearly if
not quite settled ; and the terminations of sensory filaments in integument and mucous
membranes have lately been investigated very thoroughly and with quite positive and
satisfactory results. These anatomical points are specially connected with the general
properties of the nervous system, both as a generator of the so-called nerve-force and as
a conductor.

The arrangement of the nervous elements in special organs, as in the brain and spinal
cord, has not been so successfully investigated and presents immense difficulties in its
study ; and we can hardly hope to acquire any thing like a definite and thorough knowl-
edge of the functions of these parts, until we have much more positive information con-
cerning their anatomical characters.

Anatomical Divisions of the Nervous Tissue. — The physiological division of the
nervous system into nerves and nerve-centres is pretty well carried out as regards the
anatomical structure of these parts. The two great divisions of the system, anatomically
considered, are into nerve-cells and nerve-fibres.

The nerve-cells, as far as we know, are the only parts capable, under any circum-
stances, of generating the nerve-force ; and, as a rule, they cannot receive impressions
in any other way than through the nerve-fibres. There are, however, some exceptions,
either apparent or real, to this rule, as in the case of direct irritation of the ganglion of
the tuber annulare, portions of the cerebrum, and the sympathetic ganglia, which seem
sensible to direct irritation ; but the cells of most of the ganglia belonging to the great
cerebro-spinal axis are insensible to direct stimulation and can only receive impressions
conducted to them by the nerves.

The nerve-fibres act only as conductors and are incapable of generating nerve-force.
There is no exception to this rule, but there are differences in the properties of certain
fibres. The nerves generally, for example, receive direct impressions, the motor fila-
ments conducting these to the muscles and the sensory filaments conveying the impres-
sions to the centres. These fibres also conduct the force generated by the nerve-centres.
But there are many fibres, such as those composing the white matter of the encephalon
and the spinal cord, that are insensible to direct irritation, while they convey to the
centres impressions made by the sensitive nerves and conduct to the motor nerves the
stimulus generated by nerve-cells.

Structure of the Nerves. — There are few anatomical elements that present greater
variations in size and appearance than the nerve-fibres. Certain fibres found in the
course of the nerves between the muscles are as large as T?TZ of an inch, have dark
borders, and possess three well-marked structures, viz., a tubular membrane, medullary
contents, and an axial band ; others, with the same structure, are only ^^- of an inch

566 NERVOUS SYSTEM.

in diameter ; others have only the medullary covering and the axial band ; and others
present the axial band alone. Most of these anatomical elements have essentially the
same physiological conducting properties; the variations in their structure depending
upon differences in their anatomical relations. In view of these facts, it will be con-
venient to adopt some anatomical classification of the fibres.

In the most simple classification of the nerve-fibres, they are divided into two groups;
one embracing those fibres which have the conducting element alone, and the other pre-
senting this element surrounded by certain accessory structures. In the course of the
nerves, the simple fibres are the exception, and the other variety is the rule ; but, as the
nerves are followed to their terminations in muscles or sensitive parts, or are traced to
their origin in the nerve-centres, we find that they lose one or another of their adven-
titious elements. These two varieties we shall term : 1. The medullated fibres, and 2.
The simple, or non-medullated fibres.

Medullated Nerve-fibres. — These fibres are so called by French and German writers
because, in addition to the axis-cylinder, or conducting element, they contain, enclosed
in a tubular sheath, a soft substance called the medulla. This substance is strongly
refractive and gives the nerves a peculiar appearance under the microscope, from which
they are sometimes called the dark-bordered nerve-fibres. As the whole substance of
the fibre is enclosed in a tubular membrane, these are frequently spoken of as nerve-
tubes.

If the nerves be examined while perfectly fresh and unchanged, their anatomical ele-
ments appear in the form of simple fibres with strongly-accentuated borders. The diame-
ter of these fibres is from ^^Vo ^° TTOIT °f an inch- To observe the fibres in this way, it is
necessary to take a nerve from an animal just killed and examine it without delay. In a
very short time, the borders become darker and the fibre assumes an entirely different
appearance. By the use of certain reagents, it can be demonstrated that a medullated
nerve-fibre is composed of three distinct portions ; viz., a homogeneous sheath, a semi-
fluid matter contained in the sheath, and a delicate central band.

The tubular sheath of the nerve-fibres is a somewhat elastic, homogeneous membrane,
never striated or fibrillated, and presenting generally oval nuclei, with their long diame-
ter in the direction of the tube. This is sometimes called the neurilemma, a name, how-
ever, which is more generally applied to another membrane. It is sometimes spoken of,
also, as the "limiting membrane of Valentin," or "the sheath of Schwann." In its
chemical and general properties, this membrane resembles the sarcolemma, although it is
less elastic and resisting. It exists in all the medullated nerve-fibres, large and small,
except those in the white portions of the encephalon and spinal cord. It is not certain
that it does not exist in the small, non-medullated fibres, although its presence here has
never been satisfactorily demonstrated. As we before remarked, the tubular membrane
cannot be seen in the perfectly fresh nerves ; and, even after they have become changed
by desiccation, its demonstration requires the use of reagents. In the ordinary medul-
lated fibres, however, it may be isolated by boiling the nerve in absolute alcohol and then
in acetic acid, or by treating it with cold caustic soda. By then boiling the nerve for an
instant in the caustic soda, fragments of the tube may be isolated, when they resemble
the membrane forming the canals of the kidney. Another method is to treat the nerve
with fuming nitric acid, afterward adding a solution of caustic potash. The fatty sub-
stance is then discharged in small drops, the central band is dissolved, and the empty
sheath is seen, swollen and tinged with yellow.

The medullary substance fills the tube and surrounds the central band. This is called
by various names, as myeline, white substance of Schwann, medullary sheath, nervous
medulla, etc. It does not exist either at the origin of the nerves in the gray substance
of the nerve-centres or at the peripheral termination of the nerves, and it is probably not
an essential conducting element. When the nerves are perfectly fresh, this substance is
transparent, homogeneous, and strongly refracting, like oil ; but, as the nerves become

PHYSIOLOGICAL ANATOMY OF THE NERVOUS TISSUE. 567

altered by desiccation, the action of water, acetic acid, and various other reagents, it
coagulates into an opaque, granular mass. The consistence of this substance gives to the
raedullated fibres a very peculiar appearance. The tubular membrane being very thin
and not elastic, the white substance, by very slight pressure, is made to till the tubes
irregularly, giving them a varicose appearance, which is entirely characteristic. In
examining a preparation of the nervous tissue, large drops, coagulated in irregular shapes,
are seen scattered over the field and frequently fringing the divided ends of the tubes.
In the white substance of the encephalon and spinal cord, where the tubular membrane
is wanting, the varicose appearance of the fibres is more remarkable than in any other
situation.

The axis-cylinder is, in all probability, the essential anatomical element of the nerves.
It exists in all the nerves except in those termed gelatinous fibres, or fibres of Remak,
which will be described hereafter. In the ordinary medullated fibres, the axis-cylinder
cannot be seen in the natural condition of the tissue, because it refracts in the same
manner as the medullary substance, and it cannot be demonstrated afterward, on account
of the opacity of the coagulated matter. If a fresh nerve, however, be treated with
strong acetic acid, the divided^ ends of the fibres will retract, leaving the axis-cylinder,
which is but slightly affected by reagents. It then presents itself in the form of a pale,
slightly-flattened band, with outlines tolerably regular, though slightly varicose at inter-
vals, somewhat granular, and sometimes very finely striated in a longitudinal direction.
This band is elastic but not very resisting. Its granules are excessively pale. What
serves to distinguish it from all other portions of the nerve-fibre is its insolubility in most
of the reagents employed in anatomical investigations. It is slightly swollen by acetic
acid but is dissolved after prolonged boiling. If a solution of carmine be applied to the
nervous tissue, the axis-cylinder only is colored. It has been remarked that the nerve-
fibres treated with nitrate of silver present in the axis-cylinder well-marked transverse
striations ; and some observers are disposed to regard both the nerve-cells and the axes
of the fibres as composed of two substances, the limits of which are marked by the regu-
lar striae developed by the nitrate of silver. This, however, is a point of purely anatomi-
cal interest. The presence of regular and well-marked stria3 in the axis cylinder after
the addition of a solution of nitrate of silver and the action of light cannot be doubted ;
but it has not yet been determined beyond question whether these markings be entirely
artificial, or whether the axis-cylinder be really composed of two kinds of substance.

A still more important question with regard to the intimate structure of the axis-
cylinder refers to the longitudinal striations. These are observed in many fibres, but
they are not constant. Some authors have adopted the view that the markings are pro-
duced by fibrillse, analogous to the fibrillaQ of the muscular fibres, in all the fibres, as well
as in those of the retina, the olfactory, and some of the sympathetic nerves. In the organs
of special sense, there can be no doubt of the existence of fibrillas ; but this is by no
means so clearly demonstrable in the general system of nerves. Still, it is necessary to
take into consideration, in this connection, certain facts with regard to the origin of the
nerve-fibres in the cells and their ultimate distribution in sensitive parts. In the final
distribution of sensitive nerves, we shall see that the fibres break up into filaments
resembling fibrilla3 ; and, although the fibrillated character of the poles of the nerve-cells
is not unreservedly accepted by anatomists, many observers positively state that such is
their structure. In the present condition of the science, we cannot do more than state
that, while a fibrillated structure has perhaps been shown in the nerves of some of the
lower orders of animals, its existence in man and in the mammalia is somewhat doubtful.

The diameter of the axis-cylinder is about one-half or one-third that of the tube in
which it is contained. The various appearances which the nerve-fibres present under
different conditions are represented in Fig. 174.

Simple, or Non-mcdullatcd Nerve- Fibres.— These fibres are found very largely dis-
tributed in the nervous system. When we come to study the structure and relations of

568

NERVOUS SYSTEM.

medium-sized fibre with borders of single con-
tour, and four large fibres ; of the latter, two
have a double contour, and two contain granu-
lar matter.

these small fibres, which seem in many instances to be simple prolongations, without
alteration, of the axis-cylinder of the medulluted fibres, it will be seen that they are
chiefly found in the peripheral terminations of the nerves and in the filaments of connec-
tion of the fibres with the cells. The study of
the fibres in these relations constitutes the most
important part, physiologically, of the anatomy
of the nerves and presents the greatest difficul-
ties in the way of direct observation ; and, for
these reasons, we shall treat of these questions sep-
arately, and defer, for the present, the full con-
sideration of the non-medullated fibres.

Gelatinous Nerve-Fibres (Fibres of Remak). —
These fibres are entirely diiferent in their anat-
omy from either of the varieties of fibres just
considered. They are found chiefly in the sym-
pathetic system and in that particular portion of
this system connected with involuntary move-
ments. For instance, these fibres are very abun-
dant in the gray filaments sent to parts provided
with non-striated muscular fibres and endowed
with undoubted motor properties ; but they are

from the human subject; not foun(l jn foe wnite filaments of the sympa-
magmfied 3oO diameters. (Kolliker.)

Four small fibres, of which two are varicose, one thetic, which seem to be incapable of exciting

movements.

There is considerable difference of opinion
among physiologists with regard to the gelatinous
filaments. Some are disposed to regard them as elements of connective tissue, not
endowed with properties characteristic of nerves, while others consider that they are
nerve-fibres, probably possessing functions distinct from those of the fibres of diiferent
structure. The latter is the view now adopted by the best anatomists. While it is
certain that elements of connective tissue exist in the nerves, and that these have been
mistaken for true nerve-fibres, there are in the nerves, particularly in those belonging to
the great sympathetic system, fibres exactly resembling the nerve-fibres of the embryon.
These are the true gelatinous nerve-fibres, or fibres of Remak. It is stated that the
nerves generally have this structure up to the fifth month of intra-uterine life, and that,
in the regeneration of nerves after division or injury, the new elements assume this
form before they arrive at their full development.

The true gelatinous nerve-fibres present the following characters : They are flattened,
with regular and sharp borders, grayish and pale, presenting numerous very fine granu-
lations, and a number of oval, longitudinal nuclei, a characteristic which has given them
the name of nucleated nerve-fibres. The diameter of the fibres is about y-fa-y of an inch.
The nuclei have nearly the same diameter as the fibres and are about J^TT °f an inch
in length. They are finely granular and present no nucleoli. The fibres are rendered
pale by the action of acetic acid, but they are slightly swollen only, and present, in this
regard, a marked contrast with the elements of a connective tissue. The microscopical
appearances of these fibres, which are strongly characteristic, are represented in Fig. 175.

Accessory Anatomical Elements of the Nerves. — The nerves present, in addition to the
different varieties of true nerve-fibres just described, certain accessory anatomical ele-
ments common to nearly all of the tissues of the organism, such as connective tissue,
blood-vessels, and perhaps lymphatics, although these have never been demonstrated,
except in the nerve-centres.

Like the muscular tissue, the nerves are made up of their true anatomical elements —
the nerve-fibres — held together into primitive, secondary, and tertiary bundles, and so

PHYSIOLOGICAL ANATOMY OF THE NERVOUS TISSUE.

569

on, in proportion to the size of the nerve. The primitive fasciculi are surrounded by a
delicate membrane, described by Robin under the name of perinevre, but which had been
already noted by other anatomists under different names. This membrane is homogeneous
or very finely granular, sometimes marked with longitudinal striae, and possessing elon-
gated nuclei, finely granular, from ^Vfr to ^Vrr of an incn in
length by from ^Vfr to Jinrv °f an mcn wide. The thickness of
the membrane is from 12ft66 to -^^ of an inch. It commences at
the point where the nerve-fibres emerge from the white portion of
the nervous centres, and it extends to their terminal extremities,
being interrupted by the ganglia in the course of the nerves. This
membrane generally envelops a primitive fasciculus of fibres, branch-
ing as the bundles divide and pass from one trunk to another ; but
it is sometimes found surrounding single fibres. It is not usually
penetrated by blood-vessels, the smallest capillaries of the nerves
ramifying in its substance but seldom passing through to the indi-
vidual nerve-fibres. Within the perinerve, are sometimes found
elements of connective tissue, with very rarely a few capillary
blood-vessels in the largest fasciculi.

The amount of fibrous tissue in the different nerves is very
variable and depends upon the conditions to which they are sub-
jected. In the nerves within the bony cavities, where they are
entirely protected, the fibrous tissue is very scanty; but, in the
nerves between muscles, we find a tolerably strong investing mem-
brane or sheath surrounding the whole nerve and sending pro-
cesses into its interior, which envelop smaller bundles of fibres.
This sheath is formed of inelastic fibres, with small elastic fibres
and nucleated connective-tissue fibres. These latter may be distin-
guished from the gelatinous nerve-fibres by the action of acetic
acid, which swells and finally dissolves them, while the nerve-
fibres are but slightly affected.

The late researches of Sappey have shown that the structure
of the fibrous sheath of the nerves possesses certain important
anatomical peculiarities. The greatest part of this membrane is composed of bundles
of white inelastic tissue, interlacing in every direction ; but it contains also numerous
elastic fibres, adipose tissue, a net-work of arteries and veins, and "nervi-nervorurn,"
which are to these structures what the vasa-vasorum are to the blood-vessels. The
adipose tissue is constant, being found even in extremely emaciated persons.

The vascular supply to most of the nerves is rather scanty. The arteries break up into
a plexus of very fine capillaries, arranged in oblong, longitudinal meshes surrounding the
fasciculi of fibres ; but they rarely penetrate the perinerve, and they do not usually come in
contact with the ultimate nervous elements. The veins are rather more voluminous and
follow the arrangement of the arteries. It is not certain that the nerves in their course
contain lymphatics ; at least these vessels have never been demonstrated in their substance.

Branching and Course of the Nerves. — The ultimate nerve-fibres in the course of the
nerves have no connection with each other by branching or inosculation. A bundle of
fibres frequently sends branches to other nerves and receives branches in the same way ;
but this is simply the passage of fibres from one sheath to another, the ultimate fibres them-
selves maintaining throughout their course their integrity and their individual physiologi-
cal properties. This view with regard to the course of the fibres in the nerves is held by
nearly all anatomists. The nerve-fibres do not branch or inosculate except at the point
where they change their character just before their termination. The branching and inos-
culation of the ultimate nerve-fibres will be considered in connection with the very inter-
esting and important question of their ultimate distribution to muscles and sensitive parts.

Fro. 175. — Fibres of Re-
inak ; magnified 300
diameters. (Robin.)

"With the gelatinous fibres,
are seen two of the or-
dinary, dark-bordered
nerve-fibres.

570 NERVOUS SYSTEM.

Mode of Termination of the Nerves in the Voluntary Muscles. — For a long time, the
mode of termination of the nerve-fibres in the muscles was a question of great uncer-
tainty ; but, within the last few years, thanks to the elaborate researches of French and
German anatomists, the peripheral extremities of the nerves have been so accurately
described and figured, that the great question of the mode of connection between the
anatomical element conducting the stimulus to the muscles and the contractile elements
of the muscles themselves may be considered as definitively settled. In 1840, Doy£re gave
an account of the peripheral termination of the motor nerves, probably as accurate as
was possible with his imperfect means of investigation ; but this observation, though
confirmed a few years later by Quatrefages, seems to have been lost sight of by most
physiological writers. Without underestimating the value of other researches, we may
state that those of Rouget represent, perhaps, the present condition of the question as
well as any. The differences, however, between the most reliable observations of recent
writers are nearly all unimportant ; and, while future investigations may enable us to go
farther in following out some of the elements of the nerve-fibres, they will, in all probabil-
ity, simply extend our knowledge, without invalidating the information already acquired.

The observations of Rouget were published in 1862 and were made upon lizards,
frogs, Guinea-pigs, rats, and other animals, and have been confirmed in the human subject.
The tissues were taken either from the living animal or from an animal just killed, and
they were examined, in some instances, without the addition of reagents ; hut the most
satisfactory results were obtained by macerating the muscles for from six to twenty-four
hours in a liquid containing ^-^ of hydrochloric acid, and adding to the preparation on
the glass slide a drop of a solution of sugar in water. In preparations made in this way,
it is easy to trace the course of the nerves to their termination. The following is the
description given by Rouget :

" The nervous trunks and the branches of distribution generally cross the course of
the muscular fibres. As regards the terminal ramifications, sometimes they meet the
muscular fibres at nearly a right angle, and sometimes they are placed nearly parallel to
the axis of the primitive fasciculi. Branches of distribution are detached sometimes
from branches containing two or three fibres, and sometimes from isolated fibres. After
a very short course these tubes divide, and may present as many as seven or eight suc-
cessive divisions. Most commonly, the termination takes place either by divisions of the
second or third order, or the same tube gives off, successively, divisions which pass to the
adjacent primitive fasciculi and terminate here without new divisions and after a very
short course. They have a less diameter than the primitive nerve-tubes, but they pre-
serve even to the terminal extremity their double contour, and there can be demonstrated,
very easily, a sheath provided with nuclei, a medullary layer, and the axis-cylinder.
Never do we observe at the termination of the motor nerves the pale and non-medullated
fibres described by Ktihne and Kolliker. At the point where the tube terminates, we
remark constantly a special arrangement which has no analogy with that which has been
described in the batrachia by these two observers, and which Ktihne believed could be
extended to the higher vertebrata, to. the mammalia, and to the human subject. The
nerve-tube, with a double contour, preserving still a diameter of from ^Vo to T^ of an
inch at the point where it touches the primitive fasciculus to become arrested at its sur-
face, terminates by an expansion of the central nerve-substance, the axis- cylinder, which
is in immediate contact with the contractile fibres (fibrillse) of the primitive fasciculus.
The layer of medullary substance ceases abruptly at this point, the sheath of the tube is
spread out and blended with the sarcolemma; but in immediate continuity with the axis-
cylinder, a layer, a plate of granular substance, from -^Vs- to ¥ oVo of an incn in thick-
ness, is spread out beneath the sarcolemma, on the surface of the fibrilla?, in a space
generally oval and about T^77 of an inch wide in its short diameter, and -5-^ of an inch
in its long diameter. This granular substance masks more or less completely, in the
space which corresponds to it, the transverse stri.88 of the muscular fasciculus. The disk

PHYSIOLOGICAL ANATOMY OF THE NERVOUS TISSUE.

571

itself has exactly the granular appearance of the substance of the axis-cylinder in the
vertebrata, and of that of the nerve-tubes in most of the invertebrata, especially after
being treated by diluted acids. But that which essentially characterizes the terminal
plates of the motor nerves is an agglomeration of nuclei observed at their site. With a
low magnifying power, even, we can distinguish the point where a nerve-tube touches
the primitive fasciculus to which it belongs, and ends abruptly at its surface, by a collec-
tion of from six to twelve or even sixteen nuclei which occupy the site of the terminal
plate. These nuclei are distinguished by their size as well as by their form, which is less
elongated than the nuclei of the muscular tissue (connective-tissue nuclei of the primitive
fasciculi). They present, however, the most complete analogy with the nuclei of the
nerve-sheath (connective- tissue nuclei of the nerves'). They are, without any doubt, nothing
else than the nuclei which, scattered throughout the entire length of the sheath, are col-
lected in a mass at the point where the covering of the nerve-fibre is spread out and fuses
with the sarcolemma of the primitive fasciculus."

There can be little if any doubt that the description just given represents the mode
of termination of the nerves in the voluntary muscles in man and in the mammalia. The
observations of Kolliker, who describes a plexus of pale fibres with nuclei instead of a
well-defined terminal plate, were made upon frogs, and are probably correct ; and Kolli-
ker admits the accuracy of the observations of Rouget as regards reptiles, birds, and the
mammalia.

Although the sensibility of the muscles is slight as compared with that of the tegu-
mentary tissues, they undoubtedly possess nerve-fibres other than those exclusively
devoted to motion. In addition to the fibres just described, Kolliker and some others
have noted fibres with a different mode
of termination. These Kolliker believes
to be sensitive nerves, and their mode of
termination has not been so definitely de-
scribed as that of the fibres with terminal
motor plates. We refrain from giving a
very full description even of what has
been observed with regard to the termi-
nation of these fibres, for future and
more successful researches will probably
modify the views now held with regard
to this point. Kolliker states that the
fibres in question are very fine, dark-bor-
dered tubes, with a medullated sheath,
which, when studied in muscular tissue
rendered pale by acetic acid, may be seen
to give off exceedingly fine, non-medul-
lated fibres, which terminate in fibres of
the same appearance, but provided with
nuclei. It does not appear to be certain
how these fibres end. Kolliker is not
satisfied that the free extremities, as
they appear to be, are the actual termi-
nations ; but he asserts that in some rare
instances they communicate with each
other. For the present this point must

FIG.

176.— Mode of termination of the motor nerves.
(Rouget.)

A, primitive fasciculus of the thyro-hyoid muscle of the human

subject, and its nerve-tube : 1, 1. primitive muscular fas-
ciculus ; 2, nerve-tube ; 8, medullary substance of the
tube, which is seen extending to the terminal plate, where
it disappears ; 4, terminal plate situated beneath the sar-
colemma, that is to say, between it and the elementary
fibrilla?; 5, 5. sarcolemma.

B, primitive fasciculus of the intercostal muscle of the lizard,

in which a nerve-tube terminates : 1, 1, sheath of the
nerve-tube, 2, nucleus of the sheath : 2, 3, sarcolemma
becoming continuous with the sheath: 4, medullary sub-
stance of the nerve-tube ceasing abruptly at tin- site of the
terminal plate ; 5, 5, terminal plate; <>. <!, nuclei of the
plate; 7, 7, granular substance which forms the principal
element of the terminal plate, and which is continuous
with the axis-cylinder ; s. s. undulations of the sarcolem-
ma reproducing those of the flbrillae; 9, 9, nuclei of the
sarcolemma.

be considered as unsettled.

Mode of Termination of the Nerves in the Involuntary Muscular Tissue. — The nerves
have not been followed out so satisfactorily in the involuntary as in the striated mus-
cular system ; and, as most if not all of the fibres are derived from the sympathetic

572

NERVOUS SYSTEM.

system, which contains numerous fibres of Remak the terminations of which have not
been described, it is evident that our information concerning this part of the peripheral
nervous system must be incomplete. Perhaps the most remarkable of the late observa-
tions upon this point are those of Dr. Frankenhaeuser, upon the nerves of the uterus.
These researches were very elaborate ; but the point most interesting in this connection
is that the nerves, having formed a plexus in the connective tissue, send exceedingly
small fibres into the sheets or layers of muscular-fibre cells, which branch and finally go
into the nucleoli of these structures. Arnold has confirmed these observations and has
shown farther that, in many instances, the fine terminal nerve-fibres branch and go into
the nuclei of the muscular fibres and then pass out to join with other fibres and form
a plexus.

Termination of the Nerves in Glands. — The great influence which the nervous system
exerts upon secretion attaches considerable interest to recent researches into the ultimate
distribution of the nerves in the glands. It must be remembered, however, in these, as
in all observations upon the destination of the smallest nerve-fibres, that the problem is
one of the most difficult in the whole range of minute anatomy ; and the results arrived
at must be received with a certain amount of caution, until they shall have been amply
confirmed.

FIG. 177 — Termination of the nerves in the salivary glands. (Pfliiger.)

I, II, branching of the nerves between the glandular cells ; III, terminations of the nerves in the nuclei of the cells ;

IV, multipolar nerve-cell.

The researches of Pfluger upon the salivary glands leave no doubt as to the fact that
medullated nerve-fibres pass to the cells of these organs and there abruptly terminate, at
least as dark -bordered fibres. This author believes, however, that, having formed a more
or less branching plexus, non-medullated fibres pass directly into the glandular cells, and
he gives figures which seem to illustrate this arrangement pretty clearly. The same
observer describes and figures multipolar cells, mixed with the glandular cells, in which
some of the nerve-fibres terminate.

Modes of Termination of the Sensory Nerves. — There are undoubtedly several modes
of termination of the sensitive nerves in integument and in mucous membranes, some of
which have been accurately enough described, while others are still somewhat uncertain.
In the first place, anatomists now recognize three varieties of corpuscular terminations,
differing in their structure, probably, according to the different functions connected with
sensation, with which the parts are endowed. In addition, it is probable that many
sensitive nerves are connected with the hair- follicles, which are so largely distributed

PHYSIOLOGICAL ANATOMY OF THE NERVOUS TISSUE.

573

throughout the cutaneous surface. There are, also, terminal filaments not connected
with any special organs, some of them, perhaps, ending simply in free extremities, and
some connected with epithelium. There is still considerable difference of opinion
among anatomists concerning all of these various points, but, with regard to the terminal
corpuscles, these differences are purely anatomical, and they do not materially affect our
ideas of the physiology of sensation. We do not propose, therefore, to enter fully into the
discussions upon these questions, and we shall simply present what seem to be the most
reasonable views of the latest and most reliable observers.

Corpuscles of Pacini, or of Vater. — These corpuscles, which were the first discovered
and described in connection with the sensitive nerves, were called corpuscles of Pacini,
until it was shown that they had been seen about a century and a half ago by Vater.
Their actual mode of connection with the nerves, however, has only been ascertained
within the last few years. The following are the measurements of these bodies and the
situations in which they are found, taken from Kolliker :

In man, these corpuscles are oval or egg-shaped and measure from •£$ to | of an inch
in length. They are always found in the subcutaneous layer on the palms of the hands
and the soles of the feet, and are most numerous on the palmar surfaces of the fingers
and toes, particularly the third phalanges. In the entire hand there are about six hun-
dred, and about the same number on the feet. They are sometimes, but not constantly,
found in the following situations : The dorsal surfaces of the hands and feet, on the
cutaneous nerves of the arm, the forearm and the neck, the internal pudic nerve, the
intercostal nerves, all of the articular nerves of the extremities, the nerves beneath the
mammary glands, the nerves of the nipples, and in the substance of
the muscles of the hands and feet. They are found without excep-
tion on all of the great plexuses of the sympathetic system, in front
of and by the sides of the abdominal aorta, and behind the peri-
toneum, particularly in the vicinity of the pancreas. They some-
times exist in the mesentery and have been observed near the
coccygeal gland.

The structure of the corpuscles consists simply of several layers
of connective tissue enclosing a central bulb in which is found
the terminal extremity of the nerve. This bulb is finely granu-
lar, nucleated, and is regarded by most anatomists as composed
of connective tissue. At the base of the corpuscle, is a pedicle
formed of connective tissue surrounding a medullated nerve-fibre
which penetrates the corpuscle and terminates in the central bulb.

The only really important point of discussion with reference to
the structure of the nerve-fibre in the central bulb, and this is
purely anatomical, is whether or not the medullary substance ex-
tend into the corpuscle itself. Probably the fibre is here reduced
simply to the axis- cylinder. All anatomists agree that a single
thin, flat fibre penetrates the corpuscle and terminates near its
summit by a slightly - enlarged and granular extremity. The
arrangement of the different anatomical elements is shown in
Fig. 178.

The situation of these corpuscles beneath, instead of in the
substance of the true skin, shows that they cannot be properly
considered as tactile corpuscles, a name which is applied to other
structures situated in the papillae of the corium ; and it is impos-
sible to assign to them any special function connected with sen-
sation, such as the sense of temperature, or the appreciation of

pressure or weight. All that we can say with regard to them is that they constitute
one of the several modes of termination of the nerves of general sensibility.

FIG. 178.— Pacinian cor-
puscles. (Sappey.)

1, base of the corpuscle; 2,
apex ; 3, 3, 8, substance
of the corpuscle, in lay-
ers ; 4, 4, nerve pene-
trating the corpuscle;
6, cavity of the corpus-
cle ; (>, nerve ; 7, nerve,
which has lost its me-
dullary substance and
sheath ; 8, termination
of the nerve ; 9, pranu-
lar substance continuous
with the nerve.

574 NEKVOUS SYSTEM.

Tactile Corpuscles. — The name tactile corpuscles implies that these bodies are con-
nected with the sense of touch ; and this view is sustained by the fact that they are
found almost exclusively in parts endowed to a marked degree with tactile sensibility.
They are sometimes called the corpuscles of Meissner and Wagner, after the anatomists
by whom they were first described. The true tactile corpuscles are found in greatest
number on the palmar surfaces of the hands and fingers and the plantar surfaces of the
feet and toes. They exist, also, in the skin on the backs of the hands and feet, the nip-
ples, and a few on the anterior surface of the forearm. As we shall see when we come
to describe them fully, they are situated in the substance of the papillae of the skin, and
they cannot fail to have an important function in connection with the sense of touch.

We have already treated of the general structure of the skin and have seen that the
largest papillae, measuring from ^^ to -g^-§ of an inch in length, are found on the hands,
feet, and nipples, precisely where the tactile corpuscles are most abundant. Corpuscles do
not exist in all papillaa, and they are found chiefly in those called compound. In a space
of about -fa of an inch square on the third phalanx of the index-finger, Meissner counted
four hundred papillae, in one hundred and eight of which he found tactile corpuscles, or

FIG. 119.— Papilla of the skin of the palm of the hand, (Sappey.)

1, papilla with two vascular loops ; 2, papilla with a tactile corpuscle ; 3, papilla with three vascular loops ; 4, 5, large
compound papillae ; 6, 6, vascular net-work beneath the papillae ; 7, 7, 7, 7, vascular loops in the papillae ; 8, 8, 8, 8,
nerves beneath the papulae ; 9, 9, 10, 11, tactile corpuscles.

about one in four. In the same space on the second phalanx, he found forty corpuscles ;
on the first phalanx, fifteen ; eight on the skin of the hypothenar eminence ; thirty-four
on the plantar surface of the ungual phalanx of the great-toe ; and seven or eight in the
skin on the middle of the sole of the foot. In the skin of the forearm, the corpuscles are
very rare. Kolliker states, also, that the tactile corpuscles usually occupy special papilla,
which are not provided with blood-vessels ; so that the papillae of the hand may be
properly divided into vascular and nervous.

The form of the tactile corpuscles is oblong, with their long diameter in the direction
of the papillae. Their length is from -^ to -gfa of an inch. In the palm of the hand,
they are from -^ to -^ of an inch long, and from -5-^ to -^ of an inch in thickness.
They are generally situated at the summits of the secondary eminences of the compound
papillae. According to Kolliker, the tactile corpuscles consist of a central bulb of homo-
geneous or slightly-granular connective-tissue substance, analogous to the central bulb
of the Pacinian corpuscles, and a covering. Treated with acetic acid, the covering pre-
sents numerous elongated nuclei arranged in a circular manner, which he believes to be
nuclei of connective tissue, and a few fine elastic fibres. One, two, and sometimes three
or four dark-bordered 'nerve-fibres pass from the subcutaneous nervous plexus to the
base of each corpuscle. These surround the corpuscle with two or three spiral turns,
and they terminate by pale extremities at the surface of the central bulb. This arrange-
ment is shown in Fig. 180.

PHYSIOLOGICAL ANATOMY OF THE NERVOUS TISSUE.

575

Terminal Bulls. — Under this name, a variety of corpuscles has lately heen described
by Krause, as existing in the conjunctiva covering the eye and in the semilunar fold, in
the floor of the buccal cavity, the tongue, the glans penis, and the clitoris. They bear
some analogy to the tactile corpuscles, but they are much smaller and more simple in
their structure. They form simply a rounded or oblong enlargement at the ends of the
nerves, which is composed of homogeneous matter, with an exceedingly delicate invest-

ment of connective tissue. They measure from T-^Vtr ^° FS"TT °f an inch in diameter. In the
parts provided with papilla}, they are situated at the summits of the secondary elevations.

FIG. 180. — Cutaneous papilla and tactile corpuscle.
(Kolliker.)

a, cortical layer with plasmatic cells and fine elastic fibres ; &,
tactile corpuscle, with transverse nuclei; c, afferent ner-
vous branch, with its nucleated neurilemma ; c?, d, nerve-
fibres encircling the corpuscle ; e, the apparent termination
of one of these fibres.

The arrangement of the nerve-fibres in these
corpuscles is very simple. One, two, or three
medullated fibres pass from the submucous
plexus to the corpuscles. The investing sheath
of the fibres is here continuous with the connec-
tive-tissue covering of the corpuscle, and the
nerve-fibres pass into the corpuscle, break up
into two or three divisions, and terminate in
convoluted or knotted coils. The nerve-fibres
are medullated for a certain distance, but their
terminations are generally pale. The above is
one form of these corpuscles. Sometimes, how-
ever, the terminal bulbs are oblong, and some-
times but a single nerve-fibre penetrates the
bulb and terminates in a simple pale filament.
The principal forms of the terminal bulbs are
shown in Fig. 181.

General Mode of Termination of the Sen-
sory Nerves. — The actual termination of the sen-
sitive nerves upon the general surface and in
mucous membranes is still a question of great

TIG. 1S1.— Corpuscle* of Krause. (Ludden.)

A, three corpuscles of Krause from the conjunctiva

of man, treated with acetic acid ; magnified 300
diameters : 1, spherical corpuscle, with two
nerve-fibres which form a knot in its interior.
Portions of two pale nerve-fibres are also seen.
2. a rounded corpuscle presenting a nerve-fibre
and fatty granulations in the Internal bulb; 8,
an elongated corpuscle with a distinct terminal
fibre. In these three corpuscles, the covering,
nucleated in 1 and 2. is distinguished.

B, terminal bulbs from the conjunctiva of the calf,

treated with acetic acid; magnified 800 diame-
ters : 1, extremity of a nerve-fibre with its
bulb ; 2, double bifurcation of a nerve-fibre, wttl
two terminal bulbs : a, covering of the termini
bulbs; ft, internal bulb; c, pale nerve-fibre.

obscurity. Although we have arrived at a

pretty definite knowledge of the sensitive corpuscles, it must be remembered that there
is an immense cutaneous and mucous surface in which no corpuscles have as yet been
demonstrated ; and it is in these parts, endowed with what we may call general sensi-

576 NERVOUS SYSTEM.

bility, as distinguished from the sense of touch, that we have to study the mode of ter-
mination of the nerves.

Kolliker is of the opinion that, in the immense majority of instances, the sensitive
nerves terminate in some way in the hair-follicles. If this be true, it will account for
the termination of the nerves in by far the greatest portion of the skin, as there are few
parts in which hair-follicles do not exist ; but, unfortunately, the exact mode of connec-
tion of the nerves with these follicles is not apparent. The following is all we know
positively of the terminations of the nerves on the general surface :

Medullated nerve-fibres form a plexus in the deeper layers of the true skin, from
which fibres, some pale and nucleated and others medullated, pass to the hair-follicles,
divide into branches, penetrate into their interior, and are there lost. A certain number
of fibres pass to the non-striated muscular fibres of the skin. A certain number pass to
papillae and terminate in tactile corpuscles, and others pass to papillaa that have no tac-
tile corpuscles.

In the mucous membranes, as far as we know, the mode of termination is, in general
terms, by a delicate plexus just beneath the epithelium, coming from a submucous plexus
analogous to the deep cutaneous plexus. In certain membranes, we have already noted
the termination in bulbs (corpuscles of Krause). In the cornea, the fibres have been
followed more minutely than in any other situation, and the results of recent researches
upon this subject are very remarkable. These results are so recent and unexpected, that
we are hardly prepared to admit them unreservedly without full confirmation. At
present we can only state that the observations of Hoyer, Lipmann, and others, con-
firmed in part by Kolliker, seem to show that branching nerve-fibres pass to the nucleoli
of the corpuscles of the cornea and to the nucleoli of the cells of the posterior layer of
epithelium.

Structure of the Nerve-centres.

A peculiar pigmentary matter in the nerve-cells and the surrounding granular sub-
stance gives to the nerve-centres a grayish color, by which they are readily distinguished
from the white, or fibrous division of the nervous system. Wherever this gray matter is
found, the anatomical elements of the tissue are cellular, except in the nerves formed of
gray, or gelatinous fibres. Under the general division of nerve-centres, we include, ana-
tomically at least, the gray matter of the cerebro-spinal centres, the ganglia of the roots
of the spinal and certain of the cranial nerves, and the numerous ganglia of the sympa-
thetic system. In these parts are found cells, which constitute the essential anatomical
element of the tissue, granular matter resembling the contents of the cells, pale fibres
originating in prolongations of the cells, elements of connective tissue, delicate mem-
branes enveloping some of the cells, and blood-vessels. The most interesting and im-
portant of these structures, in their physiological relations, are the cells and the prolon-
gations by which they are connected with the nerves.

Nerve-cells. — Anatomists are now pretty well agreed that the following varieties of
cells exist in the nerve-centres and constitute their essential anatomical elements; viz.,
apolar, unipolar, bipolar, and multipolar cells. Although some have denied the existence
of apolar cells, there can be little doubt of their presence in the centres in small numbers,
and, as is suggested by Kolliker, they may be nerve-cells in an imperfect state of devel-
opment. The nerve-cells present great differences in their size and general appearance,
and some distinct varieties are found in particular portions of the nervous system and
are probably connected with special functions.

The apolar cells are simply rounded bodies, with granular contents, a nucleus and
nucleolus like other cells, but without any prolongations connecting them with the nerve-
fibres. They have been observed in the cerebro-spinal centres, and they always exist in
the sympathetic ganglia. Those who deny their existence believe that the poles have

STRUCTURE OF THE NERVE-CENTRES.

577

been detached in preparing specimens for examination. Unipolar cells exist in some of
the lower orders of animals, but their presence in the human subject is doubtful. Bipo-
lar cells are found in the ganglia of the posterior roots of the spinal nerves, where they
are of considerable size. Smaller bipolar cells are found in the sympathetic ganglia.
Multipolar cells present three or more prolongations.

Small cells, with three, and rarely four prolongations, are found in the posterior cor-
nua of the gray matter of the spinal cord. From their situation they have been called
sensory cells. They are undoubtedly found in greatest number in parts known to be
endowed exclusively with sensory properties.

Large, irregularly-shaped multipolar cells, with numerous prolongations, are found
chiefly in the anterior cornua of the gray matter of the spinal cord, and these have been
called motor cells. They sometimes present as many as ten or twelve poles.

With all these differences in the size and form of the nerve-cells, they present toler-
ably uniform general characters as regards their structure and contents. Leaving out the
apolar and unipolar cells, the perfectly-developed cells are of an exceedingly irregular
shape, with strongly-refracting, granular contents, frequently a considerable number of pig-
mentary granules, and with a distinct nucleus and nucleolus. The nucleus in the adult is

FIG. 182. — Nerve-cell from the ferruginous substance which forms the floor of the rhomboidal sinus, in man;

magnified 350 diameters. (Kolliker.)

almost invariably single, although, in very rare instances, two have been observed. Cells
with multiple nuclei are often observed in young animals. The nucleoli are usually single^
but there may be as many as fotir or five. The strongly-refracting contents, the peculiar
shape, and the poles or prolongations, give to the nerve-cells an exceedingly characteristic
appearance, which is represented in Fig. 182.

The diameter of the cells is as variable as their form. They usually measure from
T2Vff to imr of an inch ; but there are many of larger size, and some are smaller. The
nuclei measure from ^^ to y^ of an inch.

The nerve-cells are so delicate and so prone to alteration, that their study is exceed-
37

578

NERVOUS SYSTEM.

ingly difficult. Sections of the nerve-centres must be prepared with great care, and
they are not easily made and preserved. In the numerous anatomical investigations that
have been made within the last few years, the centres have generally been hardened
artificially ; and almost every investigator has used different processes and reagents,
which may account in a measure for the differences of opinion that now exist upon all
points connected with the minute anatomy of these parts.

There is, at the present time, considerable discussion with regard to the intimate
structure of the substance of the nerve-cells, their nuclei and nucleoli, and the points
involved have a certain amount of physiological interest. In the first place, the transverse
strias in the axis-cylinder treated with nitrate of silver, noted by Frommann and confirmed
by Grandry and others, have been observed by Grandry in the substance of the nerve-
cells. "While this fact, perhaps, shows that the substance contained in the cells and their
prolongations is the same as the substance of the axis-cylinder, as we stated with regard
to the axis-cylinder, it is possible that the markings may be entirely artificial, and that
they do not demonstrate the existence of two distinct substances in the tissue.

-wy- -•-

w

FIG. 1S3. — Transverse section of the gray substance of the anterior cornua of the spinal ccrd of the ox, treated

U'it/i nitrate of stiver. (Grandry.)

The most interesting question with regard to the structure of the nerve-cells relates
to the mode of origin of their fibres or poles. Until quite recently, these have been
regarded as simple prolongations of the substance of the cells; but lately the view has
been advanced that the nerve-cells, in the human subject, are composed of regular fibrils
continuous with the poles and starting, as it were, from the nucleoli. The fibrillation of
the nerve-cells and their prolongations is figured by Schultze in an article in one of the
most authoritative of the recent works on histology (Strieker) ; but some other eminent
observers have failed to note the appearances here described, at least in the human sub-
ject and in the mammalia. "With our present knowledge of the physiology of the nerve-
cells, the question whether or not their substance be fibrillated has little more than an
anatomical interest ; but there can be no doubt that the cells in some of the lower orders

STRUCTURE OF THE NERVE-CENTRES.

579

of animals possess striations more
or less regular. These, indeed,
were described soon after the cells
were discovered. While there is
no anatomist who denies the fact
that the substance of the cells is
marked by striae in many animals,
the existence of an analogous ar-
rangement in the human subject
is still doubtful. Some anatomists,
with Schultze, admit the striations
but have failed to connect them
with the nuclei and nucleoli. All
admit that they are demonstrated
•with great difficulty; and, while
this question is so important that
it can hardly be neglected in study-
ing the physiological anatomy of
the nerve-centres, it is one con-
cerning which it seems impossible
to express a positive and definite
opinion.

Connection of the Nerve-cells
with the Fibres and with each other.
— Although the mode of connec-
tion of the nerve-cells with the
fibres and with each other is one
of the most important, in its physi-
ological bearings, of all the points
connected with the minute anat-
omy of the nerve-centres, it is im-
possible, in the present state of our
anatomical knowledge, to answer
the questions involved in a manner
entirely satisfactory. A full dis-
cussion of the different opinions
and the methods of investigation
that have been employed would
be out of place in this work. The
difficulties in the way of arriving
at positive information upon these
questions are the following :

1. The nerve-cells and their
prolongations are so delicate and
easily torn that they cannot be
isolated and followed for any con-
siderable distance, and theoretical
considerations are constantlv re-

\*

FIG. 184.— Nerve-cell from the anterior cornua of the tpinal cord
quired to ; up the deficiencies Ofthe calf, macerated for a short time in iodized serum ; mag-

nified 600 diameters. (Schultze.)
a, a, axis-cylinder prolongation; ft, ft, ft, ft, branching prolongations.

in actual observation.

2. In the study of sections of
the nerve-centres, the parts must be hardened and afterward rendered transparent by

580 NEKVOUS SYSTEM.

reagents, which must produce more or less change in the structures ; and it seems an
anatomical impossibility to make these sections so as to follow out the prolongations of
the cells far enough to establish beyond doubt their exact relations.

These two considerations alone are sufficient to account for the uncertainty so appar-
ent even in the most successful investigations into the anatomy of the central nervous
system ; and we shall content ourselves, in view of these facts, with giving a summary
of what seems to be the probable relation of the cells to the fibres of origin of the nerves
and to each other.

Apolar cells, if they exist at all and be not cells from which the poles have become
separated, are simple, rounded bodies, lying between the fibres, with which they have no
other relation than that of mere contiguity. Unipolar cells have but one prolongation,
which is continuous with a nerve-fibre. It is not certain that these exist in the human
subject.

Bipolar cells are found in the ganglia of the posterior roots of the spinal nerves and in
some of the sympathetic ganglia. In many of the lower animals, particularly in fishes,
the cells of the ganglia of the spinal nerves are simple, nucleated enlargements in the
course of the sensitive nerve-fibres, and many anatomists have inferred that the same
arrangement exists in man and in the mammalia ; but the constitution of these ganglia in
the higher classes of animals seems to be entirely different. In the first place, the roots
of the spinal nerves at the ganglia are undoubtedly reenforced by the addition of new
fibres, as Kolliker has shown by actual measurement, the roots being sensibly larger
beyond the ganglia, while the filaments of entrance and exit have the same diameter.
Direct observation upon the ganglia in man also fails to show the arrangement which is
so clearly demonstrable in fishes. The cells in the posterior roots are not continuous with
the fibres passing from the periphery to the cord, but they give origin to new fibres,
generally two in number, which sometimes are single, and sometimes bifurcated, and
which pass, in by far the greatest number of instances, if not in all, to the periphery.

The inultipolar cells, with three or more prolongations, are found in all of the ganglia,
but they predominate largely in the gray matter of the cerebro-spinal centres. It is the
question of the exact mode of connection between these cells and the fibres of origin of
the cerebro-spinal nerves and the union of the cells with each other by commissural pro-
longations, that presents the greatest difficulty and uncertainty. One point, which has
been raised within a few years, is with regard to the character of the different poles
connected with the same cell. In ordinary preparations of the central nervous system,
it is impossible, even with the highest available magnifying powers, to distinguish any
one pole which, in its general characters and connections, is different from the others ;
yet, some anatomists describe a single pole, more distinct in its outlines than the
others, which does not branch and is to be regarded as an axis-cylinder. The other poles
are supposed to be of a different character, not connected with the nerve-fibres, and
always presenting a greater or less number of branches. These views are accepted by
Schultze, who gives a figure, after Deiters, in which the contrast between the poles is
represented as very marked ; but, although this opinion is accepted by other high authori-
ties, it is not easy to understand how it can be received without reserve, when it is so
difficult, if not impossible, to follow out the poles, except for a very short distance.

With our present means of investigation, there seems to be no doubt with regard to
the following facts : Tracing the nerve-fibres toward their origin, they are seen to lose
their investing membrane as soon as they pass into the white portion of the centres, being
here composed only of the medullary substance surrounding the axis-cylinder. They
then penetrate the gray substance, in the form of axis-cylinders, losing here the medul-
lary substance. In the gray substance, it is impossible to make out all of their rela-
tions distinctly, and we cannot assume, as a matter of positive demonstration, that all
of them are connected with the poles of the nerve-cells. Still, it has been shown,
in the gray matter of the spinal cord, that many of the fibres are actual prolongations

STKUCTURE OF THE NERVE-CENTRES.

581

FIQ. lS5.—Jfultipolar nerve-cell from the anterior cornu of the spinal cord of the ox; magnified 200 diametert.

(Deiters.)
a, axis-cylinder prolongation ; &, 6, Z>, &, &, 6, branching prolongations.

582

NERVOUS SYSTEM.

of the cells, the others probably passing upward to be connected with cells in the
encephalon.

Tracing the prolongations from the cells, we find that one or more of the poles branch
and subdivide in the gray substance and give origin to fibres, but that these fibres do
not branch after they pass into the white substance. Other poles connect the nerve-cells
with each other by commissural fibres of greater or less length ; but it has never been
positively demonstrated that the cells are thus connected into separate and distinct
groups, although this is possible.

The accompanying figure, taken from the excellent monograph on the lumbar enlarge-

FIG. 186.— Group of cells connected with the anterior roots, as seen in a transverse section, from the anterior

cornu of the sheep. (Dean.)

A, entrance of the anterior roots into tlie cornu; &, 6, &, &, cells connected by long, slender processes with the ante-
rior roots. In this figure, almost every variety of cell-connection may be seen, with bundles of fibres crossing
in every direction.

COMPOSITION OF THE NERVOUS SUBSTANCE. 583

ment of the spinal cord, by Dean, shows the mode of connection between certain of the
cellular prolongations and the fibres of the anterior roots, and the comraissural fibres by
which the cells are connected with each other.

Accessory Anatomical Elements of the Nerve-centres. — While we must regard the cells
of the gray matter and the axis-cylinder of the nerves as probably the only anatomical
elements concerned in inner vation, there are other structures in the nervous system
which it is important for us to study. These are the following : 1, Outer coverings sur-
rounding some of the cells ; 2, intercellular, granular matter ; 3, peculiar corpuscles,
called myelocytes ; 4, connective- tissue elements ; 5, blood-vessels and -Iymphat4cs.

Certain of the cells in the spinal ganglia and in the ganglia of the sympathetic system
are surrounded with a nucleated covering, removed a certain distance from the cell itself,
so as to be nearly twice the diameter of the cell, which is continuous with the sheath of the
dark-bordered fibres. This membrane is always nucleated, and Kolliker has lately shown
that it is not homogeneous, as was at one time supposed, but is composed of a layer of
very delicate epithelium. The physiological significance of this covering is not apparent.

In the gray matter of the nerve-centres, there is a finely granular substance between
the cells, which closely resembles the granular contents of the cells themselves. In addi-
tion to this granular matter, Robin has described new anatomical elements which he has
called myelocytes. These are found in the cerebro-spinal centres, forming a layer near the
boundary of the white substance, and they are particularly abundant in the cerebellum.
They exist in the form of free nuclei and nucleated cells, the free nuclei being by far the
more numerous. The nuclei are rounded or ovoid, with strongly-accentuated borders,
are unaffected by acetic acid, finely granular, and generally without nucleoli. The cells
are rounded or slightly polyhedric, pale, clear, or very slightly granular, and contain
bodies similar to the free nuclei. The free nuclei are from T^Vrr to ^Yfr °f an mcn m
diameter, and the cells measure from ^Vfr to YTHTTT) an(i sometimes j^Vrr °f an inch.
These elements also exist in the second layer of the retina.

There has been a great deal of discussion with regard to the presence or absence of
connective-tissue elements in the cerebro-spiual centres. In the other ganglia, there has
never been any doubt with regard to the presence of connective tissue in greater or less
amount, and in the cerebro-spinal centres there can be hardly any question of the exist-
ence of an exceedingly delicate stroma, chiefly in the form of stellate, branching cells,
serving, in a measure, to support the nervous elements.

The blood-vessels of the nerve-centres form an exceedingly graceful caoillary net-work
with very large meshes. The gray substance is much richer in capillaries than the white.

A remarkable peculiarity of the vascular arrangement in the cerebro-spinal centres
has already been described in connection with the lymphatic system. The blood-vessels
here are surrounded by what have been called perivascular canals, first described by
Robin, and afterward shown by His and Robin to be radicles of the lymphatic system.

Composition of the Nervous Substance.

Our knowledge of the chemical constitution of the nervous system is, in many regards,
quite unsatisfactory ; but these tissues contain certain elements that have been very satis-
factorily determined. The chemical characters of cholesterine, for example, have long been
known to physiologists, as well as the fact that this principle is a constant constituent of
the nervous substance, united in some way with the other proximate principles, so that
it does not appear in a crystalline form. Since we demonstrated, in 1802, the relations
of cholesterine to the processes of disassimilation, this principle has assumed its proper
place as one of the most important of the products of physiological waste of the organ-
ism. The origin and function of cholesterine, with the processes for its extraction from
the fluids and tissues of the body, have been fully considered under the head of excretion.

584 NERVOUS SYSTEM.

Regarding cholesteriue as an excrementitious product, to be classed with principles
destined simply to be eliminated from the organism, the nerve-substance proper has been
found to contain the following proximate principles, the chemical properties of which
have been more or less accurately determined ; viz., protagon, neurine, fatty matters
combined with phosphorus, and bases combined with peculiar fatty acids.

Protagon. — This principle was discovered by Liebreich and was first described in 18G5.
Its formula is CneHauOaaNYP. It may be extracted by the following process: The cere-
bral substance is bruised in a mortar and afterward shaken with water and ether in a
closed vessel. The mixture is then exposed to a temperature of 32° Fahr., and the
ethereal layer, containing cholesterine, is removed. The insoluble mass is then extracted
with alcohol (85 per cent.) at 113°, is again filtered, and is exposed to a temperature of
32°. An abundant precipitate then separates, which is washed with ether and desiccated
in vacuo. The protagon is thus obtained in the form of a white powder. Since this
principle has been described in the brain-substance, a compound analogous to if not
identical with protagon has been discovered by Hermann in the blood-corpuscles. In
its general and chemical characters, protagon resembles the albuminoid proximate prin-
ciples ; but it presents the remarkable difference, that the sulphur, which exists in many
of the principles of tins class, is replaced by phosphorus. It is stated by Robin that pro-
tagon is not a true proximate principle but is simply impure or imperfectly-prepared
lecithene.

Neurine. — This name has been applied to a rather indefinite principle supposed to
represent the albuminoid element of the nervous tissue ; but its characters as a proximate
constituent of the nerve-substance have never been well determined. Robin and Verdeil
place neurine among the proximate principles of probable existence. According to these
authors, this is the organic substance of the brain, not soluble in alcohol. When inciner-
ated it does not leave a residue impregnated with phosphoric acid, like the cerebral fatty
matter. According to more recent investigations, particularly those of Liebreich, neurine
is a derivative of protagon. The neurine of Liebreich is obtained by boiling protagon
for twenty-four hours in baryta-water, when there are formed the phospho-glycerate of
baryta, and a new base, neurine. It is evident that this substance cannot properly be
regarded as a well-determined proximate principle.

The observations of Wurtz upon the synthesis of neurine are important as a step tow-
ard the synthesis of organic nitrogenized principles, but they do not afford an example
of the actual formation of a characteristic nitrogenized constituent of the nerve-tissue.
They simply show that the chlorohydrate of an artificial organic compound presents crys-
tals identical with the chlorohydrate of neurine extracted from the brain.

Cerebral Fatty Principles. — Researches into the composition of the fatty principles
found in the nervous substance have been so indefinite and unsatisfactory in their results, .
that, even now, they possess but little physiological interest. In the earlier observations,
the fats extracted from the nerve-tissue were generally combined with cholesterine.
This substance has now been isolated, and the residue contains a variety of principles,
which seem, under physiological conditions, to be intimately united with the nitrogen-
ized substance, presenting one of the exceptions to the general law that fats exist in the
body uncombined except with each other. In this mass of fatty matter, we can deter-
mine the presence of oleine, margarine, and stearine ; but these are combined with other
fats, fatty acids, etc., the remarkable peculiarity of most of which is, that they contain
a certain proportion of phosphorus. These peculiar principles have received a variety
of names, as they have been described more or less minutely by different observers, such
as cerebrine, white and red phosphorized fat, lecithene, cerebric acid, and cerebrate of
soda. The application of most of these names is very indefinite, and when we say that

REGENERATION OF THE NERVOUS TISSUE.

585

FIG. 187.— Corpora amylacea. (Funke.)

the substances are, in greatest part, peculiar to the nervous tissue, and that they contain
phosphorus, we have stated about all that is physiologically important. Lecithene is a
neutral phosphorized fat, probably composed of a number of different fatty principles,
which exists, not only in the nervous substance, but in the blood, bile, and the yolk of
egg. Its chemical history has no physiological interest. It is said to be identical with
protagon (Robin). The same may be said of cerebric acid, the cerebrate of soda, of oleo-
phosphoric acid and its compounds with soda and lime.

Corpora Amylacea. — Little rounded or ovoid
bodies, about y^V^ of an inch in diameter, have
been described by Virchow and others as exist-
ing normally in the corpora striata, the medulla
oblongata, and in some other parts of the cere-
bro-spinal system. With regard to the actual
composition of these bodies, there is considera-
ble difference of opinion. Virchow and many
others regard them as identical with starch, the
granules of which they certainly resemble very
closely, being of the same shape, with borders
well defined, frequently presenting concentric
laminsB and a hilum. When carefully treated,
first with a solution of iodine and then with a
little sulphuric acid, they assume a blue color.
Some observers consider them as analogous to
cellulose, others have supposed that they are formed of cholesterine, and others regard
them as nitrogenized bodies. These points are of purely anatomical interest, and the
physiological relationg of these bodies are not known.

Regeneration of the Nervous Tissue.

We do not propose to discuss fully the question of the regeneration of nerves after
section or even excision of a portion of their substance, although it is one of great patho-
logical interest; but, in this connection, we shall refer to some experiments recently
made, in which it appears that it is possible for certain of the most important of the
nerve-centres to be regenerated and their function restored after extirpation.

With regard to the simple reunion of nerves after division or excision, it has long
been known that this takes place in the human subject and in the inferior animals, with
restoration of function. The new tissue connecting the divided extremities of the nerve
seems to pass through the regular stages of development observed in the nerve-tissue of
the embryon, the gelatinous fibres, or the fibres of Remak, first appearing, and these
being subsequently developed into true nerve-tubes. In this process there is not a cica-
trix, as in the skin or muscular tissue, but a development of new elements possessing the
anatomical and physiological characters of the original structure.

A point of considerable physiological interest connected with the regeneration of the
nervous tissue is involved in the recent observations of Voit upon the regeneration of
the cerebral lobes after removal in a pigeon, and in those of Masius and Vanlair upon the
anatomical and functional regeneration of the spinal cord in frogs.

The experiments recorded by Voit, and his deductions, are very curious and have
given rise to a great deal of comment and criticism. In one observation, the cerebral
lobes were removed from a young pigeon in the usual way, an operation very easily per-
formed, and one which we practise yearly as a class-demonstration. It is particularly
stated that the operation was complete, and that the entire posterior lobes were removed.
Immediately after the operation, the pigeon presented the condition of stupor ordinarily
observed. As he gradually recovered from this condition, he began to execute a number

586 NERVOUS SYSTEM.

of mechanical movements, which it is unnecessary to detail fully, in the most extraor-
dinary mariner. The animal continued to improve, ceased the mechanical movements,
and began to fly about, exhibiting timidity when approached, and, in short, seemed, after
a time, to have nearly or quite returned to the normal condition. One thing, however,
was remarked : the animal never took food (it was probably kept alive by stuffing, as is
frequently done in such experiments). After five months, the pigeon was killed. The
cranial cavity was found to be filled with a white mass, occupying the place from which
the cerebrum had been removed. This mass had the consistence of the white substance
of the brain and presented a perfect continuity with the cerebral peduncles, which had
not been removed. It had the form of the two hemispheres, presenting a cavity filled
with liquid, and a septum. The whole mass consisted of perfect primitive fibres of double
contour, and, in their meshes, ganglionic cells. This observation is certainly one of the
most remarkable on record, and, from the extraordinary character of its results, it would
hardly be accepted for a moment, but for the established reputation of Prof. Voit. As
it is, such an observation demands full confirmation. It is well known, to all who have
been in the habit of extirpating the cerebral lobes, that it is absolutely necessary to
remove every portion of their substance, in order to obtain uniform results, and that
this is accomplished sometimes with considerable difficulty, In demonstrations to a
medical class, we have frequently verified this fact, and have observed recovery, more
or less complete, when but a small portion of the posterior lobes escaped. This criticism
upon the remarkable observation just detailed is made by Vulpian, and its pertinence
will be recognized by every practical physiologist. We have only to study the experi-
ments first made by Flourens, to learn how, in the lower animals, a part of one of the
great central ganglia may gradually assume the function of the whole, after this function
has been interrupted by the first mutilation. "We have cited the essential points in this
observation because it has been so extensively commented upon by physiologists, but it
is far from establishing the principle that a great nervous centre, like the cerebrum, may
be anatomically and functionally regenerated after complete extirpation.

The general results of the experiments of Masius and Vanlair upon the regeneration
of parts of the spinal cord in frogs, after loss of a small portion of its substance, show
that such reparation may take place and be attended with restoration of function. The
formation of cells precedes the development of fibres, and voluntary motion appears in
the parts situated below the lesion, before sensation. There are no instances on record
of such regeneration in the human subject or in the warm-blooded animals.

Motor and Sensory Nerves.

The physiological property of nerves which enables them to conduct to and from the
centres the impressions, stimulus, force, or whatever the imponderable nervous agent
may be, is one inherent in the tissue itself, belonging to no other structure, and is
dependent for its continuance upon proper conditions of nutrition. So long as the nerves
maintain these conditions, they retain this characteristic physiological property, which
is generally known under the name of irritability.

Aside from the special senses, the sense of temperature, and the appreciation of
weight, it is known to every one that, through the nerves, we appreciate what are
called ordinary sensations and are enabled to execute voluntary movements. If a nerve
distributed to a part endowed with sensation and the power of motion be divided, both
of these properties are lost and can only be regained through a reunion of the divided
nerve. Again, it is equally well known that, if such a nerve be exposed in its course
and irritated, violent movements take place in the muscles to which it is distributed,
and pain is appreciated, referred to parts supplied from the same source. These facts,
which were fully appreciated by the ancients, show that the general system of. nerves is
endowed with motor and sensory properties, the question being simply whether these be

MOTOR AND SENSORY NERVES. 587

inherent in the same fibres or belong to fibres physiologically distinct and derived from
different parts of the central system. This question, which was solved only about half a
century ago, will be the first to engage our attention.

Distinct Seat of the Motor and Sensory Properties of the Spinal Nerves. — All of the
nerves that take their origin from the spinal cord are endowed with motor and sensory
properties. These nerves supply the whole body, except the head and other parts
receiving branches from the cranial nerves. They arise by thirty-one pairs from the
sides of the spinal cord, and each nerve has an anterior and a posterior root. The ana-
tomical differences between the two roots are that the anterior is the smaller and has no
ganglion. The larger, posterior root presents a ganglionic enlargement in the interver-
tebral foramen. Just beyond the ganglion, the two roots coalesce and form a single
trunk. The nerve-fibres in the two roots are not of the same size, the anterior fibres
measuring on an average about one-fourth more than the posterior fibres. The structure
of the ganglia of the posterior roots has already been considered sufficiently in detail.

It would be unprofitable to discuss the vague ideas of the older anatomists and physi-
ologists with regard to the properties of the roots of the spinal nerves, and we can
date our information upon this point from the suggestion of Alexander Walker, in 1809,
that one of these roots was for sensation alone and the other for motion. It is most
remarkable, however, that Walker, from purely theoretical considerations, should have
stated that the posterior roots were motor and the anterior roots sensory, precisely the
reverse of the truth, and should have advanced this view in a publication as late as
1844. In the work alluded to, which contains some of the most extraordinary pseudo-
scientific vagaries ever published, it is curious to see how near Walker came to the great-
est discovery in physiology since the description of the circulation of the blood.

It is unnecessary to enlarge upon the importance of the discovery that the anterior
roots of the spinal nerves are motor, and the posterior, sensory, and that the union of
these two roots in the mixed nerves gives them their double properties, for we can hard-
ly imagine a physiology of the cerebro-spinal nervous system without this fact as the
starting-point. In an article published in English, in October, 1868,1 and in French,
during the same year,2 we have given an elaborate review of the whole subject, being
prompted to do so by the perusal of what purported to be an exact reprint of the origi-
nal pamphlet by Charles Bell. This pamphlet was printed for private circulation, in
1811, and was never published. It has been entirely inaccessible, and its contents were
only to be divined by references and quotations in the subsequent writings of Sir Charles
Bell and of his brother-in-law, Mr. Shaw.

Physiological literature does not present another instance of the merit of a great dis-
covery resting upon references to an unpublished pamphlet, which no student could pos-
sibly consult in the original, none of these references, upon close analysis, proving to be
entirely distinct and satisfactory. It is not to be wondered at, therefore, that, in our
study of the origin of one of the greatest discoveries of all ages, a reprint of the original
memoir should be examined with the most critical care. That this reprint was correct,
seemed probable from a comparison of its text with the quotations from the original to
be found in the writings of Sir Charles Bell and Mr. Shaw, and from the testimony of
reviewers who claimed to have compared it with the original. Within a short time,
however, an authorized reprint in full, from a manuscript in the hands of the widow of
the author, has appeared in the Journal of Anatomy.

When the only reprint of the celebrated pamphlet of Sir Charles Bell was itself «
sively rare, we thought it desirable to make long quotations to indicate the ideas enter-
tained by Bell regarding the properties of the two roots of the spinal nerves ; but, now

1 FLINT, JR., Historical Considerations concerning tlte Properties of the Roots of the Spinal Nerves— Quar-
terly Journal of Psychological Medicine, New York, 1863, vol. ii., p. 625, et seq.
a Journal de Fanatomie, Paris, 1S6S, tome v., p. 520, et seq., and p. 675, et seq.

588 NERVOUS SYSTEM.

that an authorized reprint can be so readily consulted, it is only necessary to refer to
this to show that Bell did not at that time regard the anterior roots as motor and the
posterior roots as sensory, but that he thought that the anterior roots were for both
motion and sensation and the posterior roots presided over " the secret operations of
the bodily frame, or the connections which unite the parts of the body into a system."

In August, 1822, Magendie published his first experiments upon the functions of the
roots of the nerves. Unlike any of the observations made by Charles Bell upon the
spinal nerves, these were made upon living animals. The spinal canal was opened, and
the cord, with the roots of the nerves, was exposed. The posterior roots of the lumbar
and sacral nerves were then divided upon one side and the wound was united with
sutures. The result of this observation was as follows :

*' I thought at first that the limb corresponding to the divided nerves was entirely
paralyzed ; it was insensible to pricking and to the most severe pinching, it also appeared
to me to be motionless ; but soon, to my great surprise, I saw it move in a very marked
manner, although the sensibility was still entirely extinct. A second, a third experi-
ment, gave me exactly the same result ; I commenced to regard it as probable that the
posterior roots of the spinal nerves might have functions different from the anterior roots,
and that they were more particularly devoted to sensibility."

The experiments in which the anterior roots were divided were no less striking :

" As in the preceding experiments, I only made the division upon one side, in order
to have a term of comparison. One can conceive with what curiosity I followed the
effects of this division ; they were not at all doubtful, the limb was completely motion-
less and flaccid, while it preserved a marked sensibility. Finally, that nothing should be
neglected, I divided at the same time the anterior and the posterior roots ; then followed
absolute loss of sensation and of motion."

From these experiments Magendie drew the following conclusions :

"I am following out my researches, and shall give a more detailed account of them in
the following number ; it is sufficient for me to be able to announce at present as positive,
that the anterior and the posterior roots of the nerves which arise from the spinal cord
have different functions, that the posterior seem more particularly devoted to sensibility,
while the anterior seem more especially connected with motion."

In the second note, published in the same volume of the Journal de physiologic
(1822), Magendie exposed and irritated the two roots of the nerves, with the following
results :

" I commenced by examining in this regard the posterior roots, or the nerves of sen-
sation. The following is the result which I observed: on pinching, pulling, or pricking
these roots, the animal manifested pain ; but this was not to be compared as regards
intensity with that which was developed if the spinal cord were touched, even lightly,
at the point of origin of the roots. Nearly every time that the posterior roots were thus
stimulated, contractions were produced in the muscles to which the nerves were distrib-
uted ; these contractions, however, are not well marked, and are infinitely more feeble
than when the cord itself is touched. When, at the same time, a bundle of the posterior
root is cut, there is produced a movement in totality in the limb to which the bundle is
distributed.

" I repeated the same experiments on the anterior roots, and I obtained analogous
results, but in an opposite sense ; for the contractions excited by the contusion, the prick-
ing, etc., are very forcible, and even convulsive, while the signs of sensibility are hardly
visible. These facts are, then, confirmatory of those which I have announced ; only they
seem to establish that sensation is not exclusively in the posterior roots, any more than
motion in the anterior roots. Nevertheless, a difficulty may arise. When, in the pre-
ceding experiments, the roots had been cut, they were attached to the spinal cord. Might
not the disturbance communicated to the cord be the real cause either of the contrac-
tions or of the pain which the animals experienced ? To remove this doubt, I repeated

MOTOR AND SENSORY NERVES. 539

the experiments after having separated the roots from the cord ; and I must say that,
except in two animals, in which I saw contractions when I pinched or pulled the anterior
and posterior roots, in all the other instances I did not observe any sensible effect of irrita-
tion of the anterior or posterior roots thus separated from the cord."

Magendie then goes on to say that, when he published the note in the preceding num-
ber of the journal, he supposed that he was the first who had thought of cutting the roots
of the spinal nerves; but he was soon undeceived by a letter from Mr. Shaw, who stated
that Bell had divided the roots thirteen years before. Magendie afterward received from
Mr. Shaw a copy of Bell's essay ("Idea of a New Anatomy of the Brain"), arid, us will
be seen by the following extract, gave Bell full credit for all his observations :

" It is seen by this quotation from a work which I could not be acquainted with, inas-
much as it had not been published, that Mr. Bell, led by his ingenious ideas concerning
the nervous system, was very near discovering the functions of the spinal roots; still the
fact that the anterior are devoted to movement, while the posterior belong more particu-
larly to sensation, seems to have escaped him ; it is, then, to having established this fact
in a positive manner that I must limit my pretensions."

Such are the experiments by which the properties of the roots of the spinal nerves
were discovered. From that time, the fact took its place in science, that the posterior
roots are for sensation and the anterior are for motion. Some discussion has arisen as to
whether the anterior roots do not possess a certain amount of sensibility, called recur-
rent sensibility, and this question has engaged the attention of physiologists within a few
years ; but the distinct functions of the two roots have never been doubted. Before the
days of anaesthetics, exposing the roots of the nerves in the dog was very laborious, and
painful to the animal, and the disturbances produced by so serious an operation interfered
somewhat with the effects of irritation of the different roots. But, now that the canal
may be opened without pain to the animal, the experiments are much more satisfactory
and have often been repeated by physiologists. We have frequently, indeed, demon-
strated the properties of the roots of the nerves in public teaching.

Properties of the Posterior Roots of the Spinal Nerves. — It is unnecessary to follow
out, from the date of the first experiments by Magendie to the present day, the observa-
tions that have been made from time to time upon the properties of the roots of the
spinal nerves. For many years, the difficulties in4 operating upon animals high in the
scale rendered confirmatory experiments somewhat unsatisfactory. The great German
physiologist, J. Mtiller, showed, in experiments made upon frogs, in 1831, that irritation
of the posterior roots produced no convulsive movements ; but he despaired of operating
satisfactorily upon warm-blooded animals. Magendie, in his later experiments, and
Longet, in experiments performed upon dogs, published in 1841, showed very satisfactorily
that the posterior roots were exclusively sensory, and this fact has been abundantly con-
firmed by more recent observations upon the higher classes of animals. We have our-
selves frequently exposed and irritated the roots of the nerves in dogs in public demon-
strations, in experiments upon the recurrent sensibility of the anterior roots, and in
another series of observations upon the properties of the spinal cord, which will be
referred to hereafter.

The remarkable anatomical peculiarity of the posterior roots, which they have in
common with all of the exclusively sensitive nerves, is the presence of a ganglion. While
we have no distinct idea of the function of these ganglia in connection with the trans-
mission of impressions from the periphery to the centres, it has been shown that they
have a remarkable influence upon the nutrition of the nerves after their division. Oper-
ating upon the second cervical nerves, in which the ganglia can be reached without
exposing the spinal cord, Waller has demonstrated the following interesting facts :

When the roots are divided between the ganglion and the cord, the central end of the
anterior root, attached to the cord, preserves its normal structure, while the peripheral
end in a few days becomes degenerated, the tubes are filled with granular matter, etc., and

590 NERVOUS SYSTEM.

in short, it undergoes those changes observed in all nerves separated from their centres.
On the other hand, in the posterior roots, the end attached to the cord undergoes degen-
eration, and the peripheral end, the one to which the ganglion is attached, preserves its
normal histological characters. From these experiments, which have been confirmed and
somewhat extended by Bernard, it is concluded that the ganglia of the posterior roots
have an influence over the nutrition of the sensitive nerves, in the same way as the cen-
tres influence the nutrition of the motor nerves with which they are connected. These
points are interesting, as showing the existence of centres attached to the sensory system
of nerves, which have, as far as we know, a purely trophic influence over the nerves,
while the centres to which the motor nerves are attached regulate, to a certain extent,
the nutrition of the nerves, and also are capable of generating nerve-force. We do not
know that the ganglia of the roots of sensitive nerves have any function except that
which has just been indicated.

Properties of the Anterior JKoots of the Spinal Nerves. — The same experiments that
demonstrated that the posterior roots of the spinal nerves are sensitive showed that the
anterior roots are motor. If the two roots be exposed in an animal just killed, no con-
vulsive movements are produced by stimulating the posterior roots ; but, if the anterior
roots be irritated, movements of the most violent character occur, confined to those
muscles to which the filaments of the roots are distributed. There has never been any
doubt upon this point since the experiments of Magendie ; and it is now universally
admitted by physiologists, that the motor properties of the mixed nerves are derived
exclusively from their anterior roots of origin from the spinal cord. The question has
arisen, however, whether the anterior roots be not also endowed with sensibility, nota-
bly less in degree than the posterior roots, but still marked and invariable. The sensi-
bility observed in the anterior roots is abolished by section of the posterior roots ; and
this property, which is thought to be derived from the posterior roots, has been called
recurrent sensibility.

Recurrent Sensibility. — The experimental facts with regard to the recurrent sensi-
bility of the anterior roots of the spinal nerves are very simple. If the two roots of a
spinal nerve be exposed, and if the animal be allowed to recover, by a few hours' repose,
from the shock of the operation, irritation of the posterior root will produce pain and
the general movements incident to it, but no localized contractions of muscles ; and irri-
tation of the anterior root will produce contraction of certain muscles and a certain
amount of pain, always less, however, than the pain resulting from stimulation of the
posterior roots. If the anterior root be divided, the end attached to the cord will be
found completely insensible, but the peripheral end will manifest the same sensibility as
the undivided root ; showing that the sensory properties of the anterior roots are not
derived from the cord. If the posterior root be divided, the sensibility of the anterior
root is instantly abolished; showing that the sensibility of the anterior root is recurrent,
being derived from the posterior root through the periphery. "With regard to these
facts, which were first noted by Magendie, there can be no doubt, and we ourselves veri-
fied them in a series of experiments published in 1861. Experiments have simply
demonstrated the fact that the recurrent sensibility comes through the periphery, with-
out actually showing any recurrent fibres ; and division of the mixed nerve beyond the
point of union of the two roots deprives the anterior root of its sensibility, showing
that the recurrent fibres, if they exist, must turn back near the periphery.

The question now arises with regard to the exact mechanism of recurrent sensibility.
The explanation offered by Magendie and Bernard is, that there are actually fibres return-
ing from the posterior to the anterior roots ; that these fibres are, of course, sensitive ;
and that irritation of the anterior roots is propagated toward the periphery and returns
to the centres through the posterior roots. This explanation satisfies all of the experi-
mental conditions, and it is farther sustained by the microscopical examinations of Schiff
and of Philipeaux and Vulpian. It will be remembered that the ganglia of the posterior

MOTOR AND SENSORY NERVES. 591

nerves, after division of these roots, Lave the remarkable power of preserving the ana-
tomical integrity of the fibres to which they are attached. Now, it has been shown by
Schiff that, after division of the posterior roots beyond the ganglia, the anterior roots
contain altered fibres, which he believes come from the posterior roots and give to these
roots their sensibility.

Dr. Brown-Sequard offers a different explanation of the pain developed upon irrita-
tion of the anterior roots. He believes this to be due entirely to cramp or convulsive
contractions of the muscles. This may be accepted, perhaps, as a partial explanation,
for there can be no doubt of the fact that violent muscular action, produced indepen-
dently of volition, is more or less painful ; but it does not explain the great sensibility
sometimes observed when the muscular contraction is comparatively feeble. There can
be hardly any doubt that the explanation offered by Magendie, and sustained by the
ingenious histological observations cited above, is in the main correct.

Mode of Action of the Motor Nerves. — Having established the anatomical distinction
between the motor and sensory nerves, it becomes necessary to study the differences in
the mode of action of these two kinds of nervous conductors. In the first place, it is
evident, taking the nerves and their roots as we find them in the organism in a normal
condition, that certain fibres act from the centres to the periphery, conducting motor
stimulus, while others act from the periphery to the centres, conducting sensory impres-
sions.

As regards the motor nerves, the force, whatever it may be, generated in the centres,
is conducted from the centres to the peripheral distribution of the nerves in the muscles,
and is here manifested by contraction. Their mode of action, therefore, is centrifugal.
When these motor filaments are divided, the connection between the parts animated by
them and the centre is interrupted, and motion in these parts, in obedience to the natural
stimulus, becomes impossible. But, while we cannot always induce generation of nerve-
force in the centres by the direct application of any agent to them, this force may be
imitated by stimulation applied to the nerve itself. A nerve that will respond to direct
stimulation is said to be excitable ; but this property does not extend throughout the
entire conducting motor system. For example, we shall see, when we come to study
the properties of the encephalon, that certain fasciculi capable of conducting the motor
stimulus from the centres to the muscles are not affected by direct stimulation and seem
to be inexcitable.

If a motor nerve be divided, galvanic, mechanical, or other stimulation applied to the
extremity connected with the centres produces no effect ; but the same stimulation applied
to the extremity connected with the muscles is followed by contraction. The phenomena
indicating that a nerve retains its physiological properties are always manifested at its
peripheral distribution, and these do not essentially vary when the nerve is stimulated at
different points in its course. For example, stimulation of the anterior roots near the
cord produces contraction in those muscles to which the fibres of these roots are dis-
tributed ; but the same effect follows stimulation of the nerve going to these muscles in
any part of its course.

As far as their physiological action is concerned, the different nerve-fibres are entirely
independent, and the relations which they bear to each other in the nervous fasciculi and
in the so-called anastomoses of nerves involve simple contiguity. If we compare the
nerve-force to galvanism, each individual fibre seems completely insulated ; and a stimulus
conducted by it to muscles never extends to the adjacent fibres. That it is the axis-
cylinder which conducts and the medullary tube which insulates, it is impossible to say
with positiveness; but, as we have already seen, it is more than probable that the central
band is the only conducting element.

We have incidentally noted the fact that direct stimulation applied to the centres,
even when the connection between these and the muscles is perfect, is generally inca-

592 NERVOUS SYSTEM.

pable of inducing the generation of nerve-force ; but the generation of a motor stimulus
may be induced by an impression made upon sensitive nerves and conveyed by them to
the centres. If, for example, we isolate a certain portion of the central nervous system,
as the spinal cord, and leave its connections with the motor and sensitive nerves intact,
these phenomena may be readily observed. An impression made upon the sensitive nerves
will be conveyed to the gray matter of the cord and will induce the generation of a motor
stimulus by the cells of this part, which will be conducted to the muscles and gives rise to
contraction. As the stimulus, in such observations, seems to be reflected from the cord
through the motor nerves to the muscles, this action has been called reflex. These phe-
nomena constitute an important division of the physiology of the nervous system and will
be fully considered by themselves.

Associated Movements. — It is well known that the action of certain muscles is with
difficulty isolated by an effort of the will. This applies to sets of muscles upon one side
of the body and to corresponding muscles upon the two sides. For example, it is almost
impossible, without great practice, to move some of the fingers, at the same time restrain-
ing the movements of the others ; and the action of certain sets of muscles of the extrem-
ities is always simultaneous. The toes, which are but little used as the foot is confined
in the ordinary dress, are capable of very little independent action. It is difficult to
move one eye without the other, or to make rapid rotary movements of one hand while
an entirely different order of movements is executed by the other ; and instances of this
kind might be multiplied. In studying these associated movements, the question arises
as to how far they are due to the anatomical relations of the nerves to the centres and
their connections with muscles, and how far they depend upon habit and exercise. We
can imagine that there may be certain sets of nerve-cells, connected with each other by
commissural fibres and giving origin to motor nerves distributed to sets of muscles ; an
anatomical arrangement that might render a separate action of these cells impossible.
The anatomy of the nerve-centres and their connection with fibres are so difficult of
investigation, that demonstrative proof of the existence of such systems is impracticable;
but this affords a ready explanation of the fact that we cannot, as a rule, by an effort of
the will, cause only a portion of a single muscle to contract ; yet some of the larger mus-
cles receive an immense number of motor nerve-fibres which are probably connected
with gray matter composed of numerous anastomosing cells.

Many of the associated movements are capable of being influenced to a surprising
degree by education, of which no better example can be found than in the case of skilful
performers upon certain musical instruments, such as the piano, harp, violin, and other
stringed instruments. In the technical study of such instruments, not only does one hand
become almost independent of the other, but very complex associated movements may be
acquired. An accomplished pianist or violinist executes the different scales automatically
by a single effort of the will, and frequently pianists execute at the same time scales with
both hands, the action being entirely opposed to the natural association of movements.
Feats of sleight of hand also show how wonderfully the muscles may be educated, and to
what an extent the power of association and disassociation of movements may be acquired
by long practice.

Looking at the associated movements in their relations to the mode of action of the
motor nerves, it seems probable that, as a rule, the anatomical relations of the nerves are
such that a motor stimulus, or an effort of the will, cannot be conducted to a portion only
of a muscle, but must act upon the whole muscle, and the same is true, probably, of cer-
tain restricted sets of muscles ; but the association of movements of corresponding muscles
upon the two sides of the body, with the exception, perhaps, of the muscles of the eyes,
is due mainly to habit and may be greatly modified by education.

Mode of Action of the Sensory Nerves. — The sensory nerve-fibres, like the fibres of the
motor system, are entirely independent of each other in their action ; and, in the so-called

MOTOR AND SENSORY NERVES. 593

anastomoses that take place between sensory nerves, the fibres assume no new relations,
except as regards contiguity.

As motor fibres convey to their peripheral distribution the stimulus engendered by an
irritation applied in any portion of their course, so an impression made upon a sensitive
nerve is always referred to the periphery. A familiar example of this is afforded by the
very common accident of contusion of the ulnar nerve as it passes between the olecranon
and the condyle of the humerus. This is attended with painful tingling of the ring and
little finger and other parts to which the filaments of this nerve are distributed, without,
necessarily, any pain at the point of injury. More striking examples are afforded in neu-
ralgic affections dependent upon disease of or pressure upon the trunk of a sensitive nerve.
In such cases, excision of the nerve is often practised, but no permanent relief follows
unless the section be made between the affected portion of the nerve and the nerve-
centres; and the pain produced by the disease is always referred to the termination of
the nerve, even after it has been divided between the seat of the disease and the periphery,
leaving the parts supplied by the nerve insensible to direct irritation. In cases of disease
it is not unusual to note great pain in parts of the skin that are insensible to direct im-
pressions. The explanation of this is, that the nerves are paralyzed near their terminal
distribution, so that an impression made upon the skin cannot be conveyed to the senso-
rium ; but that the trunks of the nerves still retain their conducting power and are the
seat of diseased action, producing pain, which is referred by the patient to the periphery.

In multiplying examples showing the mode of action of the sensory nerves, we may
refer to the sensations experienced after certain plastic operations. In the very common
operation of restoring the nose by transplanting skin from the forehead, after the opera-
tion has been completed, the skin having been entirely separated and cicatrized in its
new relations, the patient feels that the forehead is touched when the finger is applied to
the artificial nose. After a time, however, the sensorium becomes accustomed to the
new arrangement of the parts, and this deceptive feeling disappears.

There are certain curious nervous phenomena, that are not without physiological
interest, presented in persons who have suffered amputations. It has been long observed
that after loss of a limb the sensation of the part remains, and pain is frequently experi-
enced, which is referred to the amputated member. Thus a patient will feel distinctly
the fingers or toes after an arm or a leg has been removed, and irritation of the ends of
the nerves at the stump produces sensations referred to the missing member. A few
years since, we observed a very striking example of this in a soldier who had suffered
amputation of the leg. While this patient was walking about on crutches, before the
stump had entirely healed, upon getting up suddenly from his seat, in attempting to
walk he put the stump to the ground, producing considerable injury. His explanation
was, that he felt the foot perfectly, and it was necessary for him to be constantly on his
guard to prevent such an accident.

A very curious fact has been observed with regard to the imaginary presence of limbs
after amputation, which we have had ample opportunities of verifying. After a time the
sense of possession of the lost limb becomes blunted, and it may, in some cases, entirely
disappear. This 'may take place a few months after the amputation, or the sensations
may remain in their full intensity for years. Examples are reported by Mtiller where
the sense was undiminished thirteen, and, in one case, twenty years after amputation.
In a certain number of cases, however, the sense of the intermediate part is lost, the
feeling in the hand or foot, as the case may be, remaining as distinct as ever, the impres-
sion being that the limb is gradually becoming shorter. These curious facts, noted by M.
Gueniot, show that the sense of the limb becoming shorter is observed in about half of
the cases of amputation in which cicatrization goes on regularly ; and, in these cases,
the patient finally experiences a feeling as though the hand or foot were in direct contact
with the stump. By careful inquiries among a large number of patients in military hos-
pitals, we have been enabled to verify these observations in the most satisfactory manner.
38

594 NERVOUS SYSTEM.

General Properties of the Nerves.

Numerous experiments have been made, especially upon the cerebro-spinal nerves,
with regard to their action under different kinds of stimulation, the probable nature of
the nervous agent or nerve-force, the extent and duration of their excitability and sensi-
bility, etc., which have developed facts of more or less physiological interest and impor-
tance. As far as the nerves of general sensibility are concerned, the phenomena of con-
duction of impressions are essentially the same in all, if we except certain variations in
different nerves as regards the degree of sensibility. The motor nerves all respond in
the same manner to stimulation ; and it is upon this portion of the nervous system that
the most important observations have been made. This being the case, it is evident that
the cerebro-spinal nerves, in their behavior under the experimental conditions above
mentioned, possess certain general properties, and that the functions of special nerves
are to be studied, after a full consideration of these general properties, in connection
with their anatomical distribution to the different organs in the economy.

The points to be considered, aside from the simple division of the nerves into motor
and sensory, are as follows :

1. The conditions of excitability and sensibility of the nerves, or what is known as
nervous irritability.

2. The nature of the nervous agent, or the so-called nerve-force.

3. Certain phenomena following the application of electricity to the nerves.

Nervous Irritability. — We have already alluded in a general way to what is known
as nervous irritability. The term is used by physiologists to express the condition of
nerves which enables them to respond to artificial stimulation, or to conduct the natural
stimulus or external impressions. So long as a nerve retains this property it is said to
be irritable. Of course, while in a normal condition and during life, irritability, as
applied to nerves, simply means that these parts are capable of performing their peculiar
functions ; but, after death, for a certain time the nerves will respond to artificial stimu-
lation ; and it is to this property that the term " irritability " seems to be most applicable.
At a certain time after death, varying in different classes of animals with the activity of
their nutrition, the irritability of the nerves disappears. This occurs very soon in warm-
blooded animals, but it is later in animals lower in the scale, so that the latter present
the most favorable conditions for experimentation. Most observations upon nervous irri-
tability, indeed, have been made upon frogs and other cold-blooded animals. Analogous
facts have already been noted with regard to the muscular system, although, as we have
seen, the irritability of the muscular tissue is entirely distinct from that of the nerves.

Immediately or soon after death, when the irritability of the nerves is at its maxi-
mum, they may be excited by mechanical, chemical, or galvanic stimulus, all of these
agents producing contraction of the muscles to which the motor filaments are distributed.
Mechanical irritation, simply pinching a portion of the nerve, for example, produces a
single muscular contraction ; but, if the injury to the nerve be such as to disorganize its
fibres, that portion of the nerve will no longer conduct a stimulus. Among the irritants
of this kind, we may cite the extremes of heat and cold. If an exposed nerve be cau-
terized, a vigorous muscular contraction follows. The same effect, though less marked,
may be produced by the sudden application of intense cold. Among chemical reagents,
there are some which excite the nerves and others which produce no effect; but these
are not important from a physiological point of view. Suffice it to say, that mechanical
irritation and the action of certain chemicals are capable of exciting the nerves ; but
that, when their action goes so far as to disorganize the fibres, the conducting power of
these fibres is lost. While, however, irritation of the nerve above the point of injury has
no effect, stimulation between this point and the muscles is still followed by contraction.

The most convenient method of exciting the nerves in physiological experiments is

GENERAL PROPERTIES OF THE NERVES.

595

by means of electricity, a stimulus more closely resembling the nerve-force than any
other, and one which may be employed without disorganizing the nerve-tissue, and which
consequently admits of extended and repeated application. The action of electricity,
however, with the methods of preparing the nerves and muscles for experimentation,
will be fully considered under a separate head.

The irritability of the motor system is entirely distinct from that of the sensory
nerves, and one may be destroyed, leaving the other intact. This follows almost as a
matter of course upon the fact of the anatomical distinction between motor and sensory
nerves ; but it is interesting to note the limits of the irritability after death in nerves of
different properties and the differences in the manner of its disappearance. The woorara-
poison, a very curious agent prepared by the South-American Indians, has the remarkable
property of paralyzing the motor nerves, leaving the nerves of sensation intact. This
fact has been demonstrated by Bernard and others by <very curious and ingenious experi-
ments. The poison, like those of animal origin, acts most vigorously after introduction
under the skin or absorption from wounds, and it produces no toxic effects when taken
into the stomach, except when introduced in large quantity in fasting animals. Under
the influence of this agent, an animal
dies with complete paralysis of the
motor system, presenting, among other
phenomena, arrest of respiration. Most
of the varieties of the poison affect only
the motor nerves and do not influence
the action of the heart ; and, in animals
brought completely under its influence,
artificial respiration will enable the
heart to continue its action, and, in
some instances, if this be persisted in,
recovery will take place.

The fact that the woorara-poison
affects the motor nerves only has been
experimentally illustrated by Bernard,
taking advantage of the reflex func-
tions of the spinal cord to show the
persistence of the irritability of the
sensory nerves. The most striking of
these experiments is the following : A
frog is prepared by exposing the nerves
in the lumbar region, and then isolating
the posterior extremities by applying a
strong ligature, including the aorta and
all the parts except the nerves; so that,
practically, the only communication be-
tween the posterior extremities and the
body is by the nerves. It is evident,
therefore, that, if the poison be intro-
duced under the skin of the body, act-
ing, as it does, through the blood, it
will affect all parts except the posterior FIG. ig8.— Frog prepared so as to show that icoorara de-
extremities: for the poison acts from strays the properties of the motor nerves. (Bernard.)

. , A, A, lumbar nerves ; B, aorta.

the periphery to the centres and must

circulate in the parts to which the motor nerves are distributed. If the posterior
extremities be now irritated, the impression is conveyed to the spinal cord through the
sensory filaments of the lumbar nerves, which are intact; this gives rise to a stimulus,

596 NERVOUS SYSTEM.

which is reflected back through the motor filaments of the same nerve, and the ordinary
reflex movements are observed in the posterior extremities. This is to be expected, inas-
much as the posterior extremities have been removed from the influence of the poison.
If the anterior extremities, which are completely under the influence of the poison, be now
irritated, no movements are observed in these parts, but they take place, as before, in
the posterior extremities. The mechanism of this action is easily understood. Reflex
phenomena, consisting in the movements of muscles, may be manifested throughout the
entire system, following irritation of a single part. An impression made upon the surface
is conveyed to the spinal cord, and, if this be sufficiently powerful, motor stimulus may
be sent through all of the anterior roots coining from the cord. The impression made
upon the anterior, or poisoned extremities, is conveyed by the sensory filaments to the
cord and is transmitted to the posterior extremities through their motor nerves, which
are intact. The fact of the transmission of the impression from the anterior extremities
to the cord shows that the poison does not affect the sensory system.

In the same way that the woorara-poison paralyzes the motor nerves, leaving the
sensory system intact, other agents, as anaesthetics, will abolish the sensibility of the
nerves without affecting the motor filaments.

As we have already intimated in another connection, the nerves soon lose their irrita-
bility after they have been separated from the centres. This loss of conducting power
is attended with important structural changes in the nerve fibres. The tubes lose their
normal appearance, and the medullary matter becomes opaque and coagulates in large
drops. The axis-cylinder is not so much modified in structure, but it certainly loses
its characteristic physiological properties.

The excitability of the motor nerves disappears in about four days after resection.
Of course, in experiments upon this point, it is necessary to excise a portion of the
nerve to prevent reunion of the divided extremities ; but, when this is done, after the
fourth day, galvanization of the nerve will produce no contraction in the muscles,
although the latter retain their contractility, as may be shown by the application of direct
irritation. This loss of irritability is gradual, and it continues, whether the nerve be
exposed and stimulated from time to time or be left to itself; and the loss of excitability
progresses from the centres to the periphery. In the researches of Longet upon this sub-
ject, it was found that the lower portion of the peduncles of the brain lost their irrita-
bility first, then the anterior columns of the cord, then the motor roots of the nerves,
and, last of all, the branches of the nerves near their termination in the muscles.

The sensibility of the sensory nerves disappears from the periphery to the centres, as
is shown in dying animals and in experiments with anaesthetics. The sensibility is lost,
first in the terminal branches of the nerves, next in the trunks and in the posterior roots
of the spinal nerves, and so on to the centres. We have often illustrated this fact in
experiments upon the roots of the spinal nerves and in section of the large root of the
fifth pair within the cranial cavity. When an animal is brought so completely under
the influence of ether that the operation of opening the spinal canal may be performed
without inflicting the slightest pain, the posterior roots will be found to be distinctly
sensible. We have lately been in the habit, in class-demonstrations, of dividing the fifth
pair in the cranium without using an anaesthetic, as the operation is instantaneous and
the effects are much more striking than when the animal has been rendered insensible
and is allowed to recover ; but, when we have used an anaesthetic, we could never push
the effects sufficiently to abolish the sensibility of the root of the nerve. In an animal
brought so fully under the influence of ether that the conjunctiva, supplied with branches
of the fifth, had become absolutely insensible, the instant the instrument touched the
root of the nerve in the cranium, there were evidences of acute pain. Nothing could
more strikingly illustrate the mode of disappearance of the sensibility of the nerves
from the periphery to the centres.

The nervous irritability may be momentarily destroyed by severe shock in killing an

GENERAL PROPERTIES OF THE NERVES. 597

animal. This is sometimes illustrated in preparing frogs for experiments upon the
nerves; as the shock of killing the frog by decapitation, tearing off the skin, etc.,
abolishes the irritability of the nerves for the moment. It has been observed, also,
that a galvanic shock sufficiently powerful to destroy life instantly destroys the excita-
bility of the motor nerves.

Nerve-Force. — The so-called nervous irritability, artificially manifested by the applica-
tion of a stimulus directly to the nerve-tissue, enables the nerves to conduct from the
centres to the periphery a force which is generated in the gray substance. This we may
call the nerve-force. Its production is one of the most remarkable of the phenomena of
life ; and its essence, or the exact mechanism of its generation, is one of the problems
that has thus far eluded the investigations of physiologists. We know, however, that,
in the operations of the nervous system, tho nerves serve simply as conductors and the
nerve-cells generate the nerve-force. It is evident, also, that nearly all of the so-called
vital phenomena are more or less influenced and controlled through this wonderful agent ;
and, throughout our study of the nervous system, we shall be constantly investigating the
phenomena attending the operation of nerve-force, while we are compelled to admit our
ignorance of its essential nature.

Non-identity of Nerve-Force with Electricity. — When we come to study fully the
action of electricity upon the nerves, we shall see that this is by far the most convenient
stimulus for exciting the nervous action and one by which we closely imitate the true
nerve-force. So great is the similarity, indeed, between certain of the phenomena pro-
duced by the application of electricity and those attending the physiological action of
nerves, that some physiologists have regarded the nerve-cells as generators of an electric
current. This hypothesis explains the nature of nerve-force, in so far as it assimilates it
to a force, with the action of which, as artificially generated, we are more or less familiar.
No one at the present day, however, pretends that the nerve-force has been demonstrated
to be identical with any form of electricity ; and the question does not now demand
extended discussion.

A series of experiments made by Pre" vost and Dumas, in 1823, are worthy of note as
showing the absence of a true electric current in nerves in action ; but these have been
confirmed in later years with apparatus sufficiently delicate to settle the question beyond
a doubt. The most conclusive experiments upon this subject are those of Matteucci and
Longet, made upon horses, at the veterinary school at Alfort. These physiologists
exposed the sciatic nerves in the living animal, and, when there was evidently a conduc-
tion in both directions, as evinced by pain and muscular action, they failed to detect the
slightest evidence of an electric current with the most delicate galvanometer that could
be constructed. The fact of the absence of a galvanic current in nerves during their
physiological action was even more strikingly illustrated by Matteucci, who demonstrated,
in the electric eel, that, although the electric discharges from the peculiar organs of this
animal were under the control of the nervous system and could be excited by galvanic
stimulation of the proper nerves immediately after death, no galvanic current existed in
these nerves during their physiological action.

When we abandon the hypothesis of the identity of nerve-force with electricity, we
are compelled to admit that the agent generated by the nerve-centres is sui generis
and not to be compared with any force known outside of living organisms or artificially
produced by direct stimulation of the nerves ; but we admit, nevertheless, the fact that
electricity may be generated by animals, as the electric fishes, and that electric currents
exist in different anatomical structures in the living body, including the nerves, under
certain conditions. Our study of the nerve-force, then, leaving its essential nature unex-
plained, is mainly confined to a description of its characteristic phenomena.

Rapidity of Nervous Conduction. — The first rigorous estimates of the velocity of the
nerve-current were made in 1850, by Helmholtz, and were applied to the motor nerves.

598 NERVOUS SYSTEM.

The important and interesting results of these experiments were arrived at by an inge-
nious application of the graphic method, which has since been so largely improved and
extended by Marey, and their accuracy was rendered possible by the exceedingly delicate
chronometric apparatus which has been devised within the last few years.

It is unnecessary to describe fully the exact methods employed by Helmholtz and
by those who immediately followed in his investigations. Suffice it to say, that this dis-
tinguished physiologist and physicist constructed apparatus which, though somewhat
complex, was so accurate as to leave no doubt as to the reliability of his results. Taking
into account all of the disturbing conditions, and allowing for the interval of pose, or the
length of time between the excitation of a muscle and the commencement of its con-
traction, he estimated the rapidity of conduction in the motor nerves of the frog at about
eighty-five feet per second. The results obtained by Marey upon frogs give a much
slower rate of nervous conduction. These were followed, however, by the observations
of Helmholtz and Baxt upon the human subject, which are, of course, the most interest-
ing of all.

The process devised by Marey is admirably simple. He employed, to estimate small
fractions of a second, a cylinder graduated in the following manner : An ordinary tun-
ing-fork, vibrating, say, five hundred times per second, is so arranged that a point con-
nected with one of its arms is made to play against a strip of blackened paper. As the
paper remains stationary, the point makes but a single mark; but when the paper
moves, as the point vibrates, a line is produced with regular curves, every curve repre-
senting -y-i-g- of a second. Now, if a lever be attached to a muscle and be so arranged as
to mark upon the paper, moving at the same rate, the instant when contraction takes
place, it is evident that the interval between two contractions produced by stimulating
the nerve at different points in its course will be most accurately indicated ; and, if the
length of the nerve between the two points of stimulation be known, the difference in
time will represent the rate of nervous conduction.

In experiments upon frogs, the leg is prepared by cutting away the muscles and bone
of the thigh, leaving the nerve attached. The lever is then applied to the muscles of
the leg, and the stimulation is applied successively to two points in the nerve, the distance
between them being carefully measured. The results obtained in this way showed a
rate of conduction of from thirty-six to forty-six feet per second ; but these are not
regarded by Marey as invalidating the estimates by Helmholtz, in view of the various
conditions by which the rapidity of conduction is modified.

Employing the myograph of Marey, Baxt, in the laboratory of Helmholtz, has suc-
ceeded in measuring the rate of nervous conduction in the human subject. In these
experiments, the swelling of the muscle during contraction was limited by enclosing the
arm in a plaster-mould and noting the contraction through a small opening. By then
exciting the contraction by stimulating the radial nerve successively at different distances
from the muscle, the estimate was made. The rate in the human subject was thus esti-
mated at one hundred and eleven feet per second. The latest experiments upon this sub-
ject by Helmholtz and Baxt, in which great care was taken in the adjustment of the
apparatus, showed a mean of rapidity for the motor nerves, in man, of about two hun-
dred and fifty-four feet per second. These observations were made in the summer of
1869 ; and the difference in the results is in part explained by the fact, which was ascer-
tained experimentally at that time, that a high temperature increases, and a diminished
temperature retards the velocity of nervous conduction. It has been farther shown by
Munk, that the rate of conduction is different in different portions of the nervous trunk ;
the rapidity progressively increasing as the nerve approaches its termination.

Helmholtz, Du Bois-Reymond, Marey, and others, have noted certain conditions
which modify the rate of nervous conduction. One of the most prominent of these,
first observed by Helmholtz, is due to modifications in temperature. By a reduction of
temperature, in the frog at least, the rate is very much reduced ; and at 32° it is not

GENERAL PROPERTIES OF THE NERVES. 599

more than one-tenth as rapid as at 60° or 70°. Marey has also noted that the rate is
sensibly reduced by fatigue of the muscles.

The same principle which has led to the determination of the rate of conduction in
motor nerves, viz., an estimation of the difference in time of the passage of a stimulus
applied to a nerve at two points situated at a known distance from each other, has been
applied to the conduction of sensations. Hirsch is quoted as having made the first
attempt to resolve this question, in 1851. He employed the delicate chronometric instru-
ments used in astronomy, and noted the difference in time between the appreciation of
an impression made upon a part of the body far removed from the brain, as the toe, and
an impression made upon the cheek. This process admitted of a rough estimate of
about one hundred and. eleven feet per second. The later and more elaborate researches
of Schelske showed a rapidity of conduction by the sensory nerves of about ninety-seven
feet per second.

Attempts have been made to estimate the duration of acts involving the central ner-
vous system, such as the reflex phenomena of the spinal cord or the operations of the
cerebral hemispheres. These have been partially successful, or, at least, they have
shown that the reflex and the cerebral acts require a distinctly appreciable period of
time. This, in itself, is an important fact ; although the duration of these acts has not
yet been measured with all the accuracy that could be desired. As the general result
of experiments upon these points, it is found that the reflex action of the spinal cord
occupies more than twelve times the period required for the transmission of stimulus
or impressions through the nerves. Donders found, in experiments upon his own person,
that an act of volition required one-twenty-eighth of a second, and one of simple dis-
tinction or recognition of an impression, one-twenty-fifth of a second. These estimates,
however, are merely approximative ; and, until they attain greater certainty, it is unne-
cessary to describe in detail the apparatus employed.

The general result of the various observations we have detailed upon the rate of ner-
vous conduction as applied to the human subject is, in the first place, that this can be
measured with tolerable accuracy ; second, that it is in no wise to be compared with the
rate of conduction of light or electricity ; and, finally, that the rate in the human subject
is essentially the same in the motor and sensory nerves, being, according to the most
reliable estimates, about one hundred and eleven feet per second.

Action of Electricity upon the Nerves. — A great deal has been written with regard to
the effects of electricity upon the nervous system, and facts elicited by experiments upon
this subject are highly important in their bearing upon physiology and pathology. Still,
there are numerous observations upon this subject which have but little importance, in a
purely physiological sense, except that they are curious and interesting. These we do
not propose to discuss elaborately ; and we shall confine ourselves chiefly to those points
which bear directly upon our knowledge of the properties and functions of the nerves.

The first important fact — to which we have already alluded — is, that electricity is the
best means that we have of artificially exciting the nerves. Using electricity, we can
regulate with exquisite nicety the degree of stimulation ; we can excite the nerves long
after they have ceased to respond to mechanical or chemical irritation ; the effects of
different currents can be noted ; and, finally, this mode of stimulation produces a peculiar
and interesting condition of the parts of the nerve not included between the poles of the
battery. For these reasons, it seems proper to devote some consideration, in this con-
nection, to the effects of the application of this agent to the nerves.

So long as the nerves retain their irritability, they will respond to an electrical stimu-
lus. Experiments may be made upon the exposed nerves in living animals or in ani-
mals just killed; and, of all classes, the cold-blooded animals present the most favorable
conditions, on account of the persistence of nervous and muscular irritability for a con-
siderable time after death. Experimenters most commonly use frogs, on account of the

600

NERVOUS SYSTEM.

long persistence of the irritability of their tissues and the facility with which certain por-
tions of the nervous system can be exposed. For ordinary experiments upon the nervous
conduction, the parts are prepared by detaching the posterior extremities, removing the
skin, and cutting away the bone and muscles of the thigh, so as to leave the leg with the
sciatic nerve attached. A frog's leg thus isolated presents a nervous trunk one or two
inches in length, attached to the muscles, which will respond to the slightest stimulus.
It is by experiments made upon frogs prepared in this way that most of the important
facts relative to the action of electricity upon the nervous system have been developed.
A form of galvanic apparatus which we have long used and found very convenient for
these experiments is essentially the one described by Bernard. It consists simply of
alternate copper and zinc wires wound around a piece of wood bent in the form of a
horseshoe and terminating in two platinum points representing the positive and negative
poles. This forms a sort of electric forceps, about eight inches long, which, when moist-
ened with water slightly acidulated with acetic acid, will give a current of about the
strength required for most experiments.

It is evident that the galvanic current may be applied to a nerve so that the direction

may, in the one case, follow the course of the
nerve, that is, from the centre to the periphery,
and, in the other, be opposite to the course of the
nerve. These currents have been called respec-
tively the descending, or direct, and the ascending,
or inverse. When the positive pole (the copper) is
placed nearer the origin of the nerve, and the
negative pole (the zinc), below this point in the
course of the nerve, the galvanic current follows
the normal direction of the motor conduction, and
this is called the descending current. When the
poles are reversed, and the direction of the galvan-
ic current is from the periphery toward the centre,
it is called the ascending current. It will be con-
venient to speak of these two currents respectively
as descending and ascending, in detailing experi-
ments upon the action of electricity upon the nerves.
The points to be noted with regard to the effects
of the application of electricity to an exposed nerve
are the action of constant currents of different de-
grees of intensity, the phenomena observed on
closing and opening the circuit, and the effects
of an interrupted current.

During the passage of a feeble constant current
through an exposed nerve, whatever be its direc-
tion, there are no convulsive movements and no
evidences of pain. This fact has long been recog-
nized by physiologists, who at first limited the
effects of electricity upon the nerves to two pe-
riods, one at the closing of the circuit and the
other at its opening. We shall see, however, that
the passage of electricity through a portion of a
nervous trunk produces a peculiar condition in
parts of the nerve in the neighborhood of tho
poles of the battery, described under the name of
electrotonus ; but the fact that neither motion nor sensation is excited in a mixed nerve
during the actual passage of a feeble constant current is not invalidated.

FIG. 189.— Electric forceps. (Liegeois.)

C, copper ; 2", zinc ; P, P, positive poles ; N, N,

negative poles.

GENERAL PROPERTIES OF THE NERVES. 601

If a sufficiently powerful constant current be passed through a nerve, disorganization
of its tissue takes place, and the nerve finally loses its excitability, as it does when
bruised, ligatured, or when its structure is destroyed in any other way. It was thought
by Galvani, and the idea has been adopted by Matteucci, Guerard, and Longet, that a
current directed exactly across a nerve, so as to pass at right angles to its fibres, does
not give rise to muscular contraction. This view is now accepted by most modern
experimenters.

All who have experimented upon the action of galvanism upon the mixed nerves
have noted the fact alluded to above, that the phenomena of contraction are manifested
only on closing or on opening the circuit. Take, for example, a frog's leg prepared
with the nerve attached; place one pole of a galvanic apparatus on the nerve and
then make the connection, including a portion of the nerve in the circuit ; with the
feeblest current, contraction occurs only on closing the circuit. This takes place only
when the current follows the direction of the nerve (descending), and there is no con-
traction either on closing or opening the circuit with the ascending current. With what
is called the " weak " current (Pfliiger), contraction occurs only on closing the circuit,
for currents of either direction. With the " moderate" current, contraction occurs both
on closing and on opening the circuit, for currents of both directions. With the
"strong" current, contraction occurs only on closing the circuit with the descending
current and only on opening the circuit with the ascending current. The above con-
stitute what is called Pfltiger's " law of contraction." After a time the nervous irrita-
bility becomes somewhat enfeebled by exposure of the parts. The phenomena then ob-
served belong to the conditions involved in the process of " dying " of the nerve. In the
later stages of this condition, the phenomena may be formularized as follows:

If the sciatic nerve attached to the leg of a frog, prepared in the usual way for such
experiments, be subjected to a feeble galvanic current, there is a time when muscular
contraction takes place only at the instant when the circuit is closed, no contraction
occurring when the circuit is opened ; and this occurs only with the descending current;
viz., when the current flows toward the periphery, the positive pole being above and the
negative below. If the poles be reversed, so that the galvanic current flows from the
periphery toward the centres (the ascending current), contraction of the muscles occurs
only when the circuit is opened and none takes place when the circuit is closed. These
phenomena are distinct after the irritability of the parts has become somewhat dimin-
ished by exposure or by electric stimulation of the nerve.

FIG. 190.— Frog* s legs prepared so as to show the contrasted action of the descending and the ascending cur-
rent. (Matteucci).

A very simple experiment made by Matteucci strikingly illustrates the contrasted
action of the descending and the ascending currents. The posterior extremities of a frog
are prepared so as to leave the nerves of the two sides connected together by a portion

602 NERVOUS SYSTEM.

of the spinal column. The legs are then placed each one in a vessel of water, and a
feeble galvanic current is passed from one glass to the other. It is evident that, with
this arrangement, the current will pass through both nerves, being descending for the
.one and ascending for the other. In this case, if the irritability of the nerves be not too
great, there will be a contraction in the leg for which the current is descending at the
time of closing the circuit, and the other leg will contract when the circuit is opened.
This experiment has been modified by Chauveau and applied to the two facial nerves in a
living horse. A Leyden jar is very feebly charged, and the two facials are exposed.
The current is then passed instantaneously through both the nerves, which gives but a
single stimulus, and that corresponds to the time of closing the circuit. In this experi-
ment, the current is descending for one nerve and ascending for the other, and con-
traction takes place only in those muscles supplied with the nerve for which the current
is descending.

The muscular contraction produced by galvanic stimulation of a nerve is more vig-
orous the greater the extent of the nerve included between the poles of the battery.
This fact has long been observed, and its accuracy is easily verified. It would naturally
be expected that, the greater the amount of stimulation, the more marked would be the
muscular action ; and the stimulation seems to be increased in proportion to the extent
of nerve through which the galvanic current is made to pass.

The irritability of a nerve, it is well known, may be exhausted by the repeated appli-
cation of electricity, whatever be the direction of the current, and it is more or less com-
pletely restored by repose. It is a curious fact, in this connection, that, when the irrita-
bility of a nerve has been exhausted for the descending current, it will respond to the
ascending current, and vice versa; and it is even more remarkable that, after the irrita-
bility has been exhausted by the descending current, it is restored more promptly by
stimulation with the ascending current than by absolute repose, and vice versa. This
phenomenon, observed by Volta, is sometimes known as " voltaic alternation." It is very
strikingly illustrated in frogs prepared as above described, with the two posterior ex-
tremities, the nerves attached through a portion of the spinal cord, placed in vessels of
water so that a current may be simultaneously passed through both nerves, being descend-
ing for the one and ascending for the other. As we have already seen, after a time, con-
traction occurs only in one leg, for which the current is descending, on closing the cir-
cuit, and in the other, only on opening the circuit. By repeatedly passing the current
in this way, after a time there will be no contraction in either leg, the irritability of the

nerves having become exhausted. If the
poles of the battery be now reversed, so as
to make the ascending current take the place
of the descending, contractions on closing
and opening the circuit will again occur.

Induced Muscular Contraction. — A cu-
rious phenomenon was discovered by Mat-
teucci, in experimenting upon nervous and
muscular irritability, which has been call-
ed " induced muscular contraction." It
was found that, if the nerve of a gal-
vanoscopic frog's leg (the leg prepared
with the nerve attached in the way al-
FIG. m.-Arraiwement offrotfs legs prepared so as read describecl) be placed in contact with
to sfiow induced contraction. (Liegeois.) , n , .

the muscles of another leg prepared in

the same way, galvanization of the nerve, giving rise to contraction of the mus-
cles with which the nerve of the first leg is in contact, will induce contraction in
the muscles of both. This experiment may be, extended, and contractions may thus be

GENERAL PROPERTIES OF THE NERVES. 603

induced in a series of legs, the nerve of one being in contact with the muscles of another.
This illustrates the great delicacy of. the galvanoscopic frog's leg, as it will indicate a
current due to a single muscular contraction, which does not affect an ordinary galva-
nometer. It is conclusively proven that the "induced contraction," as just described, is
not due to an actual propagation of the galvanic current, but to a stimulus attending the
muscular contraction itself, by the fact that the same phenomena occur when the first
muscular contraction is induced by mechanical or chemical excitation of the nerve.

Galvanic Current from the Exterior to the Cut Surface of a Nerve. — Before we study
certain phenomena presented in nerves of which a portion is subjected to the action of
a constant galvanic current, it is important to note the fact that there exists in the
nerves, as in the muscles, a galvanic current from the exterior to their cut surface. This
fact has been noted by all who have investigated the subject of electro-physiology. It
has been roughly estimated by Matteucci that the nerve-current has from one-eighth
to one-tenth the intensity of the muscular current. The existence of the nerve-current
has, as far as we know, no more physiological significance than the analogous fact ob-
served in the muscular tissue. It is presented in nerves removed from the body and has
no relation to their functional activity, whether in normal action or excited by artificial
stimulation.

Effects of a Constant Galvanic Current upon the Nervous Irritability. — Aside from
the disorganizing effect upon the nerves of a powerful constant current, which is due
solely to decomposition of their substance, a feeble current has been found to exert an
important influence upon the nervous irritability, according to the direction in which the
current is passed. The law in accordance with which this influence is exerted is stated
by Matteucci as follows :

"A continued electric current passed through a mixed nerve, the crural or the lum-
bar, for example, modifies the excitability of the nerve in a very different manner, accord-
ing to its direction. The excitability is enfeebled by the passage of the descending cur-
rent, and, on the contrary, it is preserved and augmented, at least within certain limits,
by the ascending current. The time necessary in order that the current shall produce
this modification is proportionate to the degree of excitability of the nerve and in in-
verse ratio to the intensity of the current. After opening the circuit, the modification
of the nerve tends to cease at a period that is short in proportion as the excitability of
the nerve is great and the intensity of the current is feeble. This proposition explains
the difference in the electro-physiological effects of the continued current according to
its direction, and the well-known phenomenon of voltaic alternations."

This law has been carefully studied and formularized, as above, by Matteucci, but its
discovery is attributed by physiological writers to Pfaff. After a time, varying with the
excitability of the nerve and the intensity of the current, the descending current will
destroy the nervous irritability, but this may be restored by repose, or more quickly by
the passage of an ascending current. If the ascending current be passed first for a few
seconds, a contraction follows the opening of the circuit ; and this contraction, within
certain limits, is more vigorous the longer the current is passed. At the same time, the
prolonged passage of the ascending current increases the excitability of the nerve for any
kind of stimulus. When the ascending current has been passed through the nerves for
several hours, opening the circuit is followed by very violent contraction and a tetanic
condition of the muscles, enduring for several seconds.

Electrotonus, Anelectrotonus, and Catelectrotonus.

Many years ago, Du Bois-Reymond discovered the curious and interesting fact that,
when a constant galvanic current is passed through a portion of a freshly-prepared nerve,
those parts of the nerve not included between the poles are brought into a peculiar con-

604 NERVOUS SYSTEM.

dition. While in this state, the nerve will deflect the needle of a delicate galvanometer,
and its excitability is modified. The deflection of the needle, in this instance, is not due
to the normal nerve-current, for it occurs when the galvanometer is applied to the surface
of the nerve only. It is due to an electric tension of the entire nerve, induced by the
passage of a current through a portion of its extent. This condition is called electrotonus.
The phenomena thus produced have been most elaborately studied by Pfluger, who
farther recognized a peculiar condition of that portion of the nerve near the anode, or
positive pole, differing from the condition of the nerve near the cathode, or negative pole.
Near the anode, the excitability of the nerve is diminished, and this condition has been
called anelectrotonus. Near the cathode, the excitability is increased, and this condition
has been called catelectrotonus.

These varied phenomena have been the subject of extended investigation by electro-
physiologists ; and, although they are not to be ranked among the physiological properties
of the nerves, they have considerable pathological and therapeutical importance. It is
well known, for example, that electricity is one of the most efficient agents at our com-
mand for the restoration of the functions of nerves affected with disease ; and the con-
stant current has, particularly of late, been extensively and successfully used as a thera-
peutical agent. The constant current, in restoring the normal condition of nerves, must
influence, not only that portion included between the poles of the battery, but the entire
nerve; and the electrotonic condition, with its modifications, explains how this result
may be obtained. Undoubtedly the sensory nerves are affected as well as the motor,
although we have as yet but little positive information upon this point. A knowledge of
the fact that the constant current diminishes the excitability of the nerve near the anode
(anelectrotonus) and increases it near the cathode (catelectrotonus) may become important
in determining the direction of the current to be employed in different cases of disease.

In the present condition of the subject of electro-physiology, it will be unnecessary to
do more than to indicate, as clearly and simply as possible, the laws of the phenomena
attending the passage of a constant current through nerves, as far as they have been
definitively ascertained.

The phenomena of electrotonus are very simple ; and it is only when we attempt to
construct a theory to account for these phenomena that the subject becomes obscure.
Suppose, for example, that a nerve be exposed in a living animal or in one just killed,
and a galvanic current be applied from a Grove's battery, in which about twelve square
inches of zinc are exposed to the action of a liquid containing one part of ordinary sul-
phuric acid to eight of water. A delicate galvanometer applied to the nerve either above
or below the poles will indicate a decided current, much more intense than the tranquil
nerve-current between the exterior and the cut surface. This electrotonic condition exists
so long as the galvanic current is continued ; and, as has been shown by Matteucci in
operating upon the higher animals — rabbits, dogs, fowls, and sheep — when the galvanic
current has been sufficiently powerful and prolonged, the electrotonic condition persists
for a certain time after the stimulus has ceased. As we have seen that the muscular
contraction following galvanic stimulation of a nerve is powerful in proportion to the
extent of nerve included between the poles of the battery, so the electrotonic condition
increases in intensity with the length of the nerve subjected to the constant current;
provided, always, that the strength of the current be slightly increased to compensate the
enfeebling action due to the resistance in the increased length of the circuit.

We do not propose to discuss fully the various theories that have been advanced in
explanation of the phenomena of electrotonus. Matteucci has made a series of interesting
observations upon conductors formed of very fine wires, one of platinum and the other
of amalgamated zinc, covered with cotton thread soaked in a neutral solution of sulphate
of zinc. The experiments were then arranged so as to operate first with the platinum
wire and afterward with the zinc, by passing a galvanic current through a small portion
of the conductor, in the same way as it is passed through a portion of a nerve. He found

GENERAL PROPERTIES OF THE NERVES. 605

that in this way he could produce a strong electrotonic current in the platinum wire, even
at a distance of more than three feet from the electrodes, while no such current was
observed in the zinc. He remarks that in the platinum wire " secondary polarities" are
produced very powerfully and rapidly, while these are not developed in the zinc. From
these experiments alone, it might seem that the phenomena of electrotonus are to be
explained entirely by the physical properties of the nerves as conductors of electricity ;
but various observations on the nerves under different conditions have conclusively proven
the contrary. All observers are agreed that the electrotonic condition is marked in pro-
portion to the excitability of the nerve, and it is either entirely absent or extremely feeble
in nerves that are dead or have lost their irritability. If a strong ligature be applied
to the extra-polar portion of the nerve, or if the nerve be divided and the cut ends be
brought in contact with each other, the electrotonic condition is either not observed or
is very feeble. These facts show conclusively that the phenomena of electrotonus
depend upon the physiological integrity of nerves. A dead nerve, or one that has been
divided or strongly ligatured, may present these phenomena under the stimulation of a
very powerful current (and then only to a slight degree), when the condition depends
upon the purely physical properties of the nerve as a conductor ; but there is no com-
parison between these phenomena and those observed in nerves that retain their physi-
ological properties. Were it otherwise, how could the physiological properties of a dis-
eased nerve be restored throughout its whole extent by a constant current passed through
a restricted portion, when the excitability of the nerve is only manifested at the clos-
ing or opening of the circuit?

Anelectrotonus and Catelectrotonus. — It is interesting to note that, when a portion of
a nerve is subjected to a moderately powerful constant current, the conditions of the
extra-polar portions corresponding to the two poles of the battery are entirely different.
Near the positive pole, or anode, the excitability of the nerve and the rate of nervous
conduction are diminished. If, however, we have a galvanometer applied to this portion
of the nerve, its electromotive power, measured by the deflection of the galvanometric
needle, is increased. On the other hand, near the negative pole, or cathode, the excita-
bility of the nerve is increased, as well as the rate of nervous conduction ; but the elec-
tromotive power is diminished. These facts, at least so far as they relate to the increase
of the excitability of the nerve near the cathode and its diminution near the anode,
are partially explained by Matteucci upon purely physical principles, depending upon
the electrolytic action of the current, as is shown by the following experiment :

Two cups are filled, the one with a very feebly alkaline solution, and the other with
an equally weak acid fluid. A number of galvanoscopic frogs' legs are then rapidly pre-
pared, of which one-half the number is plunged in the alkaline and one-half, in the acid
fluid, for from thirty seconds to one or two minutes. The parts are then removed from
the liquids and are carefully washed and dried in bibulous paper. By touching the
nerves with a strong solution of common salt, which is a powerful excitant for the ner-
vous irritability, the nerves that had been exposed to the alkaline solution produced
more powerful and prompt contractions than those exposed to the acid. Now, the elec-
trolytic action of a constant current tends to the accumulation of hydrogen and an alkali
near the cathode, and of oxygen and an acid near the anode ; and by this fact, Matteucci
explains the increase of excitability in catelectrotonus and the diminished excitability in
anelectrotonus. As regards this question, we have only to say, as in the case of gen-
eral electrotonus, that the conditions are susceptible of a partial explanation upon purely
physical grounds ; but precisely how far the unexplained physiological properties of tho
nerves are involved, it is impossible to say.

Neutral Point. — The anelectrotonic condition, on the one hand, and the catelectro-
tonic condition at the other pole of the battery, are marked in extra-polar portions of

606 NERVOUS SYSTEM.

the nerve and are to be recognized, as well, in that portion through which the current
is passing ; but, between the poles, is a point where these conditions meet, as it were,
and where the excitability is unchanged. This has been called the neutral point. When
the galvanic current is of moderate strength, the neutral point is about half-way between
the poles. " When a weak current is used, the neutral point approaches the positive
pole, while in a strong current, it approaches the negative pole. In other words, in a
weak current the negative pole rules over a wider territory than the positive pole,
whereas in a strong current the positive pole prevails." (Rutherford.)

Negative Variation. — There remains to be considered one curious phenomenon, dis-
covered by Du Bois-Reyrnond, which depends upon the action of a rapidly-interrupted
current applied to an excitable nerve. If a galvanometer be applied to a living nerve so
as to indicate by its deviation the normal, or tranquil nerve-current, a rapidly-interrupted
current of electricity passed through a portion of the nerve, it is well known, produces a
tetanic condition of the muscles. If we now watch the needle of the galvanometer, it
will be observed to retrograde and will finally return to zero, indicating that the proper
nerve-current has been overcome. This will be observed to a slight degree under the
influence of mechanical or chemical stimulation of the nerve, the proper nerve-current
being diminished, but generally not abolished. This variation of the needle under the
influence of the tetanic condition has been called negative variation. We do not yet
know that it has any important physiological or pathological significance.

CHAPTER XVIII.

SPINAL NERVES-MOTOR CRANIAL NERVES.

Special nerves coming from the spinal cord— Cranial nerves— Anatomical classification— Physiological classification-
Motor oculi communis (third nerve) — Physiological anatomy — Properties and functions— Influence upon the
movements of the iris— Patheticus, or trochlearis (fourth nerve)— Physiological anatomy — Properties and func-
tions— Motor oculi externus, or abducens (sixth nerve) — Physiological anatomy — Properties and functions —
Motor nerves of the face — Nerve of mastication (the small, or motor root of the fifth) — Physiological anatomy
— Deep origin — Distribution — Properties and functions of the nerve of mastication — Facial nerve, or nerve of
expression (the portio dura of the seventh)— Physiological anatomy — Intermediary nerve of Wrisberg — Decus-
sation of the fibres of origin of the facial — Alternate paralysis — Course and distribution of the facial— Anasto-
moses with sensitive nerves — Properties and functions of the facial — Functions of the branches of the facial
within the aqueduct of Fallopius— Functions of the chorda tympani— Influence of various branches of the facial
upon the movements of the palate and uvula — Functions of the external branches of the facial — Spinal accessory
nerve (third division of the eighth) — Physiological anatomy — Properties and functions of the spinal accessory —
Functions of the internal branch from the spinal accessory to the pneumogastric — Influence of the spinal acces-
sory upon the heart— Functions of the external, or muscular branch of the spinal accessory— Sublingual, or
hypoglossal nerve (ninth)— Physiological anatomy— Properties and functions of the sublingual— Glosso-labial
paralysis.

Spinal Nerves.

WITH a thorough knowledge of the general properties of the nerves belonging to the
cerebro-spinal system, the functions of most of the special nerves are apparent simply
from their anatomical relations. This is especially true of the spinal nerves. These, in
general terms, are distributed to the muscles of the trunk and extremities, to the sphinc-
ters and the integument covering these parts, the posterior segment of the head, and
a portion of the mucous membranes. It is evident, therefore, that an account of the
exact function of each nervous branch would necessitate a full description, not only of
the nerves, but of the muscles of the body, which is manifestly within the scope only of
elaborate treatises on descriptive anatomy. It is sufficient to indicate, in this connec-
tion, that there are thirty-one pairs of spinal nerves ; eight cervical, twelve dorsal, five

SPINAL NERVES.

607

lumbar, five sacral, and one coccygeal. Each nerve arises from the spinal cord by an
anterior (motor) and a posterior (sensory) root ; the posterior roots being the larger, and
each having a ganglion. Immediately beyond the ganglion, the two roots unite into a
single mixed nerve, which passes out of the spinal canal by the intervertebral foramen.
The nerve thus constituted is endowed with both motor and sensory properties. It
divides outside of the spinal canal into two branches, anterior and posterior, both con-
taining motor and sensory filaments, which are distributed respectively to the anterior
and the posterior parts of the body. The anterior branches are the larger, and they sup-
ply the limbs and all parts in front of the spinal column.

FIG. 192. — Cervical portion of FIG. 193. — Dorsal portion of FIG. 194. — Inferior portion of

the spinal cord. (Hirsch- the spinal cord. (Hirsch- the spinal cord, and caii-

feld.) feld). da equinti. (Hirschfeld.)

1, antero-inferior wall of the fourth ventricle; 2, superior peduncle of the cerebellum; 3, middle peduncle of the
cerebellum ; 4, inferior peduncle of the cerebellum ; 5. inferior portion of the posterior median columns of the
cord ; 6, glosso-pharyngeal nerve; 7, pneumogastric ; 8, spinal accessory nerve; 9, 9, 9, 9, dentated ligament; 10,
10, 10, 10, posterior roots of the spinal nerves; 11, 11, 11, 11, posterior lateral groove; 12, 12, 12, 12, ganglia
of the posterior roots of the nerves; 18, 13, anterior roots of the nerves ; 14, division of the nerves into two
branches ; 15, lower extremity of the cord; 16, 16, coccygeal ligament; 17, 17, cauda equi'na; I— VIII, cervical
nerves; I, II, III, IV — XII, dorsal nerves; I, II — V, lumbar nerves; I — V, sacral nerves.

The anterior branches of the four upper cervical nerves form the cervical plexus, and
the four inferior cervical nerves, with the first dorsal, form the brachial plexus. The
anterior branches of the dorsal nerves, with the exception of the first, supply the walls
of the chest and abdomen. These nerves go directly to their distribution, and do not
first form a plexus, like most of the other spinal nerves. The anterior branches of the
four upper lumbar nerves form the lumbar plexus. The anterior branch of the fifth
lumbar nerve and a branch from the fourth unite with the anterior branch of the first
sacral, forming the lumbo-sacral nerve, and enter into the sacral plexus. The three
upper anterior sacral nerves with a branch from the fourth form the sacral plexus. The
greatest portion of the fourth anterior sacral is distributed to the pelvic viscera and the

608

NEKYOUS SYSTEM.

muscles of the anus. The fifth anterior sacral and the coccygeal are distributed about
the coccyx.

The posterior branches of the spinal nerves are very simple in their distribution.
With one or two exceptions, which have no great physiological importance, these nerves
pass backward from the main trunk, divide into two branches, external and internal, and
their filaments of distribution go to the muscles and integument behind the spinal column.

It is farther important to note, as we shall have occasion to do more particularly in
connection with the great sympathetic nerve, that all of the cerebro- spinal nerves anas-
tomose with the sympathetic. This anatomical connection between the two systems of
nerves has great physiological interest.

Cranial JVerves.

The nerves which pass out from the cranial cavity present certain differences, in their
arrangement and general properties, from the ordinary spinal nerves. As we have seen,
the spinal nerves are exceedingly simple, each one being formed by the union of a motor

and a sensory root. The function of
most of them follows as a matter of
course when we understand their gen-
eral properties and anatomical distri-
bution. Many of the cranial nerves,
however, are peculiar, either as regards
their general properties or in their dis-
tribution to parts concerned in special
functions. In some of these nerves, the
most important facts concerning their
distribution have been ascertained only
by physiological experimentation, and
their anatomy is inseparably connected
with their physiology. It would be de-
sirable, if it were possible, to classify
these nerves with reference strictly to
their properties and functions ; but this
can be done only to a certain extent,
and we must adopt as a basis those
divisions recognized in the best works
upon anatomy.

The two classifications of the cranial
nerves adopted by most anatomists are
the arrangements of Willis and of Som-
merring. The first of these is the more
common, and in it the nerves are num-
bered from before backward, in the or-
der in which they pass out of the skull,
making nine pairs.

Anatomical Classification of the

FIG. 195.— Roots of the cranial nerves.

I. First pair ; olfactory.
II Second pair; optic.

III. Third pair ; motor oculi communis.

IV. Fourth pair ; patheticus.

V. Fifth pair; nerve of mastication and trifacial.
VI. Sixth pair ; motor oculi externus.

IX. Glosso-pharyngeal. )
X. PneumoErastric. V Eighth pair.
XI. Spinal accessory. )
XII. Ninth pair ; su'blinpual.

The numbers 1 to 15 refer to branches which will be described
hereafter.

Cranial Jt

erves.

First Pair. — Olfactory ; the special
nerve of smell.
Second Pair. — Optic ; the special nerve of sight.

Third Pair. — Motor oculi communis ; a motor nerve distributed to all of the muscles
of the eyeball, except the external rectus and the superior oblique, to the iris, and to the
levator palpebra3.

PHYSIOLOGICAL CLASSIFICATION OF THE CRANIAL NERVES. 609

Fourth Pair. — Patheticus, or trochlearis ; a motor nerve sent to the superior oblique
muscle of the eye.

Fifth Pair. — A small motor root (nerve of mastication), distributed to the muscles of
mastication, and a large root (trifacial), the nerve of general sensibility of the face.

Sixth Pair. — Motor oculi externus, or abducens ; a motor nerve passing to the exter-
nal rectus' muscle of the eye.

Seventh Pair. — Portio mollis, or auditory, a special nerve of hearing; and the portio
dura, or facial, a motor nerve distributed to the superficial muscles of the face.

Eighth Pair. — Glosso-pharyngeal ; pneumogastric, or par vaguin; and spinal acces-
sory. Three mixed nerves, with quite extensive distributions.

Ninth Pair. — Sublingual, or hypoglossal ; a motor nerve distributed to the tongue.

Physiological Classification of the Cranial Nerves.

(a) Nerves of Special Sense.
Olfactory.
Optic.
Auditory.

Gustatory, comprising a part of the glosso-pharyngeal and a small filament from the
facial to the lingual branch of the fifth.

(b) Nerves of Motion.

Nerves of motion of the eyeball, comprising the motor oculi communis", the patheti-
cus, and the motor oculi externus.

Nerve of mastication, or motor root of the fifth.
Facial, sometimes called the nerve of expression.
Spinal accessory.
Sublingual.

(c) Nerves of General Sensibility.

Trifacial, or large root of the fifth.
A portion of the glosso-pharyngeal.
Pneumogastric.

In the above arrangement, the nerves are classified according to their properties at
their roots. In their course, some of these nerves become mixed and their branches are
both motor and sensory, such as the pneumogastric and the inferior maxillary branch of
the trifacial.

The nerves of special sense are but slightly if at all endowed with general sensi-
bility; and, with the exception of the gustatory nerves, they do not present a ganglion
on their roots, in this, also, differing from the ordinary sensory nerves. They are capa-
ble, therefore, of conveying to the nerve-centres only certain peculiar impressions; such
as odors, for the olfactory nerves; light, for the optic nerves; and sound, for the auditory
nerves. The proper transmission of these impressions, however, involves the action of
accessory organs, more or less complex ; and we shall pass over the properties of these
nerves until we come to treat in full of the special senses.

Motor Oculi Communis (Third Nerve).

The third cranial nerve is the most important of the motor nerves distributed to the
muscles of the eyeball. Its physiology is readily understood in connection with its dis-
tribution, the only point at all obscure being its relations to the movements of the iris,
upon which the results of experiments are somewhat contradictory. As an introduction
to the study of the functions of this nerve, it will be necessary to describe its anatomical
relations.

39

610

NERVOUS SYSTEM.

Physiological Anatomy.— Like all of the cranial nerves, this has an apparent origin,
where it separates from the encephalon, and a deep origin, which is the last point to
which its fibres can be traced in the substance of the brain ; but the origin has not the
physiological importance attached to its ultimate distribution.

The apparent origin of the third nerve is from the inner edge of the crus cerebri, direct-
ly in front of the pons Varolii, midway between the pons and the corpora albicantia. It
presents here from eight to ten filaments, of nearly equal size, which soon unite into a
single, rounded trunk.

The deep origin of the nerve has been studied by dissections of the encephalon fresh
and hardened by different liquids. From the groove by which they emerge from the
encephalon, the fibres spread out in a fan-shape, the middle filaments passing inward, the

anterior, inward and forward, and the posterior,
inward and backward. It is probable that the
middle filaments pass to the median line and de
cussate witli corresponding fibres from the oppo-
site side. The anterior filaments pass forward
and are lost in the optic thalamus. The poste-
rior filaments on either side pass backward and
decussate beneath the aqueduct of Sylvius. This
apparent decussation of the fibres of origin of the
third nerves is important in connection with the
harmony of action of the muscles of the eyes and
the iris upon the two sides.

The • distribution of the third nerve is very
simple. As it passes into the orbit by the sphe-
noidal fissure, it divides into two branches. The
superior, which is the smaller, passes to the su-
perior rectus muscle of the eye, and certain of

FIG. 196.— Distribution of the motor ocull com- its filaments are continued to the levator palpe-

munis. (Hirschfeid.) . . „, . ,, . ,. . . ,

bra3 snpenons. I he inferior division breaks up
into three branches.

1, trunk of the motor oculi communis ; 2. supe-
rior branch ; 8, filaments which this branch
sends to the superior rectus and the lewator

palpebri sitperioris ; 4, branch to the inter- 6S to the internal rectus muscle ;
nal rectus ; 5, branch to the inferior rectus ;
6, branch to the inferior oblique, muscle ; 7,
branch to the lenticular ganglion ; 8, motor
oculi externus ; 9, filaments of the motor ocu-
li externus anastomosing with the sympathet-
ic ; 10, ciliary nerves.

The internal branch pass-
the inferior

branch, to the inferior rectus ; the external
branch, the largest of the three, is distributed to
the inferior oblique muscle, and, in its course, it
sends a short and thick filament to the lenticular,
or ophthalmic ganglion of the sympathetic. It is this branch which is supposed, through
the short ciliary nerves passing from the lenticular ganglion, to furnish the motor influ-
ence to the iris. In its course, this nerve receives a few very delicate filaments from the
cavernous plexus of the sympathetic and a branch from the ophthalmic division of
the trifacial.

Properties and Functions of the Motor Oculi Communis. — Irritation applied to the
root of the third nerve in a living animal produces contraction of the muscles to which
it is distributed, but no pain. If the irritation, however, be applied a little farther on,
in the course of the nerve, there are evidences of sensibility, which is readily explained
by its communications with the ophthalmic branch of the trifacial. At its root, there-
fore, this nerve is exclusively motor, and its functions are connected entirely with the
action of muscles.

Most of the important facts bearing upon the functions of the motor oculi are clearly
demonstrable by dividing the nerve in a living animal and are illustrated by cases of its
paralysis in the human subject. All physiologists who have divided the nerve in living
animals are agreed with regard to the phenomena following its section, which depend
upon paralysis of the voluntary muscles. These phenomena are as follows :

MOTOR OCULI COMMUNIS (THIRD NERVE). 611

1. Falling of the upper eyelid, or blepharoptosis.

2. External strabismus, immobility of the eye (except in an outward direction), ina-
bility to rotate the eye on its antero-posterior axis in certain directions, with slight pro-
trusion of the eye-ball.

3. Dilatation of the pupil, with a certain amount of interference with the movements
of the iris.

The falling of the upper eyelid is constantly observed after division of the third nerve
in living animals and always follows its complete paralysis in the human subject. An ani-
mal in which the nerve has been divided cannot raise the lid, but can approximate
the lids more closely, by a voluntary effort. In the human subject, the falling of the lid
gives to the face a very peculiar and characteristic expression. The complete loss of
power shows that the levator palpebras superioris muscle depends upon the third nerve
entirely for its motor filaments. In pathology, external strabismus is very frequently
observed without falling of the lid, the filament distributed to the levator muscle not
being affected.

The external strabismus and the immobility of the eyeball except in an outward direc-
tion are due to paralysis of the internal, superior, and inferior recti muscles, the external
rectus acting without its antagonist. This condition requires no farther explanation.
These points are well illustrated by the experiment of dividing the nerve in rabbits.
If the head of the animal be turned inward, exposing the eye to a bright light, the globe
will turn outward, by the action of the external rectus ; but, if the head be turned out-
ward, the globe remains motionless.

It is somewhat difficult to note the effects of paralysis of the inferior oblique muscle,
which is also supplied by the third nerve. This muscle, acting from its origin at the
inferior and internal part of the circumference of the base of the orbit to its attachment
at the inferior and external part of the posterior hemisphere of the eyeball, gives to the
globe a movement of rotation on an oblique, horizontal axis, downward and backward,
directing the pupil upward and outward. When this muscle is paralyzed, the superior
oblique, having no antagonist, rotates the globe upward and inward, directing the pupil
downward and outward. The action of the oblique muscles is observed when we move
the head alternately toward one shoulder and the other. In the human subject, when
the inferior oblique muscle on one side is paralyzed, the eye cannot move in a direction
opposite to the movements of the head, as it does upon the sound side, so as to keep the
pupil fixed, and the patient has double vision.

When all the muscles of the eyeball, except the external rectus and superior oblique,
are paralyzed, as they are by section of the third nerve, the globe is slightly protruded,
simply by the relaxation of most of its muscles. An opposite action is easily observed
in a cat with the facial nerve divided, so that it cannot close the lids. When the cornea
is touched, all of the muscles, particularly the four recti, act to draw the globe into the
orbit, which allows the lid to fall slightly, and projects the little membrane which serves
as a third eyelid in these animals.

Observations with regard to the influence of the third nerve upon the movements of
the iris have not been so satisfactory in their results as those relating to the muscles of the
eyeball. It will be remembered that this nerve sends a filament to the ophthalmic gan-
glion of the sympathetic, and that, from this ganglion, the short ciliary nerves take their
origin and pass to the iris. The ganglia of the sympathetic system receive branches both
from motor and sensory nerves belonging to the cerebro-spinal system, and the ophthal-
mic ganglion is no exception to this rule. While it is undoubtedly true that division of
the third nerve affects the movements of the iris, it becomes a question whether this be
a direct influence, or an influence exerted primarily upon the ganglion, not, perhaps,
differing from the general effects upon the sympathetic ganglia that follow destruction of
their branches of communication with the motor nerves.

The most important experimental observations with regard to the influence of the

612 NERVOUS SYSTEM.

third nerve upon the iris are the following : Herbert Mayo made experiments on thirty
pigeons, living or just killed, upon the action of the optic, the third, and the fifth nerves
on the iris. He states that, when the third nerves are divided in the cranial cavity in a liv-
ing pigeon, the pupils become fully dilated and do not contract on the admission of intense
light ; nnd, when the same nerves are pinched in the living or dead bird, the pupils are
contracted for an instant on each stimulation of the nerves. The same results follow
division or irritation of the optic nerves under similar conditions; but, when the third
nerves have been divided, no change in the pupil ensues upon irritating the entire or
divided optic nerves.

The above experiments are accepted by nearly all physiological writers ; and the
assumption is that the third nerves animate the muscular fibres that contract the pupil,
the contraction produced by irritation of the optic nerves being reflex in its character.
Later observers, however, have carried their experiments somewhat farther. Longet
divided the motor oculi and the optic nerve upon the right side. He found that irrita-
tion of the central end of the divided optic nerve produced no movement of the pupil
of the side upon which the motor oculi had been divided, but caused contraction of the
iris upon the opposite side. This, taken in connection with the fact that, in ainaurosis
affecting one eye, the iris upon the affected side will not contract under the stimulus of
light applied to the same eye, but will act when the uninjured eye is exposed to the
light, farther illustrates the reflex action which takes place through these nerves.

The reflex action by which the iris is contracted is not instantaneous, like most of the
analogous phenomena observed in the cerebro-spinal system, and its operations are rather
characteristic of the sympathetic system and the non-striated muscular tissue. It has
been found, also, by Bernard, in experiments upon rabbits, that the pupil is not immedi-
ately dilated after division of the third nerve. The method employed by Bernard, intro-
ducing a hook into the middle temporal fossa through the orbit and tearing the nerve,
can hardly be accomplished without touching the ophthalmic branch of the fifth, which
produces intense pain and is always followed by a more or less persistent contraction of
the pupil. Several hours after the operation, however, the pupil is generally found
dilated, and it may slowly contract when the eye is exposed to the light. In one experi-
ment, this occurred after the eye had been exposed for an hour. But farther experi-
ments by Bernard show that, although the pupil contracts feebly and slowly under the
stimulus of light after division of the motor oculi, it will dilate under the influence of
belladonna and can be made to contract by operating upon other nerves. It is well
known, for example, that division or irritation of the fifth nerve produces contraction of
the pupil. This takes place after as well as before division of the third nerve. Section
of the sympathetic in the cervical region also contracts the pupil, and this occurs after
paralysis of the motor oculi. These facts show that the third nerve is not the only one
capable of acting upon the iris, and that it is not the sole avenue for the transmission
of reflex influences.

Bernard also found that galvanization of the motor oculi itself did not produce con-
traction of the pupil, but this result followed when he galvanized the ciliary nerves
coming from the ophthalmic ganglion. Chauveau states that, in experiments upon
horses, he has not observed contraction of the pupil following galvanization of the motor
oculi, although he has sometimes seen it in rabbits. At all events, contraction is by no
means constant ; and, when it occurs, it probably depends upon stimulation of the ciliary
nerves themselves or irritation of the ophthalmic branch of the fifth, and not upon stimu-
lation of the trunks of the third pair.

The movements of the iris will be treated of again, in connection with the physiology
of vision ; but we may here allude to an interesting fact observed by Mtiller, which relates
to the action of the motores oculorum. When the eye is turned inward by a voluntary
-effort, the pupil is always contracted ; and when the axes of the two eyes are made to
•converge strongly, as in looking at near objects, the contraction is very great.

PATHETICUS, OR TROCHLEARIS (FOURTH NERVE). 613

The following case, kindly sent for examination by Dr. Althof, of the New York Eye
Infirmary, illustrates, in the human subject, nearly all of the phenomena following paraly-
sis of the motor oculi communis in experiments upon the lower animals :

The patient was a girl, nineteen years of age, with complete paralysis of the nerve
upon the left side. There was slight protrusion of the eyeball, complete ptosis, with the
pupil moderately dilated and insensible to ordinary impressions of light. The sight was
not affected, but there was double vision, except when objects were placed before the
eyes so that the axes were parallel, or when an object was seen with but one eye. The
axis of the left eye was turned outward, but it was not possible to detect any deviation
upward or downward. Upon causing the patient to incline the head alternately to one
shoulder and the other, it was evident that the affected eye did not rotate in the orbit
but moved with the head. This seemed to be a case of complete and uncomplicated
paralysis of the third nerve.

Patheticus, or Trochlearis (Fourth Ner^e).

Except as regards the influence of the motor oculi communis upon the iris, the pa-
theticus is to be classed with the other motor nerves of the eyeball. Its physiology
is extremely simple and resolves itself into the action of a single muscle, the superior
oblique. It will be necessary, therefore, only to describe its origin, distribution, and
connections.

Physiological Anatomy. — The apparent origin of the patheticus is from the superior
peduncles of the cerebellum ; but it may be easily traced to the valve of Vieussens. The
deep roots, which are covered by an extremely thin layer of nerve-substance, can be
traced, passing from without inward, to the following parts : One filament is lost in the
substance of the peduncles ; other filaments pass from before backward into the valve
of Vieussens and are lost, and a few pass into the frenulum ; a few filaments pass back-
ward and are lost in the corpora quadrigemina ; but the greatest number pass to the
median line and decussate with corresponding filaments from the opposite side. The
decussation of the fibres of origin of the fourth nerves has the same physiological signifi-
cance as the decussation of the roots of the third. From this origin, the patheticus passes
into the orbit by the sphenoidal fissure and is distributed to the superior oblique muscle
of the eyeball. In the cavernous sinus, it receives branches of communication from the
ophthalmic branch of the fifth, but these are not closely united with the nerve. A small
branch passes into the tentorium, and one joins the lachrymal nerve, these, however,
being exclusively sensitive and coming from the ophthalmic branch of the fifth. It also
receives a few filaments from the sympathetic.

Properties and Functions of the Patheticus. — Direct observations upon the patheticus
in living animals have shown that it is motor, and its galvanization excites contraction
of the superior oblique muscle only. The question of the function of the nerve, there-
fore, resolves itself simply into the mode of action of the superior oblique muscle. This
muscle arises just above the inner margin of the optic foramen, passes forward, along the
upper wall of the orbit at its inner angle, to a little cartilaginous ring which serves as a
pulley. From its origin to this point it is muscular. Its tendon becomes rounded just
before it passes through the pulley, where it makes a sharp curve, pusses outward and
slightly backward, and becomes spread out to be attached to the globe at the superior
and external part of its posterior hemisphere. It acts upon the eyeball from the pulley
at the upper and inner portion of the orbit as the fixed point and rotates the »ye upon
an oblique, horizontal axis, from below upward, from without inward, and from behind
forward. By its action, the pupil is directed downward and outward. It is the direct
antagonist of the inferior oblique, the action of which has been described in connection

614

NERVOUS SYSTEM.

with the motor oculi communis. When the patheticus is paralyzed, the eyeball is im-
movable, as far as rotation is concerned ; and, when the head is moved toward the shoul-
der, the eye does not rotate to maintain the globe in the same relative position, and we
have double vision.

FIG. 197.— Distribution of the patheticus. (Hirschfeld.)
I, olfactory nerve ; II, optic nerves ; III, motor oculi com-
munis; IV, patheticus, by the side of the ophthal-
mia branch of the fifth, and passing to the superior
oblique muscle ; VI, motor oculi externus ; 1, gan-
glion of Gasser ; 2, 3, 4, 5, 6, 7, 8, 9, 10, optnthalmic
division of the fifth nerve, with its branches.

FIG. 198. — Distribution of the motor oculi externus.
(Hirschfeld.)

1, trunk of the motor oculi communis, with its branches
(2, 3, 4, 5, 6, 7) ; 8, motor oculi externus, passing
to the external rectus muscle; 9, ft 'lament* of the
motor oculi externus anastomosing with the sym-
pathetic; 10, ciliary nerves.

Motor Oculi Externus, or Abducens (Sixth Nerve).

Like the patheticus, the motor oculi externus is distributed to but a single muscle, the
external rectus. Its uses, therefore, are apparent from a study of its distribution and
properties.

Physiological Anatomy. — The apparent origin of the sixth nerve is from the groove
which separates the anterior corpus pyramidale of the medulla oblongata from the pons
Varolii, and from the upper portion of the medulla and the lower portion of the pons
next the groove. Its origin at this point is by two roots : an inferior, which is the larger,
and comes from the corpus pyramidale ; and a superior root, sometimes wanting, which
seems to come from the lower portion of the pons. All anatomists are agreed that the
deep fibres of origin of this nerve pass to the gray matter in the floor of the fourth ven-
tricle. Vulpian has followed these fibres to within about two-fifths of an inch of the
median line, but they could not be traced beyond this point. It is not known that the
fibres of the two sides decussate. From this origin, the nerve passes into the orbit by the
sphenoidal fissure and is distributed exclusively to the external rectus muscle of the eye-
ball. In the cavernous sinus, it anastomoses with the sympathetic through the carotid
plexus and Meckel's ganglion. It also receives sensitive filaments from the ophthalmic
branch of the fifth. It is stated by some anatomists that this nerve occasionally sends a
small filament to the ophthalmic ganglion ; and it is supposed by Longet that this branch,
which is exceptional, exists in those cases in which paralysis of the motor oculi com-
munis, which usually furnishes all the motor filaments to this ganglion, is not attended
with immobility of the iris.

Properties and Functions of the Motor Oculi Externus. — Direct experiments have
shown that the motor oculi externus is entirely insensible at its origin, its stimulation

MOTOR NERVES OF THE FACE. 615

producing contraction of the external rectus muscle and no pain. The same experiments
illustrate the function of the nerve, inasmuch as its irritation is followed by powerful
contraction of the muscle and deviation of the eye outward. Division of the nerve in the
lower animals or its paralysis in the human subject is attended with internal, or con- V
verging strabismus, due to the unopposed action of the internal rectus muscle.

With regard to the associated movements of the eyeball, it is a curious fact that all
of the muscles of the eye that have a tendency to direct the pupil inward or to produce
the simple movements upward and downward, viz., the internal, inferior, and superior
recti, are animated by a single nerve, the motor oculi communis, this nerve also supplying
the inferior oblique ; and that each muscle that has a tendency to move the globe so as
to direct the pupil outward, except the inferior oblique, viz., the superior oblique and
the external rectus, is supplied by a special nerve. The various movements of the eyeball
will be studied more minutely in connection with the physiology of vision.

Motor Nerves of the Face.

The motor nerves of the face are, the small, or motor root of the fifth, and the portio
dura of the seventh, or the facial. The first of these nerves is distributed to the deep
muscles, those concerned in the act of mastication ; and the second, the facial, supplies
the superficial muscles of the face and is sometimes called the nerve of expression.
These nerves are not so simple in their anatomy and physiology as the motor nerves ot
the eyeball. The nerve of mastication, at its origin, is deeply situated at the base of the
brain and is exposed and operated upon with difficulty. It passes out of the cranium,
closely united with one of the great sensitive branches of the fifth, and its distribution
has been most successfully studied by experiments in which it is divided in the cranial
cavity. The origin of the facial is also reached with great difficulty. It communicates
with other nerves, and its physiology has been most satisfactorily studied by dividing it
at its origin or in different portions of its course. In treating of these nerves, we shall
first, as in the case of the motor nerves of the eye, study their properties at their roots,
noting the phenomena following their galvanization and section. It will be neces-
sary, also, to describe their origin and distribution, as far as has been ascertained by
dissection.

Nerve of Mastication (the Small, or Motor Hoot of the Fifth Nerve).

The motor root of the fifth nerve is entirely distinct from its sensitive portion, until
it emerges from the cranial cavity by the foramen ovale. It is then closely united with
the inferior maxillary branch of the large root ; but at its origin it has been shown to be
motor, and its section in the cranial cavity has demonstrated its distribution to a par-
ticular set of muscles.

Physiological Anatomy of the Nerve of Mastication. — The apparent origin of the fifth
nerve is from the lateral portion of the pons Varolii. The small, or motor root arises
from a point a little higher and nearer the median line than the large root, from which
it is separated by a few fibres of the white substance of the pons. At the point of
apparent origin, the small root presents from six to eight rounded filaments. If a thin
layer of the pons covering these filaments be removed, the roots will be found pene-
trating its substance, becoming flattened, passing under the superior peduncles of the
cerebellum, and going to the anterior wall of the fourth ventricle. At this point, they
change their direction, passing now from without inward and from behind forward toward
the median line, the fibres diverging rapidly. The posterior fibres pass to the median line,
and certain of them decussate with the fibres from the opposite side. The anterior
fibres pass toward the aqueduct of Sylvius and are lost. The fibres become changed
in their character when they are followed inward beyond the anterior wall of the fourth

616

NERVOUS SYSTEM.

ventricle. Here they lose their white color, become gray, and present numerous globules
of gray substance between their filaments.

From the origin above described, the small root passes beneath the ganglion of Gasser

from which it sometimes, though not constantly, receives a filament of communication —

lies behind the inferior maxillary branch of the large root, and passes out of the cranial
cavity by the foramen ovale. Within the cranium, the two roots are distinct ; but, after
the small root passes through the foramen, it is united by a mutual interlacement of
fibres with the sensitive branch.

The course of the motor root of the fifth possesses little physiological interest. It is
sufficient in this connection to note that the inferior maxillary nerve, made up of the
motor root and the inferior maxillary branch of the sensitive root, just after it passes out

FIG.- 199.— Distribution of the small root of the fifth nerve. (Ilirschfeld.)

1, branch to the masseter muscle; 2, filament of this branch to the temporal muscle; 3, buccal 'branch ; 4,
branches anastomosing with the facial nerve ; §* filament from, the buccal branch to the temporal muscle;
6, branches to the external pterygoid muscle ; 7, middle deep temporal branch ; 8, auriculo-temporal nerve ;
9, temporal branches; 10, auricular branches; 11, anastomosis with the facial nerve; 12, lingual branch;
13, branch of the small root to the mylo-hymd muscle ; 14, inferior dental nerve, with its branches (15, 15); 16,
mental branch ; 17, anastomosis of this branch with the facial nerve.

by the foramen ovale, divides into two branches, anterior and posterior. The anterior
branch, which is the smaller, is composed almost entirely of motor filaments and is distrib-
uted to the muscles of mastication. It gives off five branches. The first of these passes
to be distributed to the masseter muscle, in its course occasionally giving off a small
branch to the temporal muscle and a filament to the articulation of the inferior maxilla
with the temporal bone. The two deep temporal branches are distributed to the tem-
poral muscle. The buccal branch sends filaments to the external pterygoid and to the tem-
poral muscle, and a small branch is distributed to the internal pterygoid muscle. From the
posterior branch, which is chiefly sensitive but contains some motor filaments, branches

NERVE OF MASTICATION. 617

are sent to the mylo-byoid muscle and to the anterior belly of the digastric. In addition,
the motor branch of the fifth sends filaments to the tensor muscles of the velum palati.

The above description shows, in general terms, the distribution of the nerve of masti-
cation, without taking into consideration its various anastomoses, the most important of
which are with the facial. Physiological experiments have shown that the buccinator
muscle receives no motor filaments from the fifth but is supplied entirely by the facial.
The buccal branch of the fifth sends motor filaments only, to the external pterygoid and
the temporal, its final branches of distribution being sensitive and going to integument
and to mucous membrane.

In treating of the function of digestion, we have given a table of the muscles of mas-
tication, with a description of their action. It will be seen by reference to this table that
the following muscles depress the lower jaw ; viz., the anterior bellv of the digastric, the
mylo-hyoid, the genio-hyoid, and the platysma myoides. Of these, the digastric and the
mylo-hyoid are animated by the motor root of the fifth ; the genio-hyoid is supplied by
filaments from the sublingual ; and the platysma myoides, by branches from the facial
and from the cervical plexus. All of the muscles which elevate the lower jaw and move
it laterally and antero-posteriorly, viz., the temporal, masseter, and the internal and
external pterygoids (the muscles most actively concerned in mastication) are animated
by the motor root of the fifth.

Properties and Functions of the Nerve of Mastication. — The anatomical distribution
of the small root of the fifth nerve points at once to its function. Charles Bell, whose
ideas of the nerves were derived almost entirely from their anatomy, called it the nerve
of mastication, in 1821, although he does not state that any experiments were made with
regard to its function. All anatomical and physiological writers since that time have
adopted this view. It would be difficult, if not impossible, to galvanize the root in the
cranial cavity in a living animal ; but its galvanization in animals just killed determines
very marked movements of the lower jaw. Experiments have clearly demonstrated the
physiological properties of the small root, which is without doubt solely a nerve of motion.

The observations upon the division of the fifth pair in the cranial cavity are most
interesting in connection with the functions of its sensitive branches, and will be
referred to in detail in treating of the properties of the large root. In addition to
the loss of sensibility following section of the en-
tire nerve, Bernard has carefully noted the effects
of division of the small root, which cannot be
avoided in the operation. In rabbits, the paraly-
sis of the muscles of mastication upon one side,
and the consequent action of the muscles upon the
unaffected side only, produce, a few days after
the operation, a remarkable change in the appear-
ance of the incisor teeth. As the teeth in these
animals are gradually worn away in mastication
and reproduced, the lower jaw being deviated by
the action of the muscles of the sound side, the FlG> 200.-/«™.w™ of tJ>« rabbit, before ana
upper incisor of one side and the lower incisor of (fiLiIdof* °f the ner™ °f ma*tication"
the other touch each other but slightly and the A. incisors, normal condition.
teeth are worn unevenly. This makes the line B' in0cn8^ S8fd™n days aftel
of contact between the four incisors, when the

jaws are closed, oblique instead of horizontal. We have often divided the fifth pair in
the cranial cavity in rabbits, by the method employed by Magendie and Bernard, and
have repeatedly verified these observations.

There is little left to say with regard to the functions of the motor root of the fifth
nerve, in addition to our description of the action of the muscles of mastication, contained

618 NERVOUS SYSTEM.

in the chapters on digestion, except as regards the action of the filaments sent to the
muscles of the velum palati. In deglutition, the muscles of mastication are indirectly
involved. This act cannot he well performed unless the mouth be closed hy these muscles.
When the food is brought in contact with the velum palati, muscles are brought into
action which render this membrane tense, so that the opening is adapted to the size of
the alimentary bolus. These muscles are animated by the motor root of the fifth. This
nerve, then, is not only the nerve of mastication, animating all of the muscles concerned
in this act, except two of the most unimportant depressors of the lower jaw (the genio-
hyoid and the platysma myoides), but it is concerned indirectly in deglutition.

Facial Nerve, or Nerve of Expression (the Portio Dura of the Seventh

Nerve).

The facial, the portio dura of the seventh according to the arrangement of Willis, is
one of the most interesting of the cranial nerves. Its anatomical relations are quite intri-
cate, and its communications with other nerves, very numerous. As far as can be deter-
mined by experiments upon living animals, this nerve is exclusively motor at its origin ;
but in its course it presents anastomoses with the sympathetic, with branches of the fifth,
and with the cervical nerves, undoubtedly receiving sensory filaments. While the chief
physiological interest attached to this nerve depends upon its action upon muscles, it is
important to study its origin, distribution, and communications.

Physiological Anatomy of the Facial Nerve. — The portio dura of the seventh has its
apparent origin from the lateral portion of the medulla oblongata, in the groove between
the olivary and the restiform body, just below the border of the pons Varolii, its trunk
being internal to the trunk of the portio mollis, or auditory nerve. It is separated from
the auditory by the two filaments constituting what is known as the intermediary nerve
of Wrisberg, or the portio inter duram et mollem. As this little nerve joins the facial,
it must be included in its root.

There are certain pathological considerations which render the deep, or real origin of
the facial a question of the greatest interest and importance. In hemiplegia due to injury
of the substance of the encephalon, particularly from haemorrhage, there is almost always
more or less paralysis of the superficial muscles of the face. It has been observed that,
in certain cases, the facial paralysis exists upon the same side as the hemiplegia (the side
opposite to the cerebral lesion), while in others, the palsy of the face is upon the same side
as the lesion, the general hemiplegia being, as usual, upon the opposite side. To explain
these phenomena theoretically, we must assume that, in some cases, the brain-lesion is to
be located at a. point where it involves the filaments of origin of the facial (following
them from without inward) before they decussate, which would produce facial paralysis
upon the same side as the lesion and none upon the side affected with general hemiplegia;
while, in other cases, the injury to the brain involves the roots of the facial after they
have decussated, when the paralysis of the face would be upon the same side as the paraly-
sis of the rest of the body. It "would be interesting to see how far these pathological
fact:;, with their theoretical explanation, correspond with anatomical researches into the
real origin of the nerves.

Many anatomists have endeavored to trace the fibres of the facial from their point of
emergence from the encephalon to their true origin, but with results not entirely satis-
factory. At the present day, it is pretty generally agreed that the fibres pass inward,
with one or two deviations from a straight course, to the floor of the fourth ventricle,
where they spread out and become fan-shaped. In the floor of the fourth ventricle, cer-
tain of the fibres have been thought to terminate in the cells of the gray substance, and
others have been traced to the median line, where they decussate ; the course of most of
the fibres, however, has never been satisfactorily established.

FACIAL NERVE, OR NERVE OF EXPRESSION.

619

It is evident, from physiological experiments, that the decussation of the fibres in the
floor of the fourth ventricle itself is not very important. Vulpian has made, in dogs and
rabbits, a longitudinal section in the middle line of the ventricle, which would necessarily
have divided the fibres passing from one side to the other, without producing notable
paralysis of the facial nerves upon either side. This single fact is sufficient to show that
the main decussation of the fibres animating the muscles of the face takes place, if at all,
at some other point.

The pathological facts bearing upon the question of decussation of the filaments of
origin of the facial have long been recognized. They are, in brief, as follows: When
there is a lesion of the brain-substance anterior to the pons Varolii, the phenomena due
to paralysis of the facial are observed upon the same side as the hemiplegia, opposite the
side of injury to the brain. When the lesion is either in the pons or below it, the face is

FIG. 201.— Superficial brandies of the facial and the fifth. (Hirschfeld.)

1, trunk of the facial ; 2, posterior auricular nerve; 3, branch which it receives from the cervical plemut; 4,
occipital branch; 5, 6, branches to the muscles of the ear; 7, digastric branches; 8, branch to tin- *1>/lo-
hyoid muscle; 9, superior terminal branch; 10, temporal branches; \\, frontal branches ; \->, In-n
tJie orbicularis palpebrarum ; 13, nasal, or suborbital branches; 14, buccal branches; 1">. inffrior termi-
nal branch; 1C, mental branches; 17, cervical branches; 18, superficial temporal nerve (branch of the fifth);
19, 20, frontal nerves (branches of the fifth); 21, 22, 23, 24, 25, 26, 27, branches of the fifth; 28, 29, 30, 81, 32,
branches of the cervical nerves.

aifected upon the same side, and not upon the side of the hemiplegia. In view of these
facts, the remarkable phenomenon of hemiplegia upon one side and facial paralysis upon
the other is regarded as indicating, with tolerable certainty, that the injury to the brain has
occurred upon the same side as the facial paralysis, either within or posterior to the pons
Varolii. It is unnecessary to enter into a farther discussion of these facts, which are

620 NERVOUS SYSTEM.

accepted by nearly all writers upon diseases of the nervous system and may be regarded
as settled ; and the only question is, how far they can be explained by the anatomy of
the parts.

As we have just seen, the fibres of origin of the facial have been traced to the floor
of the fourth ventricle, where a few decussate, but the rest are lost. The question now
is, whether or not the fibres pass up through the pons and decussate above, as the patho-
logical facts just noted would seem to indicate. Anatomical researches upon this point
are entirely unsatisfactory ; and the existence of such a decussation has never been clearly
demonstrated. The pathological observations, nevertheless, remain ; and, however indefi-
nite anatomical researches may have been, there can be no doubt that lesions in one-half
of the pons affect the facial upon the same side, while lesions above have a crossed
action. The most that we can say upon this point is, that it is a reasonable inference
from pathological facts that the nerves decussate anterior to the pons.

It will be only necessary to describe in a general way the course of the fibres of dis-
tribution of the facial. The main root of the facial, the auditory nerve, and the delicate
intermediary nerve of Wrisberg pass together into the internal auditory meatus. At the
bottom of the meatus, the facial and the nerve of Wrisberg enter the aquasductus Fallopii,
following its course through the petrous portion of the temporal bone. In the aqueduct,
the nerve of Wrisberg presents a little ganglioform enlargement, of a reddish color, which
has been shown to contain nerve-cells. The main root and the intermediary nerve then
unite and form the common trunk of the facial, which emerges from the cranial cavity
by the stylo-mastoid foramen.

In the aqua3ductus Fallopii, the facial gives off numerous branches, as follows :

1. The large petrosal branch is given off at the ganglioform enlargement and goes
to Meckel's ganglion.

2. The small petrosal branch is given off at the ganglioform enlargement or a very
short distance beyond it, and passes to the otic ganglion.

3. A small branch, the tympanic, is distributed to the stapedius muscle.

4. The chorda tympani, a branch of great physiological interest, passes through the
cavity of the tympanum and joins the lingual branch of the inferior maxillary division
of the fifth as it passes between the two pterygoid muscles, with which nerve it becomes
closely united.

5. Opposite to the point of origin of the chorda tympani, a communicating branch
passes between the facial and the pneumogastric, connecting these nerves by a double
inosculation.

The five branches above described are given of in the aquaaductus Fallopii. The fol-
lowing branches are given off after the nerve has emerged from the cranial cavity :

1. Just after the facial has passed out at the stylo-niastoid foramen, it sends a small
communicating branch to the glosso-pharyngeal nerve. According to Sappey, this
branch is sometimes wanting.

2. The posterior auricular nerve is given off by the facial a little below the stylo-
mastoid foramen. Its superior branch is distributed to the retrahens aurem and the
attollens aurem. In its course, this nerve receives a communicating branch of consider-
able size from the cervical plexus, by the auricularis magnus. It sends some filaments
to the integument. The inferior, or occipital branch, the larger of the two, is dis-
tributed to the occipital portion of the occipito-frontalis muscle and to the integument.

3. The digastric branch is given off near the root of the posterior auricular. It is
distributed to the posterior belly of the digastric muscle. In its course, it anastomoses
with filaments from the glosso-pharyngeal nerve. From the plexus formed by this anas-
tomosis, filaments are given off to the digastric and to the stylo-hyoid muscle.

4. Near the stylo-mastoid foramen, a small branch is given off, which is distributed
exclusively to the stylo-hyoid muscle.

5. Near the stylo-mastoid foramen, or sometimes a little above it, a long and exceed-

FACIAL NERVE, OR NERVE OF EXPRESSION. 621

ingly delicate branch is given off, which is not noticed in most works on anatomy. It is
described, however, by Hirschfeld, under the name of the lingual branch. It passes
behind the stylo-pharyngeal muscle, and then by the sides of the pharynx to the base
of the tongue. In its course, it receives one or two branches from the glosso-pharyngeal
nerve, which are nearly as large as the original branch from the facial. As it passes to
the base of the tongue, it anastomoses again by numerous filaments with the glosso-
pharyngeal. It then sends filaments of distribution to the mucous membrane, and finally
passes to the stylo-glossus and the palato-glossus muscle.

Having given off these branches, the trunk of the facial passes through the parotid
gland, dividing into its two great terminal branches:

1. The temporo -facial branch, the larger, passes upward and forward to be distrib-
uted to the superficial muscles of the upper part of the face ; viz., the attrahens aurem,
the frontal portion of the occipito-frontalis, the obicularis palpebrarum, corrugator super-
cilii, pyramidalis nasi, levator labii superioris, levator labii superioris alaeque nasi, the
dilators and compressors of the nose, part of the buccinator, the levator anguli oris, and
the zygomatic muscles. In its course, it receives branches of communication from the
auriculo-temporal branch of the inferior maxillary nerve. It joins also with the temporal
branch of the superior maxillary and with branches of the ophthalmic. In its course, it
thus becomes a mixed nerve and is distributed in part to integument.

2. The cervico-facial nerve passes downward and forward to supply the buccinator,
orbicularis oris, risorius, levator labii inferioris, depressor labii iuferioris, depressor anguli
oris, and platysma.

Summary of the Anastomoses and Distribution of the Facial. — In the aquaeductus
Fallopii, filaments of communication go to Meckel's ganglion and the otic ganglion of
the sympathetic. The chorda tympani joins the lingual branch of the inferior maxil-
lary division of the fifth. A branch is also sent to the pneumogastric. After the nerve
has passed out by the stylo-mastoid foramen, it sends a communicating branch to the
glosso-pharyngeal, and receives a branch from the auricularis magnus. It anastomoses,
also, outside of the cranium, with the glosso-pharyngeal. In the course of the nerve, it
receives anastomosing filaments from the three great divisions of the fifth.

It is thus seen that the facial, in its course, receives numerous filaments from the great
sensitive nerve of the face. Certain of its fibres of distribution go to integument.

The muscles supplied by the facial are the stapedius, and probably the tensor tyiri
pani, of the internal ear, the muscles of the external ear, the occipito-frontalis, the pos-
terior belly of the digastric, the stylo-hyoid, the stylo-glossus, and the palato-glossus.
The two great branches of distribution, the temporo-facial and the cervico-facial, are
distributed to all of the superficial muscles of the face, leaving the deep muscles, or the
muscles of mastication, to be supplied by the motor root of the fifth. In addition, it
supplies in part the platysma myoides.

Properties and Functions of the Facial Nerve. — It has long been recognized that the
facial is the motor nerve of the superficial muscles of the face, and that its division pro-
duces paralysis of motion and no marked effects upon sensation. It is evident, also,
from the numerous communications of the facial with the fifth, that it probably contains
in its course sensitive fibres. Indeed, all who have operated upon this nerve have found
that it is slightly sensitive after it has emerged from the cranial cavity. It is a question,
however, of great importance to determine whether or not the facial be endowed with
sensibility by virtue of its own fibres of origin. The main root is evidently from the
motor tract, resembles the anterior roots of the spinal nerves, and is distributed to mus-
cles ; but this is joined by the intermediary nerve of Wrisberir, which presents a small
enlargement, undoubtedly containing nerve-cells, somewhat analogous to the ganglia
upon the posterior roots of the spinal nerves.

Direct observations upon the properties of the facial as it penetrates the auditory

622

NERVOUS SYSTEM.

canal, and before it has received any anastomosing branches from sensitive nerves, must
be to a certain extent unsatisfactory. All who have experimented upon the nerves know
that the pain and depression which attend so serious an operation as that of exposing
the roots of a nerve in the cranial cavity are sufficient to render it doubtful whether the
parts be in a condition to exhibit a slight degree of sensibility, which the nerves may
possess when perfectly normal. Magendie and Bernard, who have exposed the roots of
origin of the facial, state unreservedly that they are absolutely insensible ; but Longet
very justly remarks that the conditions under which such observations are made have
not been, in his hands, sufficiently favorable to admit of a rigorous conclusion upon this
point. The testimony of direct experimentation is in favor of the insensibility of the
facial at its origin. It is true that the intermediary nerve of Wrisberg has a certain ana-
tomical resemblance to the sensitive nerves, chiefly by virtue of its ganglioform enlarge-
ment ; but direct experiments are wanting to show that it is actually sensitive. In view
of this fact, it is impossible to reason conclusively from its anatomical characters alone.

The most convenient way to consider the functions of the facial will be to take up
seriatim the properties and distribution of its different branches.

Functions of the Branches of the Facial within the Aqueduct of Fallopius. — The first
branch, the large petrosal, is the motor root of Meckel's ganglion. This will be referred
to again in connection with the sympathetic system. The second branch, the small petro-
sal, is one of the motor roots of the otic ganglion of the sympathetic. The third branch,
the tympanic, is distributed exclusively to the stapedius muscle. The seepnd and third
branches will be again considered in connection with the physiology of the internal ear.
The fourth branch, the chorda tympani, is so important that it demands special consid-
eration. The fifth branch is given off opposite the origin of the chorda tympani and
passes to the pneumogastric, to which nerve it probably supplies motor filaments. We
have already seen, in studying the properties of the roots of the facial, that, in this
branch, sensory filaments pass from the pneumogastric and constitute a part of the sen-
sory connections of the facial.

Functions of the Chorda Tympani. — This branch passes between the bones of the ear
and through the tympanic cavity to the lingual branch of the inferior maxillary division

of the fifth, which it joins at an acute angle,
between the pterygoid muscles. It has
been a question whether this nerve be
simply enclosed in the sheath of the lingual
branch of the fifth or be so closely con-
nected with it that it cannot be traced to
a distinct distribution. Upon this point
we are disposed to adopt the opinion of
Sappey, who, as the result of minute dis-
sections, regards the union as complete,
" fibril to fibril." As regards the portion
of the facial which furnishes the filaments
of the chorda tympani, it is impossible to
determine anatomically whether these
come from the main root or from the in-
FIG. 202.— Chorda-timpani nerve. (Hirschfeid.) termediary nerve of Wrisberg, as the fibres

1, 2, 3, 4, facial nerve passing through the aquseductus Fal- /» , i

lopii; 5, gangiioform enlargement; 6, great petrosal of these roots are closely united before the

nerve; 7, spheno-palatine ganglion; 8, small petrosal P>,orfla tvmnflni k O-IVPTI off

nerve; 9, chorda tympani; 10, 11, 12, 13, various ua tyinpdni on.

branches of the facial; 14, 14, 15, glosso-pharyngeal The Only questions that we propose to

nerve.

consider in this connection relate to the

functions of the chorda tympani as a nerve of gustation, and as it influences the secretion
of the submaxillary gland.

There can be no doubt with regard to the influence of the chorda tympani upon the

FACIAL NERVE, OR NERVE OF EXPRESSION. 623

sense of taste in the anterior portion of the tongue. Without citing all of the experi- \
ments and pathological observations bearing upon this question, it is sufficient to state 1
that, in cases of disease or injury in which the root of the facial is involved so that the
chorda tyinpani is paralyzed, in addition to the ordinary phenomena of paralysis of the
superficial muscles of the face, there is loss of taste in the anterior portion of the tongue
upon the side corresponding to the lesion. Numerous cases of this kind are quoted in
works on physiology, which will be referred to more fully in connection with the subject
of gustation.

In 1863, we had under observation, for several months, a soldier who received a gun-
shot-wound, the ball passing through the head, entering just above the ala of the nose upon
the left side and emerging behind the mastoid process of the right temporal bone. The
wound was nearly healed while he was under observation, and the usual symptoms of
complete facial paralysis were manifested upon the right side. The buccinator and the
orbicularis oculi were completely paralyzed. Vision in the right eye was slightly im-
paired, but was improving. The hearing was perfect, and there were no abnormal phe-
nomena except those apparently due to injury of the facial. The sense of taste was
entirely abolished in the anterior portion of the tongue upon the right side. Experiments
upon this point were repeatedly made with salt, pepper, and other sapid substances. This
patient was exhibited in two successive years to the class at the Bellevue Hospital Medi-
cal College, when the above-mentioned facts were demonstrated.

Physiologists have observed loss of taste in the anterior portion of the tongue, in
dogs, cats, and other animals, following section of the root of the facial or of the chorda
tympani. Some observers, it is true, have failed to note the phenomena satisfactorily,
and there is some difference of opinion with regard to the real origin of the gustatory
filaments ; but the fact that the chorda tympani influences the taste can hardly be doubted.
Adopting this view, we shall defer the full consideration of the functions of the chorda
tympani until we come to treat of the special sense of taste.

Schiff, in 1851, was the first to note the influence of the chorda tympani upon the
secretion of the submaxillary gland. In his experiments, the chorda tympani was
exposed and the flow of the submaxillary saliva noted. Upon division of the chorda
tympani, the flow of saliva was momentarily increased, but was soon arrested ; and sub-
sequently, stimulation of the gustatory sense failed to induce secretion, as it does when
the nerve is intact. Similar experiments, upon a much more extended scale, were made
by Bernard, in the following way :

The duct of the submaxillary gland was exposed in a dog, and into it was fixed a
silver canula. The nervous filaments going to the gland from the lingual branch of the
fifth were then isolated. A little vinegar introduced into the mouth caused an abundant
flow of saliva from the tube. The chorda tympani was then divided, by introducing a
sharp instrument through the membrane into the tympanic cavity. After division of the
nerve, the introduction of vinegar into the mouth failed to excite the salivary secretion.
From this and similar experiments, Bernard concludes that the chorda tympani is the
motor nerve of the submaxillary gland. After having arrested the secretion by section
of the chorda tympani, the action of the gland was excited by galvanization of the pe-
ripheral end of the nerve. Section of the facial after its passage out of the stylo-mastoid
foramen did not arrest the action of the parotid ; but section of the nerve within the cra-
nium arrested the secretion, both of the parotid and submaxillary.

These observations show conclusively that the facial, either through branches from
its proper roots or its filaments of communication with other nerves, regulates the secre-
tion of at least two of the salivary glands.

Influence of Various Branches of the Facial upon the Morcmcnt* of the Palate and
Uvula. — There can be little doubt that filaments from the facial animate certain of the
movements of the velum palati and uvula. It has been observed that, in certain cases
of facial paralysis, the palate upon one side is perfectly flaccid and the uvula is drawn to

624 NEKVOUS SYSTEM.

the opposite side ; but these phenomena do not occur unless the nerve be affected at its
root or within the aquseductus Fallopii. It is true that the uvula is frequently drawn to
one side or the other in persons unaifected with facial paralysis, but it is none the less
certain that it is deviated as a consequence of paralysis of the facial in some instances.

Direct experiments upon the roots of the facial have not been followed by uniform
results. Debrou mentions one experiment in which galvanization of the facial within
the cranial cavity produced decided contraction of the muscles of the palate ; but, in
four others, the results were negative. Nuhn, however, produced contractions of these
muscles by galvanization of the nerve in the cranium in a man immediately after decapi-
tation. The experiments of Bernard upon this point are the most conclusive ; but while
they show, beyond a doubt, that the facial animates the movements of the soft palate,
they do not indicate the course of the filaments from the nerve to the muscles. Jn these
experiments, made in connection with M. Davaine, the whole of the velum palati was
exposed in a large-sized dog, by cutting through the hyoid bone. The trunk of the
glosso-pharyngeal nerve was then exposed in the neck, near its point of emergence at
the posterior foramen lacerum, and the animal was killed by section of the spinal cord
just below the origin of the cranial nerves. This being done, the glosso-pharyngeal was
galvanized, which produced violent contractions of the velum, the pillars of the fauces,
and a part of the pharynx, upon one side. The nerve was then divided, and galvanization
was applied to its peripheral end without producing any movement in the velum. The
central end was then galvanized, when the contractions were as vigorous as when the
nerve was intact. This result would lead to the supposition that contractions of the
muscles of the palate following galvanization of the glosso-pharyngeal are reflex and not
due to the direct action of filaments of distribution from this nerve. In a second experi-
ment, the parts were, exposed in the same way, and, in addition, the facial was divided
upon the right side at its entrance into the internal auditory canal. The glosso-pharyn-
geal nerve was then galvanized upon the side on which the facial had been divided, with
the effect of producing movements of the pillars of the fauces, but not of the velum
palati itself. The glosso-pharyngeal was then galvanized upon the side on which the
facial was intact, which produced movements of the velum the same as in the first ex-
periment. Galvanization of the pneumogastric, the sublingual, and the lingual branch
of the fifth, failed to produce movements of the velum.

" The first experiment proves that the glosso-pharyngeal nerve is not the motor nerve
of the velum palati, but that it induces reflex movements by the excitation which it
transmits to the nervous centre, an excitation which is carried to the parts by another
nerve.

" The second experiment proves that the reflex movements of the velum palati, in-
duced by the excitation of the glosso-pharyngeal, are in part transmitted by the facial
nerve, the movements of the pillars not being produced by filaments belonging to this
nerve."

Bernard also noted a fact, which has sometimes been observed in cases of facial
paralysis, that the point of the tongue is deviated after section of the facial ; which is
explained by the presence of a filament described by Hirschfeld, going from the facial to
the tongue.

As we before remarked, the experiments of Bernard do not indicate the mode of
communication between the facial and the muscles of the palate. Longet regards the
filaments of the facial which influence the levator palati and azygos uvulse muscles as
derived from the large petrosal branch of the nerve, passing to the muscles through
MeckeFs ganglion, the filaments to the palato-glossus and the palato-pharyngeus being
given off from the glosso-pharyngeal, but originally coming from an anastomosing branch
of the facial. As regards the branches of communication from the glosso-pharyngeal,
Longet mentions a preparation by Richet, in the museum of the ficole de medecine, of
Paris, in which branches of the facial upon one side passed directly to the palato-glossus

FACIAL NERVE, OR NERVE OF EXPRESSION. 625

and the palato-pharyngeus, without any connection with the glosso-pharyngeal nerve.
In our anatomical description of the branches of the facial, we have already noted a
filament, described by Hirschfeld, which passes to the stylo-glossus and palato-glossus
muscles. This is the filament affected in deviation of the point of the tongue.

In view of the pathological examples of paralysis of the palate and uvula in certain
cases of facial palsy, the frequent occurrence of contractions of the muscles of these
parts upon galvanization of the facial, and the reflex action through the glosso-pharyn-
geal and the facial, there can be little doubt that the muscles of the palate and uvula are
animated by filaments derived from the seventh nerve. The effects of paralysis of these
muscles are manifested by more or less difficulty in deglutition and in the pronunciation
of certain words, with great clifficulty in the expulsion of mucus collected in the back
part of the mouth and the pharynx.

Functions of the External Branches of the Facial. — The general function of the
branches of the facial going to the superficial muscles of the face is sufficiently evident,
in view of our present knowledge of the distribution of these branches and the general
properties of the nerve. Throughout the writings of Sir Charles Bell, the facial is
spoken of as the " respiratory nerve of the face." It is now recognized as the nerve
which presides over the movements of the superficial muscles of the face, not including
those directly concerned in the act of mastication. This being its general function, it is
easy to assign to each of what may be termed the external branches of the facial its
particular office.

Just after the facial nerve has passed out at the stylo-mastoid foramen, it sends to the
glosso-pharyngeal the communicating branch, the functions of which we have just con-
sidered in connection with the movements of the palate.

The posterior auricular branch, becoming sensitive by the addition of filaments from
the cervical plexus, gives sensibility to the integument on the back part of the ear and
over the occipital portion of the occipito-frontalis muscle. It animates the retrahens
and the attollens aurem, muscles but little developed in man, but very important in cer-
tain of the inferior animals. It also animates the posterior portion of the occipito-fron-
talis muscle.

The branches distributed to the posterior belly of the digastric and to the stylo-hyoid
muscle simply animate these muscles, one of the uses of which is to assist in deglutition.
The same may be said of the filaments that go to the stylo-glossus.

The two great branches distributed upon the face after the trunk of the nerve has
passed through the parotid gland have the most prominent function. Both of these
branches are somewhat sensitive, from their connections with other nerves, and are dis-
tributed in small part to integument.

The temporo-facial branch animates all of the muscles of the upper part of the face.
In complete paralysis of this branch, the eye is constantly open, even during sleep, from
paralysis of tho orbicularis muscle. In cases of long standing, the globe of the eye may
become inflamed from constant exposure, from abolition of the movements of winking by
which the tears are distributed over its surface and little foreign particles are removed,
and, in short, from absence of the protective action of the lids. In these cases, the
lower lid may become slightly everted. The frontal portion of the occipito-frontalis,
the attrahens aurem, and the corrugator supercilii muscles, are also paralyzed. The
most prominent symptom of paralysis of these muscles is inability to corrugate the brow
upon one side, as in frowning.

Paralysis of the muscles that dilate the nostrils has been shown to have an important
influence upon respiration through the nose. It was the synchronism between the art-
of dilatation of the nostrils and the movements of inspiration which first led Sir Charles
Bell to regard the facial as a respiratory nerve. In instances of complete paralysis of
the nostril of one side, there is frequently some difficulty in inspiration. Sir Charle8
Bell refers to a case in which, when " the patient lay with the sound side against the
40

626

NERVOUS SYSTEM.

pillow, he was under the necessity of holding the paralytic nostril open with the fingers,
in order to breathe freely." In the horse, the movements of the nostrils are essential to
respiration, the animal being unable to breathe through the mouth. When both facial
nerves are divided in this animal, the nostrils collapse and are occluded with each effort
at inspiration, and death takes place from suffocation.

Sir Charles Bell and others have also noted an interference with olfaction, due to the
inability to inhale with one nostril, in cases of facial paralysis. The influence of the nerve
in the act of conveying odorous emanations to the olfactory membrane is sufficiently evi-
dent after what we have remarked concerning the action of the facial in respiration.

The effects of paralysis of the other superficial muscles of the face are manifested in
the distortion of the features, from the unopposed action of the muscles upon the sound
side ; a phenomenon which is sufficiently familiar to the practical physician. When
facial palsy affects one side and is complete, the angle of the mouth is drawn to the
opposite side, the eye upon the affected side is widely and permanently opened even
during sleep, and the face has upon that side a peculiarly expressionless appearance.
When a patient affected in this way smiles or attempts to grimace, the distortion is
much increased. The lips are paralyzed upon one side, which sometimes causes a flow
of saliva from the corner of the mouth. In the lower animals that use the lips in pre-
hension, paralysis of these parts interferes considerably with the taking of food. The
flaccidity of the paralyzed lips and cheek in the human subject sometimes causes a puff-
ing movement with each act of expiration, as if the patient were smoking a pipe.

FIG. 203.

FIG. 204.

FIG. 205.

FIG. 206.

FIG. 20T.

FIG. 208.

Expressions of the face produced by contraction of the muscles under electrical excitation. (Le Bon, after

Duchenne.)

Fig. 203, front view of the face in repose.
Fig. 204, profile view.

Fig. 205, expression of laughter upon one side, produced by contraction of the zygomaticus major.
Fig. 20fi, expression of fear, produced by contraction of the frontal muscle and the depressors of the lower jaw.
Fig. 20T, expression of fear, profile view.

Fig. 208, expression of fear and great pain, produced by contraction of the corrugator supercilii and the depressors
of the lower jaw.

We have already seen that the buccinator is not supplied by filaments from the nerve
of mastication, but is animated solely by the facial. Paralysis of this muscle interferes
materially with mastication, from a tendency to accumulation of the food between the
teeth and the cheek. Patients complain of this difficulty, and they sometimes keep the

SPINAL ACCESSORY NERVE. 627

food between the teeth by pressure with the hand. In the rare instances in which both
facial nerves are paralyzed, there is very great difficulty in mastication, from the cause
just mentioned.

The functions of the external branches of the facial are thus sufficiently simple ; and
it is only as its deep branches affect the taste, the movements of deglutition, etc., that it
is difficult to ascertain their exact office. As this is the nerve of expression of the face,
it is in the human subject that the phenomena attending its paralysis are most prominent.
When both sides are affected, the appearance is most remarkable, the face being abso-
lutely expressionless and looking as if it had been covered with a mask.

Spinal Accessory and Sublingual Nerves.

A description of the properties and functions of the spinal accessory and the sublin-
gual completes the physiological history of the motor nerves emerging from the cranial
cavity. The functions of these nerves are important, and, in the case of the spinal
accessory, they possess considerable interest, from the fact that physiological investigations
have, only within a few years, determined the significance of certain of its anatomical
relations. As we have done in studying the other motor nerves, we shall treat succes-
sively of their anatomical relations, general properties and functions.

Spinal Accessor]/ Nerve. (Third Division of the Eighth Nerve.)

The spinal accessory nerve, from the remarkable extent of its origin, its important
anastomoses with other nerves, and its curious course and distribution, has long engaged
the attention of anatomists and physiologists, who have advanced many theories writh
regard to its office. We shall content ourselves, however, with a simple description of
its anatomy as it appears from late researches, and shall begin its physiological history
with comparatively recent experiments, which alone have advanced our positive knowl-
edge of its properties.

Physiological Anatomy of the Spinal Accessory. — The origin of this nerve is very, exten-
sive. A certain portion arises from the lower half of the medulla oblongata, and the rest
takes its origin below, from the upper two-thirds of the cervical portion of the spinal
cord. That portion of the root which arises from the medulla oblongata is called, by
the French, the bulbar portion, the roots from the cord constituting the spinal portion.
Inasmuch as there is a marked difference between the functions of these two portions,
the anatomical distinction just mentioned is important.

The superior roots arise by four or five filaments from the lower half of the medulla
oblongata, below the origin of the pneumogastrics. These filaments of origin, in prepara-
tions hardened by prolonged immersion in alcohol, are shown to be connected with the
lateral portion of the medulla, and not with the posterior columns. Their origin seems,
therefore, to be from the motor tract.

The spinal portion of the nerve arises from the upper part of the cervical division
of the spinal cord, between the anterior and posterior roots of the upper four or five
cervical nerves. The filaments of origin are from six to eight in number. The most
inferior of these is generally single, the other filaments being frequently arranged in
pairs. These take their origin from the lateral portion of the cord, rather nearer the
posterior median line than the roots from the medulla oblonpata.

Following the nerve from its most inferior filament of origin upward, it gradually
increases in size by union with its other roots, enters the cranial cavity by the foramen
magnum, and passes to the jugular foramen, by which it emerges, in connection with the
glosso-pharyngeal, the pneumogastric, and the internal jugular vein.

In its course, the spinal accessory anastomoses with several nerves. Just as it enters
the cranial cavity, it receives filaments of communication from the posterior roots of the

628

NERVOUS SYSTEM.

upper two cervical nerves. These filaments, however, are not constant. It frequently,
though not constantly, sends a few filaments to the superior ganglion, or the ganglion of
the root of the pneumogastric. After it has emerged by the jugular foramen, it sends a
branch of considerable size to the pneumogastric, from which nerve it also receives a few
filaments of communication. This branch will be again referred to in connection with
the distribution of the nerve. In its course, it also receives filaments of communication
from the anterior branches of the second, third, and fourth cervical nerves.

In its distribution, the spinal accessory presents two branches. The first, or anasto-
motic branch, passes to the pneumogastric just below the plexiform enlargement which
is sometimes called the ganglion of the trunk of the pneumogastric.

The internal, or anastomotic branch, is composed principally, if not entirely, of the
filaments that take their origin from the medulla oblongata. As it joins the pneumogas-
tric, it subdivides into two smaller branches. The first of these forms a portion of the

pharyngeal branch of the pneumogastric. The
second becomes intimately united with the
pneumogastric, lying at its posterior portion,
and furnishes filaments to the inferior, or re-
current laryngeal branch, which is distributed
to all of the muscles of the larynx except the
crico-thyroid. The passage of the filaments
from the spinal accessory to the pharyngeal
branch of the pneumogastric is easily observed ;
but the fact that filaments from this nerve pass
to the larynx by the recurrent laryngeal has
been ascertained only by physiological experi-
ments.

The external, or large branch of the spinal
accessory, called the muscular branch, pene-
trates and passes through the posterior portion
of the upper third of the sterno-cleido-mastoid
muscle, goes to the anterior surface of the trape-
zius, which muscle receives its ultimate branches
of distribution. In its passage through the
sterno-cleido-mastoid, it joins with branches
from the second and third cervical nerves and
sends filaments of distribution to the muscle.
Although the two muscles just mentioned re-
ceive numerous motor filaments from the spinal
accessory, they are also supplied from the cer-
vical nerves ; and, consequently, they are not
entirely paralyzed when the spinal accessory is
divided.

FIG. 209. — Spinal accessory nerve. (Hirschfeld.)
1, trunk of the facial nerve ; 2. 2, glosso-pharyngeal
nerve; 3, 3, pneumogastric; 4, 4, 4, trunk, of
the spinal accessory ; 5, sublingual nerve ; '6,
superior cervical ganglion ; T. T. anastomosis of
the first two cervical nerves ; 8. carotid branch of
the sympathetic; 9, 10, 11, 12, 13, branches of the
glosso-pharyngeal ; 14, 15, branches of the fa-
cial; 16, otic ganglion; 17, auricular branch of
the pneumogastric; 18, anastomosing branch
from the spinal accessory to the pneumogas-
tric; 19, anastomosis of the first pair of cervical
nerves with the sublingual ; 20, anastomosis of

Properties and Functions of the Spinal Ac-
cessory.— Notwithstanding the great difficulty in
exposing and in operating upon the roots of the
spinal accessory, it has been demonstrated that
their galvanization produces convulsive move-
ments in certain muscles. The most satisfactory
experiments with relation to the general proper-
ties of the roots were made by Bernard. This physiologist cut through the occipito-
atloid membranes and galvanized the filaments within the spinal canal. By galvanizing
the filaments arising from the medulla oblongata, he produced contractions of the mus-

superior laryngeal nerve ; 23, external laryngeal
nerve ; 24, middle cervical ganglion.

SPINAL ACCESSORY NERVE. 629

cles of the pharynx and larynx and no movements of the sterno-mastoid and trapezius.
Galvanization of the roots arising from the spinal cord produced movements of the two
muscles just mentioned and absolutely no movements in the larynx. In view of these
experiments, it is evident that the true filaments of origin of the spinal accessory are
motor ; and it is farther evident that the filaments from the medulla oblongata are dis-
tributed to the muscles of the pharynx and larynx, while the filaments from the spinal
cord go to the sterno-cleido-mastoid and trapezius.

The trunk of the spinal accessory, after the nerve has passed out of the cranial cavity,
is endowed with a certain degree of sensibility. If the nerve be divided, the peripheral
extremity manifests recurrent sensibility, but the central end is also sensible, proba-
bly from direct filaments of communication from the cervical nerves and the pneumo-
gastric. As we have remarked, however, in treating of the properties of some other of
the cranial nerves, it is exceedingly difficult to note satisfactorily a slight degree of sensi-
bility in nerves that can be exposed only by a tedious and painful operation.

The functions of the external, or muscular branch of the spinal accessory are suffi-
ciently evident ; and the effects of the destruction of the nerves on both sides, as far as
this branch is concerned, simply resolve themselves into the phenomena due to partial
paralysis of the sterno-mastoid and trapezius; but the functions of the branch which
joins the pneumogastric are much more complex.

Functions of the Internal Branch from the Spinal Accessory to the Pneumogastric. —
Bischoff attempted to ascertain the functions of this branch by dividing the roots of the
spinal accessory upon both sides in a living animal. The results of his experiments may be
stated in a very few words : He attempted to divide all of the roots of the nerves upon
both sides by dissecting down to the occipito-atloid space and penetrating into the cavity
of the spinal canal. In the first three experiments upon dogs, the animals died so soon
after section of the nerves, that no satisfactory results were obtained. ID two succeed-
ing experiments upon dogs, the animals recovered. After division of the nerves, the voice
became hoarse, but a few weeks later, it became normal. On killing the animals, an
examination of the parts showed that some of the filaments of origin had not been
divided. An experiment was then made upon a goat, but this was unsatisfactory, as the
roots were not completely divided. Finally, another experiment was made upon a goat.
In this the results were more satisfactory. After division of the nerve upon one side,
the voice became hoarse. As the filaments were divided upon the opposite side, the
voice was enfeebled, until finally it became extinct. The sound emitted afterward was
one which could in nowise be called voice ("qui neutiquam vox appellari potuit "). This
experiment was made in the presence of Tiedemann and Seubertus and was not re-
peated.

Bernard, whose ingenious experiments determined exactly the influence of the spinal
accessory over the vocal movements of the larynx, first repeated the experiments of Bis-
choff; but the animals operated upon died so soon, from haemorrhage or other causes,
that his observations were riot satisfactory. After many unsuccessful trials, he succeeded
in overcoming all difficulties, by following the trunk of the nerve back to the jugular
foramen, seizing it here with a strong pair of forceps, and drawing it out by the roots.
This operation is difficult, but we have several times performed it with entire success,
and have verified, in every regard, the facts observed by Bernard. Within the last year,
the excellent assistant to the chair of Physiology at the Bellevue Hospital Medical Col-
lege, Dr. C. F. Roberts, has succeeded in extirpating these nerves for class-demon-
strations. The operation is generally most successful in cats, although Bernard has
succeeded frequently in other animals.

The operative procedure employed by Bernard is the following: The trunk of the
nerve is exposed as it passes through the sterno-cleido-mastoid muscle. It is then fol-
lowed up by careful dissection, avoiding blood-vessels as much as possible, to the poste-
rior foramen lacerura. when the sublingual is seen crossing the course of the pneumo-

630 NERVOUS SYSTEM.

gastric. It is here that the anastomotic branch leaves the spinal accessory to go to the
pneumogastric. At this point, the external branch, with the anastomosing branch, is
seized with a pair of rather broad-,billed forceps, and gentle but firm traction is applied
to the entire nerve. Soon there is a cracking sensation conveyed to the hand as the
roots give way, and the nerve may then be drawn out entire. With care, either the fila-
ments of origin from the medulla or those from the cord may be extirpated alone.

When one spinal accessory is extirpated, the vocal sounds are hoarse and unnatural.
When both nerves are torn out, in addition to the disturbance of deglutition and the par-
;ial paralysis of the sterno-mastoid and trapezius muscles, the voice becomes extinct.
Animals operated upon in this way move the jaws and make evident efforts to cry, but
ao vocal sound is emitted. This condition is very striking; and, inasmuch as Bernard
las kept animals, with both nerves extirpated, for months, the question of the function
of these nerves in phonation may now be regarded as definitively settled.

It remains now to consider the experimental facts with regard to the influence of the
different filaments of origin, of the spinal accessory upon the voice. These are simple and
entirely conclusive ; and they are due exclusively to the researches of Bernard. This
experimenter found that division of the roots of origin from the spinal cord not only did
not affect the voice, but sometimes it seemed to render it clearer; but that division of the
roots of origin from the medulla oblongata abolished the voice, although the inferior roots
were intact.

It is not necessary to discuss the action of the muscles of the larynx in phonation, as
this subject has already been considered in connection with the voice. The experiments
that have demonstrated the influence of the spinal accessory nerve over these muscles
have pointed out the destination of the fibres that join the pneumogastric, which could
never have been done so satisfactorily by dissection. They have shown farther that
the movements involved in phonation are more or less independent of the respiratory
movements of the larynx.

If the larynx be exposed in a living animal, with all its nervous connections intact,
it will be seen to open widely during inspiration, being passive in expiration. The wide
opening of the glottis at this time is due to the fact that, after the operation, respiration
is usually more or less labored ; but, if we carefully observe the parts when the respira-
tory acts are perfectly tranquil, the movements of the glottis seem to be very slight.
The larynx is then permanently opened to a moderate degree, but the chink of the glottis
is slightly dilated with each expiration. If the recurrent laryngeal nerves, which are
distributed to all of the muscles of the larynx except the crico-thyroid, be now divided
upon both sides, the larynx is entirely paralyzed, and in cats and young animals, in which
the cartilages are soft and flexible, the parts are occluded by the effort of inspiration, and
death takes place from suffocation. Of course the division of the recurrent laryngeal
nerves abolishes the voice, but it arrests the other movements of the larynx as well.
The distinction thus established between the action of the spinal accessory and of the
recurrent laryngeal nerves was fully illustrated by Bernard, in the following experiments :

In a cat, in which the voice had been completely destroyed by extirpation of both
spinal accessory nerves, the larynx was exposed. The glottis was seen dilated so as to
permit the free passage of air in respiration, the mucous membrane retained its sensi-
bility, and, when the interior of the larynx was irritated, a very slight but ineffectual
effort was made to close the glottis. It was impossible for the animal to approximate
the posterior points of attachment of the vocal cords or to put the cords upon the stretch.
If such irritation be applied to the larynx of an animal with the spinal accessory nerves
intact, the glottis is instantly and firmly closed.

In a cat about five weeks old, both spinal accessory nerves were extirpated, and the
voice was thus destroyed. Two days after, both recurrent laryngeal nerves were divided,
and the animal died almost immediately of suffocation.

These experiments show conclusively that the internal, or communicating branch of

SPINAL ACCESSORY NERVE. 631

the spinal accessory is the nerve which presides over the movements of the larynx in
phonation. The filaments undoubtedly pass to the larynx in greatest part through the
recurrent laryngeal branches of the pneumogastric ; but the recurrent laryngeals also
contain motor filaments from other sources, which latter are chiefly concerned in the
respiratory movements of the glottis.

Influence of the Internal Branch of the Spinal Accessory upon Deglutition. — There
are two ways in which deglutition is affected through this nerve : 1. When the larynx is
paralyzed as a consequence of extirpation of both nerves, the glottis cannot be completely
closed to prevent the entrance of foreign bodies into the air-passages. In rabbits par-
ticularly, it has been noted that particles of food penetrate the trachea and find their
way into the lungs. 2. The spinal accessory furnishes numerous filaments to the pharyn-
geal branch of the pneumogastric, and, through this nerve, it directly affects the muscles
of deglutition ; but the muscles animated in this way by the spinal accessory have a ten-
dency to draw the lips of the glottis together, while they assist in passing the alimentary
bolus into the oesophagus. When these important acts are wanting, there is some diffi-
culty in the process of deglutition itself as well as danger of the passage of foreign
particles into the larynx.

Influence of the Spinal Accessory upon the Heart. — When we come to study the varied
functions of the pneumogastrics, we shall discuss fully the mechanism by which the con-
tractions of the heart are arrested by galvanization of both of these nerves in the neck.
A very curious and interesting observation by Waller has demonstrated that this influ-
ence, whatever be its mechanism, is derived from the spinal accessory and necessarily
comes through its communicating branch. It has been found that a powerful current of
galvanism passed through the pneumogastric upon one side will arrest the action of the
heart. Waller found that, if he extirpated the spinal accessory upon one side, the action
of the heart could not be arrested by galvanizing the pneumogastric upon the same side ;
but this result followed galvanization of the pneumogastric upon the opposite side, on
which the connections with the spinal accessory were intact. These phenomena, how-
ever, could not be observed until from ten to twelve days had elapsed after the extirpa-
tion of the spinal accessory. We have already seen, in treating of the general properties
of the nerves, that the irritability of the motor nerves disappears in about four days after
their separation from the nerve-centres. In the observation just referred to, it seemed
necessary that a sufficient time should elapse after extirpation of the spinal accessory for
the irritability of the filaments that join the pneumogastric to become extinct ; but the
experiment is sufficient to show the direct inhibitory influence of the spinal accessory
upon the heart. This subject will be more fully considered, however, in connection with
the functions of the pneumogastrics.

Functions of the External, or Muscular Branch of the Spinal Accessory. — The most
interesting feature in the recent researches into the functions of the spinal accessory is.
that experimentalists have been able to separate physiologically the internal from the
external branch. Observations have conclusively demonstrated that the internal branch,
and the internal branch only, is directly concerned in the vocal movements of the larynx,
and, to a great extent, in the closure of the glottis during deglutition. It has been noted,
in addition, that animals in which both branches have been extirpated present irregu- j
larity of the movements of the anterior extremities and suffer from shortness of breath I
after violent muscular exertion. The use of the corresponding extremities in the human I
subject is so different, that it is not easy to make a direct application of these experi-
ments ; still, we can draw from them certain inferences with regard to the functions of
the external branch in man.

In prolonged vocal efforts, the vocal cords are put upon the stretch, and the act of
expiration is very different from that in tranquil breathing. In singing, for example, the
shoulders are frequently fixed; and this is done to some extent by the action of the
sterno-cleido-mastoid and the trapezius. We may suppose, then, that the action of the

632 NERVOUS SYSTEM.

branch of the spinal accessory which goes to these muscles has a certain synchronism
with the action of the branch going to the larynx and the pharynx ; the one fixing the
upper part of the chest so that the expulsion of the air through the glottis may be more
nicely regulated by the expiratory muscles, and the other acting upon the vocal cords.

In what is known to physiologists as muscular effort, the glottis is closed, the thorax
is fixed after a full inspiration, and respiration is arrested so long as the effort, if it be
not too prolonged, is continued. The same synchronism, therefore, obtains in this as in
prolonged vocal efforts. In experiments in which the muscular branch only has been
divided, shortness of breath, after violent muscular effort, is observed ; and this is proba-
bly due to the want of synchronous action of the sterno-cleido-mastoid and trapezius.
The irregularity in the movements of progression in animals, in which either both branch-
es or the muscular branches alone have been divided, is due to anatomical peculiarities.
Bernard has observed these irregularities in the dog and the horse, but they are not so
well marked in the cat. There have been no opportunities for illustrating these points
in the human subject.

Sublingual^ or Hypoglossal Nerve. (Ninth Nerve.)

The last of the motor cranial nerves is the sublingual ; and its functions are inti-
mately connected with the physiology of the tongue in deglutition and articulation,
although it is also distributed to certain of the muscles of the neck.

Physiological Anatomy of the Sublingual Nerve. — The apparent origin of the sublin-
gual is from the medulla oblongata, in the groove between the olivary body and the
anterior pyramid, on the line of the anterior roots of the spinal nerves. At this point,
its root is formed of from ten to twelve filaments, which extend from the inferior por-
tion of the olivary body to about the junction of the upper with the middle third.
These filaments of origin are separated into two groups, superior and inferior. From
this apparent origin, the filaments have been traced into the gray matter of the floor
of the fourth ventricle, between the deep origin of the pneumogastric and the glosso-
pharyngeal. Although there is much difference of opinion upon this point, it is probable
that some of the filaments of origin of these nerves decussate in the floor of the fourth
ventricle. The superior and inferior filaments of origin of the nerve unite to form two
bundles, which pass through distinct perforations in the dura mater. These two bundles
then pass into the anterior condyloid foramen and unite into a single trunk as they
emerge from the cranial cavity.

After the sublingual has passed out of the cranial cavity, it anastomoses with several
nerves. It sends a filament of communication to the sympathetic as it branches from
the superior cervical ganglion. Soon after it has passed through the foramen, it sends a
branch to the pneumogastric. It anastomoses by two or three branches with the upper
two cervical nerves, the filaments passing in both directions between the nerves. It
anastomoses with the lingual branch of the fifth, by two or three filaments passing in
both directions.

In its distribution, the sublingual presents several remarkable peculiarities :

Its first branch, the descendens noni, passes down the neck to the sterno-hyoid, ster-
no-thyroid, and omo-hyoid muscles. From its relations with important vessels and
nerves, this branch possesses considerable surgical interest.

The thyro-hyoid branch is distributed to the thyro-hyoid muscle.

The other branches are distributed to the stylo-glossus, hyo-glossus, genio-hyoid, and
genio-hyo-glossus muscles, their terminal filaments going to the intrinsic muscles of the
tongue.

It is thus seen that the sublingual nerve is distributed to all of the muscles in the
infra-hyoid region, the action of which is to depress the larynx and the hyoid bone after

SUBLINGUAL, OR HYPO GLOSSAL NERVE.

C33

the passage of the alimentary bolus through the pharynx ; 'to one of the muscles in the
supra-hyoid region, the genio-hyoid ; to most of the muscles which move the tongue ;
and to the muscular fibres of the tongue itself. The action of these muscles and of the
tongue itself in deglutition has already been fully discussed.

FIG. 210.— Distribution of the sublingual nerve. (Sappey.)

1, root of the fifth nerve ; 2, ganglion of Gasser; 8, 4, 5, 6, T, 9. 10, 12, branches and anastomoses of the fifth nerve ;
11, submaxillary pan;.', lion; 13, anterior belly of the digastric muscle; 14. section of the mylo-hyoid muscle; 15,
glosso-pharynseal nerve; 16, ganglion of Andersch; 17, 18, branches of the glosso-pharyngeal nerve; 19, 19,
pneumogastric; 20, 21, ganglia of the pneumogastric ; 22, 22, superior laryngeal branch of the pneumogastric;
•_':'.. spinal am-ssory nerve ; 24, subUngual nerve; 25, descend ens noni ; 20. tltyro-hyoid branch ; 27, terminal
branches ; 28, two branches, one to the genio-hyo-glossus and the other to the genio-hyoid muscle.

Properties and functions of the Siiiblingual. — There is every reason to believe that j
the sublingual nerve is entirely insensible at its origin from the medulla oblongata. The ,
fuct that it arises from a continuation of the motor tract of the spinal cord and has no
ganglion upon its main root would lead to the supposition that it is an exclusively motor
nerve. In operating upon the roots of the spinal accessory, when the origin of the sub-
lingual is necessarily exposed, Longet has irritated the roots in the dog, without any evi-
dence of pain on the part of the animal. Such experiments, taken in connection with
the anatomical characters of the nerve, render it almost certain that its root is devoid
of sensibility at its origin. All modern experimenters have confirmed the observations
of Mayo and of Magendie, with regard to the sensibility of the sublingual after it has
passed out of the cranial cavity. The anastomoses of this nerve with the upper two
cervical nerves, with the pneumogastric, and with the lingual branch of the fifth, afford
a ready explanation of this fact.

The functions of the sublingual have already been so fully considered under the head
of deglutition, that they need not be discussed elaborately in this connection. We shall
here simply state the phenomena which follow stimulation of the nerve and the division
of both nerves in living animals.

634 NERVOUS SYSTEM.

The sublingual may be easily exposed in the dog by making an incision just below
the border of the lower jaw, dissecting down to the carotid artery and following the
vessel upward until we see the nerve as it crosses its course. On applying a feeble
current of galvanism at this point, there are evidences of sensibility, and the tongue is
moved convulsively at each stimulation.

The phenomena following section of both sublingual nerves point directly to their
function. The most notable fact observed after this operation is, that the movements of
the tongue are entirely lost, while general sensibility and the sense of taste are not affected, j
The phenomena which follow division of these nerves consist simply in loss of power
over the tongue, with considerable difficulty in deglutition. We have repeatedly noted
all of these points and have demonstrated them to medical classes.

In the human subject, the sublingual is usually more or less affected in hemiplegia.
In these cases, as the patient protrudes the tongue the point is .deviated. This is due to
the unopposed action of the genio-hyo-glossus upon the sound side, which, as it pro-
trudes the tongue, directs the point toward the side affected with paralysis.

A disease of rather rare occurrence has lately been described under the name of
glosso-labial paralysis, which is characterized by paralysis of the sublinguals, affecting
also the orbicularis oris and frequently the intrinsic muscles of the larynx. The phe-
nomena referable to the loss of power over the tongue correspond to those observed in
animals after section of the sublingual nerves. Patients affected in this way experience
difficulty in deglutition, and, in addition, we note an interference with articulation, which
cannot be observed in experiments upon animals. We lately had a case of this disease
under observation in the Bellevue Hospital, the phenomena of which were peculiarly
interesting from a physiological point of view. This patient presented complete paraly-
sis of the tongue, with considerable difficulty in deglutition, probably from the tongue-
affection. The orbicularis oris was also paralyzed. The paralysis probably extended
to the intrinsic muscles of the larynx, as little or no vocal sound could be made. The
patient was incapable of articulate language and communicated entirely by signs.

CHAPTER XIX.

SENSORY CRANIAL NERVES.

Trifacial, ortrigeminal nerve— Physiological anatomy of the trifacial— Properties and functions of the trifacial— Divi-
sion of the trifacial within the cranal cavity— Immediate effects of division of the trifacial— Remote effects of
division of the trifacial -Division of the trifacial before and behind the ganglion of Gasser— Communication with
the sympathetic at the canglion of Gasser — Explanation of the phenomena of disordered nutrition after division
of the trifacial — Cases of paralysis of the trifacial in the human subject— Pneumogas trie nerve (second division of
the eighth)— Physiological anatomy— Properties and functions of the pneumogastric— General properties of the
roots — Properties and functions of the auricular nerves — Properties and functions of the pharyngeal nerves —
Properties and functions of the superior laryngeal nerves — Properties and functions of the inferior, or recurrent
laryngeal nerves— Properties and functions of the cardiac nerves, and influence of the pneumogastrics upon the
circulation— Depressor-nerve of the circulation— Properties and functions of the pulmonary branches, and influ-
ence of the pneumogastrics upon respiration — Properties and functions of the oesophageal nerves — Properties and
functions of the abdominal branches.

Trifacial, or Trigeminal Nerve. (Large Root of the Fifth Nerve.)

A SINGLE nerve, the large root of the fifth pair, called the trifacial or the trigeminal,
gives general sensibility to the face and to the head as far back as the vertex. This is one
of the most interesting of the cranial nerves and is one of the first that was experimented
upon by physiologists. It is interesting, not only as the great sensitive nerve of the face,
but from its connections with other nerves and its relations to the organs of special sense.
In studying the physiology of this nerve, we must necessarily begin with its physiological
anatomy.

TRIFACIAL, OR TRIGEMINAL NERVE.

635

Physiological Anatomy of the Trifacial Nerve.— The apparent origin of the large root
of the fifth is from the lateral portion of the pons Varolii, posterior and inferior to the
origin of the small root, from which it is separated by a few transverse fibres of white
substance. The deep origin is far removed from its point of emergence from the encepha-
lon. The roots pass entirely through the substance of the pons, from without inward
and from before backward, without any connection with the fibres of the pons itself. By
this course, it reaches the medulla oblongata, where the roots divide into three bundles.
The anterior bundle passes from behind forward, between the anterior fibres of the pons
and the cerebellar portion of the restiform bodies, to anastomose with the auditory nerve.
The other bundles, which are posterior, pass, the one in the anterior wall of the fourth
ventricle to the lateral tract of the medulla oblongata, and the other, becoming grayish
in color, to the restiform bodies, from which they may be followed as far as the point
of the calamus scriptorius. A few fibres from the two sides decussate at the median line
in the anterior wall of the fourth ventricle. From this origin, the large root of the fifth
passes obliquely upward and forward to the ganglion of Gasser, which is situated in a
depression in the petrous portion of the temporal bone on the internal portion of its ante-
rior face.

FIG. 111.— Principal branches of the, large root of the
fifth nerve. (Robin.)

a, ganglion of Gasser ; a-w. ophthalmic division of
the fifth ; b, ophthalmic ganglion ; c,branch from
the ophthalmic division of the. fifth to the ophthal-
mic ganglion; d< motor oculi communis; e, ca-
rotid ; /, ciliary nerves ; ff, cornea and iris ; cr-7t,
superior maxillary division of the, fifth; i, two
branches from the superior maxillary division
of the fifth to the spheno-palatine ganglion ; .?',
deep petrosal nerve ; fc, filaments from the motor
root of the fifth to the internal muscle of the mal-
leus ; I, naso-palatine ganglion ; m, otic ganglion ;
n, small superficial petrosal nerve ; 0, branches
of the fifth to the submaxiUary ganglion ; p,
branches to the sublingual ganglion ; q, facial
nerve ; r, sympathetic ganglion ; s. nerve of mas-
tication ; £, chorda tym pant, joining the lingual
branch of the fifth ; u, Vidian nerve ; 0, branch
from the motor root to the internal pterygoid mus-
cle ; MJ, branch of the fifth to the lachrymal gland ;
X. bend of the facial nerve ; y. middle meningeal ar-
tery ; 2, filament from the carotid plexus to the
ophthalmic ganglion ; (1 and 2 are not in the figure)
8, external spheno-palatine filaments; 4, spheno-
palatine ganglion ; 5. naso-palatine nerve; f>. ante-
rior palatine nerve ; 7, inferior maxillary division
of the fifth; 8, nerve of'Jacobson.

vnr

FIG. 212.— Ophthalmic division of the fifth. (Hirachfeld.)

1, ganglion of Gasser ; 2, ophthalmic division of the
'fifth; 3 lachrymal branch; 4. frontal branch; ft,
external frontal; 6, internal frontal ; 7, Kupru-
trochUar; 8, nasal branch; 9, external nannf : K».
internal nasal; 11, anterior deep temporal nerve;
12, middle deep temporal nerve : V\ posterior deep
temporal nerve ; 14, origin of the superficial temporal
nerve ; 15, great superficial petrous nerve.

I to XII, roots of the cranial nerves.

The Gasserian ganglion is semilunar in form (sometimes it is called the semilunar
ganglion), with its concavity looking upward and inward. At the ganglion, the nerve
receives filaments of communication from the carotid plexus of the sympathetic. This

636 NERVOUS SYSTEM.

anatomical point is of importance in view of some of the remote effects which follow
division of the fifth nerve through the ganglion in living animals.

It will be necessary only to describe in a general way the numerous branches of dis-
tribution of the fifth nerve, remembering that it is the great sensitive nerve of the face.

At the ganglion of Gasser, from its anterior and external portion, are given off a few
small and unimportant branches to the dura mater and the tentorimn.

From the convex border of the ganglion, the three great branches arise, which have
given to the nerve the name of trifacial or trigeminal. These are : 1, the ophthalmic ;
2, the superior maxillary ; 3, the inferior maxillary. The ophthalmic and the superior
maxillary branch are derived entirely from the sensory root. The inferior maxillary
branch joins with the motor root and forms a mixed nerve.

The ophthalmic branch, the first division of the fifth, is the smallest of the three.
Before it enters the orbit, it receives filaments of communication from the sympathetic,
sends small branches to all of the motor nerves of the eyeball, and gives off a small recur-
rent branch which passes between the layers of the tentorium.

Just before the ophthalmic branch enters the orbit by the sphenoidal fissure, it divides
into three branches ; the lachrymal, frontal, and nasal.

The lachrymal, the smallest of the three, sends a branch to the orbital branch of the
superior maxillary nerve, passes through the lachrymal gland, to which certain of its fila-
ments are distributed, and its terminal filaments go to the conjunctiva and to the integu-
ment of the upper eyelid.

FIG. 213.— Superior maxillary division of the fifth, (Hirschfeld.)

1. ganglion of Gasser; 2, lachrymal branch of the ophthalmic division; 3. superior maxillary division of the fifth;
4, orbital branch; 5, lachrymo-palpebral filament; 6, malar branch; 7, temporal branch; 8, spheno-
palatine ganglion ; 9, Vidian nerve ; 10, great superficial petrosal nerve ; 11, facial nerve ; 12, branch of the
Vidian nerve; 13, anterior and tiro posterior dental branches ; 14, branch to the mucous membrane of the
alveolar processes ; 15, terminal branches of the superior maxillary division; 16, branch of the facial.

The frontal branch, the largest of the three, divides into the supra-trochlear and supra-
orbital nerves. The supra-trochlear passes out of the orbit between the supra-orbital
foramen and the pulley of the superior oblique muscle. It sends in its course a long,
delicate filament to the nasal branch and is finally lost in the integument of the forehead.
The supra-orbital passes through the supra-orbital foramen, sends a few filaments to the
upper eyelid, and supplies the forehead, the anterior and median portions of the scalp,
the mucous membrane of the frontal sinus, and the pericranium covering the frontal and
parietal bones.

The nasal branch, before it penetrates the orbit, gives off a long, delicate filament to
the ophthalmic ganglion, constituting its sensory root. It then gives off the long ciliary

TRIFACIAL, OK TRIGEMINAL NERVE.

637

nerves, which pass to the ciliary muscle and iris. Its trunk finally divides into the external
nasal, or infra-trochlearis, and the internal nasal, or ethmoidal. The infra-trochlearis is
distributed to the integument of the forehead and nose, to the internal surface of the
lower eyelid, the lachrymal sac, and the caruncula. The internal nasal is distributed to
the mucous membrane, and also in part to the integument of the nose.

The superior maxillary branch of the fifth passes out of the cranial cavity by the
foramen rotundum, traverses the infra-orbital canal, and emerges upon the face by the
infra-orbital foramen. Branches from this nerve are given off in the spheno-maxillary
fossa and the infra-orbital canal, before it emerges upon the face. In the spheno-maxil-
lary fossa, the first branch is the orbital, which passes into the orbit, giving off one
branch, the temporal, which passes through the temporal fossa by a foramen in the malar
bone and is distributed to the integument on the temple and the side of the forehead.
Another branch, the malar, which likewise emerges by a foramen in the malar bone, is
distributed to the integument over this bone. In the spheno-maxillary fossa, are also
given off two branches, which pass to the spheno-palatine, or Meckel's ganglion. From
this portion of the nerve, branches are given off, the two posterior dental nerves, which
are distributed to the molar and bicuspid teeth, the mucous membrane of the correspond-
ing alveolar processes, and to the antrum.

FIG. 214.— Inferior maxillary d! vision of the fifth . (\\ irschfeld.)

1, branch from the motor root to the niasseter muscle ; 2, filaments from this branch to the temporal muscle ; 8. Iniccal
brunch; 5. ti, 7. branches to the muscles; 8, auriculo-temjmral HOT? ; i», temporal branches; 10, auricular
branch,*; 11, a/iaxfoHni*;* n-jfh the facial nerve; 12, linrma? branch ; 1*. l>r:mcli of the motor root to the
mylo-hyoid nm-de; 14. l.\ in. inferior dental nerve, witii 'its branches; 16, mental branch; 17, anastomosis
(f this branch icith tJie facial nerve.

In the infra-orbital canal, a large branch, the anterior dental, is given off to the teeth
and raucous membrane of the alveolar processes not supplied by the posterior dental
nerves. This nerve anastomoses with the posterior dental.

638

NERVOUS SYSTEM.

The terminal branches upon the face are distributed to the lower eyelid (the palpebral
branches) ; to the side of the nose (the nasal branches), anastomosing with the nasal
branch of the ophthalmic ; and to the integument and mucous membrane of the upper
lip (the labial branches).

The inferior maxillary is a mixed nerve, composed of the inferior division of the large
root and the entire small root. The distribution of the motor filaments has already been
described under the head of the nerve of mastication. This nerve passes out of the cranial
cavity by the foramen ovale, and then separates into the anterior division, containing
nearly all of the motor filaments, and the posterior division, which is chiefly sensory.
The sensory portion breaks up into numerous branches :

1. The auriculo-temporal nerve supplies the integument in the temporal region, the
auditory meatus and the integument of the ear, the temporo-maxillary articulation, and
the parotid gland. It also sends important branches of communication to the facial.

2. The lingual branch is distributed to the mucous
membrane of the tongue as far as the point, the mucous
membrane of the mouth, the gums, and to the sublingual
gland. This nerve receives an important branch from
the facial (the chorda tympani) which has already been
described. From this nerve, also, are given off two or
three branches which pass to the subm axillary ganglion,
constituting its sensory roots.

3. The inferior dental nerve, the largest of the three,
passes in the substance of the inferior maxillary bone,
beneath the teeth, to the mental foramen, where it
emerges upon the face. The most important sensory
branches are those which supply the pulps of the teeth,
and the branches upon the face. The nerve, emerging
upon the face by the mental foramen, called the mental
nerve, supplies the integument of the chin and the lower
part of the face, the lower lip, and sends certain filaments
to the mucous membrane of the mouth.

FIG. 215. — Limits of cutaneous distri-
bution of sensory nerves to the face,
head, and neck. (Beclard.)

1, cutaneous distribution of the ophthal-
mic division of the fifth ; 2, distribu-
tion of the superior maxillary divi-
sion ; 3, 3, distribution of the inferior
maxillary division ; 4, distribution of
the anterior branches of the cervical
nerves ; 5, 5, distribution of the pos-
terior branches of the cervical nerves.

Properties and Functions of the Trifacial. — In 1822,
Herbert Mayo published an account of " experiments to
determine the influence of the portio dura of the sev-
enth, and of the facial branches of the fifth pair of
nerves." These experiments consisted in dividing the infra-orbital, inferior maxillary
and frontal branches of the fifth, and the branch from the fifth to the seventh, in asses,
by which it was demonstrated that these were exclusively sensory nerves. In a second
publication, the following year, it is stated that the root of the fifth was divided in the
cranial cavity in pigeons ; but this was with reference chiefly to the movements of the
iris, although Mayo notes that after division of the nerve " the surface of the eyeball ap-
pears to have lost its feeling."

In 1823, Fodera published an account of experiments in which he had divided the
roots of the fifth in living animals (rabbits) by introducing a small knife through an
opening in the parietal bone, along the base of the skull, and cutting through the roots
near the Gasserian ganglion. The operation was followed by complete loss of sensibil-
ity upon the side on which the nerve had been divided. In this and other experiments,
however, the animals died a short time after the operation. The paper in which these
experiments were detailed was presented to the Academy of Sciences, December 31, 1822,
and was published at about the same time as the experiments of Mayo.

In 1824, Magendie published an account of his experiments upon the fifth pair. He
divided the nerve at its root, by introducing a small stylet through the skull, and noted

TRIFACIAL, OR TRIGEMINAL NERVE.

639

immediate loss of sensibility upon the corresponding side of the face. Magendie was the
first to succeed in keeping the animals alive, observing certain interesting remote effects
following division of the nerve.

The operative procedure employed by Magendie has been followed, with great suc-
cess, by other physiologists, particularly Bernard, to whose researches we are indebted
for many additional facts of interest concerning the functions of the fifth nerve. As
this is an operation which we have frequently performed with success, following the
minute directions laid down by Bernard, we shall quote from him in brief the different
steps :

The nerve may be divided in the cranial cavity with tolerable certainty in rabbits,
cats, dogs, and Guinea-pigs, but it is most easily done in rabbits. The operation is diffi-
cult from the fact that one is working in the dark, and it requires a
certain amount of dexterity, to be acquired only by practice. The
instrument used is represented in Fig. 216. The operative procedure
is as follows :

1. " The head of the rabbit is firmly held in the left hand. The
operator feels with the finger of the right hand the tubercle situated in
front of the ear, formed by the condyle of the lower jaw. Behind this
tubercle, is a hard, osseous portion, the origin of the auditory canal.

2. " The operator penetrates just behind the superior border of the
condyle, directing the point of the instrument slightly forward to avoid
passing into the substance of the petrous portion of the temporal bone,
and thus passes more easily into the middle temporal fossa ; at the same
time the instrument is directed a little upward to avoid slipping into the
zygomatic fossa and thus failing to enter the cranial cavity.

3. " As soon as the instrument has penetrated the cranium, which
is recognized by the point becoming free, the pressure is arrested and
the instrument is directed downward and backward, its back sliding
along the anterior face of the bone, which should serve as a guide in the
operation.

4. " This point of departure — that is to say, the anterior face of the
bone — being found, the instrument is pushed along, following its inferior
border and proceeding gradually, as the instrument penetrates, pressing
on the bone, the resistance of which can be easily recognized. Soon,
however, the operator feels, at a certain depth, that the bony resistance
ceases : he is then on the fifth pair, and the cries of the animal give
evidence that the nerve is pressed upon.

5. " It is at this moment that it is necessary to hold firmly the instru-
ment and the head of the animal ; then the cutting edge is turned so as
to be directed downward and backward, at the same time pressing in

this direction so as to divide the nerve on the extremity of the petrous portion, behind
the ganglion of Nasser, if possible, or at least on the ganglion itself.

6. " The instrument is then drawn back, pressing upon the bone so as to accomplish
completely the section of the trunk of the fifth pair ; then it is withdrawn by passing
over the same course on the anterior face of the petrous portion so as not to lacerate the
cerebral substance.

" The accident to be feared in the operation is section of the carotid when the instru-
ment has penetrated too far, or lesion of the cavernous sinus when it is pressed too far
forward."

When this operation has been performed without accident, its immediate effects are
very striking. The cornea and the integument and mucous membrane upon that side of
the head are instantaneously deprived of sensibility and may be pricked, lacerated, or
burned, without the slightest evidence of pain on the part of the animal. Almost always

FIG. 216. — Instru-
ment for di-
viding the fifth
nerve. (Bernard.)

640

NERVOUS SYSTEM.

the small root of the fifth is divided as well as the large root, and the muscles of masti-
cation are paralyzed upon one side ; but, with this exception, there is no paralysis of
motion, sensation alone being destroyed upon one side.

FIG. 217.— Operation for dirvtion of the fifth nerre. (Bernard.)

The calvarinm and the cerebrum are removed in order to show the roots r>f the nerves and the direction of the instru-
ment used in section of the fifth. A. olfactory nerves : B. optic nerves : C. inotores ocuiorum commune.- : D,
pathetici: E. fifth nerve : H. Made oft/ie instrument in the cranial cavity ; G, G' I, I', seventh pair of nerves ;
K, section of the spinal cord.

Immediate Effects of Division of the Trif'icial. — It is hardly necessary to discuss the
functions of the trifacial, after the statement of the effects which instantly follow upon
its division, taken in connection with its physiological anatomy. The nerve has never
been exposed in the cranial cavity in living animals ; but its branches upon the face and
the lingual branch of the inferior maxillary division have been operated upon and found

TRIFACIAL, OR TRIGEMIXAL SERVE. 641

to be exquisitely sensitive. Longet and others have exposed the roots in animals imme-
diately after death, and have found that galvanization of the large root carefully insu-
lated produces no muscular contraction. All who have divided this root in living animals
must have recognized, not only that it is sensitive, but that its sensibility is far more acute
than that of any other nervous trunk in the body. It is much more satisfactory to divide
the nerve without etherizing the animal, as the evidence of pain is an important guide in
this delicate operation ; but, in using anaesthetics, we have never been able to bring an
animal under their influence so completely as to abolish the sensibility of the root itself.
For example, in cats that appear to be thoroughly etherized, as soon as the instrument
touches the nerve, there is more or less struggling. The large root of the fifth, then, is
an exclusively sensory nerve, and its sensibility is more acute than that of any other of
the cerebro-spinal nerves.

As far as audition and olfaction are concerned, there are no special effects immedi-
ately following section of the trifacial ; but there are interesting phenomena observed in
connection with the eye and the organs of taste.

At the instant of division of the fifth, by the method just described, the eyeball is pro-
truded and the pupil becomes strongly contracted. This occurs in rabbits, and the con-
traction of the pupil was observed in the first operations of Magendie. The pupil, how-
ever, is usually restored to the normal condition in a few hours. Longet states that the
pupil is dilated by division of the fifth in dogs and cats. After division of the nerve, the
lachrymal secretion becomes very much less in quantity ; but this is not the cause of the
subsequent inflammation, for the eyes are not inflamed, as was shown by Magendie, even
after extirpation of both lachrymal glands. The movements of the eyeball are not
affected by division of the fifth.

Another of the immediate effects of complete division of the fifth nerve is loss of general
sensibility in the tongue. Most experiments upon the influence of this nerve over the gen-
eral sensibility and the sense of taste in the tongue have been made by dividing the lin-
gual branch of the inferior maxillary division. When this branch is irritated, there are
evidences of intense pain. When it is divided, the general sensibility and the sense of
taste are destroyed in the anterior third or half of the tongue. It will be remembered,
however, that the chorda tympani joins the lingual branch of the fifth as it passes be-
tween the pterygoid muscles, and that section of this branch of the facial abolishes the
sense of taste in the anterior third or half of the tongue. If the gustatory properties of
the lingual branch of the fifth be derived from the chorda tympani, lesions of the fifth
not involving this nerve would be followed by loss of general sensibility, but the taste
would be unaffected. This has been shown to be the fact, by cases of paralysis of general
sensibility of the tongue without loss of taste in the human subject, which will be dis-
cussed more fully in connection with gustation.

Among the immediate effects of section of the fifth, is an interference with the reflex
phenomena of deglutition. In some recent researches upon the action of the sensitive
nerves in deglutition, by Waller and Prevost, it was found that, after section of the fifth
upon both sides, it was impossible to excite movements of deglutition by stimulating the
mucous membrane of the velum palati. After se«tion of the superior laryngeal branches
of the pneumogastrics, no movements of deglutition followed stimulation of the mucous
membrane of the top of the larynx. In these experiments, when the fifth was divided
upon one side, stimulation of :he velnm upon the corresponding side had no effect, while
movements of deglutition were produced by irritating the velum upon the sound side.
These experiments show that the fifth nerve is important in the reflex phenomena of
deglutition, as a sensory nerve, conveying the impression from the velum palati to the
nerve-centres. This action probably takes place through filaments which pass from the
fifth to the mucous membrane through Meekel's ganglion.

Itemols Efrcts of Division of the Tr( rac ial— After the ordinary operation of divid-
ing the fifth nerve in the cranial cavity, the immediate loss of sensibility of the integu-
41

642 NERVOUS SYSTEM.

ment and mucous membranes of the face and head is usually supplemented by serious
disturbances in the nutrition of the eye, the ear, and the mucous membranes of the nose
and mouth. At a period varying from a few hours to one or two days after the opera-
tion, the eye upon the affected side becomes the seat of purulent inflammation, the cor-
nea becomes opaque and ulcerates, the humors are discharged, and the organ is destroyed.
Congestion of the parts is usually very prominent a few hours after division of the nerve.
At the same time, there is an increased discharge from the mucous membranes of the
nose and mouth upon the affected side, and ulcers appear upon the tongue and lips. It
is probable, also, that disorders in the nutrition of the auditory apparatus follow the oper-
ation, although these are not so prominent. Animals affected in this way usually die in
from fifteen to twenty days.

One of the most interesting facts, particularly in view of the information derived from
later observations, in connection with the early experiments of Magendie, is, that he
noted that " the alterations in nutrition are much less marked " when the division is
effected behind the ganglion of Gasser, than when it is done in the ordinary way through
the ganglion. It is difficult enough to divide the nerve completely within the cranium,
and is almost impossible to make the operation at will through or behind the ganglion ;
and the phenomena of inflammation are absent only in exceptional and accidental in-
stances. Magendie offers no satisfactory explanation of the differences in the consecu-
tive phenomena coincident with the locality of section of the nerve. The facts, how-
ever, have been abundantly verified. In the numerous experiments that we have made
upon the fifth pair, we have generally noted the consecutive inflammatory phenomena in
the order above described ; but, in exceptional instances, these phenomena have been
wanting. The following experiment illustrates these exceptional operations :

February 6, 1868, the fifth pair of nerves was divided upon the left side in a full-
grown rabbit in the ordinary way, before the class at the Bellevue Hospital Medical Col-
lege. There followed instant and complete loss of sensibility upon the left side of the
face. Four days after, the animal having been fed ad libitum with cabbage, the loss of
sensibility was still complete. There was very little redness of the conjunctiva of the
left eye, and a very slight streak of opacity, so slight that it was distinguished with diffi-
culty. Twelve days after the operation, the sensibility of the left eye was distinct but
slight. There was no redness of the conjunctiva, and the opacity of the cornea had dis-
appeared. The animal was in good condition, and the line of contact of the upper with the
lower incisors, when the jaws were closed, was very oblique. The animal was kept alive
by careful feeding with bread and milk for one hundred and seven days after the opera-
tion, there never being any inflammation of the organs of special sense. It died at that
time of inanition, having become very much emaciated. The animal never recovered
power over the muscles of mastication of the left side, and the incisors grew to a great
length, interfering very much with mastication, which seemed to be the cause of death.

Longet, in 1842, furnished a satisfactory explanation of the absence of inflammation
in certain cases of division of the fifth. He attributed the consecutive inflammation in
most experiments to lesion of the ganglion of Gasser and of the sympathetic connections,
which are very numerous at this point. These sympathetic filaments are avoided when
the section is made behind the ganglion.

The explanation of the phenomena of disordered nutrition in the organs of special
sense, particularly the eye, following division of the fifth, is not afforded by the section
of this nerve alone ; for, as we have seen, when the loss of sensibility is complete after
division of the nerve behind the Gasserian ganglion, these results may not follow. Nor
are they explained by deficiency in the lachrymal secretion, for they are not observed
when both lachrymal glands have been extirpated. They are not due to exposure of the
eyeball, for they do not follow upon section of the facial. Nor are they due simply to an
enfeebled general condition, for, in the experiment we have detailed, the animal died of
inanition after section of the nerve, without any evidences of inflammation. In view of

TRIFACIAL, OR TRIGEMINAL NERVE. 643

the fact that section of the sympathetic filaments is well known to modify the nutrition
of parts to which they are distributed, producing congestion, increase in temperature, and
other phenomena, it is rational to infer that the modifications in nutrition which follow
section of the fifth after it receives filaments from the sympathetic system, not occurring
when these sympathetic filaments escape division, are to be attributed to lesion of the
sympathetic, and not to the division of the sensory nerve itself.

A farther explanation is demanded for the inflammatory results which follow division
of the sympathetic filaments joining the fifth, inasmuch as division of the sympathetic
alone in the neck produces simply exaggeration of the nutritive processes, as evidenced
chiefly by local increase in the animal temperature, and not the well-known phenomena
of inflammation.

It has been remarked by Bernard, that the " alterations in nutrition appear more
promptly in animals that are enfeebled." Section of the small root of the fifth, which
is unavoidable when the nerve is divided within the cranial cavity, generally interferes so
much with mastication as to influence seriously the general nutrition ; and this might
modify the nutritive processes in delicate organs, like the eye, so as to induce those
changes which are called inflammatory. The following observation, communicated by
Dr. W. H. Mason, Professor of Physiology in the Medical Department of the University
of Buffalo, is very striking in this connection :

The fifth pair of nerves was divided in a cat in the ordinary way. By feeding the
animal carefully with milk and finely-chopped meat, the nutrition was maintained at a
high standard, and no inflammation of the eye occurred for about four weeks. The sup-
ply of food was then diminished to about the quantity it would be able to take without
any special care, when the eye became inflamed, and perforation of the cornea and
destruction of the organ followed. The animal was kept for about five months; at the
end of which time, sensation upon the affected side, which had been gradually improving,
was completely restored.

The explanation we have to offer of the consecutive inflammatory effects of section
of the fifth with its communicating sympathetic filaments is the following : By dividing
the sympathetic, the eye and the mucous membranes of the nose, mouth, and ear are
rendered hyperoemic, the temperature is probably raised, and the processes of nutrition
are exaggerated. This condition of the parts would seem to require a full supply of
nutritive material from the blood, in order to maintain the condition of exaggerated
nutrition ; but, when the blood is impoverished — probably as the result of deficiency in
the introduction of nutritive matter, from paralysis of the muscles of mastication upon
one side — the nutritive processes in these delicate parts are seriously modified, so as to
constitute inflammation. The observation just detailed is an argument in favor of this
view ; for here the inflammatory action seemed to be arrested when the action of the
paralyzed muscles was supplied by careful feeding. With this view, the disorders of
nutrition observed after division of the fifth may properly be referred to the sympathetic
system.

Pathological facts in confirmation of experiments upon the fifth pair in the lower
animals are not wanting ; but it must be remembered that, in cases of paralysis of the
nerve in the human subject, it is not always possible to locate exactly the seat of the
lesion and to appreciate fully its extent, as can be done when the nerve is divided by
an operation. In studying these cases, it sometimes occurs that the phenomena, par-
ticularly those of modified nutrition, are more or less contradictory.

In nearly all works upon physiology, we find references to cases of paralysis of
the fifth in the human subject. In a recent article by Dr. H. D. Noyes, Professor of
Ophthalmology in the Bellevue Hospital Medical College, two interesting cases are re-
ported, which we had an opportunity of examining during the progress of treatment.
In both of these cases there was inflammation of the eye. In one case, the tongue was
entirely insensible upon one side, but there was no impairment of the sense of taste. An

644 NERVOUS SYSTEM.

interesting feature in one of the cases was the fact that an operation upon the eyelid of
the affected side was performed without the slightest evidence of pain on the part of the
patient.

Cases of paralysis of the fifth in the human subject in the main confirm the
results of experiments upon the inferior animals. In all the cases in which the fifth
nerve alone was involved in the disease, without the portio dura of the seventh, there
was simply loss of sensibility upon one side, the movements of the superficial muscles
of the face being unaffected. When the small root was involved, the muscles of masti-
cation upon one side were paralyzed ; but, in certain cases in which this root escaped,
there was no muscular paralysis. The senses of sight, hearing, and smell, except as they
were affected by consecutive inflammation, were little if at all disturbed in uncompli-
cated cases. The sense of taste in the anterior portion of the tongue was perfect,
except in those cases in which the seventh, the chorda tympani, or the lingual branch
of the fifth after it had been joined by the chorda tympani, was involved in the disease.
In some cases, there was no alteration in the nutrition of the organs of special sense ;
but in this respect the facts with regard to the seat of the lesion are not so satisfactory
as in experiments upon the lower animals, it being difficult, in most of them, to limit
the exact boundaries of the lesion.

Pneumogastric^ or Par Vagum Nerve. (Second JDivision of the Eighth

Nerve)

Of all the nerves emerging from the cranial cavity, the pneumogastric, the second
division of the eighth pair, presents the greatest number of anastomoses, the most
remarkable course, and the most varied and interesting functions. Arising from the
medulla oblongata by a purely sensory root, it communicates with at least five motor
nerves in its course, and it is distributed largely to muscular tissue, both of the voluntary
and the involuntary variety. Finally, there is no nerve that has been the subject of
such extended and elaborate anatomical and physiological investigations, and none,
concerning the properties and exact functions of which there has been so much differ-
ence of opinion.

We shall have to treat of the influence of the pneumogastric upon the act of degluti-
tion, the heart and circulatory system, the respiratory system, the stomach, the intestines,
and various glandular organs. An indispensable introduction to this study is a descrip-
tion of its physiological anatomy.

Physiological Anatomy of the Pneumogastric Nerte. — The apparent origin of the
pneumogastric is from the lateral portion of the medulla oblongata, just behind the
olivary body, between the roots of the glosso-pharyngeal and of the spinal accessory.
The deep origin is mainly from what is sometimes called the nucleus of the pneumogas-
tric, in the inferior portion of the gray substance in the floor of the fourth ventricle.
The course of the fibres, traced from without inward, is somewhat intricate.

The deep origins of the pneumogastric and glosso-pharyngeal nerves appear to be, in
the main, identical. Tracing the filaments from without inward, they may be followed
in four directions. The anterior filaments pass from without inward, first very superfi-
cially and directed toward the olivary body, but, turning before they reach the olivary
body, they pass deeply into the substance of the restiform body, in which they are lost.
The posterior filaments are superficial, and they pass, with the fibres of the restiform
body, toward the cerebellum. Of the intermediate filaments, the anterior pass through
the restiform body, the greatest number extending to the median line in the floor of the
fourth ventricle. A few fibres are lost in the middle fasciculi of the medulla, and a few
pass toward the brain. The posterior intermediate filaments traverse the restiform
body to the floor of the fourth ventricle, when some pass to the median line, and others

PNEUMOGASTRIC, OR PAR VAGUM NERVE.

645

descend in the substance of the medulla. It is, difficult to follow the fibres of origin of
the pneumogasfcrics beyond the median line ; but recent observations leave no doubt ol
the fact that many of these fibres decussate in the floor of the fourth ventricle.

There are two ganglionic enlargements belonging to the pneumogastric. In the
jugular foramen, is a well-marked, grayish, ovoid enlargement, from one-sixth to one-
fourth of an inch in length, called the jugular ganglion, or the ganglion of the root.
This is united by two or three filaments with the ganglion of the glosso-pharyngeal.
It is a true ganglion, containing nerve-cells. After the nerve has emerged from the cra-
nial cavity, it presents on its trunk another
grayish enlargement, from half an inch to an
inch in length, called the ganglion of the trunk.
This is of rather a plexiform structure, the
white fibres being mixed with grayish fibres
and nerve-cells. The exit of the nerve from
the cranial cavity is by the jugular foramen, or
posterior foramen lacerum, in company with
the spinal accessory, the glosso-pharyngeal, and
the internal jugular vein.

Anastomoses. — The filaments of communi-
cation which the pneumogastric receives from
other nerves are interesting from their great
importance and their varied sources. The
most important of these is the branch from
the spinal accessory. There are occasional
filaments of communication which pass from
the spinal accessory to the ganglion of the root,
but these are not constant. After both nerves
have emerged from the cranial cavity, an im-
portant branch of considerable size passes
from the spinal accessory to the pneumoga*-
tric, with which it becomes closely united.
Experiments have shown that these filaments
from the spinal accessory pass in great part to
the larynx by the inferior laryngeal nerves.

In the aquaoductus Fallopii, the facial nerve
gives off a filament of communication to the
pneumogastric at the ganglion of the root.
This filament, joined at the ganglion by sen-
sory filaments from the pneumogastric and
some filaments from the glosso-pharyngeal, is
called the auricular branch of Arnold. By
some anatomists it is regarded as a branch
from the facial, and by others it is described with the pneumogastric.

Two or three small filaments of communication pass from the sublingual to the gan-
glion of the trunk of the pneumogastric.

At the ganglion of the trunk, the pneumogastric generally receives filaments of com-
munication from the arcade formed by the anterior branches of the first two cervical
nerves. These, however, are not constant.

The pneumogastric is connected with the sympathetic system by numerous delicate
filaments of communication received from the superior cervical ganglion, passing in part
upward toward the ganglion of the root of the pneumogastric, and in part transversely
and downward. These filaments are frequently short, and they bind, as it were, the
.sympathetic ganglion to the trunk of the nerve. The main trunk of the pneumogastric

Fro 218.— Anastomoses of the pneumogastric.
(Hirschfeld.)

1, facial nerve: 2, glosso-pharyngeal nerve ; 2', anas-
tomoses of the glosso-pharyngeal with the facial ;
8, 3, pneumogatitric, icith its two ganglia; 4, 4,
spinal accessory ; 5. sublingual nerve ; 6, superior
cervical ganglion of the sympathetic; 7, anaxto-
mosie arcade of the first two cervical nertes ; 8,
carotid branch of the superior cervical ganglion
of the sympathetic; 9, nerve of Jacobson; 10,
branches of this nerve to the sympathetic; 11,
branch to the Eustachian tube ; 12, branch to the
fenestra ovalis; 13, branch to the fenestra rotunda ;
14, external deep petrous nerve; 15, internal deep
petrous nerve; 16, otic ganglion; 17, auricular
brunch of the pneumogastric; J8, anastomosis
of the pneumogastric with the spinal accessory ;
19. anastomosis of the pneumogastric u-ith the
sublingual ; 20, anastomosis of the spinal acces-
sory with the second pair of cervical iii-rves ; 21,
pharyngeal plexus ; 22, superior laryngeal nerve.

646

NERVOUS SYSTEM.

and its branches receive a few delicate filaments of communication from the middle and
inferior cervical and the upper dorsal ganglia of the sympathetic.

The pneumogastric frequently sends a very delicate filament to the glosso-pharyngeal
nerve, at or near the ganglion of Andersch. Branches from the pneumogastric join
branches from the glosso-pharyngeal, the spinal accessory, and the sympathetic, to form
the pharyngeal plexus.

Distribution. — In describing the very extensive distribution of the pneumogastrics,
while the nerves upon the two sides do not present any important differences in the
destination of their filaments as far down as the diaphragm, it will be seen that the
abdominal branches are not the same. The most important branches are the following :

1. Auricular.

2. Pharyngeal.

3. Superior laryngeal.

4. Inferior, or recurrent laryngeal.

5. Cardiac, cervical and thoracic.

6. Pulmonary, anterior and posterior.

7. (Esophageal.

8. Abdominal.

FIG. 219.— Distribution of the pneumogastric. (Hirschfeld.)

1, trunk of the left pneumogastric ; 2, ganglion of the trunk ; 3, anastomosis with the spinal accessory ; 4, anas-
tomosis with t/ie sublingual; 5, pharyngeal branch (the auricular branch is not shown in the figure); 6,
superior laryngeal branch ; 7, external laryngeal nerve ; 8, laryngeal plexus ; 9, 9, inferior laryngeal
branch; 10, cervical cardiac branch; 11, thoracic cardiac branch; 12,13, pulmonary branches; 14, lingual
branch of the fifth; 15, lower portion of the sublingual; 1(5, glosso-pharyngeal; 17, spinal accessory; 18, 19, 20,
spinal nerves ; 21, phrenic nerve ; 22, 23, spinal nerves ; 24, 25, 26, 27, 28, 29, 30, sympathetic ganglia.

PNEUMOGASTRIC, OR PAR VAGUM NERVE. 647

The auricular nerves are sometimes described in connection with the facial. They
are given off from the ganglion of the trunk of the pneumogastric, and are composed of
filaments of communication from the facial and from the glosso-pharyngeal, as well as
of filaments from the pneumogastric itself. The nerves thus constituted are distributed to
the integument of the upper portion of the external auditory meatus, and a small filament
is sent to the inembrana tympani.

The pharyngeal nerves are very remarkable in their course. They are given off from
the superior portion of the ganglion of the trunk and contain a large number of the fila-
ments of communication which the pneumogastric receives from the spinal accessory.
In their course by the sides of the superior constrictor muscles of the pharynx, these
nerves anastomose with numerous filaments from the glosso-pharyngeal and the superior
cervical ganglion of the sympathetic, to form what is known as the pharyngeal plexus.
The ultimate filaments of distribution pass to the muscles and the mucous membrane of
the pharynx. Physiological experiments have shown that the motor influence transmitted
to the pharyngeal muscles through the pharyngeal branches of the pneumogastric is
derived from the spinal accessory.

The superior laryngeal nerves are given off from the lower part of the ganglion of the
trunk. Their filaments come from the side opposite to the point of junction of the pneu-
mogastric with the communicating branch from the spinal accessory, so that probably
the superior laryngeals contain few if any motor fibres from this nerve. The superior
laryngeal gives off the external laryngeal, a long, delicate branch, which sends a few fila-
ments to the inferior constrictor of the pharynx and is distributed to the crico-thyroid
muscle and the mucous membrane of the ventricle of the larynx. The external laryngeal
anastomoses with the inferior laryngeal and with the sympathetic. The internal branch
is distributed to the mucous membrane of the epiglottis, the base of the tongue, the aryt-
eno-epiglottidean fold, and the mucous membrane of the larynx as far down as the true
vocal cords. A branch from this nerve, in its course to the larynx, penetrates the aryte-
noid muscle, to which it sends a few filaments, but these are all sensory. This branch
also supplies the crico-thyroid muscle. It anastomoses with the inferior laryngeal nerve.
An important branch, described by Cyon and Ludwig, in the rabbit, under the name of
the depressor-nerve, arises by two roots, one from the superior laryngeal and the other
from the trunk of the pneumogastric, passes down the neck by the side of the sympa-
thetic, and, in the chest, joins filaments from the thoracic sympathetic, to penetrate the
heart between jthe aorta and the pulmonary artery. This nerve will be referred to more
particularly in connection with the influence of the pneumogastrics upon the circulation.

It is important, from a physiological point of view, to note that the superior laryngeal
nerve is the nerve of sensibility of the upper part of the larynx, as well as of the supra-
laryngeal mucous membranes, and that it animates a single muscle of the larynx (the
crico-thyroid) and the inferior constrictor of the pharynx.

The inferior, or recurrent laryngeal nerves present some slight differences in their
anatomy upon the two sides. Upon the left side, the nerve is the larger and is given off
at the arch of the aorta. Passing beneath this vessel, it ascends in the groove between
the trachea and the oesophagus. In its upward course, it gives off certain filaments
which join the cardiac branches, filaments to the muscular tissue and mucous membrane
of the upper part of the oesophagus, filaments to the mucous membrane and the inter-
cartilaginous muscular tissue of the trachea, one or two filaments to the inferior con-
strictor of the pharynx, and a branch which joins the superior laryngeal. Its terminal
branches penetrate the larynx, behind the posterior articulation of the thyroid with the
cricoid cartilage, and are distributed to all of the intrinsic muscles of the larynx, except
the crico-thyroids, which are supplied by the superior laryngeal. Upon the right side,
the nerve winds from before backward around the subclavian artery, and it has essen-
tially the same course and distribution as upon the left side, except that it is smaller and
its filaments of distribution are not so numerous.

648 NERVOUS SYSTEM.

The important physiological point connected with the anatomy of the recurrent laryn-
geals is that they animate all of the intrinsic muscles of the larynx, except the crico-thy-
roid. Experiments have shown that these nerves contain numerous filaments from the
spinal accessory.

The cervical cardiac branches, two or three in number, arise from the pneumogastrics
at different points in the cervical portion and pass to the cardiac plexus, which is formed
in great part of filaments from the sympathetic. The thoracic cardiac branches are
given off from the pneumogastrics below the origin of the inferior laryngeals and join
the cardiac plexus.

The anterior pulmonary branches are few and delicate as compared with the posterior
branches. They are given off below the origin of the thoracic cardiac branches, send a
few filaments to the trachea, and then form a plexus which surrounds the bronchial tubes
and follows the bronchial tree to its terminations in the air-cells. The posterior pulmonary
branches are larger and more numerous than the anterior. They communicate freely
with sympathetic filaments from the upper three or four thoracic ganglia and then form
the great posterior pulmonary plexus. From this plexus, a few filaments go to the infe-
rior and posterior portion of the trachea, a few pass to the muscular tissue and mucous
membrane of the middle portion of the oesophagus, and a few are sent to the posterior
and superior portion of the pericardium. The plexus then surrounds the bronchial tree
and passes with its ramifications to the pulmonary tissue, like the corresponding fila-
ments .of the anterior branches. The pulmonary branches are distributed to the mucous
membrane, and not to the walls of the blood-vessels.

The oasophageal branches take their origin from the pneumogastrics above and below
the pulmonary branches. These branches from the two sides join to form the cesopha-
geal plexus, their filaments of distribution going to the muscular tissue and the mucous
membrane of the lower third of the oesophagus.

The abdominal branches are quite different in their distribution upon the two sides.

Upon the left side, the nerve, which is situated anterior to the cardiac opening of the
stomach, immediately after its passage by the side of the oesophagus into the abdomen,
divides into numerous branches, which are distributed to the muscular walls and the
mucous membrane of the stomach. As the branches pass from the lesser curvature, they
take a downward direction and go to the liver, and, with another branch running between
the folds of the gastro-hepatic omentum, they follow the course of the portal vein in the
hepatic substance. The branches of this nerve anastomose with the nerve of the right
side and with the sympathetic.

The right pneumogastric, situated posteriorly, at the cesophageal opening of the dia-
phragm, sends a few filaments to the muscular coat and the mucous membrane of the
stomach, passes backward, and is distributed to the liver, spleen, kidneys, suprarenal
capsules, and finally to the whole of the small intestine. The branches to the small intes-
tine are very important. These were accurately described in 1860, by Kollmann, in an
elaborate and beautifully-illustrated prize-essay. In the plate showing the distribution
of this nerve, it is seen that the branches to the intestine are very numerous. Accord-
ing to these researches, the branches described belong to the pneumogastric itself and
are not derived from the sympathetic. When we come to treat of the action of the pneu-
mogastric upon the small intestine, it will be seen that the anatomical researches by Koll-
mann have been fully confirmed by physiological experiments. Before the nerves pass
to the intestines, there is a free anastomosis and interchange of filaments between the
right and the left pneumogastric.

Properties and Functions of the Pneumogastric Nerves.

There is no nerve in the body that has been the subject of so many experiments, and
concerning which so much has been written, as the pneumogastric. Its accessible posi-
tion in many parts of its course, its extensive connections with the digestive, the respira-

PNEUMOGASTRIC, OR PAR VAGUM NERVE. 649

tory, and the circulatory system, and the evident importance of its relations, have ren-
dered the literature connected with its physiology somewhat redundant. We do not
propose to discuss in full all of the views entertained from time to time with regard to
its functions, but shall state merely what seem to be well-ascertained facts, and the most
reasonable inferences, where the facts are difficult of demonstration. In treating of the
functions of this nerve, we shall be compelled to make constant reference to its anatomy,
and for that reason we have described pretty fully in detail most of the important points
in its connections and distribution.

Although the extensive distribution of the pneumogastrics and their importance will
necessitate a long discussion of their physiology, we shall endeavor to separate the points
to be considered distinctly, and to simplify the subject as much as possible.

We shall first treat of the general properties of those filaments derived from the true
roots of the nerves, and, following them in their course, shall note the properties derived
from their connections with other nerves.

We shall then treat of the properties of the different branches of the nerves, under
distinct heads, taking up these branches as they are given off", from above downward. In
this, we shall consider first the properties and functions of the auricular branches ; next,
the pharyngeal branches, with their influence upon the action of the pharynx in deglu-
tition ; next, the superior and inferior laryngeal branches, with their relations to the
physiology of the larynx ; next, the cardiac branches, with their influence on the move-
ments of the heart and the circulation ; next, the pulmonary branches, with the function
of the nerves in connection with respiration ; next, the oesophageal branches, in connec-
tion with the influence of the nerves upon the action of the oesophagus, in deglutition ;
and finally, the abdominal branches, with the influence of the nerves upon digestion and
the functions of the abdominal viscera. By dividing up, in this way, the action of the
pneumogastrics, it is hoped that their physiology may be relieved of much of the com-
plexity in which it is apparently involved.

General Properties of the Roots of Origin of the Pneumogastrics. — All who have oper-
ated upon the pneumogastrics in the cervical region in living animals have noted their
exceedingly dull sensibility as compared with the ordinary sensory nerves. Bernard,
indeed, states that in this region they are generally insensible ; but we have usually found,
in dogs at least, that their division is attended with slight evidences of pain. Without
citing in detail all the experiments upon this point, it is sufficient to state that some
physiologists, on galvanizing or otherwise irritating the roots of the nerves in animals just
killed, have noted movements of the muscles of deglutition, of the oesophagus, and of the
muscular coats of the stomach. These experiments have led to the opinion that the
proper roots of the nerves are motor as well as sensory. It becomes, therefore, a difficult
as well as an important point to determine whether or not the roots be of themselves
exclusively sensory or mixed. In discussing the properties of the roots, we shall rely
almost entirely upon direct experiments ; although the arguments drawn from their
anatomical characters, in the presence of ganglia and the deep origin of their fibres,
point strongly to their sensory character. It is impossible to stimulate the roots, before
they have received motor filaments from other nerves, in living animals, and the experi-
ments are therefore made upon animals just killed, before the nervous irritability has dis-
appeared. If the true roots of the nerves be exclusively sensory, their galvanization in
animals just killed should produce, by direct action, no muscular contraction. If the
roots contain any motor filaments, contraction of muscles should follow their stimula-
tion. The proper physiological conditions in such experiments are the following :

1. It is necessary to stimulate the roots so that the filaments from the spinal accessory
and from other motor nerves are not involved.

2. It is important to ascertain, provided movements follow such irritation, whether or
not they be due to reflex action.

650 NERVOUS SYSTEM.

The first of these conditions is easily fulfilled. All that is necessary is to stimulate
the roots before the nerves have received any anastomosing filaments. To avoid contrac-
tions of muscles due to reflex action, it is best to divide the roots and to stimulate their
distal portion. If it be true that stimulation of the distal extremities of the roots— the
irritation so applied as not to involve communicating filaments from motor nerves, and
not to be conveyed to the centres, producing reflex movements through other nerves —
does not produce any movements, it is fair to assume that the true filaments of origin are
exclusively sensory. The facts upon this point demand careful and critical study; and it
will be proper to discard the earlier experiments, made before the mechanism of reflex
action had been satisfactorily established.

If the experiments of Longet be accepted without reserve, they prove — as conclusively
as is possible without exposing the roots in living animals, an operation which is imprac-
ticable— that the true filaments of origin of the pneumogastrics are exclusively sensory,
or, at least, that the nerve contains no motor filaments except those derived from other
nerves. The following quotation gives the essential points in these experiments :

" In dogs of large size and in horses, I have isolated in the cranium, with the most
minute care, the pneumogastric of the medulla oblongata and the superior filaments of
the spinal accessory (internal branch}, in order to avoid all reflex movement and any
derivative current upon the last-named nerve ; I then immediately caused the current to
act exclusively upon the filaments of origin of the pneumogastric, without having ever
seen the slightest contraction supervene, either in the muscles of the larynx or pharynx,
or in the muscular tunic of the O3sophagus, or elsewhere.

" But also I have never failed to demonstrate to all those who witnessed my experi-
ments, how it is easy to obtain opposite results in neglecting only one precaution : it
suffices, for example, to slightly moisten the slip of glass or oiled silk which serves to
isolate the two nerves, in order that the current should act immediately upon the superior
filaments of the spinal accessory, from which we have marked contractions in the organs
just mentioned."

These experiments seem entirely conclusive. In treating of the reflex phenomena of
deglutition and their relations to the superior branches of the pneumogastric, the pharyn-
geal, and the superior laryngeal, it will be seen that irritation, either of these nerves or
of the mucous membranes to which they are distributed, will produce contractions in the
muscles. All who are practically familiar with the application of electricity to the nerves
know how difficult it is to insulate the nervous trunks so as to avoid the influence of
"derived" currents. In carefully studying the experiments of Longet, it seems that all
the physiological conditions were fulfilled ; and that, when the nerve is divided at the
root and the stimulation is applied to the peripheral end, so as to cut off all reflex action
from the nervous centres, and when sufficient care is exercised to prevent the propagation
of the current to the motor connections of the pneumogastric, the nerve, from its origin
at the medulla oblongata to the ganglion of the root, contains no motor filaments and is
exclusively sensory. We shall therefore adopt, without reserve, the conclusions of Longet,
that the true filaments of origin of the pneumogastrics are exclusively sensory, or, at least,
that they have no motor properties.

Properties and Functions of the Auricular Nerves. — There is very little to be said
with regard to the auricular nerves, after the description we have given of their anatomy.
They are sometimes described with the facial and sometimes with the pneumogastric.
They contain filaments from the facial, the pneumogastric, and the glosso-pharyngeal.
The sensory filaments of these nerves give sensibility to the upper part of the external
auditory meatus and the membrana tympani.

Properties and Functions of the Pharyngeal Nerves. — The pharyngeal branches of
the pneumogastric are mixed nerves, their motor filaments being derived from the spinal

PNEUMOGASTRIC, OR PAE VAGUM NERVE. 651

accessory. Their direct action upon the muscles of deglutition belongs to the physiologi-
cal history of the last-named nerve. We have already stated, in treating of the spinal
accessory, that the filaments of communication that go to the pharyngeal branches of the
pneumogastric are distributed to the pharyngeal muscles.

It is impossible to divide all of the pharyngeal filaments in living animals and observe
directly how far the general sensibility of the pharynx and the reflex phenomena of
deglutition are influenced by this section. As far as we can judge from the distribution
of the filaments to the mucous membrane, it would seem that they combine with the
pharyngeal filaments of the fifth, and possibly with sensory filaments from the glosso-
pharyngeal, in giving general sensibility to these parts.

In some recent experiments by Waller and Prevost, upon the reflex phenomena of
deglutition, it is shown that the action of the pharyngeal muscles cannot be excited by
stimulation of the mucous membrane of the supra-laryngeal region and the pharynx, after
section of the fifth and of the superior laryngeal branch of the pneumogastric. This
would seem to show that the pharyngeal branches of the pneumogastrics are of little or
no importance in these reflex phenomena.

Properties and Functions of the Superior Laryngeal Nerves. — The distribution of
these nerves points to a double function ; viz., an action upon the crico-thyroid muscles,
and the important office of supplying general sensibility to the upper part of the larynx
and a portion of the surrounding mucous membrane. The stimulation of these nerves'
produces intense pain and contraction of the crico-thyroids ; but it has been shown
by experiment that the arytenoid muscles, through which the nerves pass, receive no
motor filaments. The action of the nerves upon the muscles is very simple, and resolves
itself into the function of the crico-thyroids, which has been treated of fully under the
head of phonation. When these muscles are paralyzed, the voice becomes hoarse. The
filaments to the inferior muscles of the pharynx are few and comparatively unimportant.
It is important in this connection to note that the superior laryngeals do not receive their
motor filaments from the spinal accessory.

The sensory filaments of the superior laryngeals have important functions connected
with the protection of the air-passages from the entrance of foreign matters, particularly
in deglutition, and are farther concerned, as we shall see, in the reflex action of the con-
strictors of the pharynx. In treating of deglutition, we have fully discussed the impor-
tance of the exquisite sensibility of the top of the larynx in the protection of the air-
passages. When both superior laryngeals have been divided in living animals, liquids
often pass into the larynx in small quantity, owing to the absence of the reflex closure
of the glottis when foreign matters are brought in contact with its superior surface, and
the occasional occurrence of inspiration during deglutition.

Aside from the protection of the air-passages, the superior laryngeal is one of the
sensory nerves through which the reflex acts in deglutition operate. There are certain
parts which depend for their sensibility entirely upon this nerve ; viz., the mucous mem-
brane of the epiglottis, the aryteno-epiglottidean fold, and the larynx as far down as
the true vocal cords. When an impression is made upon these parts, as when they
are touched with a piece of meat, regular and natural movements of deglutition ensue.

The experiments made by galvanizing the trunks of the superior laryngeal nerves are
extremely interesting. If the nerves be divided and galvanization be applied to their
central ends, movements of deglutition are observed, and there is also arrest of the
action of the diaphragm. From these experiments, it would seem that the impression
which gives rise to the movements of deglutition aids in protecting the air-passages
from the entrance of foreign matters, by temporarily arresting the inspiratory act.

An important point for our consideration, in this connection, is the action of the
superior laryngeal nerves in the ordinary phenomena of deglutition ; and, in experiments
with galvanism, a feeble current simulates most nearly the natural processes. In such

652 NERVOUS SYSTEM.

experiments the results have been quite satisfactory. The experiments in which a pow-
erful current of galvanism has been applied to the nerves also show an arrest of respi-
ration ; but it is argued that there is nothing special in the action of the superior laryn-
geals under these conditions, inasmuch as other sensitive nerves have been found to act
in the same way. This is undoubtedly true ; but it is well known that, in living animals,
strong impressions made upon any of the acutely sensitive nerves arrest respiration, and
that this is one of the phenomena commonly observed in animals struggling under painful
operations. In view of these facts, it seems unnecessary to discuss more fully the numer-
ous experiments with regard to the effects upon respiration of stimulation of the superior
laryngeals ; and we can assume that it has been demonstrated that an impression made
upon the terminal filaments of these nerves, such as occurs in the ordinary process of
deglutition, excites, by reflex action, contraction of the constrictors of the pharynx, and,
at the same time, momentarily suspends the movements of the diaphragm.

Important experiments have been made within the past few years, upon the action of
the pneumogastrics on the circulation, in which it is claimed that nervous filaments, aris-
ing, in the rabbit, in part from the trunk of the pneumogastric and in part from the
superior laryngeal branch, act as reflex depressors of the vascular tension. These experi-
ments will be fully discussed in connection with the cardiac branches.

Properties and Functions of the Inferior, or Recurrent Laryngeal Nerves. — The
anatomical distribution of these nerves shows that their most important function is con-
nected with the muscles of the larynx. The few filaments which are given off in the
neck to join the cardiac branches are probably not very important. It is proper to note,
however, that the inferior laryngeal nerves supply the muscular tissue and mucous mem-
brane of the upper part of the oesophagus and the trachea, and one or two branches are
sent to the inferior constrictor of the pharynx. The function of these filaments is suffi-
ciently evident.

The inferior laryngeals contain chiefly motor filaments, judging from their distribu-
tion as well as from the effects of direct irritation. All who have experimented upon
these nerves have noted little or no evidence of pain when they are stimulated or divided.

One of the most important functions of the recurrents is connected with the produc-
tion of vocal sounds. We have already fully treated of the mechanism of the voice and
the action of the intrinsic muscles of the larynx ; and, in our account of the physiology
of the internal, or communicating branch from the spinal accessory to the pneumogas-
tric, it has been shown that this is the true nerve of phonation. In the older works
upon physiology, before the functions of the spinal accessory were fully understood, the
experiments upon the inferior laryngeals led to the opinion that these were the nerves of
phonation, as they showed loss of voice following their division in living animals. It is
true that these nerves contain the filaments which preside over the vocal movements of
the larynx ; but it is also the fact that these vocal filaments are derived exclusively from
the spinal accessory, and that the recurrents contain as well motor filaments which pre-
side over movements of the larynx not concerned in the production of vocal sounds.

The muscles of the larynx concerned in phonation are, the crico-thyroids, animated
by the superior laryngeals, and the arytenoid, the lateral crico-arytenoids, and the thyro-
arytenoids, animated by the inferior laryngeals. The posterior crico-arytenoids are re-
spiratory muscles ; and it is curious that these are not affected by extirpation of the spinal
accessories, but that the glottis is still capable of dilatation, so that inspiration is not
impeded. If, however, the spinal accessories be extirpated, and the larynx be then
exposed in a living animal, the glottis still remains dilated, but will not close when irri-
tated. If the inferior laryngeals be then divided, the glottis is mechanically closed with
the inspiratory act, and the animals often die of suffocation. When we call to mind the
varied sources from which the pneumogastrics receive their motor filaments, it is easy to
understand how certain of these may preside over the vocal movements, and others,
from a different source, may animate the respiratory movements.

PNEUMOGASTRIC, OR PAR YAGUM NERVE. G53

As we should naturally expect from what has already been said, section of the infe- /
rior laryngeal nerves paralyzes both the vocal and the respiratory movements of the
larynx. It is not necessary to refer in detail to the ancient and modern experiments
illustrating this point, the former dating from the time of Galen. In adult animals, the
cartilages of the larynx are sufficiently rigid to allow of inspiration after the organ has
been completely paralyzed ; but, in young animals, the glottis is closed, and suffocation
ensues. We have generally observed in cats, that suffocation follows immediately upon
section of the recurrents or of the pneumogastrics in the neck.

The impediment to the entrance of air into the lungs is a sufficient explanation of the
increase in the number of the respiratory acts after division of both recurrents. The
acceleration of respiration is much greater in young than in adult animals. This does
not apply to very young animals, in which section' of the recurrents produces almost in-
stant death.

Feeble galvanization of the central ends-pf the inferior laryngeals, after their division,
produces rhythmical movements of deglutition, generally coincident with arrest of the
action of the diaphragm. These phenomena are generally observed in rabbits, but they
are not constant. The reflex action of these nerves in deglutition is probably dependent
upon the communicating filaments which they send to the superior laryngeal nerves.

Properties and Functions of the Cardiac Nerves, and Influence of the Pneumogastrics
upon the Circulation. — One of the most interesting questions connected with the physi-
ology of the pneumogastric nerves is their action upon the heart ; and the results of
experiments, which will be fully detailed hereafter, are precisely the opposite of what
would be expected in the case of a nerve containing motor filaments and distributed to
a muscular organ. Section of the pneumogastrics in the neck, far from arresting the I
action of the heart, increases the rapidity of its pulsations ; and galvanization of the |
nerves arrests the heart's action in diastole.

Within the past few years, some very remarkable experiments have been made upon
the influence of certain nerves given off near the superior laryngeals, which have been
called the depressors of the circulation ; but most observations have been made upon
the trunks of the pneumogastrics in the cervical region, as it is exceedingly difficult to
isolate the thoracic cardiac branches and to operate upon them without involving other
nervous filaments. In galvanizing the nerves in the neck, we have to consider both the
direct influence of the current and the phenomena due to reflex action.

Effects of Section of the Pneumogastrics upon the Circulation. — It is not necessary
to cite in detail the various experiments upon the effects of section of the pneumogastrics
in the neck upon the action of the heart. The division of these nerves in living animals
is sufficiently easy, and all who have performed this operation have noted the same re-
sults. By section of these nerves, the heart is at once separated from one of the most
important of its nervous connections ; and the effects show that, as far as this organ is
concerned, the motor filaments present great differences from the ordinary motor nerves
of the cerebro-spinal system. Most of the observations made by dividing the nerves
have been upon dogs, and the differences in the effects upon other animals are slight and
unimportant. The following are the important phenomena presented in typical experi-
ments :

Section of one of the pneumogastrics in the neck does not produce any very marked
effect upon the action of the heart, after the slight disturbance which usually follows the
operation has passed away. The number of pulsations is slightly increased, and the car-
diac pressure, as shown by a cardiometer fixed in the carotid artery, is slightly dimin-
ished ; but this is insignificant as compared with the effects of dividing both nerves.

Section of both pneumogastrics usually produces immediate and serious disturbance
in the respirations, which are momentarily accelerated. The animal usually becomes
agitated and suffers from want of air; and, when it is desired especially to note the car-

654 NERVOUS SYSTEM.

diac disturbance, it is often necessary to relieve the respiration by introducing a tube
into the trachea. In full-grown dogs, however, the respirations soon become calm, but
they are diminished in frequency and become unusually profound. When the animal is
in this condition, the beats of the heart are very much increased in frequency, at least
doubled ; but they are inefficient and tremulous.

An interesting point in this connection is the want of influence of certain medicinal
substances over the action of the heart in animals after division of the pneumogastrics.
Traube has shown that, while digitalis injected into the veins of a dog was capable in
an hour of reducing the pulse to about one-fourth of the normal number of beats per
minute, there was no appreciable effect upon the circulation when the injection was
made in animals with both pneumogastrics divided.

The influence of the pneurnogastrics upon the heart is one of the mqsj^ interesting
points in the physiology of the circulation; but we can discu^th^ naeehaityirHNiJif the
phenomena following section of the nerves more satisfactorily after we have considered
the effects of their galvanization.

Effects of Galvanizing the Pneumogastrics or their Branches upon the Circulation. —
The experiments upon the effects of galvanization of the pneumogastrics in the neck on
the action of the heart are almost innumerable ; and, although the explanations of the
phenomena observed present the widest differences, the facts themselves are sufficiently

simple. These facts will be discussed under the
following heads : 1. The direct influence of galvan-
ization of the nerves in the neck, undivided, or of
galvanization of the peripheral extremities of the
trunks after division. 2. Reflex phenomena follow-
ing galvanization of the central ends of the pneu-
mogastrics, after their division.

Direct Influence of the Pneumogastrics upon
the Heart. — In 1846, the brothers Weber noted
the important fact, that galvanization of the pneu-
mogastrics in the neck rendered the action of
the heart slow, and, if the galvanization were suffi-
ciently powerful, arrested the heart, which remained
flaccid and in diastole for a certain time while the
galvanization was continued. This fact has since
been confirmed by numerous experimenters.

While there is no difference of opinion among
physiologists with regard to the stoppage of the
heart by powerful galvanization, it is stated by
some that a very feeble current passed through the
peripheral ends of the divided nerves quickens the
heart's action ; but it is admitted by all that it is
very difficult to regulate the intensity of the current
so as to produce this effect. After section of the
nerves, the action of the heart is very readily modi-
fied by struggles, etc., on the part of the animal
under observation ; and, in view of the exceeding
FIG. 220.— Branches of the pneumogastric to nicety of the reported experiments, it cannot be
c,leart; £*&J&££ »*.**., ^"'d that the heart, is capable of being excited
u, branches of the pneumogastric going to to increased rapidity of action, without observations

of the most positive character. Such facts are

wanting ; and, farthermore, it has been shown by Dr. Rutherford, in a series of exceed-
ingly exact and satisfactory experiments, that whenever a galvanic current passed
through the pneumogastrics has any appreciable effect upon the action of the heart,

PKEUMOGASTRIC, OR PAR VAGUM NERVE. 655

it is to diminish the frequency of its pulsations. Inasmuch as our object is simply to
show that, imitating the nervous force by galvanism, the action of the pneurnogastrics
is inhibitory, we shall not discuss the effects of different currents, and other experi-
ments, which have little relation to the natural action of the nerves, and possess slight
interest from a purely physiological point of view.

The direct action of the pneumogastrics upon the heart is undoubtedly through their
motor filaments. All the facts developed by experiments are in accordance with this view.
If the nerves be divided in the neck, galvanization of the central ends has no effec
upon the heart, the pulsations being arrested only when the peripheral ends are stimu
lated. This shows that, at least as far as the fibres passing down the neck are con-
cerned, the action is centrifugal and direct, not reflex. Another curious fact illustrates
the same point very forcibly. It is well known that the woorara-poison completely par-
alyzes the motor nerves, leaving the muscular irritability and the sensory nerveg intact.
It has been found that, in animals poisoned with woorara, the action of the heart being
maintained by artificial respiration, galvanization of both pneumogastrics has no effect
upon its pulsations. This fact we have repeatedly verified in public demonstrations.
Still another curious fact remains bearing upon the question under consideration. If pow-
erful galvanization, which immediately arrests the cardiac pulsations, be continued for a
certain time, so that the motor filaments become temporarily exhausted and lose their
irritability, the heart resumes its contractions, notwithstanding that the galvanization is
continued ; the nerves being for the time incapable of transmitting the inhibitory influence.

The source of the motor filaments in the pneumogastrics which exert a direct inhibi-
tory action upon the heart becomes an important point to determine. In the original
experiments by the brothers Weber, it was shown that, when the galvanic stimului was
applied to that portion of the centres from which the nerves take their origin, the action
of the heart was arrested in the same way as when the nerves themselves are galvan-
ized; and it has been shown by subsequent observations that, when the heart is thus
arrested by galvanization of the medulla oblongata, if both pneumogastrics be divided in
the neck, its action is resumed. This would at first lead to the supposition that the
inhibitory filaments are derived from the roots themselves of the pneumogastrics; but it
has been conclusively demonstrated that they are really derived from the spinal acces-
sories, the upper filaments of origin of which are situated just below the roots of the
pneumogastrics.

It has been shown that powerful galvanization of one pneumogastric will arrest the
heart's action, and also that this inhibitory action is much more marked in the right
than in the left nerve. Waller, after extirpating the spinal accessory nerve upon one
side, found that galvanization of the pneumogastric upon that side had no effect upon
the heart, provided that from ten to twelve days had elapsed after extirpation of the
spinal accessory, a sufficient time to secure disorganization and loss of irritability of its
fibres. These experiments show conclusively that the motor filaments contained in the
pneumogastric, which act directly upon the heart, are derived exclusively from the com-
municating branch of the spinal accessory.

Reflex Influence, through the Pneumogastrics^ upon the Circulation. — Galvanization
of the central ends of the pneumogastrics, after their division in the neck, does not influ-
ence the action of the heart, except as the pulsations are affected by the modifications in
respiration. When the central ends are stimulated, the pupils become dilated, the eyes
protrude, sometimes vomiting occurs, and always the number of respiratory acts is
diminished, and, with a powerful current, are arrested in inspiration ; but the pulsations
of the heart are not affected.

Depressor-Nerve. — An important reflex action operating upon the circulation through
branches of the pneumogastrics has lately been described by Cyon and Ludwig, in a
memoir which received the prize for Experimental Physiology from the French Academy
of Sciences, in 18(57. The experiments upon which this memoir is based are exceedingly

;

656

NERVOUS SYSTEM.

FIG. 221. — Depressor-nerves. (Cyon and Ludwig.)

A, A, A, sympathetic nerves ; B, sublingual ; C, descending branch of the sublingual ; D, branch from the cervical
' plexus ; E, E, E, pneumogastrics ; F, superior laryngeal nerves ; G, G, G, G, depressor-nerves.

PNEUMOGASTRIC, OR PAR VAGUM NERVE. 65?

clear and satisfactory, and they afford, perhaps, the only positive explanation we have of
reflex action upon the heart. The substance of these observations is briefly as follows :

In the rabbit, is a nerve, arising by two roots, one coming from the trunk of the
pneumogastric and the other from its superior laryngeal branch, passing then toward the
carotid artery and taking its course down the neck by the side of the sympathetic as far
as the thorax. In the chest, it joins with sympathetic filaments to pass with them to the
heart, by little branches between the origin of the aorta and the pulmonary artery.
This nerve can be completely isolated in the neck from the sympathetic and the trunk
of the pneumogastric. If it be divided in this situation, after the irritation produced by
the operation has subsided, very distinct and important modifications in the circulation
may be produced by its galvanization.

In the first place, it was noted in all the experiments, that galvanization of the periph-
eral extremities produced no change, either in the number of the pulsations of the
heart or in the pressure of blood in the vascular system ; which points to the fact that
its action is not direct, but reflex, and that it is due to an impression conveyed to the
nerve-centres.

If the central ends of the nerves be galvanized, the pressure in the arteries dimin-
ishes little by little, until it may be reduced to one-half or two-thirds of the pressure
before the irritation was applied. This low pressure continues so long as the interrupted
current is applied ; but, when the galvanization is arrested, it gradually returns to the
normal standard. These phenomena are observed in all the large arterial trunks. The
length of time required to produce the greatest diminution in the pressure is somewhat
variable, but the experimenters have never seen it reach its minimum before fifteen pul-
sations of the heart.

" The diminution in the pressure is attended with a reduction of the pulse in the
instances in which the depressor-nerve only has been divided. The irritated nerve is
isolated in a manner so complete that we cannot fear the passage of the exciting current
in the trunk of the pneumogastric. The changes in the number of pulsations persist
even when the pneumogastric has been excited by the side where the irritation has been
applied, from the point where the superior laryngeal is given off to the point where the
pneumogastric enters the thoracic cavity.

" From the foregoing it is evident that the changes taking place in the number of
pulsations are due to excitation of the depressor-nerve. If we study attentively the
progress of the cardiac pulsations during the excitation, we observe always that the most
considerable reduction takes place at the beginning of the experiment ; that is to say, at
the moment when the blood-pressure descends from its normal standard to the lowest
point. When the pressure is completely depressed, the pulse is accelerated again and
even reaches almost completely the numbers presented before the oscillations. When
the irritation ceases, after a shorter or longer period, the heart generally beats more
rapidly than before the irritation, and this during all the time that is occupied in the
return of the pressure to the normal standard. This observation in itself refutes the
idea that the diminution in the pressure may depend upon the diminished number of pul-
sations. If the reduction in the rate of the pulse produced a diminished pressure, it
should be increased when the pulsations of the heart become accelerated.

" The manner in which the pulse is reduced leads to the supposition that it is due to
a reflex action of the pneumogastric.

" It was easy to verify this last opinion, and we have been able to confirm it by first
cutting the pneumogastrics on both sides, and afterward irritating the central end of the
depressor-nerve. In this case, the pressure fell to 0*62, 0*55, etc., while the number of
pulsations remained the same, or at least oscillated very slightly above and below the
number observed before the irritation."

The above extract from the observations of Cyon shows two important points :

First, galvanic stimulation of the central extremities of the divided depressor-nerves
42

658 NEKVOUS SYSTEM.

reduces the number of pulsations of the heart by a reflex action ; the impression being
conveyed to the nerve-centres by the depressor-nerves, and the force operating directly
upon the heart being transmitted through efferent filaments in the trunk of the pneumo-
gastric.

Second, the reduction in the pressure of blood in the larger arteries is independent
of the eiferent filaments of the pneumogastric and bears no relation to the reduction in
the number of cardiac pulsations.

It now remains to explain, if possible, the mechanism of the reduction in the arte-
rial pressure. This question is treated by Oyon by the method of exclusion. The dimi-
nution in the pressure followed galvanization of the central extremities of the depressor-
nerves, even when the heart was removed from its influence by section of both pneumo-
gastrics in the neck, and when all the voluntary movements and the movements of
respiration were abolished by poisoning with woorara. In the latter case, the circula-
tion was kept up by artificial respiration. Without following out the various observa-
tions which go to show that the influence of the depressor-nerve upon the arterial pressure
is independent of the force or frequency of the heart's action and is due to some cause
which operates upon the vessels themselves, we shall simply give the results of the
experiments upon the splanchnic nerves. If the abdomen be opened, and one or more
of these nerves be divided, the arterial pressure is immediately diminished. After this,
if the peripheral extremities of the divided nerves be galvanized, the pressure rapidly
returns to the normal standard. These experiments " demonstrate that the splanchnic
nerves constitute the most important vaso-motor nerves in the entire organism." This
point being settled, the depressor-nerves were galvanized after section of the splanch-
nic nerves, in some cases exaggerating the general arterial pressure by compressing
the aorta, and in others, leaving the aorta free. " The irritation of the depressor-nerve
after section of the splanchnic nerve produced still a diminution in the blood-pressure,
but the absolute value of this diminution is much less than it was during the irritation of
the depressor-nerve before the section of the splanchnic." These experiments show
pretty conclusively that the diminished pressure in the arterial system following stimula-
tion of the central ends of the depressor-nerves after division is due to a reflex action on
the blood-vessels of the abdominal organs, taking place through the splanchnic nerves.
We are sufficiently familiar with reflex paralyzing action upon the blood- vessels through
the sympathetic system ; and, when we call to mind the immense extent of the abdominal
vascular system, we can readily understand how, if the resistance to the flow of blood be
diminished by paralysis of the muscular coats of the small arteries, the pressure in the
larger arteries would be reduced.

Mechanism of the Influence of the Pneumogastrics upon the Action of the Heart. — It
is useless to speculate upon the exact mechanism of the action of the pneumogastrics upon
the heart. Although various explanations have been presented of the effects following
division of the nerves in the neck, and of the opposite phenomena which attend the gal-
vanization of their peripheral ends, they are all more or less unsatisfactory. All that can
be said, in the present state of our knowledge, is, that the pneumogastrics, by virtue of
the communicating branches from the spinal accessories, have a direct inhibitory influence
upon the heart. When they are divided and the heart is removed from their influence, the
pulsations become more rapid. When the peripheral ends of the divided nerves are
galvanized, the heart beats more slowly, or its action may be arrested by a current of
sufficient power. This action may also be reflex, due to an impression conveyed to the
centres by the depressor-nerves.

Properties and Functions of the Pulmonary Branches, and Influence of the Pneumo-
gcistrics upon Respiration. — The trachea, bronchi, and the pulmonary structure are sup-
plied with motor and sensory filaments by branches of the pneumogastrics. The recurrent
laryngeals supply the upper, and the pulmonary branches, the lower part of the trachea,

PNEUMOGASTRIC, OR PAR VAGUM NERVE. 659

the lungs themselves being supplied by the pulmonary branches alone. The sensibility
of the mucous membrane of the trachea and bronchi is due to the pneumogastrics, for
these parts are insensible to irritation when the nerves have been divided in the neck.
Longet has shown that, while an animal coughed and showed signs of pain when the
mucous membrane of the respiratory passages was irritated, after division of the pneumo-
gastrics there was no evidence of sensibility, even when the tracheal mucous membrane
was treated with strong acid, or even cauterized. He also saw the muscular fibres of the
small bronchial tubes contract when a galvanic stimulus was applied to the branches of
the pneumogastrics.

The main interest, in this connection, is attached to the pulmonary branches and their
relations to the respiratory acts. These are undoubtedly connected with important reflex
phenomena, acting as centripetal nerves ; and their direct action in respiration is probably
much less important. They are exposed and operated upon in living animals with so
much difficulty, that we know little of the direct effects of their irritation and must judge
of their general properties chiefly by experiments showing their action upon respiration.
Wa shall have to study, in connection with the functions of these nerves, the effects of
their division, upon the lungs and the respiratory acts, and the phenomena, referable to
the respiratory organs, which follow their galvanization. We shall also consider certain
theoretical views with regard to their action in the automatic processes of respiration, and
with the sense of want of air (besoin de respirer), which gives rise to the reflex respira-
tory acts.

Effects of Division oftlie Pneumogastrics upon Respiration. — Section of both pneumo-
gastrics in the neck, in mammals and birds, is usually followed by daath, in from two to
five days. In young animals, death may occur almost instantly, from paralysis of the
respiratory movements of the glottis, a fact which we have already noted in connection
with the recurrent laryngeal nerves.

Very little of importance, with regard to the functions of the pneumogastrics in con-
nection with respiration, has been ascertained by the numerous experiments on record of
section of one or both of these nerves in the cervical region. It has been found by all
experimenters, that animals survived and presented no very distinct abnormal phenomena
after section of one nerve. Longet states that animals operated upon in this way present
hoarseness of the voice and a slight increase in the number of respiratory acts. Some
observers have found the corresponding lung partly emphysematous and partly engorged
with blood, and others have not noted any change in the pulmonary structure.

When both nerves are divided in full-grown dogs, an experiment which we have often
repeated, the effect upon the respiratory movements is very marked. For a few seconds,
the number of respiratory acts may be increased ; but, as soon as the animal becomes
tranquil, the number is very much diminished, and the movements change their character.
The inspiratory acts become unusually profound and are attended with excessive dilata-
tion of the thorax. The animal is generally quiet and indisposed to move. We have
seen, under these conditions, the number of respirations fall from sixteen or eighteen to
four per minute.

In most animals that die from section of both pneumogastrics, the lungs are found
engorged with blood, and, as it were, carnified, so that they sink in water. This curious
foot, although its physiological significance is not apparent, has been the subject of much
speculation and experimental research. Bernard found that the pulmonary lesion did not
exist in birds, although section of both nerves was fatal. It had previously been ascer-
tained that, in some animals, death takes place with no alteration of the lungs. When
the entrance of the secretions into the air-passages was prevented by the introduction of
n canula into the trachea, the carnification of the lungs was nevertheless observed.
Without detailing all o£ the experiments upon which the explanation offered by Bernard
is based, it is sufficient to state that he observed a traumatic emphysema as a consequence
of the excessively labored and profound inspirations. Indeed, this can be actually seen

660 NERVOUS SYSTEM.

when the pleura' is exposed in living animals. As a result of this distention of the air-
cells, the pulmonary capillaries are ruptured in different parts, the blood becomes coagu-
lated, and the lungs are finally carnified. This cannot occur in birds, because the lungs
are fixed, and their relations are such that they are not exposed to excessive distention in
inspiration.

There is no satisfactory explanation of the remarkable changes in the respiratory
movements that follow section of the pneumogastrics.

In this connection we may note a curious fact, observed by Prof. Balton and others,
that the pneumogastrics sometimes reunite after division. In January, 1874, we divided
both pneumogastrics in a medium-sized dog. The pulse was immediately increased from
one hundred and twenty to two hundred and forty in the minute, and the number of
respirations fell from twenty-four to four or six. In ten days, the pulse and respirations
had become normal. The dog was then killed by section of the medulla oblongata, and
the reunion of the divided ends of the nerves was found to be nearly complete.

Sense of Want of Air. — The pneumogastrics may regulate the respiratory acts, but
they are not the medium through which the sense of want of air (besoin de respirer),
which gives rise to the movements of respiration, is conveyed to the nerve-centres. If
it be true, as it undoubtedly is, that section of both pneumogastrics in the neck modifies
the number and the character of the respirations, and that, after division of the nerves,
galvanization of their central ends arrests respiration, it is probable that this function is
normally influenced through these nerves, by impressions conveyed to the centres ; but
what this influence is or what is the mechanism of its action, we do not know.

The positive statement that the sense of want of air is not conveyed to the nerve-
centres through the pneumogastrics is based, to a great extent, upon our own experi-
ments, which have been fully detailed under the head of respiration ; and we shall here
give simply their results and the conclusions to which they lead.

The acts of respiration are involuntary, although they may be modified, within cer-
tain limits, through the will ; and they are due to an impression made upon the respira-
tory nervous centre, the medulla oblongata, which gives rise to the stimulus that ex-
cites the action of the inspiratory muscles. It has been conclusively shown by experi-
ments that, if artificial respiration be efficiently carried on in a living animal, so as to
supply air fully to the system, the sense of want of air is not appreciated, and the animal
makes no effort to breathe ; but, if respiration be imperfectly performed, the animal
almost immediately feels the want of air, and, in our experiments, the exposed respira-
tory muscles were thrown into violent but ineffectual contraction.

The principal points with reference to the location of the sense of want of air and its
action upon the nerve-centres, developed by our own experiments, are the following :

A dog was etherized, the chest was opened, exposing the heart and lungs, and arti-
ficial respiration was carried on by means of a bellows secured in the trachea. So long
as the supply of air was sufficient, the animal made no respiratory effort.

An artery was then exposed and the color of the blood noted. When the artificial
respiration was arrested, the animal made efforts to breathe as soon as the blood became
dark in the arterial system. We concluded from this, that the impression made upon
the respiratory nervous centre, giving rise to the movements of respiration, was due to
the action of non- oxygenated blood.

We assume, as a conclusion drawn from experiments upon the different nerve-centres,
that the medulla oblongata is the sole centre presiding over the respiratory acts. In dogs
prepared as indicated above, when the vessels given off from the arch of the aorta were
constricted so as to cut off the supply of oxygen-carrying fluid to the medulla oblongata,
the trunk and lower extremities being still supplied with arterial blood and the lungs
being efficiently supplied with fresh air by the bellows, the animals began to make
respiratory efforts in a little more than two minutes after constriction of the vessels.

These experiments demonstrate that the sense of want of air is felt when the supply

PNEUMOGASTRIC, OR PAR VAGUM NERVE. 661

of arterial blood to the medulla oblongata is cut off; and it is evident, also, from these
and other experiments, that this sense is not due necessarily to an irritation produced by
the circulation of blood containing an excess of carbonic acid in the respiratory nervous
centre.

These phenomena were observed without any modification, after division of both
pneumogastric nerves in the neck, and they seem to prove conclusively that the sense of
want of air is not transmitted to the respiratory nervous centre through the medium of
these nerves.1

Effects of Galvanization of the Pneumogastrics upon Respiration. — The phenomena
which follow galvanization of the pneumogastrics, although they are curious and inter-
esting, do not throw much light upon the relations of these nerves to respiration. We
have already mentioned the arrest of the respiratory movements by galvanization of the
superior laryngeal branches and of the central ends of the pneumogastrics after their divi-
sion in the neck. The main point of interest in this connection is the fact that the effects
observed are entirely reflex, galvanization of the peripheral ends of the divided nerves
having no direct action on the movements of the thorax.

In view of the very indefinite physiological applications of the experiments made by
galvanizing the nerves, we shall not give in detail the numerous observations upon this
subject, but shall simply state the results, as given in a recent and very elaborate work
upon respiration, by M. Bert :

" 1. Respiration may be arrested by excitation of the pneumogastrics (Traube), of the
larynx (01. Bernard), of the nostrils (M. Schiff), of most of the sensory nerves (M. Schiff,
an assertion that I have not been able to verify).

" 2. This arrest may take place either in inspiration or in expiration, through any one
of these nerves, without attributing it to the action of derived currents.

" 3. A feeble excitation accelerates the respiration ; a more powerful excitation
retards it ; a very powerful excitation arrests it. These words ' feeble ' and * powerful '
having, it is understood, only a relative sense for any one animal and under certain con-
ditions : what is feeble for one would be powerful for another, etc.

" I believe, in opposition to the opinion of Rosenthal, that section of the pneumogas-
trics does not increase the difficulty of arresting respiration ; at least, death by excitation
occurs much more easily in this case.

" 4. When the respiratory movements are completely arrested, it is always the same
for the general movements of the animal, which remains motionless.

" 5. Respiration returns even during excitation, and when this is arrested, it almost
always becomes accelerated.

" 6. Arrest in expiration is more easily obtained than arrest in inspiration ; there are
animals, indeed, in which it is impossible to effect the latter.

" V. If an excitation be employed sufficiently powerful to arrest respiration in inspi-
ration, all respiratory movements may be made to cease at the very moment when the
excitation is applied (inspiration, half-inspiration, expiration), either by operating upon
the pneumogastric, or operating upon the laryngeal. . . .

" Any feeble excitation of centripetal nerves increases the number of the respiratory
movements ; any powerful excitation diminishes them. A powerful excitation of the
pneumogastrics, of the superior laryngeal, of the nasal branch of the infra-orbital, may
arrest them completely ; if the excitation be sufficiently energetic, the arrest takes place
at the very moment it is applied. Finally, sudden death of the animal may follow a too
powerful impression, thus transmitted to the respiratory centre : all this being true for
certain mammalia, birds, and reptiles."

1 For a full account of these experiments, with their bearing upon certain respiratory phenomena before birth,
the reader is referred to the original article, entitled Experiment* on the Effects upon Re*pirntion <;rt;ittin<joffthe
Supply of Blood from the Brain and Medulla Oblongata, published in the New York Medical Journal, Novem-
ber, 1S7I. Since this publication, the experiments have been frequently repeated in public demonstrations, and the
conclusions verified.

662 NERVOUS SYSTEM.

The above formulated statements express the experimental facts at present known
•with regard to the influence of the pneumogastrics upon respiration. The pulmonary
branches themselves are so deeply situated that they have not as yet been made the sub-
ject of direct experiment, with any positive and satisfactory results.

Properties and Functions of the (Esopliageal Nerves. — The muscular walls and the
mucous membrane of the oesophagus are supplied entirely by branches from the pneumo-
gastrics. The upper portion is supplied by filaments from the inferior laryngeal branches,
the middle portion, by filaments from the posterior pulmonary branches, and the inferior
portion receives the cesophageal branches. These branches are both sensory and motor ;
but probably the motor filaments largely predominate, for the mucous membrane, although
it is sensible to the extremes of heat and cold, the feeling of distention, and a burning
sensation upon the application of strong irritants, is by no means acutely sensitive.

That the movements of the oesophagus are animated by branches from the pneumo-
gastrics, has been clearly shown by experiments. In the first place, except in animals in
which the anatomical distribution of the nerves is different from the arrangement in the
human subject, the entire oesophagus is paralyzed by dividing the nerves in the neck.
When the pneumogastrics are divided in the cervical region, in dogs, if the animals
attempt to swallow a considerable quantity of food, the upper part of the oesophagus is
found enormously distended. Bernard noted in a dog in which a gastric fistula had been
established, that articles of food given to the animal did not pass into the stomach, although
he made great efforts to swallow. An instant after the attempt, the matters were
regurgitated, mixed with mucus, but of course did not come from the stomach.

Direct experiments upon the roots of the pneumogastrics have shown that these
nerves influence the movements of the oesophagus, and that the motor filaments involved
do not come from the spinal accessory; but it is not known from what nerves these
motor filaments are derived.

Properties and Functions of the Abdominal Branches. — In view of the very extensive
distribution of the terminal branches of the pneumogastrics to the abdominal organs, it
is evident that the functions of these nerves must be very important, particularly since
it has been shown that the right nerve is distributed to the whole of the small intestine.
We shall consider the functions of these branches in their relations to the liver, the
stomach, and the intestines. We have no positive information with regard to their action
upon the spleen, kidneys, and suprarenal capsules.

Influence of the Pneumogastrics upon the Liver. — There is very little known with regard
to the influence of the pneumogastrics upon the secretion of bile ; and the most important
experiments upon the innervation of the liver relate to its glycogenic function. We
shall have little to say upon this subject, however, in addition to what we have already
stated in treating of the liver as a sugar-producing organ. The view which we have
advanced with regard to the glycogenic function is that the liver is constantly producing
sugar during life, which is completely washed out by the blood in its passage through
this organ, the liver itself containing little or no sugar, under normal conditions. With
this view, we are to look for sugar in the blood in certain situations, and not in the liver
itself; although, after death, a change of the glycogenic matter in the liver into sugar
takes place with great rapidity, and sugar may then be found in its substance. Normally,
sugar disappears in the lungs and is not found in the blood of the arterial system. The
presence of sugar in the urine is abnormal. If both pneumogastrics be divided in the
neck, and the animal be killed at a period varying from a few hours to one or two days
after, the liver contains no sugar, under the conditions in which it is generally found,
viz., a certain time after death. From experiments of this kind, Bernard concludes that
the glycogenic function is suspended when the nerves are divided. The experiments,
however, made by irritating the pneumogastrics. were more satisfactory, as in these he

PNEUMOGASTRIC, OR PAR VAGUM NERVE. 6G3

looked for sugar in the blood and in the urine and did not confine his examinations to
the substance of the liver.

After division of the pneumogastrics in the neck, if the peripheral ends be galvanized,
there is no effect upon the liver ; but, if galvanization be applied to the central ends, the
glycogenic function becomes exaggerated, and sugar makes its appearance in the blood
and in the urine. Bernard has made a number of experiments illustrating this point,
upon dogs and rabbits. The galvanic current employed was generally feeble, and it was
continued for from five to ten minutes, two or three times in an hour. In some instances
the irritation was kept up for thirty minutes. From these experiments, it is assumed that
the physiological production of sugar by the liver is reflex and is due to an impression
conveyed to the nerve-centres through the pneumogastrics. A very interesting and
adroit experiment by the same observer shows that section of the pneumogastrics be-
tween the lungs and the liver does not affect the production of sugar. This delicate
operation is performed by making a valvular opening in the chest, preventing the ingress
of air by suddenly forcing the finger into the wound, and then introducing a long, deli-
cate hook with a cutting edge, and dividing the nerves, which may be reached by the
finger in small dogs, and feel like tense cords by the side of the oesophagus. We have
already noted that the inhalation of irritating vapors and of anaesthetics produces a
hypersecretion of sugar by the liver.

The remarkable effects of irritating the floor of the fourth ventricle, by which we
can produce temporary diabetes, have been considered fully in connection with the gly-
cogenic function of the liver. This effect is not due to a direct transmission of the irri-
tation to the liver through the pneumogastrics, for the phenomena of hypersecretion are
observed in animals upon which this operation has been performed after section of both
pneumogastrics in the neck. It is probable, indeed, that the impression is conveyed to
the liver through the -sympathetic system, for it has been shown that animals do not
become diabetic after irritation of the floor of the fourth ventricle, when the branches
of the sympathetic going to the solar plexus have been divided. The operation, how-
ever, of dividing the sympathetic nerves in this situation is so serious, that it may inter-
fere with the experiment in some other way than by the direct influence of the nerves
upon the liver.

Influence of the Pneumogastrics upon tlie Stomach and Intestines. — The number of
observations that have been made upon the influence of the pneumogastric nerves on
digestion in the stomach is immense, and many of the earlier experiments were quite
contradictory. "We do not propose, however, to treat of this subject from a purely his-
torical point of view, for the reason that, before 1842 and 1843, when gastric fistulee
were first established in living animals, little was known of the normal movements of the
stomach and of the mechanism of the secretion of the gastric juice ; and, farthermore,
before the observations of Bouchardat and Sandras, in 1847, the effects of section of the
nerves in the neck upon the action of the oesophagus in deglutition were not understood.
If we study the literature of the subject anterior to 1842, we find a great deal of confu-
sion, due to the facts just stated. Leaving out of the question most of the earlier ex-
periments, we shall treat of the influence of the pneumogastrics upon the stomach and
intestines, under the following heads :

1. The effects of galvanization of the nerves.

2. The effects of section of the nerves upon the movements of the stomach in digestion.

3. The effects of section of the nerves upon the secretion of the gastric juice and the
chemical processes of digestion.

4. The influence of the nerves upon the small intestine.

Effects of Galvanization. — As the result of recent experiments, the effects of galvan-
ization of the pneumogastrics upon the movements of the stomach are unquestionable.
Longet has shown that the stomach contracts as a consequence of irritation of the nerves,
not instantly, but after the lapse of five or six seconds. lie explains some of the contra-

664 NERVOUS SYSTEM.

dictory results obtained by other observers by the fact that these contractions are very
marked during stomach-digestion, while they are wanting "when the stomach is entirely
empty, retracted on itself and in a measure in repose." According to the same author,
irritation of the splanchnic nerves, while it produces movements of the intestines, does
not affect the stomach. Judging from the tardy contraction of the stomach and the
analogy between the action of the pneumogastrics upon this organ and the action of the
sympathetic nerves upon the non-striated muscular tissue, Longet assumes that the motor
action of the pneumogastrics is due, not to the proper filaments of these nerves, but to
filaments derived from the sympathetic system. " This interpretation removes the sin-
gular physiological anomaly that an organ, the action of which is entirely removed from
the control of the will, should depend upon a voluntary, or cerebro-spinal nerve." This
explanation of the contradictory results of experiments and of the mechanism of the
action of the pneumogastrics upon the stomach seems entirely satisfactory and may be
accepted without reserve.

Effects of Section of the Pneumogastrics upon the Movements of the Stomach. — If the
pneumogastrics be divided in the neck in a dog in full digestion, in which a gastric fistula
has been established so that the interior of the organ can be explored, the following
phenomena are observed :

In the first place, before division of the nerves, the mucous membrane of the stomach
is turgid, its reaction is intensely acid, and, if the finger be introduced through the fis-
tula, it will be firmly grasped by the contractions of the muscular walls. When the
pneumogastrics are divided, under these conditions, the contractions of the muscular walls
instantly cease, the mucous membrane becomes pale, the secretion of gastric juice is
apparently arrested, and the sensibility of the organ is abolished. Paralysis of the
stomach, etc., had been noted, long before the observations of Bernard ; but his experi-
ments upon animals with a fistulous opening into the stomach are the most striking.

Notwithstanding the apparent arrest of the movements of the stomach in digestion by
section of the pneumogastrics, experiments carefully performed show that substances may
be very slowly passed to the pylorus, and that the movements, although they are greatly
diminished in activity, are not entirely abolished. This fact has been established beyond
question by the experiments of Schiff, who attributes the movements occurring after sec-
tion of the nerves to local irritation of the intramuscular terminal nervous filaments.

Effects of Section of the Pneumogastrics upon Digestion, etc. — When both nerves
are divided, in an animal in full digestion, the mucous membrane becomes pale and
flaccid, and the secretion of gastric juice is apparently arrested at once; but, if the ani-
mal survive the operation for a day or two, a certain quantity of juice may be secreted as
the result of local stimulation, and digestion of a very small quantity of food, finely divided
and introduced into the stomach by a fistulous opening, may take place. A serious
difficulty in the digestion of large masses of food after division of the nerves is due to the
cessation of the movements of the stomach. It is stated that digestion may be to a cer-
tain extent reestablished, under these conditions, by galvanizing the peripheral extremi-
ties of the divided nerves.

There is very little to be said with regard to the relations of the pneumogastrics to
the sensations of hunger and thirst. It would be very natural to infer, from the distribu-
tion of these nerves to the mucous membrane of the stomach, that they should be involved
in these sensations; but, in treating of this subject elaborately, in connection with ali-
mentation, we have shown that hunger and thirst really have their origin in the general
system, although the sensations are referred subjectively to the stomach and fauces, and
that, in all probability, the sensations persist after division of both pneumogastrics.

With regard to the influence of the pneumogastrics upon absorption from the stomach,
we have also mentioned the fact that the passage of poisons from the stomach into the
blood-vessels may be retarded by section of the nerves, but is not prevented.

Physiologists have given but little attention to the influence of the pneumogastrics

PNEUMOGASTRIC, OR PAR VAGUM NERVE. 665

upon the intestinal canal, for the reason that the distribution of the abdominal branches
to the small intestine, notwithstanding the researches of Kollmann, in 1860, does not
appear to have been generally recognized. The right, or posterior abdominal branch was
formerly supposed to be lost in the semilunar ganglion and the solar plexus, after sending a
few filaments to the stomach ; but, since it has been shown that this nerve is supplied to
the whole of the small intestine, its physiology, in connection with intestinal secretion,
has assumed considerable importance.

In a series of experiments, by Prof. Horatio C. Wood, Jr., of Philadelphia, the impor-
tance of the abdominal branches of the right nerve is fully illustrated. These experi-
ments show, in the most conclusive and satisfactory manner, that the pneumogastrics
influence intestinal as well as gastric secretion. One of the most interesting and curious
points in connection with their function is that, after section of the nerves in the cervical
region, the most powerful cathartics, croton-oil, calomel, podophyllin, jalap, arsenic, etc.,
fail to produce purgation, even in doses sufficient to cause death. The articles used were
either given by the mouth, just before dividing the nerves, or were injected under the
skin.

Although the observations of Dr. Wood are not entirely new, they are by far the most
extended and satisfactory, and were made with a knowledge of the fact of the distribu-
tion of the nerves to the small intestine. Dr. Wood quotes freely from the experiments
made by Sir Benjamin Brodie and by Dr. John Reid. Brodie failed to produce purging
in dogs, when both pneumogastrics had been divided in the neck, after the administration
of arsenic by the mouth and after injecting it under the skin. Dr. Reid made five experi-
ments, and, in all but one, it is stated that diarrhoea existed after division of the nerves. In
twenty experiments by Dr. Wood, there was no purgation after division of the nerves, in
one there was free purgation, and in one there was " some slight muco-fecal discharge.1'
From these, Dr. Wood concludes that, while section of the cervical pneumogastrics, in
the great majority of instances, arrests gastro-intestinal secretion and prevents the action
of purgatives upon the intestinal canal, a few exceptional cases occur in which these
effects are not observed.

The facts just mentioned are exceedingly interesting in connection with the experi-
ments of Traube upon the action of digitalis after section of the pneumogastrics. It will
be remembered that, in these experiments, digitalis failed to diminish the number of beats
of the heart when the nerves had been divided in the neck, showing that the separation
of the heart from its connections with the cerebro-spinal system removed the organ from
the peculiar and characteristic effects of the poison.

It would be interesting to determine whether the pneumogastrics influence the intes-
tinal secretions through their own fibres or through filaments received from the sympa-
thetic system ; but there are no experimental facts sufficiently definite to admit of a posi-
tive answer to this question. If the action take place through the sympathetic system,
as in the case of the stomach, the filaments of communication join the pneumogastrics
high up in the neck.

666 NERVOUS SYSTEM.

CHAPTER XX.

FUNCTIONS OF THE SPINAL COED.

General arrangement of the cerebro-spinal axis — Membranes of the encephalon and spinal cord — Cephalo-rachidian
fluid— Physiological anatomy of the spinal cord — Direction of the fibres after they have penetrated the cord by the
roots of the spinal nerves — General properties of the spinal cord — Action of the spinal cord as a conductor — Trans-
mission of motor stimulus in the cord— Decussation of the motor conductors of the cord— Transmission of sen-
sory impressions in the cord — The white substance of the posterior columns does not conduct sensory impres-
sions— Action of the gray matter as a conductor — Probable function of the cord in connection with muscular co-
ordination—Decussation of the sensory conductors of the cord— Summary of the action of the cord as a conductor
—Action of the spinal cord as a nerve-centre— Movements in decapitated animals— Definition and applications
of the term " reflex " — Eeflex action of the spinal cord — Question of sensation and volition in frogs after decapita-
tion— Character of movements following irritation of the surface in decapitated animals — Dispersion of impres-
sions in the cord— Conditions essential to the manifestation of reflex phenomena— Exaggeration of reflex excita-
bility by decapitation, poisoning with strychnine, etc. — Keflex phenomena observed in the human subject.

UNDER the head of special senses, we shall consider, in succeeding chapters, the prop-
erties and functions of the first and second nerves, the portio mollis of the seventh, or
auditory, and the gustatory nerves, comprising a part of the glosso-pharyngeal and a
small filament from the facial (the chorda tympani) going to the lingual branch of the
fifth. This will include a full account of the organs of smell, taste, sight, and hearing,
with a description of the general sensory nerves, as far as they are concerned in the sense
of touch. We shall here begin our history of the cerebro-spinal axis, which will include
the physiological anatomy, properties, and functions of the encephalon and the spinal cord.

General Arrangement of the Cerebro-spinal Axis. — The nervous matter contained in
the cavity of the cranium and in the spinal canal, exclusive of the roots of the cranial
and spinal nerves, is known as the cerebro-spinal axis. This portion of the nervous sys-
tem is composed of white and gray nervous matter. The fibres of the white matter act
as conductors. The gray matter constitutes a chain of ganglia, which act as nerve-
centres, receiving impressions and generating the so-called nerve-force. The gray matter
of the spinal cord also serves, to a greater or less extent, as a conductor.

The cerebro-spinal axis is enveloped in membranes, which are for its protection and
for the support of its nutrient vessels. It is surrounded, to a certain extent, with liquid,
and it presents cavities, as the ventricles of the brain and the central canal of the chord,
which contain liquid. The gray matter is distinct from the white, even to the naked
eye. In the spinal cord, the white substance is external and the gray is internal. The
surface of the brain presents an external layer of gray matter, the white substance being
internal. In the white substance of the brain, also, we find collections of gray matter.
As we should expect, from the similarity in function between the white matter and the
nerves, this portion of the cebro-spinal axis is composed largely of fibres. The gray
substance is composed chiefly of cells.

The encephalon is contained in the cranial cavity. In the human subject and in
many of the higher animals, its surface is marked by numerous convolutions, by which
the extent of its gray substance is very much increased. The cerebrum, the cerebellum,
and all of the encephalic ganglia are connected with the white substance of the encepha-
lon and with the spinal cord. With the encephalon and the cord, all of the cerebro-
spinal nerves are connected. The cerebro-spinal axis acts as a conductor, and its differ-
ent collections of gray matter, or ganglia, receive impressions conveyed by the sensory
conducting fibres, and generate nerve-force, which is transmitted to the proper organs
by -the motor fibres.

Membranes of the Encephalon and, Spinal Cord. — The membranes of the brain and
spinal cord are, the dura mater, the arachnoid, and the pia mater.

ARRANGEMENT OF THE CEREBRO-SPINAL AXIS. 667

The dura mater of the encephalon is a dense, fibrous membrane, in two layers, com-
posed chiefly of inelastic tissue, which lines the cranial cavity and is adherent to the
bones. In certain situations, its two layers become separated and form what are known
as the venous sinuses. The dura mater also sends off folds or processes of its internal
layer. One of these passes into the longitudinal fissure and is called the falx cerebri ;
another lies between the cerebrum and the cerebellum and is called the tentorium ;
another is situated between the lateral halves of the cerebellum and is called the falx
cerebelli. The dura mater is closely attached to the bone at the border of the foramen
magnum. From this point it passes into the spinal canal and forms a loose covering for
the cord. In the spinal canal, this membrane is not adherent to the bones, which have,
like most other bones in the body, a special periosteum. At the foramina of exit of the
cranial and the spinal nerves, the dura mater sends out processes which envelop the
nerves, with the fibrous sheaths of which they soon become continuous.

The arachnoid is an excessively delicate serous membrane, in two layers, the surfaces
of which are nearly in contact. The external layer lines the internal surface of the dura
mater. Like the other serous membranes, the arachnoid is covered with a layer of tes-
selated epithelium. There is a small amount of liquid between the two layers of the
arachnoid ; but by far the greatest quantity of liquid surrounding the cerebro-spinal
axis lies beneath both layers, in what is called the subarachnoid space. This is called
the cerebro-spinal, or cephalo-rachidian fluid. The arachnoid does not follow the con-
volutions and fissures of the encephalon or the sulci of the cord, but it simply covers their
surfaces. Magendie pointed out a longitudinal, incomplete, cribriform, fibrous septum in
the cord, passing from the inner layer of the arachnoid to the pia mater. A similar
arrangement is found in certain situations at the base of the skull.

The pia mater of the encephalon is a delicate, fibrous structure, exceedingly vascular,
seeming to present, indeed, only a skeleton net-work of fibres for the support of the ves
sels going to the nervous substance. This membrane covers the surface of the encephalon
immediately, follows the sulci and fissures, and is prolonged into the ventricles, where it
forms the choroid plexus and the velum interpositum. From its internal surface, small
vessels are given off which pass into the nervous substance.

The pia mater of the encephalon is continuous with the corresponding membrane of
the cord ; but, in the spinal canal, it is thicker, stronger, more closely adherent to the
subjacent parts, and its blood-vessels are by no means so numerous. In this situation,
many of the fibres are arranged in longitudinal bands. This membrane lines the anterior
snlcus and a portion of the posterior sulcus of the cord. It is sometimes spoken of as the
neurilemma of the cord. At the foramina of exit of the cranial and the spinal nerves,
the fibrous structure of the pia mater becomes continuous with the nerve-sheaths.

Between the anterior and posterior roots of the spinal nerves, on either side of the
cord, is a narrow, ligamentous band, the ligamentum denticulatum, which assists in hold-
ing the cord in place. This extends from the foramen magnum to the terminal filament
of the cord, and is attached, internally, to the pia mater, and externally, to the dura
mater.

It is not necessary to enter into a detailed description of the arrangement of the blood-
vessels, nerves, and lymphatics of the membranes of the brain and spinal cord, or of the
vascular arrangement in the substance of the cerebro-spinal axis, as these points are
chiefly of anatomical interest. The circulation in these parts presents certain pecu-
liarities. In the first place, the encephalon being contained in an air-tight case of inva-
riable capacity, it has been a question whether or not the vessels be capable of contrac-
tion and dilatation, or whether the quantity of blood in the brain be subject to modifi-
cations in health or disease. These questions may certainly be answered in the affirmative.
In infancy and in the adult, when an opening has been made in the skull, the volume of
the encephalon is evidently increased during expiration and is diminished in inspiration.
Under normal conditions, in the adult, it is probable that the amount of blood is increased

668 NERVOUS SYSTEM.

in expiration and diminished in inspiration ; but it is not probable that the cerebro-spinal
axis undergoes any considerable movements. The important peculiarities in the cerebral
circulation have already been fully considered in connection with the circulation. It
has been shown that the encephalic capillaries are surrounded or nearly surrounded by
canals (perivascular canal-system), which exceed the blood-vessels in diameter by from
T^_ to 4^-5- of an inch, and are connected with lymphatic trunks or reservoirs situated
under the pia mater. The system of canals may, by variations in its contents, serve to
equalize the amount of liquid in the brain as the blood-vessels are distended or contracted.

Cephalo-rachidian Fluid. — The greatest part of the fluid in the cranium and in the
spinal canal is contained in what is known as the subarachnoid space ; that is, between
the inner layer of the arachnoid and the pia mater, and not between the two layers of
the arachnoid. The ventricles of the encephalon are in communication with the central
canal of the cord, and are also connected with the general subarachnoid space, by a nar-
row, triangular orifice, situated at the inferior angle of the fourth ventricle. By this
arrangement, the liquid in the ventricles of the encephalon and in the central canal of the
cord communicates with the liquid surrounding the cerebro-spinal axis, and the pressure
upon these delicate parts is equalized.

As far as we know, the function of the cephalo-rachidian fluid is simply mechanical,
and its properties and composition have no very definite physiological significance. Its
quantity was estimated by Magendie, in the human subject, at about two fluidounces ;
but this was the smallest amount obtained by placing the subject upright, making an
opening in the lumbar region and a counter-opening in the head to admit the pressure
of the atmosphere. The exact quantity in the living subject could hardly be estimated in
this way ; and it is difficult, indeed, to see how any. thing more than a roughly approx-
imative idea could be obtained. The quantity obtained by Magendie probably does not
represent the entire amount of liquid contained in the ventricles and in the subarachnoid
space, but it is the most definite estimate that has been given.

The discharge of a certain quantity of the cephalo-rachidian fluid does not produce
any marked derangement in the action of the nervous system. When the liquid is
allowed to flow spontaneously through a small trocar introduced without division of the
muscles of the neck, there follows no serious nervous disturbance ; but, when the liquid
is drawn out forcibly with a syringe, the animal first becomes enfeebled and afterward
seems affected with general paralysis. These phenomena are probably due, not so much
to removal of the fluid, as to congestion of blood-vessels and even effusion of blood,
which follow sudden diminution in the pressure. Sudden increase in the quantity of
liquid surrounding the cerebro-spinal axis produces coma, probably from compression of
the centres. This fact was demonstrated by Magendie, by injecting water in animals,
and also by compressing the tumor, in cases of spina bifida in the human subject, by
which the fluid was pressed back into the spinal canal. In the cases of spina bifida, the
subject, during the compression, fell into coma, which was instantly relieved by remov-
ing the pressure. The cephalo-rachidian fluid is speedily reproduced after its evacuation.
In all probability it is secreted by the pia mater.

The general properties and composition of the fluid under consideration are, in brief,
the following : It is perfectly transparent and colorless, free from viscidity, of a distinctly
saline taste, alkaline reaction, and it resists putrefaction for a long time. It is not affected
by heat or acids. As we should expect from its low specific gravity and purely mechani-
cal function, it contains a large proportion of water (981 to 985 parts per thousand). It
contains a considerable quantity of chloride of sodium, a trace of chloride of potassium,
sulphates, carbonates, and alkaline and earthy phosphates. In addition, it contains
traces of urea, glucose, lactate of soda, fatty matter, cholesterine, and albumen.

As a summary of the function of the cephalo-rachidian fluid, it may be stated, in gen-
eral terms, that it serves to protect the cerebro-spinal axis, chiefly by equalization of the

PHYSIOLOGICAL ANATOMY OF THE SPINAL CORD. C69

pressure in the varying condition of the blood-vessels, accurately filling the space be-
tween the centres and the bony cavities in which they are contained. That the blood-
vessels of the cerebro-spinal axis are subject to variations in tension, is readily shown by
introducing a canula into the subarachnoid space, when the jet of fluid discharged will
be increased with every violent muscular effort. The pressure of the fluid, in this in-
stance, could only be affected through the blood-vessels.

Physiological Anatomy of the Spinal Cord.

The spinal cord, with its membranes, the roots of the spinal nerves, and the sur-
rounding liquid, occupies the spinal canal and is continuous with the encephalon. Its
length is from fifteen to eighteen inches, and its weight is about an ounce and a half.
Its form is cylindrical, being slightly flattened in certain portions. It extends from the
foramen magnum to the first lumbar vertebra. It presents, at the origin of the brachial
nerves, an elongated enlargement, and a corresponding enlargement at the origin of the
nerves which supply the lower extremities. It terminates below in a slender, gray fila-
ment, called the filum terminale. The sacral and coccygeal nerves, after their origin
from the lower portion of the cord, pass downward to emerge by the sacral foramina,
and they form what is known as the cauda equina.

The substance of the cord is formed of white and gray matter, the white matter
being external. The proportion of white matter to the gray is greatest in the cervical
region. This fact is important in studying the course of the fibres and in view of the
functions of the cord as a conductor. The inferior, pointed termination of the cord con-
sists entirely of gray matter.

The cord is marked by an anterior and a posterior medium fissure, and by imperfect
and somewhat indistinct anterior and posterior lateral grooves, from which latter arise the
anterior and the posterior roots of the spinal nerves. The posterior lateral groove is
tolerably well marked, but there is no distinct line at the origin of the anterior roots.
The anterior median fissure, or sulcus, is perfectly distinct. It penetrates the anterior
portion of the cord in the median line for about one-third of its thickness and receives a
highly vascular fold of the pia mater. It extends to the anterior white commissure. The
posterior fissure is not so distinct as the anterior, and it is not lined throughout by a fold
of the pia mater, but is filled with connective tissue and blood-vessels, which form a sep-
tum posteriorly, between the lateral halves of the cord. The posterior median fissure, so
called, extends nearly to the centre of the cord, as far as the posterior gray commissure.

Physiologically and anatomically, the cord is divided into two lateral halves ; but the
division of each half into columns is not so distinct. Anatomists generally regard a half
of the cord as consisting of three columns : The anterior column is bounded by the
anterior fissure and the origin of the anterior roots of the spinal nerves ; the lateral col-
umn is included between the anterior and the posterior roots of the nerves ; the poste-
rior column is bounded by the line of origin of the posterior roots and by the posterior
fissure. Some anatomists include the lateral with the anterior column, under the name of
the antero-lateral column, taking in about .two-thirds of the cord. Next the posterior
median fissure, is a narrow band, marked by a faint line, which is sometimes called the
posterior median column.

The arrangement of the white and the gray matter in the cord is seen in a trans\vr-r
section. The gray substance is in the form of n letter IT, presenting two anterior and
two posterior cornua connected by what is called the gray commissure. The anterior
cornua are the shorter and broader, and they do not reach to the surface of the cord.
The posterior cornua are larger and narrow, and they extend nearly to the surface. ;it
the point of origin of the posterior roots of the spinal nerves. In the centre of tin- irmy
commissure, is a very narrow canal, lined by cells of ciliated epithelium, called tin.-
central canal. This is in communication above with the fourth ventricle, and it extends

670 NERVOUS SYSTEM.

below to the filum terminate. That portion of the gray commissure situated in front
of this canal is sometimes called the anterior gray commissure, the posterior portion
being known as the posterior gray commissure. The central canal is immediately sur-
rounded by connective tissue. In front of the gray commissure, is a mass of white
substance known as the anterior white commissure.

13

12

10

FIG. 222.— Transverse section of the spinal cord at the origin of the ffth pair of cervical nerves. (Stilling.)

In this figure, the white substance of the cord is represented in black, to show more clearly the limits of the gray
matter: 1, 1, antero-lateral columns; 2, 2, posterior white columns; 8, anterior median fissure; 4, posterior
median fissure; 5, white commissure ; 6, gray commissure: 7, central canal; 8, 9, anterior cornua of gray mat-
ter; 10, 10, group of large multipolar cells ; 11, 11, 11, anterior roots of the spinal nerves; 12, posterior cornua
of gray matter ; 18, posterior roots of the spinal nerves.

The proportion of the white to the gray substance is variable in different portions of
the cord. In the cervical region, the white substance is most abundant, and, in fact, it
progressively increases in quantity from below upward throughout the whole extent of
the cord. In the dorsal region, the gray matter is least abundant, and it exists in great-
est quantity in the lumbar enlargement.

The white substance of the cord is composed of nerve-fibres, connective-tissue ele-
ments, and blood-vessels, the latter arranged in a very wide and delicate plexus. The
nerve-fibres are variable in their size and are composed of the axis-cylinder surrounded
by the medullary substance, without, however, the investing membrane. We shall speak
farther on of the direction of the fibres in the cord.

The anterior cornua of gray matter contain blood-vessels, connective-tissue elements,
very fine nerve-fibres, and large multipolar nerve-cells, which are sometimes called motor
cells. The posterior cornua are composed of the same elements, the cells being much
smaller, and the fibres exceedingly small, presenting very fine plexuses. The cells in this
situation are sometimes called sensory cells. Near the posterior portion of each poste-
rior cornu, is an enlargement, of a gelatiniform appearance, containing numerous small
cells and fibres, called the substantia gelatinosa.

The foregoing description of the different structures and parts of the cord is neces-
sary to a comprehension of the direction of the fibres in the spinal axis and their con-
nections with the nerve-cells, which is the anatomical basis of our knowledge of its
physiology. The connections between the cells and the fibres have already been de-
scribed in the chapter upon the general structure of the nervous system. The multipolar
nerve-cells are supposed to present certain prolongations which do not branch and are
directly connected with the medullated nerve-fibres. These are called nerve-prolonga-

PHYSIOLOGICAL ANATOMY OF THE SPINAL CORD.

671

tions. In addition, fine, branching poles are described under the name of protoplasmic
prolongations.

The direction of the fibres in the cord is one of the most difficult and complicated
problems in physiological anatomy ; and, especially as regards the posterior roots of the
nerves, it is one which cannot as yet be elucidated by purely anatomical investigations,
but requires the aid of experimental and pathological observations. In order to under-
stand fully the importance of this question, it is necessary to bear in mind the following
physiological facts, which it is desirable, if possible, to explain by the anatomical rela-
tions and connections of the fibres and cells :

1. The cord serves as a conductor of impressions to the brain, conveyed to it through
the posterior roots, and of stimulus generated by the brain and passing from the cord
by the anterior roots of the spinal nerves. This action is crossed, the decussation taking
place mainly at the medulla oblongata, for the anterior portions, and throughout the
whole extent of the cord, for the posterior portions.

FIG. 223.— Transverse section of the spinal cord of a child *?> months ol<L (it the middle of the I umlar enlarge-
ment, t/- ,'(>'/ iritli, potasrio-chlorid* of gold and nitrate of uranium; magnified 20 diameters. Bu
means of these reagent*, the direction of the fibres in the gray substance is rendered unusually distinct.
(Gerlach.)

a, anterior columns; &, posterior columns ; c, lateral columns ; d, anterior roots ; e, posterior roots : /. anterior white
commissure, in communication with the fasciculi of the anterior cornua and the anterior columns : (/. centra]
canal with its epithelium; h, surrounding connective substance of the central canal; /. transverse fasciculi ot
the gray commissure in front of the central canal; k, transverse fasciculi of the gray commissure behind toe
central canal; /, transverse section of the two central veins ; m. anterior cornua : >t, great, lateral cellular layer
of the anterior cornua; <>. lesser, anterior cellular layer; />, smallest, median cellular layer; q, posterior cornua;
r, ascending fasciculi in the posterior cornua; s, substantia gelutinosa.

2. Independently of its action as a conductor, the cord, disconnected from the rest of
the eeivbro-spinal axis, acts as a nerve-centre, by virtue of its gray matter and the fibres
connected with the cellular elements of this substance.

Bearing in mind these points, which are matters of positive demonstration, we are
prepared to study the anatomical relations of the fibres and cells. In this, we shall con-

672 NEEYOUS SYSTEM.

tent ourselves with the following very recent description, quoted in full from Gerlacb,
which embodies about all of our positive knowledge upon the subject, presented in the
clearest manner possible. This extract, the translation of which is almost literal, should
be carefully studied by those who desire to learn what is known at the present day
with regard to the physiological anatomy of the cord. As a preparation for this study,
it would be well to closely examine Fig. 223, which gives a general view of the different
parts of the cord, shown in a transverse section :

" With the present methods and means of investigation at our command, we can
scarcely give an exact, detailed description of the course of the fibres in the spinal cord,
the groundwork of the physiology of this organ. Investigations up to this time afford
at least the outlines of a sketch which, as regards' the course of the fasciculi of the ante-
rior roots, has a tolerably definite basis ; and, on the other hand, with regard to the fas-
ciculi going to the spinal cord through the posterior roots, is quite incomplete and un-
certain.

" The fasciculi of the anterior roots, after their entrance into the cord, pass diagonally
through the white substance, and, as such, are not at all concerned in its formation. On
the contrary, they pass immediately to the gray substance of the anterior cornua, and, by
their prolongations, are in direct connection with the nerve-cells in this situation, which,
accordingly, are to be regarded as the elements of origin of the anterior roots in the
cord. The protoplasmic processes of these nerve-cells form parts of the fine plexuses of
nerve-fibres in the gray substance, from which larger nerve-fibres take their origin.
These, extending in two directions, leave the gray substance, to pass up in the white sub-
stance to the brain. In consequence of the entrance of additional nerve-fibres, the
white substance is necessarily increased in quantity in the cord from below upward.
With regard to the course of the fasciculi which pass out of the gray substance of the
anterior cornua, these are to be divided into median and lateral. The median fasciculi
pass immediately into the anterior white commissure, where they decussate with corre-
sponding fasciculi from the opposite side, to pass upward again in the anterior column of
the other half of the cord. The lateral fasciculi go to the lateral columns of the same
side, in which they pass to the brain, having first undergone decussation in the anterior
pyramids of the medulla oblongata.

" The posterior nerve-roots enter horizontally, running in the white substance of the
spinal cord, in a direction from without inward toward the median line, and here divide
into two portions. The lateral portion, the smaller, retains the horizontal direction and
passes through the substantia gelatinosa, dividing into fine and the finest bundles, in the
manner mentioned above, to take part in the formation of the vertical bundle of fibres,
which lies immediately in front. Here the fibres pass onward, a portion of them ascend-
ing and a portion descending. The fibres of the lateral portion of the posterior roots do
not remain very long in the vertical bundle, but curve forward in a horizontal plane,
and in this way reach the portion of the posterior cornua containing a fine plexus of
nerve-fibres.

" The median (larger) portion of the posterior root-fibres passes to that portion of the
posterior column which bounds the substantia gelatinosa internally and posteriorly; and
curbing, takes here a vertical course to pass into the posterior columns, extending chiefly
upward, but perhaps downward as well. The median posterior root-fibres then under-
go another deflection, by which they again take a horizontal direction, and pass to the
gray substance of the posterior cornua, in part through the median portion and in part
by the inner border of the substantia gelatinosa. With regard to the farther course of
the posterior root-fibres, it is impossible to present positive explanations, for the reason
that the present methods of investigation do not afford any means of distinguishing the
posterior fibres from the nerve-tubes in the vertical fasciculi of the posterior cornua, or
those passing from the gray substance into the posterior columns to ascend to the brain.
The numerous divisions which the posterior root-fibres penetrating the posterior cornua

GENERAL PROPERTIES OF THE SPINAL CORD. 673

immediately undergo indicate, however, that a portion of them is lost directly in the fine
nerve-plexus of the gray substance. But at the same time there are numerous fibres
which extend forward, and others which take a more or less wavy course toward the
median line. The first, perhaps, can be regarded as posterior root-fibres, which pass in
a forward direction in the nervous plexus ; the latter, on the other hand, belong to the
commissural fibres, which cross the median line in the gray substance in front of and
behind the central canal. In my opinion, the fibres which penetrate the posterior com-
missure are not to be regarded as belonging directly to the posterior roots, but are to be
considered as fibres which pass backward to go either to the vertical fasciculi of the gray
substance or to pass to the brain in the posterior columns. If this idea be correct, and
it is sustained by analogous conditions in the anterior cornua, the following view may be
given of the course of the fibres of the posterior roots which penetrate the gray sub-
stance: 'A portion of the posterior root-fibres, immediately after their entrance into
that portion of the gray substance which contains a nerve-plexus, is lost in this plexus ;
another portion extends farther forward, and, in proportion as the fibres pass forward,
they likewise take part, by constant divisions, in the formation of the nerve-plexus. This
plexus, in which larger and smaller nerve-cells are interspersed as it were as knotted
points (Knotenpunlcte\ is in direct connection with the plexus of the anterior cornua.
From these cells nerve-fibres arise, which cross the median line in the gray commissure
in front of and behind the central canal, then curve backward to pass up to the brain, in
part in the vertical fasciculi of the posterior cornua, in part in the posterior columns,
between both of which numerous connections may exist which are as yet inextricable.'
This view involves a complete decussation in the spinal cord, through the fibrous elements
of the posterior roots passing into this part. Whether this be in reality a complete or a
partial decussation in this situation, a part of the fibres arising from the nerve-plexus
passing simply backward without crossing the median line, cannot be determined by
definite anatomical investigations ; but pathological researches, as well as the experi-
mental results of that most competent observer, Brown-Sequard, are decidedly in favor
of a complete decussation.

" Finally, it must be admitted that two points especially are evident :
" 1. In the direction of the nerve-fibres which enter through the posterior roots, the
gray substance has more numerous connections than in those which pass to the spinal
cord through the anterior roots.

"2. The morphological distinction determinable between the anterior and the pos-
terior roots is, that the former take their origin directly from the nerve-cells by means
of the nerve-prolongations, while, in the latter, it is only indirect through the nerve-plexus
with the protoplasmic prolongations, and in this wise they are in communication with
the nerve-cells."

General Properties of the Spinal Cord.

In treating of the functions of the spinal cord, we shall consider, first, its general
properties, as shown by direct stimulation of its substance in different situations ; next,
its functions as a conductor ; and, finally, its action as a nerve-centre.

The first indication that the different columns of the cord were possessed of different
properties is to be found in the experiments of Magendie. This observer, however, was
somewhat indefinite in his conclusions, particularly with regard to the anterior columns ;
but he stated distinctly that the posterior columns are sensitive : " If we lay bare the
cord in any portion of its extent, and if we touch, or prick slightly posteriorly, the two
fasciculi situated between the posterior roots, the animal gives signs of exquisite sensi-
bility; if, on the other hand, we make the same trials upon the anterior portion, the
evidences of sensibility are scarcely apparent." Since this time, numerous observers
have experimented upon the different columns, both on the surface and in the deep por-
tions of the cord, with varying results. These observations we do not propose to discuss
43

674 NERVOUS SYSTEM.

fully in detail, but shall refer simply to certain of them, made within a few years with
the advantage of a knowledge of the reflex phenomena following irritation of the cord,
which must always be taken into consideration in such experiments.

In 1861, Chauveau, as the result of numerous experiments performed upon horses,
cows, sheep, goats, rabbits, pigs, dogs, and cats, stated that the antero-lateral columns
of the cord were inexcitable, both on the surface and in the deep portions. The facts
upon which this assertion was based were, that direct stimulation of these portions of the
cord in living animals, whether by mechanical means or by feeble galvanic shocks, pro-
duced no contraction of muscles and no pain. Upon irritating the posterior columns,
either by mechanical or galvanic stimulus, Chauveau noted pain and reflex movements
when the irritation was applied to the surface, but the results were negative when the
deep portions of the columns were operated upon. The surface of the posterior columns
seemed to possess the same general properties as the posterior roots of the nerves, espe-
cially near the roots, where the sensibility was most marked, gradually diminishing in
intensity toward the median line ; but the deep portions of the cord were everywhere
found completely insensible and inexcitable.

The experiments and conclusions of Chauveau have a most important bearing upon
the physiology of the cord, and they are opposed to the views of the majority of physio-
logical writers, although they have been admitted by some experimenters. We shall dis-
cuss first the experiments upon the antero-lateral columns, which are most remarkable
in their negative results. We shall use the term excitability as signifying the property of
the cord which enables it to conduct a stimulus applied directly to it to certain muscles,
producing convulsive movements confined to these muscles, and not of a reflex character.
We shall apply the term sensibility to the property by virtue of which an irritation directly
applied is conveyed to the brain and produces a painful impression.

The experiments of Chauveau and some others upon the antero-lateral columns are
simply negative ; but their results are directly opposed to those of numerous experimenters,
who have produced local and restricted convulsive movements by direct irritation of both
the superficial and the deep portions of these columns.

With regard to the posterior columns, the views of Chauveau are in advance of those
of previous observers, only in so far as he has shown that, although the surface of this
portion of the cord is endowed with sensibility, its deeper portions are entirely insensible,
except in the immediate proximity of the posterior roots of the nerves.

In view of the importance of the question under consideration, and of the contradic-
tory results of experiments, we repeated, in 1863, the experiments of Chauveau, under
conditions as nearly physiological as possible. We had often had occasion to note the
diminished sensibility of the roots of the spinal nerves immediately following the very
severe operation of opening the spinal canal, and had also noted that the sensibility
increased, probably approaching the normal standard, after the animal had been allowed
a few hours of repose. For this reason, we made our observations about two hours after
the first operation. To avoid the suspicion of an extension of the galvanic current beyond
the portion of the cord which we desired to stimulate, the irritation was first made by
simply scratching the parts with the point of a needle. The following experiment is the
type of several, in all of which the results were identical :

May 28, 1863, at 1 p. M., the laminae and the spinous processes of the three lower
lumbar vertebras were removed from a medium-sized dog. There was no very great
haemorrhage. The spinal cord and the roots of three of the nerves were exposed, and the
wound was then closed. The operation was performed with the animal under the influ-
ence of ether, and it lasted about three-quarters of an hour.

About two hours after the first operation, the animal was brought before the class at
the Long Island College Hospital. The wound was opened, and the properties of the
anterior and posterior roots were demonstrated. The following observations were then
made upon the spinal cord :

GENERAL PROPERTIES OF THE SPINAL CORD. 675

The external surface of the posterior columns was irritated by scratching with the
point of a needle. This produced pain, the more marked the nearer the irritation was
brought to the origin of the posterior roots. The surface of the cord was almost insen-
sible at the median line. A feeble galvanic stimulus was then applied by means of a
pince electrique, with the same results. The deep portions of the posterior columns
were then irritated, but without effect.

The cord was then divided transversely, and mechanical and galvanic stimulus were
applied to the cut surfaces.

The surface of the upper end of the cord was irritated with the needle, and the needle
was plunged deeply into its substance, without effect. The same negative results followed
application of the galvanic stimulus.

The lower end of the cord was then elevated with a hook, and the surface of the
anterior columns was irritated by the needle and by galvanism. The invariable effect
was convulsive movements in the lower extremities, without pain. The same irritation
was applied to the deep portions of the anterior columns with like results ; viz., con-
vulsive movements in the lower extremities, following the irritation immediately.

The above-mentioned phenomena were fully verified by repeated experiments, and
the animal was then killed by section of the medulla oblongata.

The general movements accompanied by evidences of pain were readily distinguish-
able from the local convulsive movements with no pain.

This experiment fully confirms the observations of Chauveau with regard to the pos-
terior columns, but it shows, in opposition to Chauveau, that the anterior columns are
excitable, both at the surface and in the deep portions. The recent observations of
Vulpian are also opposed to the results obtained by Chauveau with regard to the antero-
lateral columns. From a number of carefully-executed experiments, Vulpian draws the
following conclusions :

ul. The gray substance is absolutely inexcitable.

" 2. The anterior fasciculi possess a certain degree of motor excitability.

"3. There is no doubt that the posterior fasciculi are very excitable. They are
sensitive and excito-motor if the cord be left intact, and simply excito-motor if the
cord be divided transversely and separated from the encephalon. It is the same, but
to a less degree, in that portion of the lateral fasciculi contiguous to the posterior
fasciculi."

In the face of definite and positive experiments showing the excitability of certain
portions of the cord, it is impossible to accept the purely negative results obtained by
Chauveau and others.

As the result of the most definite and reliable experiments of others, bearing upon the
question of the properties of the cord, and of our own observations, we have arrived at
the following conclusions:

The gray substance is probably inexcitable and insensible under direct stimulation.

The antero-lateral columns are insensible, but are excitable both on the surface and
in their substance ; and direct stimulation of these columns produces convulsive move-
ments in certain muscles, which movements are not reflex and are not attended with
pain. The lateral columns are less excitable than the anterior columns.

The surface, at least, of the posterior columns is very sensitive, especially near the
posterior roots of the nerves. The deep portions of the posterior columns are probably
insensible, except very near the origin of the nerves.

The above conclusions refer only to the general properties of different portions of the
cord, as shown by direct stimulation, in the same way that we demonstrate the general
properties of the nerves in their course. In all probability, the fibres in the white and
gray substance of the central nervous system conduct motor stimulus from the brain and
sensory impressions to the brain, while they themselves may be insensible and inexcit-
able under direct stimulation.

676 NERVOUS SYSTEM.

Transmission of Motor Stimulus in the Cord. — The antero-lateral columns of the cord,
in both the white and the gray substance, are entirely insensible to direct irritation, and
they conduct the motor stimulus from the centres to the periphery. This statement may
be accepted, as the result of positive demonstration, with very little qualification. If the
posterior columns of the cord be divided or even removed for a certain length, the animal
retains the power of voluntary motion intact. On the other hand, if the antero-lateral
columns of the cord be divided on both sides, the power of voluntary motion is lost abso-
lutely in all parts supplied . with nerves coming from the cord below the section. It
would be an interesting point to determine positively the relative importance of the white
and the gray substance of the anterior columns in the transmission of motor stimulus ;
but this has thus far been impossible. We cannot with certainty divide the gray matter
of the anterior columns completely and leave the white substance intact, nor can we
divide the white substance without injuring the gray. As far as experiments go, however,
they seem to show that transmission is not effected exclusively by the white substance,
but that the gray matter plays an important part in this function. We shall refer far-
ther on to the action of the gray substance in the transmission of sensory impressions.

It is evident, from anatomical facts as well as from the results of direct experimenta-
tion, that the fibres of conduction of the motor stimulus pass from the brain to the anterior
roots of the nerves, through the spinal cord, from above downward, and that there is no
other medium for the transmission of the will to the muscles. Wherever the cord be
divided, all the muscles supplied by nerves given off below the section are paralyzed.
From the brachial enlargement of the cord, nerves of motion pass to the superior extremi-
ties, and the inferior extremities are supplied mainly by nerves coming from the lumbar
enlargement. The direction of these motor fibres in the cord itself has been elucidated
only by experiments upon living animals. If the anterior columns alone be divided in
the dorsal region, there is almost complete paralysis of the lower extremities. If the
lateral columns be divided in this situation, without injuring the anterior columns, volun-
tary movements of the lower extremities are diminished but are not abolished. If the
anterior columns be divided high up in the cervical region, there is a diminution in the
voluntary movements, but this is by no means so marked as when the section is made in
the dorsal region ; but, if the lateral columns be divided in the upper cervical region, the
paralysis is almost or quite complete. These facts clearly show that the situation of the
chief motor conductors of the cord is different in the dorsal and in the cervical region.
In the dorsal region, while conduction of the motor stimulus takes place through fibres
contained both in the anterior and in the lateral columns, the transmission is mainly
through the anterior columns, the lateral columns being much less important. In the
cervical region, the conditions are reversed, and the conduction takes place chiefly by
means of the lateral columns. Passing from above downward, therefore, the motor
fibres are situated, in the cervical region, mainly in the lateral columns ; but progres-
sively, as they pass through the dorsal and the lumbar portions of the cord, these fibres
change their location and are found chiefly in the anterior columns.

Eecent observations have not sustained the old idea that the lateral columns of the
cord contain fibres which preside specially over the movements of the thorax. The
experiments of Yulpian upon this point are conclusive. If the lateral column be divided
upon one side at about the third or fourth cervical vertebra, there is considerable enfee-
blement of the muscles of the thorax upon the corresponding side, but there is also partial
loss of power in the limbs, which is more marked in the anterior extremity. This
diminution in power in the thoracic muscles is such that, in ordinary tranquil respiration,
the side corresponding to the section does not move ; but, in difficult respiration or in
crying, the movements are very marked.

Decussation of the Motor Conductors of the Cord. — Well-established anatomical and
pathological facts show conclusively that there is a complete decussation of the motor

FUNCTIONS OF THE SPINAL CORD AS A CONDUCTOR. 677

conductors of the cord ; so that the stimulus of volition generated in one lateral half of
the brain always passes to the opposite half of the body. If a lesion occur in the brain
upon one side, so as to produce total paralysis of motion, the opposite side of the body is
paralyzed, while voluntary motion is absolutely intact on the side corresponding to the
injury. In the anterior pyramids of the medulla oblongata, the decussation of the fibres
is easily demonstrated anatomically. In view of these facts, concerning which there is
no difference of opinion, it only remains to show by physiological experiments that decus-
sation actually takes place at the medulla oblongata, and to submit to the same method
of inquiry the following important question : Assuming that crossing of motor fibres takes
place at the medulla, is this the sole seat of decussation of these fibres, or does it also
take place in certain portions of the cord below ?

The question of decussation at the medulla oblongata is easily answered. In the first
place, we have the crossed action in hemiplegia and the easy anatomical demonstration
of the decussating fibres. The experimental confirmation of these facts is not so simple,
for the reason that animals survive operations upon the medulla oblongata for a very
short time. As far as can be learned, however, from the latter mode of inquiry, the con-
clusions drawn from anatomy and pathology are fully sustained. If the medulla be
exposed in a living animal, and "if a section is made longitudinally just at the place of
the decussation of the anterior pyramids, so as to divide completely all of the decussating
elements, we find that, although the animal lives some time after the operation, it has no
voluntary movement at all in any of the limbs, which are almost always the seat of con-
vulsions." (Brown-Sequard.)

The question of decussation of motor fibres in the cord itself is one which can be
settled only by physiological experiments, as the course of the decussating fibres, if they
exist, cannot be demonstrated anatomically. It is remarkable that Galen submitted this
point to experimental investigation, by dividing the cord longitudinally in the median
line in the lumbar region. This operation was not followed by loss of voluntary power
in the lower extremities, showing that the motor fibres do not cross the median line, at
least in this portion of the cord. Recent experiments upon the cervical portions of the
cord show that there is a very slight decussation of motor fibres in this situation. The
first observations pointing to this conclusion are those of Brown-Sequard. "There is
always, even in mammals, after a transversal section of the whole or a lateral half of the
spinal cord, at least some appearance of voluntary movements in the side of the injury,
and always also a diminution of voluntary movements in the opposite side; so that, in
animals, there seems to be in the spinal cord a decussation of a few of the voluntary
motor conductors. As there seems to be no such decussation in man, at least according
to several pathological facts, we shall not insist upon its existence in animals."

Van Kempen has repeated and extended the very remarkable experiment of Galen,
with the most satisfactory results. This observer made a median, longitudinal section
of the cord in dogs and rabbits, at the site of the fifth, sixth, and seventh cervical ver-
tebra. " This experiment was followed by partial paralysis of voluntary movements in
the posterior extremities, so that the animal thus operated upon moved the posterior
limbs and was able to change his position, without, however, being able to raise
himself."

As there is some difference in the results of observations upon different animals, and
as decussating motor fibres have never been demonstrated in man, it is impossible to
apply the above experiments without reserve to the human subject ; but they show,
nevertheless, that, in mammals, the motor columns of the cord probably do not decussate
in the dorso-lumbar region; that partial decussation occurs in the cervical ivgion ; and
that the decussation is completed in the anterior pyramids of the medulla oblongata.

Transmission of Sensory Impressions in the Cord.— Early in the physiological his-
tory of this portion of the nervous system, Longet made a number of experiments, which

678 NERVOUS SYSTEM.

seemed to show that the posterior columns of the cord were the conductors of sensory
impressions to the brain, and that the antero-lateral columns transmitted the motor stim-
ulus. These were made hy applying a stimulus directly to the cord itself. Longet dis-
credited observations made by dividing different portions of the cord, for the reason that
he supposed that the mere operation of exposing the cord and of removing the dura
mater was followed by a depression of the nervous action sufficient to render the evidences
of sensibility in the lower extremities scarcely appreciable. The conclusions drawn from
these experiments were at first accepted by nearly all physiological writers, and it was
generally admitted that the transmission of sensory impressions was effected solely by
the posterior columns. It was found that the gray matter of the cord was both insen-
sible and inexcitable, and the conduction was supposed to take place exclusively through
the white substance. The views of Longet, however, were in direct opposition to those
of Bellingeri, who claimed, in 1823, to have demonstrated by experiment, that sensory
impressions were conveyed to the brain exclusively by the gray substance of the cord,
and that sensibility persisted in the lower extremities after complete section of the pos-
terior white columns.

At the time the above-mentioned experiments were made, our knowledge of the prop-
erties of the cord was very incomplete, and it was difficult to understand how any of its
fibres could conduct sensory impressions and yet be insensible to direct stimulation ; but
now we know that the gray matter does act as a conductor, and yet it is certainly insen-
sible. The simple questions now to be determined are the following :

1. Does or does not the white substance of the posterior columns of the cord conduct
sensory impressions to the brain ?

2. Does the entire gray substance of the cord act as a conductor of sensation ?

3. Do both the gray matter of the cord and the white substance of the posterior col-
umns act as conductors, or does either one act to the exclusion of the other ?

These questions may now be considered as definitively answered by the most positive
and unmistakable results of experiments upon living animals, which, while they render
the precise function of the white substance of the posterior columns to a certain extent
a matter of conjecture, leave no doubt with regard to the parts of the cord which act as
conductors of sensory impressions.

The experimental answer to the first question is capable of but one construction. If
the white substance of both posterior columns be divided, the sensibility of the posterior
extremities is not diminished, at least as far as can be shown by experiments upon ani-
mals, in which these points are always difficult of determination. On the other hand, if
every portion of the cord be divided except the posterior white columns, sensibility is
completely lost in the parts below the section. The accuracy of these results cannot be
called in question, especially when controlled by experiments showing the conducting
properties of the gray substance of the cord ; and they show that, whatever may be the
functions of the posterior white columns, they do not serve as conductors of sensory
impressions.

The second question admits of an equally positive answer from the results of experi-
mental inquiry. If the entire substance of the cord, except the posterior columns of
white matter, be divided transversely, as we have jnst seen, sensibility is abolished in all
parts below the section ; but, as we have stated in treating of the transmission of motor
stimulus by the cord, voluntary motion is also destroyed. Experiments show, farther-
more, that sensory impressions are conveyed exclusively by the gray substance. "If the
anterior, the lateral, and the posterior columns of the spinal cord are divided transversely,
at the dorsal region, one set at one place, another at a distance of one or two inches, and
the third also at the same distance from the second, so that the only channel of commu-
nication between the posterior limbs and the sensorium is the gray matter, of which,
however, several parts have, unavoidably, been divided (such as the anterior and the
posterior gray cornua, and also more or less of the central gray matter), we find that the

FUNCTIONS OF THE SPINAL CORD AS A CONDUCTOR. 679

posterior limbs are still sensitive, though evidently less than in the normal condition."
(Brown-Sequard.)

It is impossible to divide the gray matter of the cord alone, without injuring, more or
less, the white substance; but, when the gray matter is divided with very slight injury
of the white substance, sensibility in the parts below the point of section is totally
destroyed. As regards the part of the gray substance specially concerned in the trans-
mission of sensory impressions, the results of experimental investigation have not been so
definite ; but Brown-Se"quard is of the opinion that the transmission takes place chiefly
in the gray matter surrounding the central canal, while it may also occur to some extent
in other portions.

The answer to the third question is deduced from the answers to the first two. The
gray matter and the white substance of the cord do not participate in the transmission
of sensory impressions, this being etfected by the gray substance, especially its central
portion, to the exclusion of the white.

The precise office of the posterior white columns of the cord is still a matter of con-
jecture. If these parts be insensible, except on the surface and near the posterior roots
of the nerves, and if they take no part in the transmission of sensory impressions to the
brain (which seems to have been conclusively proven), what is their function ?

The anatomical relations of the posterior white columns, the results of experiments
upon living animals, and certain well-marked pathological phenomena, point very strongly
to a connection between these columns and the coordination of muscular movements.

Provable Function of the Cord in Connection with Muscular Coordination. — Anato-
mists have not been able to trace satisfactorily the direction of all of the fibres contained
in the posterior columns ; but it is probable that at least some of these fibres serve as
longitudinal commissures, and connect together the nerve-cells, extending for a greater
or less distance both upward and downward in the cord. This anatomical arrangement
is rendered probable chiefly by the results of experiments.

If the posterior columns be completely divided, by two or three sections made at inter-
vals of from three-fourths of an inch to an inch and a quarter, the most prominent effect
is a remarkable trouble in locomotion, consisting in a want of proper coordination of
movements.

In the remarkable disease known under the name of locomotor ataxia, there is a very
peculiar condition of the muscular system, in which, while the power of the muscles is
but slightly diminished, the movements of progression show great deficiency in coordi-
nating power, frequently attended with more or less disturbance in the sensibility of the
parts affected. These symptoms are associated with structural disease of the cord, gen-
erally limited to the posterior columns and the posterior roots of the spinal nerves.

Many years ago, before locomotor ataxia had been generally recognized by patholo-
gists, Todd made the following remarkable statement with regard to the posterior col-
umns: " I have long been impressed with the opinion, that the office of the posterior
columns of the spinal cord is very different from any yet assigned to them. They may
be in part commissural between the several segments of the cord, serving to unite them
and harmonize them in their various actions, and in part subservient to the function of
the cerebellum in regulating and coordinating the movements necessary for perfect loco-
motion/' Todd farther states that this view is supported by the phenomena observed in
cases of disease " distinguished by a diminution or total loss of the power of coordinating
movements. ... In two examples' of this variety of paralysis, I ventured to predict
disease of the posterior columns, the diagnosis being founded upon the views of their
functions which I now advocate ; and this was found to exist on post-mortem inspection ;
and in looking through the accounts of recorded cases in which the posterior columns
were the seat of lesion, all seemed to have commenced by evincing more or less disturb-
ance of the locomotive powers, sensation being affected only when the morbid change

680 NERVOUS SYSTEM.

of structure extended to and more or less involved the posterior roots of the spinal
nerves."

It is only necessary to add that the views of Todd have been in the main confirmed
in the numerous cases of locomotor ataxia that have lately been so fully described by
pathologists ; and, from these facts, it is more than probable that the posterior columns
contain fibres connecting the different segments of the cord, and that they play an im-
portant part in the coordination of muscular movements. The general function of coor-
dination will be considered more fully in connection with the cerebellum.

Decussation of the Sensory Conductors of the Cord. — In hemiplegia due to injury of
the brain, the paralysis occurs upon the side of the body opposite to the cerebral lesion.
The phenomenon ordinarily observed is simply paralysis of motion ; but in those cases,
however, in which both motion and sensation are abolished upon one side of the body,
the lesion in the brain is also found to be upon the opposite side. It is evident, there-
fore, that there is a decussation of the conductors of sensory impressions as well as of
the conductors of the motor stimulus.

As early as 1822, Fodera made a longitudinal section of the spinal cord in the lumbar
region, exactly in the median line. In this experiment, " sensation was destroyed, and
in part motion upon the two sides.1' Inasmuch as in this section it is only possible to
divide the fibres passing from one lateral half of the cord to the other, it is evident that
the sensory conductors must decussate in the spinal cord itself. As far as we know, this
is the first experiment pointing to the decussation of sensory fibres in the cord, the ob-
servations of Galen, to which we have already referred, being limited to the phenomena
of motion.

The next experiments bearing upon the decussation of the sensory conductors in the
cord are those of Van Deen. Among the numerous observations made upon the spinal
cord by this physiologist, are one or two in which he noted the fact that, after section of
one lateral half of the cord in the frog, at the site to the third dorsal vertebra, " the
animal &ad no real loss of sensibility in the posterior extremity on the side on which the
half of the spinal cord had been cut." Although Van Deen did not distinctly state, as a
conclusion drawn from these observations, that there is decussation of the sensory con-
ductors in the cord, the fact of section of one lateral half of the cord with no loss of
sensation on the corresponding side of the body remains as one of the first experimental
arguments in favor of the crossed action.

Experiments upon living animals as well as pathological facts show that, after section
or injury confined to one lateral half of the cord, the general sensibility upon the cor-
responding side of the body is very much exaggerated, producing a condition of well-
marked hyperaesthesia. This remarkable fact was distinctly noted by Fodera, in 1822.
This observation has been confirmed, and the experiments very much extended, by
Brown-Sequard. Cases presenting the same phenomena have also been observed in the
human subject, when one side of the cord has been invaded by disease.

Physiologists are at a loss to explain the hyperassthesia which follows section of the
sensory conductors of the cord, but the fact nevertheless remains. The exaggeration of
sensibility is not due to section of certain fibres, which might be supposed to increase the
impressibility of the remaining fibres, for, as was shown by Vulpian, it is sufficient to
prick with a pin one of the lateral halves of the cord to observe these remarkable phe-
nomena. With these few words, we shall leave the subject of hyperassthesia from injury
to the cord, and pass to the crossed action of its sensory conductors.

In treating of the cord as a conductor of sensory impressions, we have already shown
that this function is performed by the gray substance alone. We have also seen, in con-
nection with the phenomena of conduction of the motor stimulus, that this is effected by
the antero-lateral columns, which do not act as sensory conductors, except by virtue of
their gray matter. As it is impossible to divide the gray matter with certainty without

FUNCTIONS OF THE SPINAL CORD AS A CONDUCTOR. 681

injuring the white substance, and, as we are fully acquainted with the motor properties
of the cord, we are prepared to comprehend the effects upon conduction of sensory im-
pressions which follow division of one or the other lateral half. In our detail of experi-
ments, we shall not consider the phenomena of hyperresthesia, but confine ourselves to
the loss or diminution of sensibility.

Brown-Se"quard was the first to demonstrate decussation of the sensory conductors in
the cord itself; and, although his experiments upon this subject are almost innumerable,
and his writings, scattered, voluminous, and sometimes not free from the obscurity due
to unnecessary refinement and elaborateness of detail, the main facts can be expressed in
a very few words; and he may justly be said to have created the physiology of the sen-
sory conductors.

Brown-Sequard repeated the experiments of Galen and of Fodera, dividing the cord
longitudinally in the median line, producing complete paralysis of sensation upon both
sides in all the parts below the section. By this operation, if the section had been made
accurately in the median line, the only fibres that could be divided were those passing
from one side of the cord to the other.

The second experimental proof of the decussation of sensory fibres consists in trans-
verse section of one or the other of the lateral halves of the cord. If one lateral half of
the cord be divided, sensibility is abolished in the parts below the section, upon the oppo-
site side of the body. In an article published in 1858, Brown-Sequard details very suc-
cinctly an experiment showing this fact, though his first experiments were made in 1849.
He denuded the cord in the lumbar region in a vigorous dog, and made sections upon one
side, progressively deeper and deeper, from without inward. When the section included
about one-third of the lateral half, the sensibility seemed slightly augmented upon the
opposite side. This section involved only a part of the lateral white column and a small
portion of the anterior cornu of gray matter. When the section was extended so as to
involve about two-thirds of the lateral half, the sensibility was notably diminished upon
the opposite side. When the section extended to the median line, the sensibility was
very much diminished ; and, when it extended just beyond the median line, it was entirely
abolished upon the opposite side. These observations, and others of the same nature,
show conclusively that, in the animals experimented upon at least, there is a decussation
of the greatest part of the sensory conductors in the cord itself.

The course of the fibres in their decussation is indicated by farther experiments, which
show that the sensitive fibres from the posterior roots of the nerves " pass along the pos-
terior columns only a little way, and leave them to enter the central gray matter." It is
undoubtedly in this gray substance that they pass from one side to the other, probably
through the cell-prolongations. The fact that the fibres pass in the cord a short distance
before they decussate, and that they pass downward as well as upward, is well shown by
the following experiment :

" If we divide transversely a lateral half of the spinal cord in two places, so as to have
three pairs of nerves between the two sections, we find that the middle pair has almost
the same degree of sensibility as if nothing had been done to the spinal cord, while the
two other pairs have a diminished sensibility, the upper one particularly in its upper
roots, and the lower one in its lower roots ; which facts seem to show that the ascending
fibres of the upper pair, and the descending fibres of the lower one, have been divided
before they had made their decussation.

" If there is only one pair of nerves between two sections, its sensibility is almost
entirely lost, as then the transversal fibres are almost alone uninjured (most of the ascend-
ing and descending being divided), which fibres are employed for reflex action, and hardly
for the transmission of sensitive impressions." (Brown-Sequard.)

The experimental facts just cited conclusively show decussation of sensory conductors
in the cord in the animals operated upon ; and this has been sufficiently confirmed by
other experimenters to render the fact certain. It is possible that the crossed action may

682 NERVOUS SYSTEM.

not be so complete in some other classes of animals, which would account for the results
obtained by those who have denied decussation; but cases of disease of the cord in the
human subject all go to show that the crossed action is complete in man.

Summary of the Action of the Spinal Cord as a Conductor.

The antero-lateral columns of the cord, comprising that portion included between the
anterior median fissure and the origin of the posterior roots of the nerves, are insensible
to direct irritation, and serve as conductors of the motor stimulus from the brain to the
anterior roots of the nerves. If these columns be divided, voluntary motion is lost in all
parts below the section. If the rest of the cord be divided, leaving the antero-lateral col-
umns intact, the power of voluntary motion remains. Throughout the greater part of the
cord, this action is direct, and division of the antero-lateral columns upon one side pro-
duces paralysis of motion upon the corresponding side of the body. There is a decussa-
tion of the motor fibres at the medulla oblongata, and probably a partial decussation in
the cord itself in the upper cervical region. In the dorsal region and below, the motor
conducting fibres are situated chiefly in the anterior columns ; but, in the cervical region,
these fibres pass to the sides and are contained chiefly in the lateral columns. The con-
duction of motor stimulus is probably not effected exclusively by the white substance,
but is transmitted in part by the gray matter.

The gray substance of the cord serves as the medium of transmission of sensory im-
pressions to the brain. This is effected chiefly by the gray matter surrounding the central
canal, but it may take place to some extent in other portions. If the entire gray matter
be divided, with but slight injury to the white substance, sensation is lost in all parts
situated below the section. The white substance does not conduct sensory impressions
to the brain, either in the antero-lateral or the posterior columns. The most probable
function of the white substance of the posterior columns is to unite the different seg-
ments of the cord together by longitudinal commissural fibres; and this portion of the
cord has an important influence in coordinating the muscular movements.

The sensitive nerve-fibres from the posterior roots of the spinal nerves pass in the
cord for a short distance upward and downward. They then penetrate the gray matter
and decussate throughout the entire length of the cord. Division of one lateral half of
the cord is followed by complete paralysis of motion upon the corresponding side of the
body in all parts below the section, by anaesthesia in all parts below the section, upon the
opposite side of the body, and by hyperasthesia in the parts below the section, upon the
corresponding side of the body.

The anatomical points bearing upon the physiological action of the cord are the fol-
lowing :

The fibres from the anterior roots penetrate the anterior gray cornua directly and are
in immediate connection with the prolongations of the motor cells. The motor cc>lls also
have prolongations which pass to the brain in the white substance. The motor fibres
are thus directly connected with the cellular structures in the cord (the elements prob-
ably concerned in reflex movements) and the cells are in connection with conducting
fibres to the brain.

The fibres from the posterior roots take several directions. Some of them pass to the
gray substance. A portion passes to the posterior columns, some extending upward and
others downward. The decussation, which is rendered certain by physiological experi-
ments, has not been satisfactorily followed by anatomists. It undoubtedly takes place
chiefly in the gray substance, probably in part by a crossing of the fibres themselves,
and in part by a crossing of prolongations from the cells with which certain fibres from
the posterior roots are connected.

KEFLEX ACTION OF THE SPINAL CORD. 683

Action of the Spinal Cord as a Nerve- Centre.

It has long been known that decapitation of animals does not immediately arrest mus-
cular action ; and the movements observed after this mutilation present a certain degree
of regularity, and, of late years, have been shown to be in accordance with well-defined
laws. Under these conditions, the regulation of such movements is effected through the
spinal cord and the nerves connected with it. If an animal be decapitated, leaving only
the cord and its nerves, there is no sensation, for the parts capable of appreciating sensa-
tion are absent ; nor are there any true voluntary movements, as the organ of the will is
destroyed. Still, in decapitated animals, the sensory nerves are for a time capable of
conducting impressions, and the motor nerves can transmit a stimulus to the muscles ;
but the only part capable of receiving an impression or of generating a motor stimulus is
the gray matter of the cord. If, in addition to the removal of all of the encephalic
ganglia, the cord itself be destroyed, all movements of voluntary muscles are abolished,
except as they may be produced by direct stimulation of the muscular tissue or of indi-
vidual motor nerves.

We must regard the gray matter of the brain and spinal cord as a connected chain of
ganglia, capable of receiving impressions through the sensory nerves and of generating
the so-called nerve-force. The great cerebro-spinal axis, taken as a whole, has this gen-
eral function ; but some parts have separate and distinct properties and can act inde-
pendently of the others. The cord, regarded as a conductor, connects the brain with the
parts to which the spinal nerves are distributed. If the cord be separated from the
brain in a living animal, it may act as a centre, independently of the brain ; but the
encephalon has no communication with the parts supplied with nerves from the cord, and
it can only act upon the parts which receive nerves from the brain itself.

It has been pretty clearly shown that, when the cord is separated from the encephalon,
an impression made upon the general sensory nerves is conveyed to its gray substance,
and is transformed, as it were, into a stimulus, which is transmitted to the voluntary
muscles, giving rise to certain movements, independently of sensation and volition.
This impression is said to be reflected back from the cord through the motor nerves ;
and the movements occurring under these conditions are called reflex. As they are
movements excited by stimulation of sensory nerves, they are sometimes called excito-
motor.

The term reflex, as it is now generally understood by physiologists, may properly be
applied to any generation of nerve-force which occurs as a consequence of an impression
received by a nerve-centre ; and it is evident that true reflex phenomena are by no means
confined to the action of the spinal cord. The movements of the iris are reflex, and yet
they take place in many instances without the intervention of the cord. Movements of
the intestines and of the involuntary muscles generally are reflex, and they involve the
action of the sympathetic system of nerves. Impressions made upon the nerves of special
sense, as those of smell, sight, hearing, etc., give rise to certain trains of thought. These
involve the action of the brain, but still they are reflex. In this last example of reflex
action, it is sometimes difficult to connect the operations of the mind with external im-
pressions as an exciting cause ; but it is evident, from a little reflection, that this is often
the case. This fact is illustrated by operations of the brain which take place, as it were,
without consciousness, as in dreams. It has been clearly shown that a particular direc-
tion may be given to the thoughts during sleep, by impressions made upon the sense of
hearing. A person sleeping may be made to dream of certain things, as a consequence
of hearing peculiar noises. Examples of this kind of mental reflex action are sufficiently
frequent and well-authenticated.

From the above considerations, it is evident that the term reflex may he properly used
in connection with many phenomena involving the action of the sympathetic system and
of the brain ; but it is generally understood as applying specially to involuntary move-

684 NERVOUS SYSTEM.

ments, occurring without consciousness, as the result of impressions made upon the affe-
rent nerves and involving the independent action of the spinal cord.

Reflex Action of the Spinal Cord.— In 1832 and 1833, Marshall Hall described
minutely the movements which take place in decapitated animals as a consequence of
stimulation of the sensory nerves, and he formularized these phenomena under the head of
" the reflex function of the medulla oblongata and medulla spinalis." Since this publica-
tion, a new interest has been attached to the writings of some of the older physiologists,
in which reflex action, as it is now understood, had been mentioned more or less defi-
nitely. In the history of important advances in physiological knowledge, it has often
been the case that discoveries have been foreshadowed by the earlier writers ; and bibli-
ographical research shows that the literature of the cord as a nerve-centre forms no
exception to this, which is almost the rule. Some of the allusions to the cord as a centre
of reflex action, made anterior to 1833, are vague and indefinite ; but, on the other hand,
certain excito-motor actions were very accurately described by Legallois, as early as
1812. Marshall Hall grouped and classified these phenomena and showed their relations
to the cord as an independent centre ; but he has no claim to the title of the discoverer
of reflex action, and his experiments themselves presented little that was really new.

The experiments of Marshall Hall, published in 1832 and 1833, are familiar to every
physiologist, as supplying nearly all of the omissions of previous observers. The points
which he assumed to have experimentally demonstrated by his researches are the follow-
ing-: A decapitated animal, the only part of the cerebro-spinal axis which remains being
the spinal cord, will make no movements, if completely protected from all external im-
pressions. An impression made upon the sensory nerves of a decapitated animal is
reflected by the cord, through the motor nerves, to the muscles, and gives rise to reflex
movements. If the cord be destroyed, no movements follow stimulation of the surface.
If the centripetal and the centrifugal nerves be divided, no reflex movements can take
place. Experiments upon decapitated animals accord with the results of observations
upon acephalous foetuses and in cases of complete paraplegia from injury to the cord.
All of the involuntary movements observed in the healthy body are explained by the
theory of reflex action. These observations of Marshall Hall were, in the main, con-
firmed by Miiller, in the year succeeding their first publication ; and, by some writers,
the credit of the discovery of the mechanism of reflex action is given to both Miiller and
Marshall Hall.

From the point of view which the present condition of science enables ns to take with
regard to the reflex action of the cord, we have to determine the accuracy of the obser-
vations of Marshall Hall, and to follow out the advances that have been made by more
recent observers. It is important, as the first step in our inquiry, to ascertain the exact
condition of decapitated animals as regards their capacity for muscular movements ; and
upon this point there is some difference of opinion. Marshall Hall thought that an
animal (a frog, for example) after decapitation, was incapable of any voluntary move-,
ment, or of any movement which did not have, for its exciting cause, an external
impression. We take the example of frogs, because these are the animals most com-
monly used by experimenters.

All who have experimented upon frogs have seen them jump about vigorously after
decapitation ; and the question whether these be spontaneous movements, so called, or
an excito-motor action, is more difficult to determine than would at first sight appear.
It would be unphilosophical to assume that, because the animal has been decapitated, the
movements are due to external impressions only, if we use this as evidence against the
possibility of spontaneous movements under these conditions. The obvious necessity of
the argument is to remove all possibility of external impressions or of irritation of the
cord itself. Upon this point, we can only speak positively from our own experiments.
If a frog be decapitated, so as to leave only the spinal cord intact, if we wait for from

ACTION OF THE SPINAL CORD AS A NERVE-CENTRE. 685

one to three minutes until the effects of the shock and local irritation have subsided, if
we then, when the animal has become perfectly quiet, cover it with a bell-glass, and
finally, if we reiuove all possibility of jarring the table on which the animal is placed,
there is no movement of muscles. In making an experiment of this kind, we occasionally
see movements which are due to a very feeble impression, such as a breath of air or a
jar from the street, but which is perfectly evident to the observer ; and, when a move-
ment is once made, this gives rise to another impression, and thus, successive actions of
the muscles may take place. The movements in jumping are so simple that they seem,
sometimes under these conditions, to be voluntary. The effect of feeble excitations is
also very marked in animals poisoned with strychnine ; but, even here, we do not have
movements unless an impression be first made upon the sensory nerves. When we
come to experiments upon the mammalia, there can hardly be any question of this kind ;
for here, as the rule, no movements are observed after the encephalic ganglia have been
removed, unless the sensory nerves be pretty strongly stimulated. Analogous phenomena
are observed in the lower extremities, in cases of paraplegia in the human subject.

The next important question to determine is with regard to the nature of movements
excited by external stimulation in decapitated animals, especially frogs ; for some of these
movements are so regular as to appear to be connected with sensation and volition. The
experiments of Pfluger upon this point are very remarkable. These have been repeatedly
confirmed, and there can be no doubt with regard to their accuracy. Pfluger carefully re-
moved from a frog the entire encephalon, leaving only the spinal cord. He then touched
the surface of the thigh over the inner condyle with acetic acid, to the irritation of which
frogs are peculiarly sensitive. The animal thereupon rubbed the irritated surface with the
foot of the same side, apparently appreciating the locality of the irritation, and endeavor-
ing, by a voluntary effort, to remove it. The foot of this side was then amputated, and
the irritation was renewed in the same place. The animal made an ineffectual effort to
reach the spot with the amputated member, and, failing in this, after some general move-
ments of the limbs, rubbed the spot with the foot of the opposite side. Although this
experiment does not always progress precisely in the manner described, it has succeeded
perfectly in so many instances as to lead some physiologists to conclude that sensation
and volition are not entirely abolished by removal of the encephalon, at least in frogs.

The remarkable phenomena just detailed are to be regarded from two points of view :
first, with reference to their bearing upon the question of the existence of perception and
volition in the spinal cord of the frog ; and second, the question of the application of
these phenomena to the physiology of the cord in man and the higher classes of animals.
The conditions of the experiment in the frog are simply these : Instead of exposing the
surface to a single and instantaneous stimulation, the excito-motor effects of which are
observed as a direct response to the irritation and immediately cease, we have, by the
application of acetic acid to the surface, a prolonged impression upon the sensory nerves,
which, by virtue of the anatomical connections between the different parts of the cord,
is probably dispersed throughout the entire spinal axis. That powerful impressions may
be thus dispersed, there can be no doubt, as we shall see farther on. The phenomena
under consideration certainly point to an appreciation by the cord of the locality of a
powerful impression, and this could be manifested in an animal only by an apparent
muscular effort to reach the irritated spot ; but we can hardly reason from this fact that,
in man and the higher animals, the spinal cord shares with the brain the power of appre-
ciating what we know as sensation and of generating the stimulus of true voluntary
movement. If a sudden and very powerful painful impression be made upon the surface
in man under normal conditions, the hand may be instantly applied to the affected part,
apparently before we really appreciate the pain or have time to make a distinct effort of
the will ; but the connections between the different parts of the cerebro-spinal axis do
not permit us to isolate the action of the cord. Certain it is that, in the higher animals,
after removal of the encephalon, and in experiments upon decapitated criminals and

686 NERVOUS SYSTEM.

patients suffering from paraplegia, there is no evidence of true sensation or volition in the
spinal cord ; and, in man and the higher animals, we must regard all muscular movements
which depend solely upon the action of the cord as a nerve-centre as automatic and
entirely independent of consciousness and of the will.

It is easy to determine, by experiments to which we have already incidentally alluded,
that the muscular movements dependent upon nervous action, occurring in decapitated
animals, are due to the action of the spinal cord as a nerve-centre. In an animal in which
the reflex phenomena are very marked, as they are after decapitation, especially if the
animal be poisoned with strychnine or opium, all movements immediately cease when
the cord is destroyed. That the gray matter of the cord is the part concerned as a centre
in the production of these phenomena, is probable, in view of what we know with regard
to the general functions and properties of this substance ; and experiments have shown
that this is the fact. If, in a decapitated frog, we make an incomplete longitudinal sec-
tion of the cord in the median line, leaving only a slight communication between the two
sides, we may sometimes succeed, by strongly irritating the skin of one leg, in producing
reflex movements, not only in the same leg, but in the leg of the opposite side ; and it is
reasonable to suppose that the irritation is propagated from one side to the other through
the cells of the gray matter.

The conditions essential to the manifestations of reflex phenomena depending upon
the action of the cord are very simple and easily understood.

In the first place, it is necessary that one or more of the posterior roots of the spinal
nerves should be in communication with the cord, in order to conduct the impression to
this nerve-centre. If all of the posterior roots be divided, there is no nervous commu-
nication between the periphery and the centre, and no movements follow irritation of the
surface. When the excitability of the cord is exaggerated, as in poisoning by strychnine,
a single posterior root is sufficient to conduct an impression to the cord, which will give
rise to violent contractions of all the muscles. This is due to a dispersion of the impres-
sion, under these conditions of increased excitability, from the single point of entrance of
the posterior root, throughout the cord. In animals that have been simply decapitated,
a similar diffusion of impressions may also take place. If a comparatively feeble single
impression be made upon any part of the general surface, as the rule, the subjacent muscles
only are the seat of contraction ; but, if the impression be more powerful, or if it be
prolonged, as when we apply a drop of acetic acid to any part of the skin of a frog, this
impression may be diffused throughout the cord, producing contractions of the general mus-
cular system. We have already shown, in treating of the general properties of the
sensory nerves, that an impression made at any point in the course of a nerve is conducted
to the centre. Reflex movements may, consequently, be produced by stimulating the
sensory nerves in their course or by irritating the posterior roots of the spinal nerves.

We have already stated that the cord must retain its anatomical integrity, in order to
receive an impression made upon the centripetal nerves and transform it, as it were, into
a stimulus, which is reflected back by the motor nerves and produces muscular contrac-
tion. It is also evident that the motor nerves must retain their connection with the cord
and be in a condition to conduct the stimulus reflected by the cord to the muscles.

The reflex excitability of the spinal cord is increased to a marked degree by separating
this portion of the cerebro-spinal axis from the encephalon, and the same is true for the
lower portion of the cord, when a section is made in the dorsal or lumbar region. It
is difficult to find an entirely satisfactory explanation of this fact ; and the phenomena
observed under these conditions are, in this regard, like the exaggerated sensibility of
portions of the general surface after section of certain columns of the cord.

In experiments upon the lower animals, the reflex phenomena are greatly exaggerated in
intensity in the tetanic condition observed in poisoning by opium or strychnine. Take, for
example, a frog decapitated and poisoned with strychnine. No reflex movements
occur unless an impression be made upon the sensory nerves ; but the slightest irrita-

ACTION OF THE SPINAL CORD AS A NERVE-CENTRE.

687

tion, such as a breath of air or a slight jar, throws the entire muscular system into a
condition of violent tetanic spasm. The same phenomena are observed in cases of poison-
ing by strychnine or of tetanus in the human subject. This fact is important in its rela-
tions to the treatment of these conditions ; for it is evident that,
in such cases, the exhaustion due to the violent spasms may be
moderated by carefully avoiding all unnecessary irritation of
the surface.

It was shown a number pf years ago, that the inhalation
of anaesthetic agents may abolish all of the ordinary reflex phe-
nomena. Whether this be due to an action upon the cord itself
or to a paralysis of the sensory nerves, it is difficult to determine.
Ordinarily, in animals rendered insensible by anaesthetics, the
movements of respiration continue ; but these also may be
arrested, as has been observed by all who have experimented
with anaesthetics, especially with chloroform. A common way
of determining that an animal is completely under the influence
of an annesthetic is by an absence of the reflex act of closing
the eyelids when the cornea is touched.

It now only remains to show that the phenomena of reflex
action observed in experiments upon the inferior animals, espe-
cially frogs, are applicable to the human subject, and to indi-
cate the muscular actions which depend upon the cord as a
nerve-centre.

It is only necessary, after what has gone before, to indicate
in a general way the phenomena observed in the human sub-
ject which illustrate the reflex action of the cord. It is a
common observation, in cases of paraplegia in which the lower
portion of the cord is intact, that movements of the limbs fol-
low titillation of the soles of the feet, these movements taking
place independently of the consciousness or the will ot the subject
experimented upon. Acephalous foetuses will present general
reflex movements and movements of respiration, and will even
suck when the finger is introduced into the mouth. Observations
FIG. 224.— Frog poisoned with of this kind are so numerous and familiar that they need not be
cited in detail. Experiments have also been made upon crimi-
nals after decapitation ; and, although the reflex phenomena are not so well marked and
cannot be excited so long after death as in cold-blooded animals, they are sufficiently distinct.
It is difficult, in studying, in the human subject, the ordinary phenomena of move-
ments in the voluntary muscular system, to isolate the reflex phenomena from those acts
involving sensation and volition. In many persons, titillation of the soles of the feet pro-
duces violent contractions of muscles, which cannot be arrested by an effort of the will, and
this may even be followed by general convulsions. When we unexpectedly touch an irri-
tating surface with the hand, the muscles of the arm act so quickly that we may suppose
that this takes place before we really appreciate the painful sensation, and, if the impres-
sion be very severe, we may have movements more or less general ; in operating upon
highly-sensitive parts, it is frequently impossible to arrest reflex movements, as the closing
of the eyelids when the cornea is touched ; true reflex movements may be produced by
carefully-executed experiments upon persons asleep ; we cannot arrest the act of vomit-
ing induced by titillation of the fauces ; and other instances of this kind might be cited.

Most of the true involuntary movements are reflex ; but these have been or will be
considered under their proper heads. The movements of deglutition depend upon an
impression made upon the mucous membrane of the pharynx, etc. The ejaculation of
semen is also reflex, although it may be produced without titillation of the genital orpin*,
as in emissions occurring during sleep. Important reflex actions take place through the

688 NERVOUS SYSTEM.

sympathetic nerves, such as the movements of the intestines, vaso-motor movements,
etc. ; but these will be considered fully under the head of the sympathetic system. Se-
cretion, 1he action of the heart, the contractions of the uterus, the action of the sphincters,
the movements of the iris, etc., are regulated by the sympathetic and the cerebro-spinal
system.

As regards the farther action of the cord as a nerve-centre, there are undoubtedly many
functions which are influenced more or less by this portion of the cerebro-spinal axis; but
these have been treated of under their appropriate heads or will be considered hereafter.

CHAPTER XXI.

THE ENCEPHALIC GANGLIA.

Physiological divisions of the encephalon— Weight of different parts of the brain and of tho entire encephalon— Some
points in the physiological anatomy of the encephalon and its connections— The cerebrum— General properties of
the cerebrum — Functions of the cerebrum — Extirpation of the cerebrum in the lower animals — Pathological facts
bearing upon the functions of the cerebrum — Comparative development of the cerebrum in the lower animals —
Development of the cerebrum in different races of men anti in different individuals— Location of the faculty of artic-
ulate language in a restricted portion of the anterior cerebral lobes — The cerebellum — Some points in the physio-
logical anatomy of the cerebellum — Course of the fibres in the cerebellum — General properties of the cerebellum —
Functions of the cerebellum — Extirpation of the cerebellum in animals — Pathological facts bearing upon the func-
tions of the cerebellum— Connection of the cerebellum with the generative function— Development of the cerebel-
lum in the lower animals — Ganglia at the base of the encephalon — Corpora striata— Optic thalami — Tubercula
quadrigemina, or optic lobes — Ganglion of the tuber annulare — Medulla oblongata — Physiological anatomy of the
medulla oblongata— Functions of the medulla oblongata— Connection of the medulla oblongata with respiration-
Vital point — Connection of the medulla oblongata with various reflex acts — Eolling and turning movements fol-
lowing injury of certain parts of the encephalon — General properties of the peduncles.

THE anatomy of the encephalon is so complex, that it can be treated of with advan-
tage only by a very minute and carefully -illustrated description, such as is to be found in
some of the elaborate anatomical works or in special treatises upon the nervous system.
We shall not consider under a distinct head the general physiological anatomy of the
brain, for the reason just given, and also because we are as yet ignorant of the exact
connection between the structure and arrangement of many of its parts and their physi-
ology. We know that the gray substance is capable of appreciating general and special
impressions received by the peripheral nervous system, and of generating the so-called
nerve-force. Impressions are conveyed to this portion of the cerebro-spinal axis by the
sensory conductors, passing to the brain, either through the cord or by the cranial
nerves, and by the nerves of special sense, as well as those of general sensibility. The
stimulus which gives rise to voluntary movements is generated in the brain and is con-
veyed by the motor nerves to the appropriate muscles. We have seen, also, that the
centres of the encephalon may be concerned in reflex action. In addition, parts of the
brain act as centres of sensation and volition and are concerned in the varied phenomena
of intellection.

The encephalon, or what is ordinarily known as the brain, consists of a number of
ganglia, or collections of gray matter, connected with each other, and also, by the differ-
ent columns of the cord, with the motor and sensory nerves of the general system. Cer-
tain of these ganglia have separate find distinct functions which are more or less com-
pletely understood ; while there are, in addition, masses of gray substance, the physio-
logical relations of which are as yet obscure or entirely unknown. The greatest and
the most important of all, the gray matter of the cerebral hemispheres, undoubtedly has
subdivisions connected with distinct attributes of the mind ; but our positive knowledge
with regard to these divisions is, at the present day, very meagre, although this subject
lias long been a favorite field for philosophical speculation.

Confining ourselves strictly within the limits of positive information, we recognize

THE CEREBRAL HEMISPHERES. 689

the following parts of the encephalon as distinct ganglia : 1. The gray matter of the
cerebral hemispheres ; 2. The gray matter of the cerebellum ; 3. The olfactory ganglia ;
4. The gray matter of the corpora striata ; 5. The gray matter of the optic thalami ; 6.
The tubercula quadrigemina ; 7. The gray matter of the tuber annulare, or pons Varolii ;
8. The ganglion of the medulla oblongata. In addition, the following parts have been
made the subject of physiological investigation or speculation, with results more or less

FIG. 225.— Vertical section of the encephalon. (Hirschfeld.)

1, medulla oblongata ; 2, tuber annulare; 8, cerebral peduncle; 4, cerebellum; 5, aqueduct of Sylvius ; 6, valve
of Vieussens; 7, tubercula quadrigemina; 8, pineal gland; 9, inferior peduncle ; 10, superior peduncle;
11, middle portion of the great cerebral fissure ; 12. optic thalamus ; 18, 13, gray commissure; 14. choroid
plexus; 15, iniundibulum ; 1(5, pituitary body; 17, tuber cineieum; 18, bulb of the fornix; 19, anterior per-
forated space; 2 >, root of the motor oculi communis; 21, optic nerve; 22, anterior commissure of the cerebrum;
23, foramen of Monro; 24, section of the fornix ; 25, septum lucidum ; 26, 27, 28, corpus callosum; 29, 80, 81,
82, 33, 34, convolutions and sulci of the cerebrum. The olfactory ganglia and corpora striata are not shown in
this section.

definite : The peduncles of the cerebrum and of the cerebellum ; the pineal gland ; the
corpus callosum ; the septum lucidum ; the cerebral ventricles ; and the pituitary body.

Weights of different Parts of the Brain and of the entire Encephalon. — Most of the
tables of the weight of the healthy adult brain of the Caucasian, given by different ob-
servers, show essentially the same results, the differences amounting to only one or two
ounces for the entire encephalon. The average given by Quain, combining the tables
of Sims, Clend inning, and Reid, is 49£ ounces for the male, and 44 ounces for the
fc-male. The number of male brains weighed was 278, and of female brains, 191. In
males, the minimum weight was 34 ounces, and the maximum, 65 ounces. In 170 cases
out of the 278, the weights ranged from 46 to 53 ounces, which may be taken as the
general average. In females, the minimum was 31 ounces, and the maximum, 56 ounces.
In 125 cases out of the 191, the weights ranged from 41 to 47 ounces.

Quain assumes, from various researches, that, in new-born infants, the brain weighs
11-65 ounces, for the male, and 10 ounces, for the female. In both sexes, "the weight of
the brain generally increases rapidly up to the seventh year, then more slowly to between
sixteen and twenty, and again more slowly to between thirty-one and forty, at which
time it reaches its maximum point. Beyond that period, there appears a slow but pro-
gressive diminution in weight of about one ounce during each subsequent decennial period;
thus confirming the opinion, that the brain diminishes in advanced life."

The comparative weights of the several parts of the encephalon, calculated by Reid
from observations upon the brains of fifty-three males and thirty-four females, between
the ages of twenty-five and fifty-five, are as follows:
44

690

NERVOUS SYSTEM.

Divisions of the Encephalon.

Males.

Females.

Average weight of the cerebrum

43-98 oz.
5-25 "
0-98 "

38-75 oz.
4-76 "
1-U1 "

50-21 oz.

44'52 oz.

The proportionate weight of the cerebellum to that of the cerebrum, in the male, is
as 1 to 8f, and in the female, as 1 to 8J. (Quain.)

The specific gravity of the whole encephalon is about 1036, that of the gray matter
being 1034, and of the white, 1040. (Quain.)

Some Points in the Physiological Anatomy of the Encephalon and its Connections. —
The direction of the fibres in the encephalon, their connections with the cells of the
gray substance, the course of commissural fibres connecting together the different parts
of the gray substance of the cerebrum, the cerebellum, and the deeper ganglia, and
finally the avenues of communication between the fibres of the encephalon and the cord,
are points of exceeding intricacy ; and many of them are still so uncertain and obscure,

FIG. 226.— Diagrammatic representation of the direction of the fibres in the cerebrum. (Le Bon.)

that they cannot as yet be connected satisfactorily with the exact results of physiological
inquiry. All that we can do at present, is to recognize certain ganglionic masses, the
separate functions of which have been more or less accurately defined, and to show, as
far as possible, their anatomical relations to each other and to the spinal cord. Perhaps
the most elaborate and, to a certain extent, the most satisfactory observations upon the
various points to be considered, are those of Luys; but this author describes the course

THE CEREBRAL HEMISPHERES. 691

of the fibres with an exactitude that seems hardly justified, in all instances, by the facts,
in view of the inevitable difficulty and uncertainty of some of the processes employed;
and the graphic and admirable delineations by which the work is illustrated, though pro-
fessedly schematic, present a degree of ideality which inspires some distrust with regard
to the accuracy of the general conclusions. According to Luys, the fibres of the en-
cephalon have several directions, as follows :

The gray matter of the cerebral hemispheres, as we shall see farther on, is composed
of a mass of nerve-cells, connected together by their prolongations into a plexus, which,
in its turn, is connected with the fibres of the white substance. From this cortical cellu-
lar plexus, white fibres arise, which may be divided, according to their direction and
destination, into two classes : The first class consists of curved commissural fibres, which
pass into the white substance to a certain depth and return to the gray matter, connect-
ing thus the gray substance of adjacent convolutions. The existence of these fibres
and their direction are well established. The second class consists of fibres which,
arising from the gray substance of the convolutions, connect these with the corpora
striata and the optic thalami. These may be called the converging fibres ; and their
general direction, as far as it has been ascertained, is shown in figure 226.

Arising from the internal, concave surface of the cortical substance of the cerebrum,
the converging fibres, at first running side by side with the curved commissural fibres,
separate from the latter as they curve backward to pass again to the cortical substance,
and are directed toward the corpora striata and the optic thalami. The limits of the
irregular planes of separation of the commissural and the converging fibres contribute to
form the boundaries of the ventricular cavities of the brain. If we study the course of
the converging fibres arising from all points in the concave surface of the cerebral gray
matter, we find that they take various directions. The fibres from the anterior region of
the cerebrum pass backward and form distinct fasciculi which converge to the gray sub-
stance of the corpora striata. The fibres from the middle portion converge regularly to
the middle region of the external portions of the optic thalami. The fibres from the pos-
terior portion pass from behind forward and distribute themselves in the posterior portion
of the optic thalami. The fibres from the convolutions of the hippocampi and the fascia
dentata are lost in the gray substance lining the internal borders of the optic thalami. In
addition to these converging fibres and the curved commissural fibres connecting the
different convolutions of each hemisphere with each other, are commissural fibres which
connect the two hemispheres, as well as fibres connecting together the corpora striata
and the optic thalami of the two sides.

Certain of the fibres converging from the gray substance of the hemispheres to the
corpora striata and optic thalami are probably connected with the cells in the gray mat-
ter of these parts. Other fibres pass through the corpora striata and optic thalami to
become finally connected with the fibres of the medulla oblougata, and, through the
medulla oblongata, with the columns of the spinal cord. Following the antero-lateral
columns of the cord from below upward, they ascend to the medulla oblongata, decussate
in the median line, and pass from the medulla to the brain. Certain of these ascending
fibres, which are nearly all continuations of the antero-lateral columns of the cord, ascend
to the brain by passing deeply through the pons Varolii ; other fibres ascend in the
cerebral peduncles, or crura cerebri ; and other fibres pass to the tubercula quadrigemina.
As the bundles of fibres ascend from the medulla oblongata, they increase in number by
reinforcements of fibres, probably derived from the cells of the collections of gray mat-
ter in their course.

The Cerebral Convolutions.

The cerebrum, as we have already stated, constitutes more than four-fifths of the en-
cephalic mass. Its surface is marked by fissures and convolutions, which latter serve

692

NERVOUS SYSTEM.

to greatly increase the extent of the gray substance. While these convolutions are not
exactly the same in all human brains, or even in both sides of the brain, their arrange-
ment and relations may be described in a general way with sufficient accuracy to enable
us to recognize easily the most important physiological points in the descriptive anatomy
of the cerebral surface. The diagrammatic figure 226*, taken from Dalton, gives a gen-
eral view of the fissures and of the most important convolutions.

FIG. 226*. — Diagrammatic figure showing the cerebral convolutions. (Dalton.)

Aside from the great longitudinal fissure which divides the hemispheres in the median
line, the diagram shows three deep fissures, marked by heavy, dark lines, and five fissures
of less importance indicated by lighter dark lines. Each cerebral hemisphere is divided,
according to Sappey, into two lobes. The anterior lobe includes that portion lying in
front of S, the fissure of Sylvius, and the posterior lobe, all that portion lying behind the
fissure of Sylvius. English anatomists, however, generally describe three lobes : the
anterior lobe, lying in front of the fissure of Sylvius ; a middle lobe, occupying the middle
fossa of the skull; and a posterior lobe, lying just above the cerebellum ; but there is no
distinct line of demarkation between the middle and the posterior lobe.

S, in Fig. 226*, represents the fissure of Sylvius, with its branches a and 5, 5, I ; R
represents the fissure of Rolando, and P represents the parietal fissure. Above and in
front of the anterior portion of the fissure of Sylvius, is a short, curved fissure, bounding
anteriorly the third frontal convolution (3, 3, 3) which, in the left hemisphere, is sup-
posed to be the seat of the faculty of articulate language.

The first frontal convolution (1, 1, 1) is bounded internally by the great median fissure
and externally by a shallow fissure nearly parallel to the median fissure. The second
frontal convolution (2, 2, 2, 2) lies next the first frontal convolution, and is bounded ex-
ternally by two shallow fissures lying in front of the fissure of Sylvius and the fissure of
Rolando. The third frontal convolution (3, 3, 3) curves around the short branch (a) of
the fissure of Sylvius. On either side of the fissure of Rolando, we have the anterior
central convolution (4, 4, 4) and the posterior central convolution (5, 5, 5). Curving

THE CEREBRAL HEMISPHERES. 693

around the posterior extremity of the fissure of Sylvius, is the supra-Sylvian convolution
(6, 6, 6), which is continuous with the first temporal convolution (7, 7, 7), the latter lying
behind the fissure of Sylvius and parallel with it. External to the posterior portion of
the parietal fissure, is the angular convolution (8, 8, 8), which is continuous with the mid-
dle temporal convolution (9, 9, 9). At the inferior border of the temporal lobe, is the
third temporal convolution (10). The upper parietal convolution (11, 11) lies by the side
of the median fissure and is the posterior continuation of the first frontal convolution.
12, 12, 12 in the diagram indicates the situation of the occipital convolutions. In addi-
tion to these convolutions upon the general surface of the cerebrum, there are convolu-
tions on the surface of the base of the brain and in the gray matter of the sides of the
great median fissure. In the fissure of Sylvius, near its ascending branch, between the
anterior and the posterior lobes of the brain, and beneath the third frontal convolution,
is a group of convolutions constituting the island of Reil.1

The gray matter of the cerebrum, which is external and follows the convolutions, is
from T^ to i of an inch in thickness. Writers have described this substance as existing
in several layers, but this division is mainly artificial. In certain parts, however, par-
ticularly in the posterior portion of the cerebrum, the gray substance is quite distinctly
divided into two layers, by a very delicate intermediate layer of a whitish color.

There is a marked difference in the appearance of the cells in the most superficial and
in the deepest portions of the gray -substance. The superficial cells are small and present
a net-work of delicate, anastomosing fibres, resembling the cells of the posterior cornua
of the gray substance of the cord ; while the deepest cells are large and resemble the so-
called motor cells of the cord. Between these two extremes, in the intermediate layers,
there is a gradual transition in the size of the cells. This anatomical fact points to the
possibility of distinct functions of the cells belonging to the superficial and the deep layers ;
viz., that the larger cells are for the generation of the motor stimulus, while the smaller
are for the reception of sensory impressions.

The mode of connection between the cellular and the fibrous elements of the nervous
system has already been considered and does not demand farther mention. We shall also
pass over the amorphous matter, nuclei, myelocytes, etc., found in the central nervous
matter, as these points possess little or no physiological interest.

General Properties of the Cerebrum. — By the general properties of the cerebrum, we
mean the effect, or the absence of effect, observed when the gray or white substance is
subjected to direct stimulation. While some of the older writers state that the brain is
both irritable and sensible, nearly all authorities, up to a very recent date, have been
agreed that direct stimulation of the white or the gray substance of the greatest part
of the brain produces neither pain nor convulsive movements. In a number of experi-
ments upon pigeons, we have invariably noted complete insensibility and inexcitability
of both the gray and the white substance of the cerebral hemispheres. The generally-
accepted view has been that a great part of the substance of the cerebrum is neither
excitable nor sensible, in the sense in which these terms are applied to the ordinary
mixed nerves. There can be no doubt with regard to the conducting properties of
the white matter of the brain, but the nerve-fibres here seem to conduct sensory im-
pressions and the stimulus generated by the nerve-cells, without being capable of receiv-
ing or conducting artificial impressions applied directly to their substance.

We have said that a great part of the cerebral substance seems to be neither excitable
nor sensible to direct stimulation ; but we must make an exception in favor of certain
portions of the cerebrum, which have lately been shown to possess excitability, their
action being confined to particular sets of muscles. In 1870, Fritsch and Hitzig, expos-
ing the cerebral hemispheres in dogs, found that certain parts of their anterior portion

1 Our sketch of the fissures and convolutions of the brain is taken mainly from the description given by Dalton in
hia Treatise on Human Physiology, Philadelphia, 1875, p. 472, et seq.

694 NERVOUS SYSTEM.

responded to a feeble galvanic current. Each galvanization produced movements re-
stricted to certain muscles, and different centres for the sets of muscles were accurately
determined. The centre for the muscles of the neck was located in the middle of the
frontal convolution ; external to that, was a centre for the extensor and abductor mus-
cles of the forelegs ; and so on, other centres for sets of muscles being found in the an-
terior portion of the hemispheres. By passing an interrupted current through these
parts, tetanus of particular muscles was produced. In other observations, when the
gray substance was removed at the points mentioned, there was partial loss of power,
but not paralysis, of the sets of muscles corresponding to the centres operated upon. In
these experiments the action was always crossed. It was also found that, after severe
hemorrhage, the excitability of the cerebrum quickly disappeared, which may account
for the negative results obtained by previous experimenters. No motor properties were
discovered in the posterior portion of the cerebrum.

The experiments just cited throw a new light upon the properties of the cerebral
substance. It has always been found difficult to experiment upon the great encephalic
centres without disturbing the physiological conditions so seriously as to render the
results of direct observations of this kind more or less indefinite. Now that it is ascer-
tained that, in all probability, these centres readily lose their normal properties, as a sim-
ple consequence of hemorrhage and exposure of the parts, we are less disposed to accept
the older experiments, in which the cerebral tissue was apparently shown to be incapable
of receiving direct artificial impressions.

Since the first publication of the remarkable experiments to which we have just
referred, the question of the excitability of certain parts of the cerebral hemispheres has
attracted a great deal of attention and has been made the subject of many experi-
ments. The most notable of the later observations on this subject are those of Ferrier,
of London, by whom the original experiments of Fritsch and Hitzig have been fully con-
firmed. Many other physiologists have since confirmed the essential points developed in
the original investigations; and the only serious objection to the results is the possibility
of diffusion of the galvanic current to recognized motor tracts. This question is pretty
well settled by the following experiment made by Dr. Putnam, of Boston: Having local-
ized experimentally a distinct motor centre on the surface of the brain, he made a flap,
about one-twelfth of an inch thick, by a section parallel to the surface of the brain and
involving this centre. With the flap in situ, the current which had before excited mus-
cular contraction had no effect. It is evident that the section of the brain-substance
would necessarily cut off the physiological conduction of a stimulus; but, with the
flap in situ, the section would probably not interfere with the diffusion of the galvanic
current itself.

In the present condition of the question, the above is all that it seems necessary to
say, in a systematic work upon physiology, concerning the excitable centres of the cere-
brum. That these excitable centres exist, there can be little doubt; and the idea that
the movements produced by their galvanization are reflex is not justified by experimental
facts. These observations have been confirmed by Hitzig as late as in 1874; and his last
experiments fully substantiate the views advanced in his first paper, showing loss of
power in certain muscles, following destruction of portions of the brain-substance cor-
responding to the excitable points.

functions of the Cerebrum.

The history of the functions of the encephalon belongs without question to physiol-
ogy and is one of the most extensive and interesting of the subdivisions of the science ;
but its range is so extensive, that it has long been regarded as a science by itself and is
treated of exhaustively only in special treatises upon psychology. The study of psychology
has been pursued by the method of observation much more than by direct experiment.

THE CEREBRAL HEMISPHERES. 695

It comprehends, it is true, the facts deduced from experiments upon living animals, but
the results obtained by this method are comparatively few and their scope is restricted.
Nevertheless, they are sufficiently definite ; and, if these results be corrected and applied
to the human subject by a comparison with pathological facts, there still remains in psy-
chology much that may be regarded as within the range of experimental physiology ; for
pathological cases are very frequently available to the physiologist as accidental experi-
ments indicating the functions of parts of the human organism. We cannot restrict
ourselves, however, to this method in the study of the intellectual phenomena ; and we
must draw upon facts in comparative anatomy and physiology, anthropology, and, finally,
upon the direct observation and classification of the intellectual processes.

The experimental physiologist has shown that the encephalon may receive impres-
sions and appreciate them as sensations ; that impressions may be here connected and
give rise to various of the phenomena of animal and intellectual existence; that im-
pressions are recorded by the memory; and, finally, that certain parts are endowed
with special functions. But beyond this, psychology is a science mainly of introspec-
tive observation, the facts contributed by the experimentalist being few and barren.
The observer of intellectual phenomena studies the process of development of the
mind ; he soon separates the instinctive phenomena, observed in the lower animals
and in the human being without experience, from the acts which follow experience,
observation, the recording of impressions by memory, and the generation of ideas ; he
brings his perfected intelligence to bear upon the process of development of the same
kind of intelligence in the human being progressing from infancy to adult life; and,
finally, the psychological philosopher attempts, by introspective observation, to study
the workings of the perfect intellect, his only means of investigation being the very
intelligence he is endeavoring to comprehend.

At the present day, we are in possession of a sufficient number of positive facts to
render it certain that there is and can be no intelligence without brain-substance; that,
when brain-substance exists in a normal condition, intellectual phenomena are manifested,
with a vigor proportionate to the amount of matter existing; that destruction of brain-
substance produces loss of intellectual power ; and, finally, that exercise of the intellectual
faculties involves a physiological destruction of nervous substance, necessitating regenera-
tion by nutrition, here, as in other tissues in the living organism. The brain is not, strictly
speaking, the organ of the mind, for this statement would imply that the mind exists as
a force, independently of the brain ; but the mind is produced by the brain-substance ;
and intellectual force, if we may term the intellect a force, can be produced only by the
transmutation of a certain quantity of matter.

In treating of the functions of the cerebrum, we shall not discuss psychology, except
in so far as physiologists have been able to connect the mind, taken as a whole, with a
distinct division of the nervous system. In this we shall draw upon experiments on living
animals, facts in comparative physiology, in pathology, and, to a certain extent, the rela-
tions clearly shown to exist between the development of intelligence and certain of the
nerve-centres, in different races of men and different individuals. With regard to the
location of particular functions in distinct portions of the cerebrum, we have but little
definite knowledge, beyond the experiments already cited in treating of the irritability
of the cerebral substance, and the probable location of the faculty of speech.

Extirpation of the Cerebrum in the lower Animals. — It is, perhaps, sufficiently evident,
from anthropological and pathological observations as well as the study of comparative
physiology, that the intellectual faculties reside in the encephalon ; but these methods of
investigation do not clearly indicate the special functions of different parts of the cranial
contents. We have seen, in our general sketch of the anatomy of the brain, that this is
by no means a simple organ, and that certain parts, although they are hound together by
commissural fibres, have sufficient anatomical distinctness to lead the physiologist to sup-

696 NERVOUS SYSTEM.

pose that they may have separate and peculiar properties and functions. One of the
most valuable methods of investigation of the functions of these separate ganglia is that
of extirpation of one or more, leaving the others, as far as possible, intact. This method
was first employed with marked success by Flourens and has since been adopted by
many experimenters. It must be remembered, however, that there is no subject of
physiological inquiry in which it is so difficult to apply experiments upon the inferior
animals to the human subject, and none in which the results of experiments should be
received with greater caution. The reason for this is apparent enough. The brain and
the intellectual power of man are so far superior to the development of this organ and
its properties in the lower animals, that some philosophers have regarded the human
intelligence as distinct in nature as well as in amount. Although we are by no means
prepared to accept this proposition, regarding, as we must, the intelligence of man as
simply superior in development to that of the lower animals, it is evident that this differ-
ence in the degree of development is so enormous as to render the human mind hardly
comparable with the intellectual attributes of animals low in the scale.

Experiments upon different classes of animals show clearly that the brain is less im-
portant, as regards the ordinary manifestations of animal life, in proportion as its rela-
tive development is smaller. For example : if we remove the cerebral hemispheres in
fishes or reptiles, the movements which we call voluntary may be but little affected ;
while, if the same mutilation be performed in birds or some of the mammalia, the dimin-
ished power of voluntary motion is much more marked. It would be plainly unphilo-
sophical to assume, because a fish or a frog will swim in water and execute movements
after removal of the hemispheres very like those of the uninjured animal, that the feeble
intelligence possessed by these animals is not destroyed by the operation. It is not only
possible, but probable, that, in the very lowest of the vertebrates, the functions of the
nervous centres are not the same as in higher animals. There is, for example, a fish (the
lancet-fish, AmpJiioxus lanceolatus), that has no brain, all of the functions of animal life
being regulated by the gray substance of the spinal cord. It is essential, in endeavoring
to apply the results of experiments upon the brain in the lower animals to human physi-
ology, to isolate, as far as possible, the distinct manifestations of intelligence, from auto-
matic movements. Bearing in mind, then, the difficulties of the question and the caution
with which observations upon the great nerve-centres of the lower animals must be
received in their applications to human physiology, we shall proceed to discuss the phe-
nomena following removal of the cerebrum in direct experiments.

In 1822 and 1823, Flourens communicated to the French Academy of Sciences his
remarkable observations upon the different parts composing the encephalon. His experi-
ments are so familiar to physiologists, that it is only necessary here to give his general
conclusions. As regards the cerebral hemispheres, he found that the complete removal
of these parts in living animals (frogs, pigeons, fowls, mice, moles, cats, and dogs), was
invariably followed by stupor, apparent loss of intelligence, and absence of even the
ordinary instinctive acts. Animals thus mutilated retained general sensibility and the
power of voluntary movements, but were thought to be deprived of the special senses of
sight, hearing, smell, and taste. As regards general sensibility and voluntary movements,
Flourens was of the opinion that animals deprived of their cerebral lobes possessed sen-
sation, but had lost the power of perception, and that they could execute voluntary
movements when an irritation was applied to any part, but had lost the power of making
such movements in obedience to a spontaneous effort of the will. One of the most
remarkable phenomena observed was entire loss of memory and of the power of connect-
ing ideas. The voluntary muscular system was enfeebled but not paralyzed. Removal
of one hemisphere produced, in the higher classes of animals experimented upon, enfee-
blement of the muscles upon the opposite side, but the intellectual faculties were in part
or entirely retained.

The observations of Flourens have been repeated by many experimentalists and

FUNCTIONS OF THE CEREBRUM. 697

were, in the main, confirmed, except as regards the special senses. Bouilland, in 1826,
made a large number of observations upon pigeons, fowls, rabbits, etc., in which, after
removal of the hemispheres, he noted the persistence of the senses of sight and hearing.
Longet finally demonstrated the fact that both sight and hearing are retained after extir-
pation of the hemispheres, even more clearly than Bouillaud, by the following experi-
ments : He removed the hemispheres from a pigeon, the animal surviving the operation
eighteen days. When this animal was placed in a dark room and a light was suddenly
brought near the eyes, the iris contracted and the animal winked ; " but it was remark-
able, that when a lighted candle was moved in a circle, and at a sufficient distance, so
that there should be no sensation of heat, the pigeon executed an analogous movement
of the head/' An examination after death showed that the removal of the cerebrum
had been complete. An animal deprived of the hemispheres also opened the eyes at the
report of a pistol and gave other evidence that the sense of hearing was retained.

With regard to the senses of smell and taste, it is more difficult to determine their
presence than to ascertain that the senses of sight and hearing are retained. It is prob-
able, however, that the sense of smell is not abolished, if the hemispheres be carefully
removed, leaving the olfactory ganglia intact ; and there is no direct evidence that extir-
pation of the cerebrum affects the sense of taste ; indeed, in young cats and dogs, Longet
has noted evidences of a disagreeable impression following the introduction of a concen-
trated solution of colocynth into the mouth, as distinctly as in the same animals under
normal conditions.

We shall now proceed to describe, as accurately as possible, the condition of an ani-
mal after complete extirpation of the cerebrum, as observed in numerous experiments
that we have ourselves made upon this subject, premising the statement that these are
merely repetitions of observations made by other physiologists.

A pigeon, in a perfectly normal condition, is deprived of the hemispheres, by remov-
ing the calvarium and carefully scooping out the parts with the handle of a scalpel.
This operation is usually not difficult, and the haemorrhage is soon arrested spon-
taneously. The slit in the scalp is closed with sutures, and the animal is set at liber-
ty. The appearance of the animal after this mutilation is peculiar and characteristic.
There immediately supervenes a condition of stupor. There is usually no attempt at
movement, and, though the pigeon stands upon its feet, the head is almost buried in the
feathers of the neck, the eyes are closed, and the attitude is one of absolute indifference
to surrounding conditions. The muscles seem to act with just sufficient vigor to main-
tain the standing position. If we pinch one of the toes or grasp the beak, there is evi-
dent sensation, and a persistent and more or less vigorous effort is made to release the
l>:irt. It is sufficiently evident, from these and other tests, that sensation and the power
of voluntary motion are retained ; but, as soon as the animal is left quiet, it relapses into
its stupid condition, makes no effort to escape, and apparently loses immediately all
recollection of having been disturbed. The irritation has evidently produced a sensation
of discomfort and has given rise to a voluntary muscular effort ; but there has been no
idea of danger, nor an intelligent effort to avoid a repetition of the disagreeable or pain-
ful impression.

It is easy to demonstrate, by experiments such as we have just detailed, that the
animal sees and hears ; but it connects no idea with any thing seen, and the report of a
pistol, which, under natural conditions, would excite terror and an idea of danger, simply
causes the pigeon to give evidence that the sound has been heard. As we have already
stated, it is probable that the animal has the sense of smell, but it is difficult, if not impos-
sible, to establish this point experimentally. The same remark applies to the sensations of
hunger and thirst. The animal may feel the want of water and food, but it has no idea of
relieving these sensations by drinking and eating, and, if left to itself, will die of inanition.

There has been a great deal of discussion among experimentalists with regard to
spontaneous voluntary movements in animals deprived of the cerebral hemispheres. The

698 NERVOUS SYSTEM.

experimental conditions necessary for determining this point are the following: The
observer must be certain that the removal of the hemispheres has been complete ; for it
has been clearly shown that, even when a small amount ot cerebral substance has es-
caped, the functions of these parts are not entirely abolished. Again, we must be equally
certain that movements which seem to be due to a spontaneous act of volition take place
when the animsl has not been aroused from the condition of stupor which results from
the operation. Generally, when the animal is left to itself, the condition of stupor per-
sists ; but, when aroused by artificial means, it will walk a few steps, plume the feathers,
shake its head, and make various voluntary movements without farther irritation, soon
relapsing, however, into somnolency. One of the most accurate and reliable of the
recent observers of these phenomena, Vulpian, asserts without reserve, that an animal,
deprived completely of the cerebral hemispheres, is incapable of a spontaneous voluntary
effort; and we are inclined to an unqualified adoption of this opinion. With regard to a
rabbit from which Vulpian had removed the cerebral hemispheres and the corpora stri-
ata, he makes the following statement: "I do not hesitate to say that this rabbit is
completely deprived of spontaneous volition. All its movements, which are, indeed,
much less varied than those of a bird operated upon in the same manner, are exclusively
and directly due to a stimulation produced by exterior excitations, or by interior inclina-
tions, such as fatigue, etc."

In view of the very great variety of movements that occur in animals after removal
of the cerebrum, it is quite difficult to define precisely what movements are due to volun-
tary action depending upon some external or interior impression, which are really reflex
voluntary movements, and to distinguish them from those which arise from a spontaneous
and, perhaps, an intelligent effort of the will. These points have been so admirably
described in a recent article, by Onimus, that we quote his concluding summary :

" As a summary, in the inferior animals, as in the superior animals, the removal of the
cerebral hemispheres does not cause to disappear any of the movements that previously
existed. Only, these movements assume certain peculiar characters. In the first place,
they are more regular, they have the true normal type, for no psychical influence inter-
venes to modify them ; the locomotor apparatus is brought into action without interfer-
ences, and one could almost say that the ensemble of movements is then more normal
than in the normal condition.

" In the second place, the movements executed take place inevitably after certain
excitations. It is a necessity that the frog placed in water should swim, and that the
pigeon thrown into the air should fly. The physiologist can then, at will, in an animal
without the brain, determine such and such an act, limit it, arrest it ; he can anticipate
the movements and affirm in advance that they will take place under certain conditions,
absolutely as the chemist knows in advance the reactions that he will obtain in mixing
certain bodies.

"Another peculiarity in the movements that take place, when the cerebral lobes are
removed, is their continuation after a first impression. On the ground, a frog without
the brain when irritated makes, in general, two or three jumps at the most ; it is rare
that it makes but one. Placed in water, it continues the movement of natation until it
meets with an obstacle ; it is the same in the carp, eel, etc. The pigeon continues to
fly, the duck and goose continue to swim, etc. We should say that there is a spring
which needs for its action a first impulsion, and which is stopped by the slightest resist-
ance. But, what is striking, is precisely that continuation of the condition once deter-
mined, and we cannot refrain from connecting the facts observed in an animal deprived
of the cerebral lobes with those which constitute the characteristic properties of inor-
ganic matter. Brought into movement, the animal without a brain retains the move-
ment until there is exhaustion of the conditions of movement, or until it meets with
resistance ; taken in repose, it remains in the state of inertia until an exterior cause
intervenes to bring it out of this condition. It is living, inert matter"

FUNCTIONS OF THE CEREBRUM. 699

There is now no room for discussion with regard to the persistence of general sensi-
bility after removal of the hemispheres. The experiment upon a pigeon leaves no doubt
upon this point, but the susceptibility to pain has been much more strikingly illustrated
in other animals. Vulpitiu, in describing the condition of animals operated upon in this
way, illustrates the persistence of sensibility in rats and rabbits, by the violent cries
which follow painful impressions.

In concluding our consideration of the observations upon inferior animals, it only
remains for us to discuss briefly certain late experiments, which have attracted a great
deal of attention from the fact that they seem to show that spontaneous volition exists
after complete extirpation of the cerebrum. These experiments have been most ably
and satisfactorily analyzed by Vulpian. Goltz argues, from experiments upon frogs and
the movements executed after extirpation of the brain, that these animals make intelli-
gent muscular efforts when deprived of the hemispheres ; and the phenomena observed
after this mutilation are indeed very curious. As was shown by Vulpian, in his own
experiments, frogs and fishes thrown into water will swim about and the frogs will even
succeed in getting out of the water, but then they immediately relapse into a torpid con-
dition. We do not conceive that these facts are in opposition to the statement just
made with regard to the absence of spontaneous volition in birds and the mammalia,
particularly in view of the slight importance of the functions of the cerebrum as com-
pared with the spinal cord in the lower orders of vertebrate animals. The views lately
advanced by Voit are based upon an isolated experiment upon a pigeon that was kept
alive for five months after the cerebral lobes had been, as stated by Voit, completely
removed. At first the pigeon presented the phenomena usually observed after this opera-
tion ; but it gradually recovered, until finally it seemed entirely normal, with the single
exception that it never would eat, all food being introduced forcibly. Five months after
the operation, the pigeon was killed and the encephalic cavity was found filled with a
white substance containing dark-bordered nerve-fibres and nerve-cells. Voit never before
observed any thing like regeneration of the nervous substance or so complete a restora-
tion of the cerebral functions ; and he regarded this as an instance of anatomical and
physiological regeneration of the hemispheres. The objections to accepting this observa-
tion with the physiological conclusions presented by Voit are, that it is not only possible
but probable, that the hemispheres were not entirely removed and that the posterior
portion of the encephalon had advanced to occupy in part the space originally filled by
the extirpated mass. While we do not assume that anatomical and functional regenera-
tion of the cerebrum in a pigeon is impossible, it must be admitted that such an extraor-
dinary statement as that made by Voit cannot be accepted without reserve, merely
upon the basis of a single observation.

Pathological Facts bearing upon the Functions of the Cerebrum. — A careful study of
the phenomena which attend certain pathological conditions of the brain in the human
subject, such as laceration or pressure from effusion of blood, softening of the nervous
substance, etc., taken in connection with the results of experiments upon living animals,
throws considerable light upon the functions of certain distinct portions of the encephalon.
Cerebral haemorrhage very commonly involves the corpus striatum, either directly or
indirectly, and then we have paralysis of motion limited to the side of the body opposite
to the lesion. When the optic thalamus is affected, there is impairment of sensibility
upon the opposite half of the body. These facts illustrate the course of the motor and
sensory conductors from and to the cerebrum. It is not very common to observe lesions
confined to the gray or white substance of the hemispheres, but, when this occurs and
when there is no pressure upon the corpora striata or optic thalami, there is no paralysis
of motion or sensation, although there may be a certain amount of weakness of the muscles
upon the side of the body opposite the injury. Experiments upon the inferior animals
have confirmed the conclusions to be drawn from these pathological facts. In frogs,

700 NERVOUS SYSTEM.

fishes, and birds, when one hemisphere has been removed, the evidences of feebleness of
the muscles of the opposite side are not very marked; but they are quite distinct in the
adult mammalia.

It is a fact now generally admitted in pathology, that loss of cerebral substance from
repeated hemorrhage is sooner or later followed by impairment of the intellectual facul-
ties. This point it is frequently difficult to determine in a single instance, but an analysis
of a sufficient number of cases shows impaired memory, tardy, inaccurate, and feeble
connection of ideas, abnormal irritability of temper with a childish susceptibility to petty
or imaginary annoyances, easily- excited emotional manifestations, and a variety of phe-
nomena denoting abnormally feeble intellectual power, following any considerable disor-
ganization of cerebral substance. In short, pathological conditions of the brain all go to
show that the intellectual faculties are connected with the cerebral hemispheres.

As a final argument drawn from pathology, in favor of the view just stated, we have
only to allude to the size of the brain in certain cases of idiocy. There are on record
numerous examinations of the brain in idiots, in which this organ has been found to be
less than one-half of the ordinary weight; as the cases reported by Tiedemann, of 19|,
25f, and 22£ ounces, in three idiots, whose ages were, respectively, sixteen, forty, and
fifty years. A case has been reported by Mr. Gore, of an idiotic woman, forty-two years
of age, whose brain weighed ten ounces and five grains ; and one by Mr. Marshall, of an
idiotic boy, twelve years old, whose brain weighed but 8^ ounces. Mr. Bradley, in a late
number of the Journal of Anatomy and Physiology, gives an elaborate description of the
brain of an idiot, thirty-five years of age, extremely emaciated at the time of his death,
when he weighed but sixty pounds. The encephalon, including the cerebrum, cerebellum,
and pons, weighed twenty-eight ounces, and the proportion of the cerebellum to the
cerebrum was as 1 to 5*5. In the healthy adult male of ordinary weight, the encephalon
weighs fifty ounces, and the proportion of the cerebellum to the cerebrum is as 1 to 8^.
Mr. Bradley calls attention to the proportion of the cerebellum to the cerebrum in this
case, stating that this is common in the encephalon of idiots. In idiots, the weight of the
body is generally much below the normal standard ; and, in the case reported by Bradley,
the proportionate weight of the encephalon to that of the entire body is even greater than
in the healthy adult. This point, however, cannot be admitted as an argument against
the fact that congenital idiocy is usually attended with an abnormally small development
of the hemispheres. Most idiots take little or no exercise; they are under-sized, and
have but little muscular vigor ; and it is probable that the imperfect development of the
body is more or less a consequence of the abnormal cerebral condition. We might com-
pare the weight of the body in Mr. Bradley's case with that of a child from seven to
fourteen years of age ; and, at this period of life, according to the tables compiled by
Quain, the average weight of the encephalon is 45'96 ounces, for the male, and 40*78
ounces, for the female.

The statements just made with regard to the brains of idiots refer to cases charac-
terized by complete absence of intelligence, and farthermore, probably, by very small
development of the body. On the other hand, there are instances of idiocy, the body
being of ordinary size, in which the weight of the encephalon is little if any below the
average. Le'lut reports several cases of this kind. In one of these, a deaf-mute idiot,
forty-three years of age, a little above the ordinary stature, presenting " idiocy of the
lowest degree; almost no sign of intelligence; no care of cleanliness," the encephalon
weighed 48-32 oz. Other cases of idiots of medium stature are given, in which the brain
weighed but little less than the normal average. In the West Riding Lunatic Asylum
Reports, London, 1876, p. 19, is a report of the case of a congenital imbecile, aged thirty
years, height five feet and eight inches, died of phthisis, whose brain weighed 70£ oz.
These facts illustrate the difficulty of subordinating individual observations to any general
rule, and this is particularly marked with regard to the brain, the structure of which is
so complex and difficult of investigation.

FUNCTIONS OF THE CEREBRUM. 701

Comparative Development of the Cerebrum in the Lower Animals. — It is only neces-
sary to refer very briefly to the development of the cerebrum in the lower animals as
compared with the human subject, to show the connection of the hemispheres with intel-
ligence. In man, the cerebrum presents an immense preponderance in weight over other
portions of the encephalon ; and, in some of the lower animals, the cerebrum is even less
in weight than the cerebellum. In man, also, not only the relative but the absolute
weight of the brain is greater than in lower animals, with but two exceptions. Todd
cites a number of observations made upon the brains of elephants, in which the weights
ranged from nine to ten pounds. Rudolphi gives the weight of the encephalon of a whale,
seventy-five feet long, as considerably over five pounds. With the exception of these
animals, man possesses the largest brain in the zoological scale.

Another interesting point in this connection is the development of cerebral convolu-
tions in certain animals, by which the relative amount of gray matter is increased. In
fishes, reptiles, and birds, the surface of the hemispheres is smooth ; but, in many mam-
malia, especially in those remarkable for intelligence, the cerebrum presents a greater or
less number of convolutions, as it does in the human subject.

Comparing the relative size of the brain, its complexity of organization, and the
increase of its gray substance by convolutions, with the development of intelligence in the
animal scale, it is so evident that the cerebrum is the organ presiding over the intellectual
faculties, that this point in our argument seems to need no farther discussion.

Development of the Cerebrum in Different Races of Men and in Different Individuals.
— It may be stated as a general proposition, that, in the different races of men, the cere-
brum is developed in proportion to their intellectual power ; and, in different individuals
of the same race, the same general rule obtains. Still, this law presents marked excep-
tions. Certain brains in an inferior race may be larger than the average in the superior
race ; and it is frequently observed that unusual intellectual vigor is coexistent with a
small brain, and the reverse. These exceptions, however, do not take away from the force
of the original proposition. As regards races, the rule is found to be invariable, when a
sufficient number of observations are analyzed, and the same holds true in comparing a
large number of individuals of the same race. Average men have an advantage over
average women of about six ounces of cerebral substance ; and, while many women are
far superior in intellect to many men, such instances are not sufficiently numerous to
invalidate the general law, that the greatest amount of intellectual capacity and mental
vigor is coincident with the greatest quantity of cerebral substance. If we accept the
view, which is in every way reasonable, that the gray substance of the cerebral hemi-
spheres is the generator of the mind, it would be necessary, in comparing different indi-
viduals with the view of establishing a definite relation between brain-substance and
intelligence, to estimate the amount of gray matter; but it is not easy to see how this can
be done with any degree of accuracy.

It is undoubtedly true that proper training and exercise develop and increase the vigor
of the intellectual faculties, and that thereby the brain is increased in power, as are the
muscles under analogous conditions. This will perhaps explain some of the exceptions
above indicated ; but an additional explanation may be found in differences in the quality
of brain-substance in different individuals, independently of the size of the cerebral hem-
ispheres. One evidence that these differences in the quality of intellectual working
matter exist is, that some small brains actually accomplish more and better work than
some large brains. This fact may be due to differences in training, to the extraordinary
development in some individuals of certain qualities, to intensity and pertinacity of pur
pose, capacity for persistent labor in certain directions, a fortunate direction of the men-
tal efforts, opportunity and circumstances, etc. ; but, aside from these considerations, it
is exceedingly probable that there are important individual differences in the quality of
generating nervous matter.

702

NERVOUS SYSTEM.

In concluding this portion of our argument, we present a table of an exceedingly inter-
esting series of observations upon the comparative weights of the encephalon in the Cauca-
sian, the negro, and the intermediate grades produced by the union of the two races. The
observations in this table are hardly sufficient in number to establish the exact relations
between the brains in the different grades of color, but they illustrate points of peculiar
interest in this country, where the blacks are so numerous and where the union of the
two races, white and black, is so common. We also give a list of some of the well-
authenticated weights of the encephalon in men whose intellectual faculties had been
observed during life. This latter list we have prepared with great care and have intro-
duced some observations not found in most works upon physiology. In estimating the
intellectual power of individuals, it is difficult to arrive at exact conclusions, except with
regard to men of acknowledged eminence. Still, the statements are as accurate as pos-
sible and must be taken for what they are worth. Several of the examples given in this
list are marked exceptions to the general rule, that the mental vigor is in proportion to
the amount of brain-substance.

We have not considered it necessary to enter into a discussion of the relations of the
facial angle to intelligence in the lower animals and in different races of men. It was
proposed by Camper to take the angle made at the junction of two lines, one drawn from
the most projecting part of the forehead to the alveolae of the teeth of the upper jaw,
and another passing horizontally backward from the lower extremity of the first line, as
the facial angle. This angle is, to a certain extent, a measure of the projection of the
anterior lobes of the brain. Numerous observations upon the facial angle in different
races were made by Camper and by other physiologists and ethnologists. They show, in
general terms, that the angle is larger in man than in any of the inferior animals and is
largest in those races that possess the greatest development of intellectual power.

Ethnological Table, derived from 405 Autopsies of White and Negro Brains. Made
under the Direction of Surgeon Ira Russell, 11th Massachusetts Volunteers.

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Table of Weights of the Encephalon, in ounces, av., in Individuals, in some of whom the
Degree of Intelligence is more or less accurately known.

Congenital imbecile, aged 30; height 5 feet 8 inches ; died of phthisis (West Riding Lu-
natic Asylum Reports, London, 1876, p. 19) 70'50 oz.

Bricklayer, aged 38 ; fair intelligence, but could neither read nor write (reported by Dr.

James Morris) 67*00 "

Cuvier, aged 63 (Archives gentralcs de medecine, 1832) 64*33 "

FUNCTIONS OF THE CEREBRUM. 703

Abercrombie, aged 63 (reported by Dr. Adam Hunter) 63-00 oz.

Congenital epileptic idiot (reported by Dr. Tuke) 60*00 "

Ruloff, aged 53 ; above medium stature; executed for murder, in 1871 ; well versed in
languages, imagining that he had discovered new and important principles in

philology (reported by Dr. George Burr) 59*00 "

James Fisk, Jr., aged 37 ; killed in New York, in 1872 ; illiterate, but said to possess
great executive ability ; notorious for colossal and unscrupulous financial specula-
tions (reported by Dr. Marsh) 58*00 "

Boy, aged 13 ; healthy and intelligent ; died from injuries caused by a fall (British Medi-

calJournal, Oct. 19, 1872) 58*00 "

Spurzheim (Medico- Chirurgical tieview, 1836) 55'06 "

Adult man ; an idiot since two years of age (Wagner) 54*95 "

Laborer, aged 22 ; died of fracture of the pelvis (Wagner) 53*79 "

Daniel Webster, aged 70 (reported by Dr. John Jeffries) 53*50 "

Celebrated mathematician, aged 54 ; above the ordinary stature (Wagner) 53'41 "

Agassiz, aged 66 (reported by Dr. M. Wyman) 53'40 "

Executed criminal, aged 45 ; medium stature ; of less than ordinary intelligence, and un-
cultivated (Lelut) 53-12 "

Celebrated clinical professor, aged 52 ; medium stature (Wagner) 52*88 "

Mathematician of the first rank, aged 78 ; medium stature (Wagner) 52*62 "

Executed criminal, aged 34 ; rather large in stature ; ordinary intelligence, but singu-
lar and somewhat cultivated (Lelut) 50*09 u

Dupuytren, aged 58 (Cruveilhier, Husson, and Bouillaud) 49*68 "

Day-laborer, aged 49 (Wagner) 48'85 "

Executed criminal, aged 29; medium stature; of scarcely ordinary intelligence and

uncultivated (Lelut) 48*81 "

Executed criminal, aged 42; a little above medium stature; intelligence fine, devel-
oped, and slightly cultivated (Lelut) 48*81 "

I Hot, of a very low degree of intelligence, aged 37 ; a little above medium stature ;

movements very active (Lelut) 48'67 "

Deaf-mute, aged 43 ; a little above medium stature ; an idiot, of the lowest degree of

intelligence (Lelut) 48*32 "

Executed criminal, aged 46 ; medium stature ; of ordinary intelligence, uncultivated,

but proud and vivacious (Lelut) 48*14 "

Man, slightly imbecile, aged 67 ; medium stature (Lelut) 48*14 "

Man, about 60 years of age (Wagner) 48*14 "

Celebrated philologist, aged 54 ; 5 feet 7i inches tall (Wagner) 47*90 "

Executed criminal, aged 34 ; small stature ; intelligence developed and cultivated (Lelut). 47*79 "

Man, about 24 years of age ; died of aortic insufficiency (Wagner) 47*69 "

Day-laborer, aged 51 (Wagner) 47*44 "

Man, 34 years of age ; died of pneumonia (Wagner) 47*26 "

Brigand and assassin, aged 32 ; beheaded (Wagner) 46*9 1 "

Idiot of the lowest degree of intelligence, aged 24 ; medium stature (Lelut) 46*56 "

Executed criminal, aged 27; medium stature; of ordinary and uncultivated intelligence

(Lelut) 46*21 "

Executed criminal, aged 40; at least of medium stature; intelligence developed and

cultivated (Lelut) 46*21 "

Railroad laborer, aged 23 (Wagner) 46'21 "

Executed criminal, aged 29 ; intelligence hardly ordinary, and uncultivated (Lelut) 45*50 "

Wood-cutter, aged 57 ; died of vertebral caries (Wagner) 44*90 "

Idiot, below the condition of a brute ; aged 39 (Lelut) 44*30 "

Imbecile, with difficulty in movements ; aged 57 ; intelligence correct, notwithstand-
ing its slight development (Lelut). 43*56 "

Man, 31 years of age ; died of phthisis (Wagner) 43*38 "

Celebrated mineralogist, aged 77 ; above medium stature (Wagner) 43*24 "

Executed criminal, aged 31 ; small stature ; intelligence mobile and exaggerated (Lelut) . 42*04 "
Upholsterer, aged 60 ; died of phthisis (Wagner) 40*91 "

704 NERVOUS SYSTEM.

Imbecile, aged 23 ; large stature (Lelut) 38-97 oz.

Idiot, of the lowest degree of intelligence ; aged 46 ; medium stature (Lelut) 36'86 "

Man, 46 years of age ; idiocy very profound ; very large stature (Lelut). 36'15 "

Man, 44 years of age ; idiocy very profound ; a little below medium stature (Lelut) 34'39 ''

In compiling the foregoing table, we have in every instance consulted the authentic
reports of the weights of the brain and have reduced them all to ounces av. with the
greatest care. This was found necessary, on account of the important discrepancies in
the reports quoted by different physiological authors, especially as regards the brains of
Cuvier, Webster, and Dupuytren. We believe that our figures are absolutely correct.
The weights of the brains of Cromwell (82'29 oz.) and of Byron (79 oz.) are stated by
some writers, but there can be hardly any question that the accounts are grossly exagger-
ated. A careful study of the weights given in the table shows the impossibility of ap-
plying to individuals an absolute rule that the greatest brain-power is connected with the
greatest amount of brain-substance. The men of acknowledged intellectual ability in
the table are, Cnvier, Abercrombie, Spurzheim, Webster, Agassiz, Dupuytren, and those
cited by Wagner as celebrated mathematicians, professors, etc. An imbecile, a brick-
layer, Cuvier, and Abercrombie stand at the head of the list, as regards the weight of
the brain; but above Webster and Dupuytren, are Ruloff, Fisk, two idiots, a boy thirteen
years old, and a common laborer. Far down in the list, is a celebrated mineralogist,
whose brain is at least six ounces below the average. The advanced age of the person
referred to (seventy-seven years) would not account for the small weight of the brain,
although the weight is undoubtedly diminished in old persons. We are not surprised,
then, in the tables based upon observations of thousands of healthy brains of men not re-
markable for great intellect, to find many between fifty-five and sixty ounces in weight.

As the general result of all the observations upon the human subject, while we admit
that intellectual vigor is in general coincident with large development of the cerebral
hemispheres, there are certainly many striking exceptions to this rule when it is applied
to individuals.

Location of the Faculty of Articulate Language in a Restricted Portion of the Ante-
rior Cerebral Lobes. — Physiologists are often slow to accept important facts bearing directly
upon the functions of parts, drawn exclusively from pathology, especially when these
facts are not capable of demonstration by experiments upon the lower animals; and per-
haps this is due to a certain distrust of the accuracy of pathological researches as com-
pared with the exact results of well-executed experimental observations. As regards the
faculty of speech, however, our study must be confined to man, the only animal capable
of articulate language, and our data are drawn exclusively from pathology. Some physio-
logical writers are still disposed to regard the location of the faculty of speech as not
definitively settled; but, from a careful study of the pathology of aphasia, we are con-
vinced that there is no point in the physiology of the brain more exactly determined
than that the faculty of speech is located in a well-defined and restricted portion of the
anterior lobes. This is the more interesting and important, as it is the only sharply-
delmsd faculty that has been accurately located in a distinct portion of the brain.

Aphasia is a pathological condition in which the subject is deprived, more or less
completely, of the power of language, spoken or written. This definition includes not
alone those cases in which patients are unable to express ideas by speech, but cases in
which the idea of language is lost and there is agraphia, or inability to express ideas in
writing. Certain cases of this disease present loss of speech because the subject is inca-
pable of coordinating the muscles used in articulation. The patient has a clear idea of
language and of the meaning of words and is able to write perfectly well. In other
cases, the patient can neither speak nor express ideas in writing. In these, the idea of
language is lost. In both of these varieties of the disease, the difficulty is either in the
organ presiding over the faculty of speech or in the connections of this organ with the

FUNCTIONS OF THE CEREBRUM. 705

muscles concerned in articulation. Thus regarded, aphasia does not include aphonia from
laryngeal disease, or loss of speech such as is observed frequently in hysteria, in the in-
sane, who sometimes refuse to speak from pure obstinacy, or in cases of paralysis of the
parts immediately concerned in articulation. The whole history of the disease points to
a particular part of the brain, which presides over the faculty of speech.

As a preliminary to the location of the nerve-centre presiding exclusively over speech,
it is necessary to establish the existence of the power of articulate language as a distinct
faculty ; and this is done by cases of disease in which this faculty seems to be lost, the
general mental condition being unaffected. Passing over the passages in the writings of
the ancients, in which it is stated that the power of speech is sometimes lost, and even
some writers in the beginning of the present century, who connected this difficulty with
lesions of the anterior lobes of the brain, we come to the observations of Dr. Marc Dax,
who, in 1836, read a paper before the medical congress at Montpellier, in which he indicat-
ed impairment or loss of speech in one hundred and forty cases of right hemiplegia. Dax
concluded, from these observations, that the faculty of articulate language occupies the
left anterior lobe of the cerebrum. This memoir, however, attracted but little attention,
until 1861, when the discussion was renewed by Broca; and, since then, numerous cases
of aphasia with lesion of the left anterior lobe have been reported by various writers. In
1863, M. Gr. Dax, a son of Marc Dax, limited the lesion to the anterior and middle portion
of the left anterior lobe. It was farther stated, by Broca and Hughlings Jackson, to be
that portion of the brain nourished by the left middle cerebral artery. According to
recent observers, the most frequent lesion in aphasia is in the parts supplied by the left
middle cerebral artery, particularly the lobe of the insula, or the island of Reil ; and it is
a curious fact that this part is found only in man and monkeys, being in the latter
very slightly developed. While we must agree with most authors in the statement that
the organ of language cannot be absolutely restricted to these parts, it is none the less
certain that they are most frequently the seat of lesion in aphasia.

While it is demonstrated that the cerebral lesion in aphasia involves the left anterior
lobe in the great majority of cases, there are several instances in which the right lobe
alone is affected ; and this has led physiologists and pathologists to deny the absolute
location of the organ of language upon the left side. Even if we reject a certain number of
cases of aphasia with the brain-lesion limited to the right side, in which we may suppose
that the post-mortem examinations were incomplete, or the impairment of speech was
due, perhaps, to simple paralysis of muscles, we must admit that, in a few instances,
aphasia has followed injury or disease of the brain upon the right side. Aside from
the anatomical arrangement of the arteries, which seem to furnish a greater amount of
blood to the left hemisphere, it is evident that, as far as voluntary movements are con-
cerned, the right hand, foot, eye, etc., are used in preference to the left ; and that the
motor functions of the left hemisphere are superior in activity to those of the right. It
would be interesting, then, to note the physical peculiarities of persons affected with left
hemiplegia and aphasia. Dr. Bateman quotes two cases of aphasia dependent upon lesion
of the right side of the brain and consequent left hemiplegia, in which the persons were
left-handed; and these, few as they are, are interesting, as showing that a person may use
the right side of the brain in speech, as in the other motor functions. In this connection,
it may not be uninteresting to note that, although most anatomists have failed to find any
marked difference in the weight of the two cerebral hemispheres, Dr. Boyd has shown
by an " examination of nearly two hundred cases at St. Marylebone, in which the hemi-
spheres were weighed separately, that almost invariably the weight of the left exceeded
that of the right by at least the eighth of an ounce." To conclude our citations of patho-
logical facts bearing upon the location in the brain of the organ of speech, we may refer
to an account, by Dr. Broadbent, of the brain of a deaf and dumb woman. In this case
the brain was found to be of about the usual weight, but the left third frontal convolu-
tion was of " comparatively small size and simple character."
45

706 NERVOUS SYSTEM.

Taking into consideration all of the pathological facts bearing upon the subject, it
seems certain that, in the great majority of persons, the organ or part presiding over
the faculty of articulate language is situated at or near the third frontal convolution
and the island of Reil in the left anterior lobe of the cerebrum, and mainly in the
parts nourished by the middle cerebral artery. In some few instances, the organ seems
to be located in the corresponding part upon the right side. It is possible that, origi-
nally, both sides preside over speech, and the superiority of the left lobe of the brain
over the right and its more constant use by preference in right-handed persons may
lead to a gradual abolition of the functions of the right side of the brain, in connection
with speech, simply from disuse. This view, however, is hypothetical, but it is rendered
probable by certain considerations, among the most important of which is the state-
ment by Longet, that " one cerebral hemisphere in a healthy condition may suffice for
the exercise of intelligence and the external senses." In support of this statement,
Longet cites several cases of serious injury of one hemisphere without impairment of
the intellect. In what is called the ataxic form of aphasia, the idea and memory of
words remain, and there is simply loss of speech from inability to coordinate the mus-
cles concerned in articulate language. Patients affected in this way cannot speak but
can write with ease and correctness. In the amnesic form of the disease, the idea and
memory of language are lost; patients cannot speak, and are affected with agraphia, or
inability to write. In cases in which hemiplegia is marked, the aphasia is usually of the
ataxic form ; while, in cases in which there is no hemiplegia, the aphasia is generally
amnegic.

The Cerebellum.

It is not necessary, in order to comprehend the functions of the cerebellum, as far as
these are known, to enter into a full description of its anatomical characters. The
points, in this connection, that are most interesting to us as physiologists are the follow-
ing : the division of the substance of the cerebellum into gray and white matter ; the
connection between the cells and fibres ; the connection of the fibres with the cerebrum,
and with the prolongations of the columns of the spinal cord ; and the passage of fibres
between the two lateral lobes. These points, therefore, will be the only ones that will
engage our attention.

As we have seen, in treating of the general arrangement of the encephalon, the cere-
bellum, situated beneath the posterior lobes of the cerebrum, weighs about 5*2 ounces
av. in the male, and 4'T ounces in the female. The proportionate weight to that of the
cerebrum is as 1 to 8f in the male, and as 1 to 8J in the female. It is separated from
the cerebrum by a strong process of the dura mater, called the tentorium. Like the
cerebrum, the cerebellum presents an external layer of gray matter, the interior being
formed of white, or fibrous nerve- tissue. The amount of the gray substance is very
much increased by numerous fine convolutions and is farther extended by the penetra-
tion, from the surface, of arborescent processes of gray matter. Near the centre of each
lateral lobe, embedded in the white substance, is an irregularly-dentated mass of cellular
matter, called the corpus dentatum. The cerebellar convolutions are more numerous and
the gray substance is deeper than in the cerebrum ; and these convolutions are present in
many of the inferior animals in which the surface of the cerebrum is smooth.

The cerebellum consists of two lateral hemispheres, more largely developed in man
than in the inferior animals, and a median lobe. The hemispheres are subdivided into
smaller lobes, which it is unnecessary to describe. Beneath the cerebellum, bounded in
front and below by the medulla oblongata and pons, laterally by the superior peduncles,
and superiorly by the cerebellum itself, is a lozenge-shaped cavity, called the fourth ven-
tricle. The crura, or peduncles, will be described in connection with the direction of the
fibres.

The structure of the gray substance of the convolutions presents certain peculiarities.

THE CEREBELLUM. 707

This portion is divided quite distinctly into an internal and an external layer. The inter-
nal layer presents an exceedingly delicate net-work of fine nerve-fibres, which pass to
the cells of the external layer. In the plexus of anastomosing fibres, are found numer-
ous bodies like free nuclei, called by Robin, myelocytes. The external layer is some-
what like the external layer of gray substance of the posterior lobes of the cerebrum

Fio. 227.— Cerebellum and medulla oblongata. (Hirschfeld.)

1, 1, corpus dentatum ; 2, tuber annulare ; 3, section of the middle peduncle ; 4, 4, 4, 4, 4, 4, laminae forming the arbor-
vitae; 5, 5, olivary body of the medulla oblongata ; 6, anterior pyramid of the medulla oblongata; 7, upper ex-
tremity of the spinal cord.

and is more or less sharply divided into two or more secondary layers. The most exter-
nal portion of this layer contains a few small nerve-cells and fine filaments of connective
tissue ; and the rest of the layer contains a great number of large cells, rounded or
ovoid, with two or three, and sometimes, though rarely, four prolongations. The mode
of connection between the nerve-cells and the fibres has already been described under
the head of the general structure of the nervous system.

Course of the Fibres in the Cerebellum. — Most anatomical writers give a very simple
description of the course of the nerve-fibres in the cerebellum. From the gray sub-
stance of the convolutions and their prolongations, the fibres converge to form finally the
three crura, or peduncles on each side. The superior peduncles pass forward and up-
ward to the crura cerebri and the optic thalami. These connect the cerebellum with the
cerebrum. Beneath the tubercular quadrigemina, some of these fibres decussate with the
corresponding fibres upon the opposite side; so that certain of the fibres of the superior
peduncles pass to the corresponding side of the cerebrum, and others pass to the cere-
bral hemisphere of the opposite side.

The middle peduncles arise from the lateral hemispheres of the cerebellum, pass to
the pons Varolii, where they decussate, connecting together the two sides of the cere-
bellum.

The inferior peduncles pass to the medulla oblongata and are continuous with the
restiform bodies, which, in turn, are continuations chiefly of the posterior columns of the
spinal cord.

From the above sketch, the physiological significance of the direction of the fibres,
as it appears from the most reliable and generally-accepted anatomical investigations, is
sufficiently evident. By the superior peduncles, the cerebellum is connected, as are all

708 NERVOUS SYSTEM.

of the encephalic ganglia, with the cerebrum ; by the middle peduncles, the two lateral
halves of the cerebellum are intimately connected with each other ; and, by the inferior
peduncles, the cerebellum is connected with the posterior columns of the spinal cord.
"We shall see, when we come to study the functions of the cerebellum, that its connection
with the posterior white columns of the cord is a point of great interest and importance.

General Properties of the Cerebellum. — There is now no difference of opinion among
physiologists, with regard to the general properties of the cerebellum. Flourens, who
made the first elaborate and satisfactory observations upon the cerebellum in living
animals, noted, in all of his experiments, that lesion or irritation of the cerebellum
alone produced neither pain nor convulsions ; and the same results have followed the
observations of all modern physiologists who have investigated this question practically.
We have ourselves frequently exposed and mutilated the cerebellum in pigeons and have
never observed any evidence of excitability or sensibility. From these facts, we must
conclude that the cerebellum is inexcitable and insensible to direct stimulation, at least
as far as has been shown by direct observations. It is not impossible, however, that
future experiments may reverse this generally-received opinion ; particularly in view of
the recent observations of Fritsch and Hitzig, already cited, which show that certain
parts of the cerebrum are excitable, and that the excitability of the encephalic centres
rapidly disappears in living animals, as the result of pain and haemorrhage. We should
note, also, the experiments of Budge, who observed movements in the testicles and vasa
deferentia, in males, and in the cornua of the uterus and in the Fallopian tubes, in females,
following irritation of the cerebellum.

Functions of the Cerebellum.

There are still the widest differences of opinion among physiologists, with regard to
the functions of the cerebellum, mainly for the reason that the experiments upon the
lower animals, though in themselves sufficiently definite, are apparently contradicted by
pathological observations upon the human subject. There should be no such discrep-
ancy between well-conducted experiments and carefully-observed cases of disease or
injury ; for it is certain that the functions of the cerebellum present no essential differ-
ences in different animals, at least in man, the mammalia, and birds. It is necessary,
therefore, for the physiologist, by carefully analyzing and correcting the results obtained
by direct experimentation and by applying to the study of pathological observations the
facts elicited by these experiments, to endeavor to harmonize the real or apparent con-
tradictions ; for, as we have often had occasion to remark, there are no exceptions to
the laws to which the functions of similar classes of animals are subordinated; and
observations and experiments, apparently discordant, will always be found, as our posi-
tive knowledge advances, to present differences in the conditions under which the phe-
nomena have been observed. To apply this idea to the functions of the cerebellum, it may
be safely assumed that it is impossible for this organ to preside directly and exclusively
over muscular coordination in birds and the inferior mammals, and, in man, to pos-
sess different functions. With regard to the cerebrum, man possesses, not only a higher
degree of development of certain intellectual faculties than the inferior animals,, but is
endowed with others, such as the power of articulate language. But, in man and in the
higher orders of animals, the general properties and functions of the muscular system are
essentially the same. To take one of the most generally-accepted views of the functions
of the cerebellum, if this be the centre for muscular coordination in birds and mammals,
it has the same office in man, although it may possess additional functions not found
lower in the scale of animal life. Keeping in view, then, the desirability of bringing
into accord the results of experiments and of pathological observations, we shall first
study carefully the phenomena which follow injury or extirpation of the cerebellum in
the lower animals.

FUNCTIONS OF THE CEREBELLUM. 709

Extirpation of the Cerebellum in the lower Animals. — In birds, and in certain mam-
mals in which the operation has been successful, the more or less complete extirpation
of the cerebellum is followed by well-marked phenomena, which present always the same
character but are somewhat differently interpreted by various experimenters. Experi-
ments of this kind were first made by Flourens ; and the accuracy of his observations
has never been successfully controverted, whatever may have been said of his physiolo-
gical deductions. Indeed, there are few if any important points in the phenomena fol-
lowing partial or complete removal of the cerebellum that escaped the attention of this
most accurate observer.

Laying aside, for the present, the deductions to be made from experiments upon ani-
mals, we may quote the following phenomena noted by Flourens and by all who have
repeated his observations upon the cerebellum :

u I extirpated the cerebellum by successive layers in a pigeon. During the removal
of the first layers, there only appeared slight feebleness and want of harmony in the
movements.

" At the middle layers, there was manifested an almost universal agitation, although
there was not added any sign of convulsion ; the animal executed sudden and disordered
movements ; it heard and saw.

" On the removal of the last layers, the animal, the faculty of jumping, flying, walk-
ing, and maintaining the erect position being more and more disturbed by the preceding
mutilations, lost this faculty entirely.

" Placed on the back, it was not able to recover itself. Far from resting calm and
steady, as occurs in pigeons deprived of the cerebral lobes, it became vainly and contin-
ually agitated, but it never moved in a firm and definite manner.

" For example, it saw a blow with which it was threatened, wished to avoid it, made
a thousand efforts to avoid it, but did not succeed. If it were placed on its back, it would
not rest, exhausted itself in vain efforts to get up, and finished by remaining in that posi-
tion in spite of itself.

" Finally, volition, sensation, perception, persisted ; the possibility of making general
movements persisted also ; but the coordination of the. movements in regular and definite
acts of locomotion was lost."

The above are the phenomena observed after total extirpation of the cerebellum.
Voluntary movement, sensation, general sensibility, and the special senses, seem to be
intact ; but there is always a loss of the power of equilibrium, and the movements exe-
cuted are never regular, efficient, and coordinate. Flourens farther states that animals
operated upon in this way retain their intellectual and perceptive faculties.

It is exceedingly important now to note the effects of partial removal of the cerebel-
lum, as these bear directly upon cases of disease or injury of this organ in the human
subject, in which its disorganization is very rarely complete. We may illustrate this,
also, by citing two of Flourens's typical experiments :

" I. I removed by successive layers, all of the upper half of the cerebellum in a
young cock.

" The animal immediately lost all stability, all regularity in its movements ; and its
tottering and Uzarre mode of progression reminded one entirely of the gait in alcoholic
intoxication.

" Four days after, the equilibrium was less disturbed, and the progression was more
firm and assured.

" Fifteen days after, the equilibrium was completely restored.

" II. I removed, in a pigeon, about the half of the cerebellum ; and I removed this
organ completely in a fowl.

"At the end of a certain time, the pigeon had regained its equilibrium; the fowl
did not re-am it at all : the latter lived nevertheless for more than four months after
the operation."

710 NERVOUS SYSTEM.

These important observations we have repeatedly confirmed, and we have in our pos-
session the encephalon of a pigeon which recovered completely after removal of about
two-thirds of the cerebellum, the animal first presenting marked deficiency in coordi-
nating power.

Such are the phenomena observed in experiments upon the cerebellum in birds, and
they have been extended by Flourens and others to certain mammals, as young cats,
dogs, moles, mice, etc. Our own experiments, which have been very numerous during
the last fifteen years, are simply repetitions of those of Flourens, and the results have
been the same without exception.

The only difficulties in operating upon the cerebellum arise from haemorrhage and
the danger of injuring the medulla oblongata. The skull is exposed by slitting up the
scalp, and the calvarium is removed in its posterior portion, penetrating just above the
upper insertion of the cervical muscles. It is well to leave a strip of bone in the median
line, thereby avoiding haemorrhage from the great venous sinus, although this precaution
is not essential. The cerebellum is thus exposed and may be removed in part or entirely,
by a delicate scalpel or forceps, when the characteristic phenomena just described are
observed. Animals operated upon in this way feel the sense of hunger and attempt to
eat, but, when the movements are very irregular, they are unable to take food. We
have frequently compared the phenomena presented after removal of the cerebellum with
the movements of a pigeon intoxicated by forcing down the oesophagus a little bread
impregnated with alcohol, and they present a striking similarity.

In view of the remarkable uniformity in the actual results obtained by different experi-
menters, it is hardly necessary to cite all of the observations made upon the lower animals.
The phenomena observed by Flourens have been in the main confirmed by Fode"ra,
Bouillaud, Magendie, Wagner, Lussana, Dalton, Vulpian, Mitchell, Onimus, and many
others. Certain of these authors differ from Flourens in their ideas concerning the func-
tions of the cerebellum, while they admit the accuracy of his observations.

We shall eliminate from the present discussion the experiments made upon animals low
in the scale, such as frogs and fishes (although, in some of these, the results are in accord
with the observations just cited upon birds and mammals), and shall confine ourselves to an
interpretation of the phenomena observed after extirpation of the cerebellum in animals
in which the muscular and nervous arrangement is like that of the human subject. The
results of this mutilation are as definite, distinct, and invariable, as in any experiments
upon living animals, and, taken by themselves, they lead inevitably to but one conclusion.

When the greatest part or the whole of the cerebellum is removed from a bird or a
mammal, the animal being, before the operation, in a perfectly normal condition and no
other parts being injured, there are no phenomena constantly and invariably observed
except certain modifications of the voluntary movements. The intelligence, general and
special sensibility, the involuntary movements, and the simple faculty of voluntary motion,
remain. The movements are always exceedingly irregular and incoordinate ; the animal
cannot maintain its equilibrium ; and, on account of the impossibility of making regular
movements, it cannot feed. This want of equilibrium and of the power of coordinating
the muscles of the general voluntary system causes the animal to assume the most absurd
and remarkable postures, which, to one accustomed to these experiments, are entirely
characteristic. Call this want of equilibration, of coordination, of "muscular sense," an
indication of vertigo, or what we will, the fact remains, that regular and coordinate mus-
cular action in standing, walking, or flying, is impossible, although voluntary power
remains. It is well known that many muscular acts are more or less automatic, as in
standing, and, to a certain extent, in walking. These acts, as well as nearly all voluntary
movements, require a certain coordination of the muscles, and this, and this alone, is
abolished by extirpation of the cerebellum. It is true that destruction of the semicir-
cular canals of the internal ear produces analogous disorders of movement, but this is the
only mutilation, except division of the posterior white columns of the spinal cord, which

FUNCTIONS OF THE CEREBELLUM. 711

produces any thing resembling the results of cerebellar injury. Certain important coordi-
nate muscular movements are well known to be dependent upon distinct nerve-centres.
The acts of respiration are presided over exclusively by the medulla oblongata. Deglutition
probably has its distinct nerve-centre, as well as the movements of the eyes. The centre
regulating the coordinate movements in speech is situated in the anterior cerebral lobes.
None of these peculiar movements are affected by extirpation of the cerebellum.

If there be a distinct nerve-centre which presides over the coordination of the general
voluntary movements, experiments upon the higher classes of animals show that this
centre is situated in the cerebellum. It may be either in the entire cerebellum or in a
certain portion of this organ, but, if it be confined to a restricted part, this has not yet
been determined. If the cerebellum preside over coordination, as a physiological neces-
sity, the centre must be connected by nerves with the general muscular system. If this
connection exist, a complete interruption of the avenue of communication between the
cerebellum and the muscles, we should naturally expect, would be followed by loss of
coordinating power. From the anatomical connections of the cerebellum, it appears that
the only communication between this organ and the general system is through the pos-
terior white columns of the spinal cord. We have seen that these columns are not for
the transmission of the general sensory impressions, and there is no satisfactory evidence
that they convey to the encephalon the so-called muscular sense. As regards general
sensibility and voluntary motion, we cannot ascribe any function to the posterior white
columns, except that, when they are divided at several points, we invariably have want
of coordination of the general muscular system. When the posterior white columns are
disorganized in the human subject, we have loss or impairment of coordinating power, even
though the general sensibility be not affected, as in the disease called locomotor ataxia.

Confining ourselves still to the interpretation of experiments upon living animals, and
leaving for subsequent consideration the phenomena observed in cases of disease or injury
of the cerebellum in the human subject, we are led to the following conclusions :

There is a necessity for coordination of the movements of the general voluntary system
of muscles, by means of a nerve-centre or centres.

"Whatever other functions the cerebellum may have, it acts as the centre presiding
over equilibration and general muscular coordination.

The cerebellum has its nervous connections with the general muscular system through
the posterior white columns of the spinal cord, a fact which is capable both of anatomical
and physiological demonstration.

If the cerebellum be extirpated, there is loss of coordinating power ; and, if the pos-
terior white columns of the cord be completely divided, destroying the communication
between the cerebellum and the general system, there is also loss of coordinating power.

When a small portion only of the cerebellum is removed, there is slight disturbance
of coordination, and the disordered movements are marked in proportion to the extent
of injury to the cerebellum.

After extirpation of even one-half or two-thirds of the cerebellum, the disturbances in
coordination immediately following the operation may disappear, and the animal may
entirely recover, without any regeneration of the extirpated nerve-substance. This im-
portant fact enables us to understand how, in certain cases of disease of the cerebellum in
the human subject, when the disorganization of the nerve-tissue is slow and gradual, there
may never be any disorder in the movements.

We present the above conclusions, as in our own mind positive and definite. It i-
proper to state, however, that the definition of the function of the ren-hellum is one of
the points stated by many physiological authors as doubtful and unsettled ; and this Ifl
mainly because some writers have been unable to harmonize the experimental facts ;r
detailed, with cases of disease or injury of the cerebellum in the human subject. We
conceive that this has frequently been due to an imperfect study of the pathological facts,
which we now propose to discuss.

712 NERVOUS SYSTEM.

Pathological Facts bearing upon the Functions of the Cerebellum. — Nearly all writers
upon the physiology of the nervous system, while they agree that extirpation of the cere-
bellum in the lower animals produces irregularity of movements, are arrested, as it were,
in their deductions, by the following quotation from Andral, in his report of ninety-three
cases of disease of the cerebellum :

"A more remarkable alteration of movement is noted in the observation of M. Lalle-
mand. The patient staggered on his legs, and often came near falling forward. In this
case, the only one which tends to confirm the opinion of physiologists who regard the
cerebellum as the organ of the coordination of movements, the cerebellum was entirely
transformed into a sac filled with pus."

The bare statement, such as is generally made, that Andral collected ninety-three
cases of disease of the cerebellum, only one of which tends to show that this is the
organ of muscular coordination, is sufficient to arrest any physiologist in the conclu-
sions that would naturally be drawn from experimental facts ; and many writers have
expressed themselves as uncertain upon the question of the function of the cerebellum.
Before we go any farther, we wish to settle, once for all, the physiological bearing of
these cases ; and, with this end in view, have carefully studied, analyzed, and tabulated
them. Out of the ninety-three cases, fifteen were observed by Andral, and seventy-
eight are quoted from various authors. An analysis of these cases, with reference to
conditions likely to complicate the effects of the cerebellar disease, etc., is given in the
following table :

Analysis of AndraVs Ninety-three Cases of Disease of the Cerebellum.
(Six Cases, observed ~by Andral.1)

Hemiplegia ; death in fifty hours .... 1 case.

Hemiplegia ; sudden death 1

Hemiplegia ; death in two days 1

Hemiplegia ; associated with cerebral haemorrhage 3

(Seventy -eight Cases, quoted from various Authors.)

Haemorrhage into the cerebellum ; quoted from Serres ' . 6 * cases.

" " " quoted from Dance If case.

" quoted from Bayle . . . . . . It "

" " " quoted from Guiot 1 § "

(Serres); hemiplegia 2 cases.

" " " (Gazes); coma 1 case.

(Morgagni) ; found dead 1

" " " (Sedillot) ; died in fifteen minutes . 1 "

" (Cafford) ; died suddenly 1 "

Haemorrhage (Michelet) ; apoplexy two years before death ; found an old clot in the

right lobe of the cerebellum 1 "

Haemorrhage (quoted from various authors) ; haemorrhage into the cerebrum as well

as the cerebellum 9 cases.

Atrophy of the left cerebral and the right cerebellar hemisphere .... 2 "

Cases of disease, with paralysis ; quoted from various authors 9 "

Cases of abscess, with paralysis ; quoted from various authors 3 "

Cyst (R6camier) ; convulsions 1 case.

Abscess (Laugier) ; convulsions 1 "

Abscess, involving the entire cerebellum (Lallemand) ; want of coordination 2 . .1 "
Cases, quoted from various authors, in which no disturbance was noted in the move-
ments ; the disease was confined to one lateral lobe of the cerebellum . . 5 cases.

1 In these six cases, there was haemorrhage into the cerebellum.

3 This is the single case, noted by Andral, out of the ninety-three, the only one showing want of coordination.

FUNCTIONS OF THE CEREBELLUM. 713

Cases of tumor, quoted from various authors, in which there was paralysis . .15 cases.

Cases of tumor, associated with disease of the cerebrum 7 "

Cases of tumor, associated with convulsions ; the descriptions are very indefinite . 9 "

{Nine Cases, observed ly Andral.}

Softening ; hemiplegia and convulsions 1 cagei

Softening ; hemiplegia and subsequent haemorrhage 1 "

Softening; hemiplegia and haemorrhage 1 "

Softening ; agitation, like convulsions, of the members 1 "

Cyst ; paralysis and convulsions 1 "

Tubercle ; hemiplegia 1 "

Five small tubercles in one hemisphere of the cerebellum ; movements normal . .1 "
Tuberculous mass, the size of a hazel-nut, on one side of the cerebellum ; movements

normal 1 "

Cyst, the size of a hazel-nut, on one side of the cerebellum ; movements normal . 1 — 9 cases.

Add cases of haemorrhage, previously cited, observed by Andral, .... 6 "

Add cases quoted from various authors 78 "

Total cases collected by Andral 93 cases.

In six cases, quoted from Serres, marked *, " there were observed all the signs of vio-
lent apoplexy ; nothing in particular is said with regard to disorders of movement." In
the case quoted from Dance, marked t, the patient was struck with apoplexy. In the
case quoted from Bayle, marked J, the patient suddenly lost consciousness, had convul-
sive movements on the third day, and died in coma, on the fifth day. In the case quoted
from Guiot, marked §, there was " no lesion except effusion of blood in the median lobe
of the cerebellum. The individual who was the subject of this observation had had an
attack of apoplexy. Before his attack, he had for some time a tottering gait (demarche
chancelante), and, after the attack, remained hemiplegic on the right side."

Let us now carefully review these ninety-three cases of Andral, which have been held
in terrorem over those who have ventured to argue, from experiments upon animals, that
the cerebellum is the coordinator of the muscular movements, and see how many may
properly he thrown out of the question 1

We can discard the first six cases, observed by Andral, in which there was hemiplegia,
speedy death, and in three of which there was cerebral hemorrhage; for we could
hardly observe want of coordination in hemiplegics or in cases complicated with cerebral
disease. We can discard the six cases, quoted from Serres, in which there was violent
apoplexy, as well as the case quoted from Dance, with apoplexy, and the case quoted
from Bayle, with coma and convulsions. It is evident that these cases are useless in
noting the presence or absence of coordinating power. We can discard two cases, (Serres)
with hemiplegia ; one, (Cazes) with coma ; one, (Morgagni) found dead ; one, (Se*dillot) died
in fifteen minutes; one, (Cafford) died suddenly; and one, (Michelet) apoplexy two years
before death, and an old clot in the right lobe of the cerebellum. This last case is in
accord with experiments on animals ; for we have seen that the coordinating- power may
be restored after loss of one-half of the cerebellum. We can discard nine cases quoted
from various authors, in which there was cerebral as well as cerebellar hemorrhage ; two
cases of paralysis, with atrophy of one hemisphere of the cerebrum and one hemis-
phere of the cerebellum ; nine indefinitely-described cases, with paralysis ; tlnve cases of
abscess, with paralysis ; one case of cyst and one of abscess, with paralysis ; fifteen cases
of tumor, with paralysis ; seven cases, associated with disease of the cerebrum and
paralysis ; and nine very indefinitely described cases, associated with convulsions. Of the
remaining cases observed by Andral, we can discard one, with hemiplegia and convul-
sions ; one, with hemiplegia and subsequent hemorrhage ; one, with hemiplegia ; one case
of cyst, with paralysis and convulsions ; and one, of tubercle, with hemiplegia. We can

714 NERVOUS SYSTEM.

also discard one case of five small tubercles in one hemisphere of the cerebellum ; one,
of a tuberculous mass, the size of a hazel-nut, upon one side ; and one, of a cyst, the size
of a hazel-nut, upon one side. These last cases do not present sufficient destruction of
the cerebellar substance to lead us to expect any disorder in the movements.

Thus far we have discarded eighty-five cases, leaving eight to be analyzed. Of these
eight cases, in five, it is simply stated that the movements were unaffected, and that
" one of the lateral lobes of the cerebellum was the seat of abscess." In view of this
bare statement, and of the fact that, in animals, recovery of coordinating power takes place
when half of the cerebellum has been removed, we may throw out these cases as incom-
plete. It must be remembered that the abscesses were probably of slow development ;
and, if they did not destroy a sufficiently large portion of the cerebellum to influence the
coordinating power permanently, it is not probable that the functions of this organ would
be at all affected, as there would be no shock, such as occurs in the sudden removal of
substance by an operation.

We are thus reduced to three cases ; and, in all of these, the movements were more
or less affected. These cases we shall now study as closely as is possible from the details
given.

CASE I. — The first case is quoted from Guiot. There was no lesion, except an effu-
sion of blood in the median lobe of the cerebellum, and there was probably no pressure
upon the peduncles. " The individual who was the subject of this observation had had
an attack of apoplexy. Before the attack, he had for some time a staggering gait (une
demarche chancelante), and, after the attack, he had remained hemiplegic on the left
side." From these meagre details, it seems probable that there was a certain amount of
difficulty of coordination, although the description is not as definite as could be desired.

CASE II. — The second case was observed by Andral. A groom, not quite forty years
of age, was brought into the Maison royale de sante, having suffered from severe head-
ache, vertigo, etc., for fifteen days, which finally became fixed at the occiput. During
the first three days in the hospital, " he was in a continual state of agitation ; the move-
ments of the members, on the right as well as the left side, were sometimes so brusques
and disordered that they resembled convulsive movements." Soon the respiration be-
came disturbed, and he died in asphyxia. " Upon post-mortem examination, there was
found general injection of the meninges ; nothing particular in the cerebral hemispheres ;
a moderate quantity of serum in the ventricles ; reddish softening of the left hemisphere
of the cerebellum in its posterior and inferior half; no other lesion."

The only marked symptom relating to the movements in this case was a certain
amount of irregularity and convulsive action of the muscles, while the patient was in
bed. The case is not strong in its bearings, either for or against the coordination-theory ;
for there must have been a great amount of irritation of the encephalic centres, and it
would certainly be difficult to note disturbance of equilibration or of coordination in a
patient confined to the bed.

The third case is quoted by Andral from Lalletnand, and is taken by Lallemand from
Delamare.

CASE III. — "M. Gugrin, vicar at Gezeville, forty-six years of age, of a good tempera-
ment, strong, and corpulent, with a good appetite, complained of a dull pain, which
finally became acute, under the frontal bone. For a year he experienced attacks of ver-
tigo and vomiting, without fever. He staggered on his legs, and was often near falling
forward. The treatment employed was antiphlogistic and derivative."

On post-mortem examination, the cerebrum was found entirely healthy, but the en-
velop of the cerebellum was collapsed, folded, and only contained about the half of an
egg-shell full of a brown and fetid, lymphatico-purulent liquid.

This case, as far as the description goes, shows marked difficulty in equilibration or
coordination.

If the reader have carefully studied the foregoing analysis of Andral's cases, he will

FUNCTIONS OF THE CEREBELLUM. 715

see that eighty-five may be thrown out altogether, leaving but eight ; and, of these eight
cases, five are so imperfectly described, and the disorganization of the cerebellum is so
restricted, that they may also be disregarded. The ninety-three cases are thus reduced
to three. Of these three cases, in two, it is uncertain whether or not there were defi-
ciency of coordinating power ; and in one, the difficulty in equilibration or coordination
was distinctly noted. This, we conceive, disposes of the much-quoted ninety-three cases
of Andral ; and they are certainly not opposed to the view that the cerebellum is the
organ of equilibration or muscular coordination.

In addition to the cases collected by Andral, there are numerous other instances on
record of disease confined to the cerebellum, of which the following are examples :

CASE IV. — In 1826, Petiet reported a case of disease, in which the cerebellum was
entirely destroyed, its tissue being broken down into a sort of whitish J>ouillie. The cere-
brum was healthy. The observation was made in 1V96. The patient, before death, was
observed to present a remarkable tendency to walk backward. He rose from his seat
with difficulty, and, once erect, the first movements of the feet were lateral, and he finally
walked by moving the feet from before backward. His locomotion consisted simply in
passing from his own to an adjoining bed in the ward, a distance of about six feet.

CASE Y. — One of the most remarkable cases, and the one most frequently quoted by
physiological writers, was reported by Combette, in 1831. This patient, Alexandrine
Labrosse, in her seventh year, was seen by M. Miquel. Since the age of five years only
had she been able to sustain herself on her feet. M. Miquel was struck with her slight
development and the feebleness of the extremities. At the age of nine and a half years,
she was admitted into the Orphelins. " When spoken to, she answered with difficulty
and hesitation. Her legs, although very feeble, enabled her still to walk, but she often
fell." She was first seen by M. Combette, in January, 1831. She had then kept the bed
for three months; was constantly lying on the back, and could scarcely move the legs;
she used her hands with ease. She died of some intestinal disorder, March 25, 1831. On
post-mortem examination, " in place of the cerebellum there was a cellular membrane,
gelatiniform, semicircular, from eighteen to twenty lines in its transverse diameter."
There was no trace of the pons Varolii. Combette states that Alexandrine Labrosse was
able to walk for several years, always, it is true, in an uncertain manner ; later, her legs
became more and more feeble, and finally she ceased to be able to sustain her weight.
She had the habit of masturbation. Combette farther states that this observation is not
in accord " with the experiments of Flourens, which tend to show that the cerebellum is
the regulator of movements." The encephalon was also examined by Guillot, who noted
absence of the cerebellum and of the pons.

This case is somewhat imperfect, as it was not seen by Combette until the patient had
kept the bed for three months. By some writers, it is quoted in favor of, and by some,
in opposition to the view that the cerebellum coordinates the muscular movements. It
was not a case of simple disease of the cerebellum, as the pons and the posterior pedun-
cles were also absent. It was noted, before the case was seen by Combette, that the
patient walked in an uncertain manner and often fell.

Several cases of injury of the cerebellum are reported by Larrey.

CASE VI.— One case is described, in which the patient was struck by a ball from a
blunderbuss, which grazed the occipital protuberances. There was no disturbance of
movement. The patient died on the thirty-ninth day, in opisthotonos. On p«>>t-ni«>rtcm
examination, "the occipital bone had sustained a considerable loss of substance; tlu- ^lit
into the dura mater, to which we have alluded, corresponded to the centre of tin.- ritrht
lobe of the cerebellum, which was sunk downward and was of a yellowish color, but free
from suppuration or effusion. The medulla oblongata and spinal ui arrow bore a dull,
white aspect, were of greater consistence than is natural, and had lost about a quarter of
their size ; the nerves arising from them appeared to us also to be in a state of atrophy
near their origin."

716 NERVOUS SYSTEM.

CASE VII.— Another patient was struck by a piece of wood on the right side of the
head. He was found dead a little more than three months after the injury. " The right
hemisphere of the cerebellum was entirely disorganized by an abscess which pervaded
its whole substance." No disturbances of movement were noted.

CASE VIII. — Another patient had erysipelas following a fall on the side of the head,
and abscess. He lived for three or four months. Five or six weeks after the injury, he
had severe pains in the occiput, and, " when standing, he could with difficulty only pre-
serve his equilibrium." On post-mortem examination, the deep-seated vessels of the cere-
brum were found injected. " We found, in the left lobe of the cerebellum, about three
table-spoonfuls of pus of a whitish and gelatinous aspect, which had encroached upon, or
rather displaced entirely, the hemisphere of the cerebellum ; this purulent substance was
enveloped within the pia mater, which had acquired a somewhat firmer consistence, and,
as in the subject of the preceding case, assumed a pearly color. The other half of the
cerebellum was shrivelled, and the medullary substance forming the arbor-vita was of a
grayish color and very dense."

The first of these cases was found by Larrey to be associated with extinction of sexual
appetite and atrophy of the organs of generation. In the first two cases, judging from
the results of experiments on animals, there was not enough injury of the cerebellum to
necessarily influence the power of coordination. In the last case, there was difficulty in
equilibration, but also some paralysis.

A number of cases, which it is unnecessary to detail fully, are cited by "Wagner, in the
Journal de la physiologic, 1861, in which tottering gait and want of equilibration or of
muscular coordination were noted, in connection with greater or less disorganization of
the cerebellum. In the same journal, is a brief note of a case, reported by Laborde, in
which there was a large cyst in the cerebellum, with incomplete paraplegia and " want
of coordination of the movements of progression."

CASE IX.— A most remarkable and carefully-observed case of atrophy of the cerebel-
lum was reported by Dr. Fiedler, in 1861. The subject of this observation, a man, aged
about fifty years, had remarkable peculiarities in his movements for thirty years. ' After
the age of twenty years, it is stated that " he could no longer walk with as much cer-
tainty as before; the gait was staggering (taumelnd). . . . Not only in the house, but
also in the street, the patient often fell, so that he was very frequently taken for a drunk-
ard, and was either carried home or taken to the police-station. It is said that he never
had drunk spirituous liquors.

" Sometimes the patient walked backward, but only a few steps. He never had any
turning movements; the gait was always tottering (wacklig) and slow." He never fell
forward, but always on the back. On post-mortem examination, the cerebrum was found
healthy, " but the cerebellum was atrophied, especially at its posterior and inferior portion,
and was reduced in size at least one-half." This case presented the phenomena of defec-
tive coordination to a marked degree. Nothing is said of vertigo.

Among the most striking of the cases of disease of the cerebellum, are two observed
by Vulpian.

CASE X. — The first was a woman, forty -nine years of age, in the hospital of la Sal-
petriere. " All of the movements were preserved, but locomotion was most irregular
and difficult ; she could only walk in the most bizarre manner, resting on a chair which
she placed before her at every step, and, in spite of her efforts at equilibration, she often
fell." This patient, however, retained great muscular power. On post-mortem exami-
nation, "the cortical gray substance of the cerebellum was found entirely "atrophied : all
the nerve-cells of this layer had disappeared." There was considerable reduction in the
size of the cerebellum. The corpora dentata were perfectly preserved, " showing that
these parts, at all events, have but a slight office in coordination."

CASE XL — The second case presented an old softening, about the size of a hazel-nut,
destroying a corresponding amount of the cerebellar substance of one of the hemi-

FUNCTIONS OF THE CEREBELLUM. 717

spheres. The corpus dentatum was completely destroyed. This woman " walked well
but it appears nevertheless that she vacillated very slightly in her gait, without, how-
ever, a tendency to fall."

We have thus cited quite a number of cases of disease confined to the cerebellum, in
which there was marked disturbance in the muscular movements ; but there are others
in which the movements were unaffected. As an example of the latter, we may refer to
a case quite fully reported by Bouvier :

CASE XII. — "A man, fifteen years of age, had been subject, for a length of time, to
a discharge from the ear, with deafness and frequent headache. He was suddenly seized
with more severe headache on the left side of the head, vomiting, and disorder of mind.
His symptoms were, indeed, so characteristic, that a physician who was consulted pro-
nounced him to be laboring under abscess in the head, and that death was almost certain.

" He entered the Hotel Dieu on the 15th of September, three weeks after the last
exacerbation, when he complained of fixed pain in the head, which frequently caused
him to cry out ; sensibility, in other respects, obtuse; slow answers; somnolency; face
pale ; features sunken ; look, sad and anxious ; a copious, purulent discharge from the
left ear ; deafness of the same side ; pulse slightly slower ; vomiting ; constipation ; the
movements of the limbs were preserved, an incomplete paralysis of the upper eyelid
being alone observed.

" These symptoms continued for the following days without any marked aggravation ;
and it seemed probable that the patient's life might still be prolonged for some time,
when, on the 23d of September, after vomiting, accompanied by great agitation and vio-
lent outcry, he suddenly fell into a state of complete collapse. Respiration became
embarrassed, and he died eight days after his entrance into the hospital, with symptoms
of asphyxia.

" On examining the body, there was found, as had been foretold during life, a caries
of the petrous portion of the temporal bone, and an abscess in the interior of the cra-
nium. But what was remarkable, the abscess occupied the left hemisphere of the cere-
bellum, although nothing led to the suspicion that there was any lesion of that organ.
There was an extensive cavity, which invaded the .two outer thirds of the left lobe of
the cerebellum, and which contained several table-spoonfuls of pus, somewhat similar to
that of an abscess. The substance forming its parietes were softened and of a livid tint.
The meatus auditorius was filled with reddish vegetations.

" The caries occupied the base of the pars petrosa only — the labyrinth and auditory
nerve were untouched. There was no perceptible communication between the internal
abscess and the abscess of the caries. The disease of the bone, however, extended to
the dura mater, in two very circumscribed points, at the upper and hind part of the pars
petrosa. The dura mater, opposite these points, was deeply colored ; and its coloration
extended to its inner surface, where it was in contact with the cerebellum.

"The cerebral ventricles were, moreover, distended by a limpid fluid; and the pia
mater exhibited a decided injection under the anterior part of the cerebral lobes, chiefly
on the left side.

" ' Two circumstances,' says M. Bouvier, ' give interest to this case. Tho first is the
almost entire separation, by means of the dura mater — which was scarcely affected—
between two lesions, one of which must have been the effect of the other ; so that it is
difficult to explain, merely by continuity of tissue, the transmission of the affection from
the ear to the cerebellum.

" ' The second is the absence of all the symptoms which have been of late regarded av
an effect of lesions of the cerebellum— such as augmentation of the trcnt-ml sensibility.
loss of equilibrium, and excitation of the genital organs. Could this peculiarity be owin:.'
to the slowness of the affection, or to its not having extended sufficiently far from the
side of the medulla oblongata? ' "

The interpretation of certain of the cases which we have cited depends apparently

718 NERVOUS SYSTEM.

upon the ideas concerning the functions of the cerebellum with which they are regarded.
We should certainly consider those cases in which disordered movements have been
noted, as very strong evidence, taken in connection with the results of experiments upon
living animals, that the cerebellum regulates equilibration and muscular coordination.
Some physiologists regard them as in accordance with the view that injury of the cere-
bellum does not affect coordination, but simply produces vertigo. It remains for the
reader to judge whether or not the phenomena observed in these cases indicate want of
coordinating power. In the case reported by Bouvier, the lesion of the cerebellum was
not sufficient to necessarily disturb coordination.

We now come to the main question, whether or not, in view of the results of experi-
ments upon animals and the phenomena observed in cases of disease or injury of the cere-
bellum, this nerve-centre presides over coordination of action of the muscles, which is
certainly necessary to equilibration, except the muscles of the face and those concerned
in speech. This question, it seems to us, can be definitely answered.

Every carefully-observed case that we have been able to find, in which there was
uncomplicated disease or injury of the cerebellum, provided the disease or injury involved
more than half of the organ, presented great disorder in the general movements, par-
ticularly those of progression. We have collected the more or less complete reports of
twelve cases. In Case II., there was softening of one-half of one hemisphere, with
remarkable convulsive movements. In Case V., the one so often quoted from Oombette,
the gait was uncertain, with frequent falling ; there was incomplete paralysis ; but, in
addition to the absence of the cerebellum, there was no pons Varolii. In Case VI.,
there was no disturbance of movement, and there was partial degeneration of one lateral
lobe of the cerebellum. In Case VII., there was no disturbance of movement, and dis-
organization of one lateral lobe of the cerebellum. In Case XI., there was slight loss of
substance in one lateral lobe of the cerebellum, and slight " vacillation " in the move-
ments. In Case XII., there was an abscess involving two-thirds of one lateral lobe, and the
movements of the limbs were preserved. In Cases I., III., IV., VIII., IX., X., six out of
twelve, there was difficulty in muscular coordination, which was invariably in direct ratio
to the amount of cerebellar substance involved in the disease or injury. We do not make
the reservation, that more than half of the cerebellum must be destroyed in order neces-
sarily to produce difficulty in muscular coordination, upon purely theoretical grounds, but
we regard this point as positively demonstrated by experiments upon animals. These ex-
periments show that one-half of the organ is capable of performing the function of the
whole. We have an analogy to this in the action of the kidneys, one of which is sufficient
for the elimination of the effete constituents of the urine, after the other has been removed.

Notwithstanding the contrary views of many physiological writers, we are firmly
convinced, from experiments and a careful study of pathological facts, that there is no
one point in the physiology of the nerve-centres more definitely settled than that the
cerebellum presides over equilibration and the coordination of the muscular movements,
particularly those of progression. In this statement, we make exceptions in favor of the
movements of respiration, deglutition, of the face, and of those concerned in speech, as
well as the involuntary movements generally. As another example of a nerve-centre pre-
siding over muscular coordination, we have the instance of the portion of the left anterior
lobe of the cerebrum which coordinates the action of the muscles concerned in speech.

The theory that the disordered movements which follow injury of the cerebellum are
due simply to vertigo is not tenable ; and in only one of the cases cited is vertigo men-
tioned. There is a disease, involving the semicircular canals and other parts of the inter-
nal ear, called M6niere's disease, in which there is marked want of equilibration and
muscular coordination, attended with, and probably dependent upon vertigo. The ver-
tigo is always very distinct and is mentioned in all of these cases ; and, although it is less
in the recumbent posture, it is never entirely absent. A careful study of these cases,
comparing them with the cases of deficient coordination from disease of the cerebellum,

FUNCTIONS OF THE CEREBELLUM. 719

cannot fail to show a great difference between the phenomena following cerebellar dis-
ease and the muscular phenomena due to well-marked and persistent vertigo.

Connection of the Cerebellum with the Generative Function. — The fact that the cere-
bellum is the centre for equilibration and the coordination of certain muscular move-
ments does not necessarily imply that it has no other functions. The idea of Gall, that
"the cerebellum is the organ of the instinct of generation," is sufficiently familiar; and
there are numerous facts in pathology which show a certain relation between this nerve-
centre and the organs of generation, although the idea that it presides over the genera-
tive function is not sustained by the results of experiments upon animals or by facts in
comparative anatomy.

In experiments upon animals in which the cerebellum has been removed, there is noth-
ing pointing directly to this part as the organ of the generative instinct. Flourens re-
moved a great part of the cerebellum in a cock. The animal survived for eight months.
It was put several times with hens and always attempted to mount them, but without
success, from want of equilibrium. In this animal, the testicles were enormous. This
observation has been repeatedly confirmed, and there are no instances in which the cere-
bellum has be«n removed with apparent destruction of sexual instinct. In a comparison
of the relative weights of the cerebellum in stallions, mares, and geldings, Leuret found
that, far from being atrophied, the cerebellum in geldings was even larger than in either
stallions or mares.

In the numerous cases of disease or injury of the cerebellum, to which we have
referred, there are some, in which irritation of this part has been followed by per-
sistent erection and manifest exaggeration of the sexual appetite, and others, in which
its extensive degeneration or destruction has apparently produced atrophy of the genera-
tive organs and total loss of sexual desire. There are also certain cases of this kind
which we have not yet cited. Serres gives the history of several cases, in which irrita-
tion of the cerebellum was followed by satyriasis or nymphomania, but, in other cases,
there were no symptoms referable to the generative organs. In the case reported by
Combette, the patient had the habit of masturbation. Dr. Fisher, of Boston, reported
(1838) two cases of diseased or atrophied cerebellum, with absence of sexual desire,
and one case of irritation, with satyriasis. Similar instances are given by other writers,
which it is unnecessary to detail. We have already cited the observations of Budge, in
which mechanical irritation of the cerebellum was followed by movements of the uterus,
testicles, etc.

Although there are many facts in pathology which are opposed to the view that the
cerebellum presides over the generative function, there are numerous cases which go to
show a certain connection between this portion of the central nervous system and the
organs of generation in the human subject. But this is all that we can say upon this
important point ; certain it is that the facts are not sufficiently numerous, definite, and
invariable, to sustain the doctrine that the cerebellum is the seat of the sexual instinct.

Development of the Cerebellum in the Lower Animals. — The study of the comparative
anatomy of the cerebellum has little physiological interest, except in so far as it bears
upon our knowledge of its functions. From this point of view, there is little to be said
concerning its development in the animal scale. We can hardly establish a definite rela-
tion between this particular part of the encephalon and the complicated character of the
muscular movements ; for, as we pass from the lower to the higher orders of animals, we
have other parts of the brain, as well as the cerebellum, developed in proportion to the
increased complexity of the muscular system. Nor can we connect the comparative
anatomy of the cerebellum with the ideas of the functions of this organ in connection
with generation. The amphioxus lanciolatus has no cerebellum, and tins oriran. there-
fore, is not indispensable to generation. In some animals remarkable for salacity, the
cerebellum is not unusually large ; and facts of this kind might be multiplied ad infinitum.

720

NERVOUS SYSTEM.

"We have thus discussed only those views with regard to the functions of the cerebel-
lum which are supported by experimental or pathological facts, and have not touched
upon the vague and unsupported ideas advanced by various writers before the publica-
tion of the remarkable observations of Flourens. There is no proof that the cerebellum
is the organ presiding over memory, the involuntary movements, general sensibility, or
the general voluntary movements. The only view that has any positive experimental or
pathological basis is that it presides over equilibration and the coordination of certain
muscular movements, and is, perhaps, in some way connected with the generative
function.

Ganglia at the Base of the Encephalon.

At the base of the encephalon, are found several collections of gray matter, or gan-
glia, some of which have functions distinct from those already described in connection with
the cerebrum and cerebellum; but most of them are so difficult of access in living ani-
mals, that we possess very little definite information, even with regard to their general
properties. We have, however, a tolerably complete knowledge of the functions of the
medulla oblongata and the tubercula quadrigemina, and have some idea of the physiology
of the tuber annulare ; but the functions of the corpora striata, optic thalami, ventricles,
pineal gland, peduncles, etc., are little understood, and the speculations of the older
writers, with the indefinite experiments of modern physiologists, upon these parts, will
be passed over very briefly.

Corpora Striata.

These bodies are somewhat pear-shaped, and are situated at the base of the brain,
partly without the cerebral hemispheres and partly embedded in their white substance.

FIG. 228.— Corpora striata. (Sappey.)

1, fifth ventricle ; 2, the two laminae of the septum lucidum meeting in front of the fifth ventricle ; 8, hippocampus
minor ; 4, posterior portion of the corpus callosum ; 5, middle portion of the fornix ; 6, posterior pillar of the
fornix; 7, hippocampus major; 8, eminentia collateralis ; 9, lateral portions of the fornix: 10, choroid plexus:
11, taenia semicircularis ; 12, corpus atriatum.

OPTIC THALAMI. 721

Their rounded base is directed forward, and the narrower end, backward and outward.
Their external surface is gray, and they present, on section, alternate stria of white and
gray matter, which appearance has given them the name of corpora striuta. J Jet ween
the narrow extremities of these bodies, are situated the optic thalami.

There is very little to be said with regard to the functions of the corpora striata.
Burdon-Sanderson has lately shown that, when the corpus striatum on one side, exposed
by carefully removing a small portion of the anterior lobe of the cerebrum, is stimulated
with a weak induced current of galvanism, movements of the muscles occur upon the oppo-
site side of the body. If the deepest parts be stimulated, "the animal opens its mouth,
puts out its tongue, and draws it in again alternately." When the corpora striata are
removed, disturbing the hemispheres as little as possible, there appears to be no paralysis,
either of motion or sensation.

We have obtained a little more information regarding the functions of the corpora
striata, from cases of cerebral haemorrhage in the human subject, than from experimental
investigations. In apoplexy, when the corpus striatum on one side is alone involved,
there is paralysis of motion of the opposite lateral half of the body, the general sensibility
usually being unaffected. Facts of this kind show that the action of the corpora striata
is crossed ; and they farther illustrate their connection with the motor tract from the
hemispheres.

There is no reason to suppose that the corpora striata are the centres of olfaction, as
was at one time thought, for they are sometimes absent in animals possessing very large
olfactory nerves, and they are very largely developed in the cetacea, in which the olfac-
tory apparatus is rudimentary.

Optic Thalami.

From their name, we should infer that the optic thalami have some important func-
tion in connection with vision ; but they serve merely as beds for the optic commissures
and give to the nerves but very few fibres. They are oblong bodies, situated between
the posterior extremities of the corpora striata, and resting upon the crura cerebri on the
two sides. They are white externally, and, in their interior, present a mixture of white
and gray matter. Longet has destroyed them upon the two sides, carefully avoiding
injury of the optic tracts, and he noted no interference with vision or with the move-
ments of the iris.

The optic thalami seem, from experiments upon animals, to have a peculiar crossed
action upon the muscular system. While their mechanical irritation produces neither
pain nor convulsive movements, showing that they are probably insensible and inexcita-
ble, the extirpation of one optic thalamus is followed by enfeeblement of the muscles of
the opposite lateral half of the body, without actual paralysis. When both have been
removed, there is general debility of the muscular system. It is unnecessary to refer to
other experiments upon these parts, which have been very indefinite in their results, or to
allude to the "circular" movements produced by lesion upon one side, involving also
the crus cerebri ; for, beyond the statement just made, the function of the optic thalami
is unknown.

We derive but little information concerning the optic thalami from cases of cerebral
haemorrhage in the human subject ; for it is not common to have disease involving these
parts and not affecting other centres. In some cases of lesion limited to the optic thala-
mus on one side, there is paralysis of sensation of the opposite lateral half of the body,
without actual paralysis of motion, although the movements are gem-rally foi-l>U-. When
the brain-lesion involves both the corpus striatum and the optic thalamus on one .side,
which is more common, there is paralysis of motion, with loss or disorder of sensibility,
on the opposite side of the body. These facts illustrate, to a certain extent, the anatomi-
cal connection of the optic thalami with the sensory tracts, although, in experiments upon
animals, destruction of these parts does not necessarily affect the general sensibility.
46

722 NERVOUS SYSTEM.

Tubercula Quadrigemina.

These little bodies, sometimes called the optic lobes, are rounded eminences, two
upon either side, situated just below the third ventricle. The anterior, called the nates,
are the larger. These are oblong and of a grayish color externally. The posterior,
called the testes, are situated just behind the anterior. They are rounded and are rather
lighter in color than the anterior. Both contain gray nervous matter in their interior.
They are the main points of origin of the optic nerves and are connected by commissu-
ral fibres with the optic thalami. In birds, the tubercles are two in number, instead of
four, and are called tubercula bigemina.

It is probable that the tubercula quadrigemina are inexcitable and insensible. When
pain and convulsive movements have apparently followed their mechanical irritation in
living animals, these phenomena have probably been due to excitation or stimulation of
the motory or sensory commissural fibres which pass beneath them.

As regards the function of the optic lobes, aside from their action as reflex centres
for the movements of the iris, there is little to be said, except that their office is inti-
mately connected with the sense of sight. They are easily reached and operated upon in
birds, where they are very large, and their extirpation is followed by total loss of sight
and abolition of the reflex movements of the iris. In birds and in those mammals in
which they have been operated upon, their action in vision is crossed ; i. e., when the
lobe is removed upon one side, the sight is lost in the opposite eye, vision in the eye upon
the same side being unimpaired. We have long been in the habit, in class-demonstra-
tions, of removing the optic lobe on one side from a pigeon, with the result just men-
tioned. The operation is quite simple : A part of the skull is removed by the side of one
hemisphere, and the optic lobe is seen, in the form of a large, white tubercle, between
the posterior portion of the cerebrum and the cerebellum. A little slit is then made in
its capsule, and the interior is broken up carefully with a delicate forceps. The animal
generally recovers from the operation, blinded in the eye upon the opposite side. In re-
moving the portion of the skull, it is well not to go too far back, as there is then danger
of wounding the great venous sinus and complicating the operation by haemorrhage.

In treating of the special sense of sight, we shall see that the decussation of the
optic nerves is more complex in man than in birds, in which the nerve from one optic
lobe passes totally and exclusively to the eye upon the opposite side. In man, most of
the fibres of the optic nerve from one side pass to the eye upon the opposite side ; but a
few fibres pass to the eye upon the same side, a feu- connect the tubercles upon the two
sides, and a few connect the two eyes. It is not known whether or not, in man, the
action of the tubercles in vision is exclusively crossed, as it appears to be in most of
the inferior animals.

The optic lobes have long been regarded as the sole centres presiding over the sense of
sight, and not merely as avenues of communication of this sense to the cerebral hemi-
spheres; but the experiments of Ferrier upon monkeys (1875) and of Dalton upon dogs
(1881) have demonstrated the remarkable fact that destruction of the angular convolution
of the cerebrum upon both sides produces total blindness. Destruction of this convolu-
tion upon one side was found to produce blindness of the eye upon the opposite side, while
the sight in the eye upon the same side was apparently unaffected. In all of the experi-
ments referred to, the crossed action of lesions of the angular convolution was very dis-
tinct; but in certain cases of affections of vision in the human subject, due to lesion of the
brain, which will be referred to more fully in connection with the question of decussa-
tion of the optic nerves, the injury produced loss of sight in one vertical half of the ret-
ina in either eye.

Ganglion of the Tuber Annular e.

The tuber annulare, called the pons Varolii, or the mesocephalon, is situated at the
base of the brain, just above the medulla oblongata. It is white externally and contains

GANGLION OF THE TUBER ANNULARE. 733

in its interior a large admixture of gray matter. It presents both transverse and longi-
tudinal white fibres. Its transverse fibres connect the two halves of the cerebellum. Its
longitudinal fibres are connected below, with the anterior pyramidal bodies and the oli-
vary bodies of the medulla oblongata, the lateral columns of the cord, and a certain por-
tion of the posterior columns. Above, the fibres are connected with the crura cerebri
and pass to the brain. The superficial transverse fibres are wanting in animals in which
the cerebellum has no lateral lobes.

The general properties of the tuber annulare have been demonstrated in the most sat-
isfactory manner by Longet. In his experiments, direct excitation of the superficial
transverse fibres did not produce well-marked convulsive movements, and there were no
convulsions when the posterior fibres were stimulated. When galvanization was applied
to the deeper anterior fibres, convulsive movements were distinct at each excitation.
Stimulation of the posterior portion always produced pain. This was not constantly
observed to follow irritation of the anterior portion, and, when pain occurred, it was
thought to be due to irritation of the root of the fifth nerve.

The above experiments, it is true, are not so free from uncertainty as those made upon
the more accessible parts of the encephalon, but, as far as they go, they tend to show that
the tuber annulare is both insensible and inexcitable in its superficial anterior portion,
which is composed chiefly of commissural fibres from the cerebellum ; that it is excita-
ble and probably insensible in its deeper anterior portion, which seems to be composed
chiefly of descending motor conductors ; and, finally, that it is sensible and probably
inexcitable in its posterior portion.

The tuber annulare undoubtedly acts as a conductor of sensory impressions and motor
stimulus to and from the cerebrum, as we should naturally expect from the direction of
its fibres, and as has been repeatedly shown by cases of disease, particularly as regards
motion. In addition, however, judging from the fact that it contains numerous nodules
of gray matter between fasciculi of white fibres, and that this gray matter contains cel-
lular elements similar to those found in other nerve-centres and from which nerve-
fibres undoubtedly originate, it would be inferred that these nodules have a distinct
function and give to the tuber annulare the properties of a nerve-centre. It will be
interesting, therefore, to follow out the experiments upon this part, by which its action
as a centre has been illustrated. These experiments are of two kinds : First, the re-
moval of other encephalic ganglia, leaving only the tuber annulare, the medulla oblon-
gata, and the cerebellum, and noting the properties or faculties retained by animals
under these conditions. Experiments of this kind are tolerably definite, as we already
know the general functions of most of the other encephalic ganglia. Second, to note
the effects of extirpation of the tuber annulare alone.

If the cerebral hemispheres, the olfactory ganglia, the optic lobes, the corpora striata,
and the optic thai ami, be removed, the animal loses the special senses of smell and sight
and the intellectual faculties, there is a certain amount of enfeeblement of the muscular
system, but voluntary motion and general sensibility are retained. There can be no
doubt upon these points. As far as voluntary motion is concerned, an animal oper-
ated upon in this way is in nearly the same condition as one simply deprived of the
cerebral hemispheres. There are no voluntary movements which show any degree of
intelligence, but the animal can stand, and various consecutive movements are executed,
which are entirely different from the simple reflex acts depending exclusively upon the
spinal cord. The coordination of movements is perfect, unless the cerebellum be re-
moved. As regards general sensibility, an animal deprived of all the encephalic ^an-lia
except the tuber annulare and the medulla oblongata undoubtedly feels pain. This has
been demonstrated in the most conclusive manner by Longet, and has been shown even
more satisfactorily by Yulpian. In rabbits, rats, etc., after removal of the cerebrum,
corpora striata, and optic thalami, pinching of the ear or foot is immediately followed by
prolonged and plaintive cries. Both of the experimenters referred to insist upon the

724 NERVOUS SYSTEM.

character of these cries as indicating the actual perception of painful impressions, and as
very different from cries that are purely reflex, according to the ordinary acceptation of
this term. Longet alludes to the voluntary movements and the cries observed in persons
subjected to painful surgical operations, when incompletely under the influence of an
anesthetic, concerning the character of which there can be no doubt. He regards the
movements as voluntary, and the cries as evidence of the acute perception of pain ; but
it is well known that such patients have no recollection of any painful impression,
although they have apparently experienced great suffering. As far as we can judge
from what we positively know of the functions of the encephalic centres, the pain under
these circumstances is perceived by some nerve-centre, probably the tuber annulare, but
the impression is not conveyed to the cerebrum and is not recorded by the memory.

Taking all the experimental facts into consideration, the following seems to be the
most reasonable view with regard to the function of the tuber annulare as a nerve-centre :

It is an organ capable of originating a stimulus giving rise to voluntary movements,
when the cerebrum, corpora striata, and the optic thalami, have been removed, and it
probably regulates the automatic voluntary movements of station and progression. Many
voluntary movements, the result of intellectual effort, are made in obedience to a stimu-
lus transmitted from the cerebrum, through conducting fibres in the tuber annulare, to
the motor conductors of the cord and the general motor nerves.

The tuber annulare is also capable of perceiving painful impressions, which, when all
of the encephalic ganglia are preserved, are also conducted to and are perceived by the
cerebrum, and are remembered ; but there are distinct evidences of the perception of
pain, even when the cerebrum has been removed.

Medulla Oblongata.

The chief points of interest in the physiological anatomy of the medulla oblongata
relate to the direction of its fibres, their connection with the gray matter embedded in
its substance, and the course of the filaments of origin of certain of the cranial nerves.
Concerning the deep origin of the large root of the fifth, the motor oculi externus, facial,
pneumogastric, spinal accessory, and the sublingual, we shall have nothing to say in this
connection, as we have already treated of the physiological anatomy of these nerves with
sufficient minuteness ; and we have now to study the functions of the medulla oblongata,
and particularly its action as a nerve-centre.

Physiological Anatomy of the Medulla Oblongata. — The medulla oblongata is the
oblong enlargement which connects the spinal cord with the various encephalic ganglia.
It is about an inch and a quarter in length, and nearly an inch broad at its widest por-
tion. It rests in the basilar groove of the occipital bone, extending from the atlas to the
lower border of the tuber annulare, with its broad extremity above. Like the cord, it
has an anterior and a posterior median fissure.

Apparently continuous with the anterior columns of the cord, are the two anterior
pyramids, one on either side. Viewed superficially, the innermost fibres of these pyra-
mids are seen to decussate in the median line ; but, if these fibres be traced from the
cord, it is found that they come from the white substance of its lateral columns, and that
none of them are derived from the anterior columns. The fibres of the external portion
of the anterior pyramids come from the anterior columns of the cord. At the site of the
decussation, the pyramids are composed entirely of white matter; but, as the fibres
spread out to pass to the encephalon above, they present nodules of gray matter between
the fasciculi.

External to the anterior pyramids, are the corpora olivaria. These are oval and are
surrounded by a distinct groove. They are white externally and contain a gray nucleus,
called the corpus dentatum.

MEDULLA OBLONGATA.

725

External to the corpora olivaria, are the restiform bodies, formed exclusively of
white matter and constituting the postero-lateral portion of the medulla. They are
continuous with the posterior columns of the cord. The restiform bodies spread out
as they ascend, and pass to the cerebellum, forming a great portion of the inferior
peduncles.

Beneath the olivary bodies and between the anterior pyramids and the restiform
bodies, are the lateral tracts of the medulla, called by the French, the intermediary fas-
ciculi. These are composed of an intimate mixture of white and gray matter and have
a yellowish-gray color. They receive all that portion
of the antero-lateral columns of the cord which does
not enter into the composition of the anterior pyra-
mids. They are frequently considered as parts of the
restiform bodies, but they are peculiarly interesting,
from the fact that they contain the gray centre pre-
siding over respiration ; and, for that reason, we have
described them as distinct fasciculi.

The posterior pyramids (fasciculi graciles) are the
smallest of all. They pass upward to the cerebrum,
without decussating, and are composed exclusively
of white matter. As they pass upward, they diverge,
leaving a space at the fourth ventricle.

The fourth ventricle is in the medulla, and is
bounded above, by the valve of Vieussens and the
under surface of the cerebellum. In the lower part
of the floor of the fourth ventricle, are several trans-
verse fasciculi of white matter ; but the greatest part
of this portion is composed of a layer of gray sub-
stance.

The two lateral halves of the posterior portion of
the medulla are connected together by fibres arising
from the gray matter of the lateral tracts, or inter-
mediary fasciculi, passing obliquely, in a curved
direction from behind forward, to the rap he in the
median line. There are also fibres passing from be-
fore backward, to form a posterior commissure, and
fibres arising from the cells of the olivary bodies,
which connect the gray substance of the lateral
halves. Commissural fibres also connect the gray
matter of the. lateral tracts with the corpora dentata
of the olivary bodies, and the olivary bodies with the
cerebellum, their fibres forming part of the inferior
peduncles of the cerebellum. In addition, it is prob-
able that fibres, taking their origin from all of the
gray nodules of the medulla, pass to the parts of the
encephalon situated above.

As far as the fibres of origin of the nerves are
concerned, it may be stated in general terms that a
number of the motor roots arise from the gray matter

of the floor of the fourth ventricle, the roots of the sensory nerves arising from -ray
matter in the posterior portions.

Aside from purely anatomical demonstrations, the connection of the anterior pyra-
mids of the medulla with the corpora striata has been shown by pathological observa-
tions. It is well known that, when the connection between the nerve-centres and the

FIG. 229.— Anterior view of tlie, medulla
oiblongata. (Sappey.)

1, infundibulum ; 2, tnber cinereum ; 8,
corpora albicantia ; 4, cerebral pedun-
cle; 5, tuber annulare ; 6, origin of the
middle peduncle of the cert-helium : 7,
anterior pyramid x of tfn- meitnlla rt-
longata ; 8. <1< ruxntition <>f the anterior
pyramids ; 9. olir<t rn /,«//>>* ;
form bodies; 11. arc/form .rfbrfs; 12,
upper extremity of tin- spinal cord: 13.
Ugunentom denttcutatum ; 14, 14, dura
mater of the cord: 1">. optic tract-; if).
chiasm of the optic nerves; 17. motor
oculi communis; 18, pathetfcni; H>.
fifth nerve; '20. motor oculi rxtcnms;
21, facial nerve; •_'•-'. am litory nerve ; -'•:.
nerve of Wrisberff; -.'4. gloMo-pharyn-
geal nerve: 26, pnemnogMtrks: •-''•. •-'•».
spinal iiceessory : '-'7. suhlin^iial nerve;
28, 2i>, 80. cervical B

726 NERVOUS SYSTEM.

fibres is destroyed, these fibres after a time become degenerated. In old lesions of the
corpora striata, it has been shown that, when the white substance is injured upon one
side, there follow degeneration and atrophy of the fibres of the corresponding cerebral
peduncle and anterior pyramid of the medulla, and of the lateral portion of the spinal
cord upon the opposite side. This important fact illustrates the connection between the
lateral columns of the cord and the anterior pyramids of the medulla oblongata, the
decussation of the anterior pyramids, and the passage of fibres from the anterior pyra-
mids to the corpora striata, in the substance of the cerebral peduncles.

Functions of the Medulla Oblongata.

It is hardly necessary to discuss the functions of the medulla oblongata as a conductor
of sensory impressions and of motor stimulus to and from the brain. We know that there
is conduction of this kind from the spinal cord to the ganglia of the encephalon, and this
must take place through the medulla; a fact which is inevitable, from its anatomical rela-
tions, and which is demonstrated by its section in living animals. Nor is it necessary to
dwell upon its general properties, in which it resembles the spinal cord, at least as far as
has been demonstrated by experiments upon living animals or upon animals just killed.
It is difficult to expose this part in the higher classes of animals, but experiments show
that it is sensitive on its posterior surface and insensible in front. The difficulty of ob-
serving the phenomena which follow its irritation in living animals has rendered it im-
possible to determine the limits of its excitability and sensibility as exactly as has been
done for the different portions of the cord.

It is also somewhat difficult to determine whether the action of the medulla itself, in
its relations to motion and sensation, be crossed or direct. As regards conduction from
the brain, the direction is sufficiently well shown by cases of cerebral disease, in which
the paralysis, in simple lesions, is always on the opposite side of the body.

The action of the medulla as a reflex nerve-centre depends upon its gray matter.
When this gray substance is destroyed, certain of the important reflex functions are
instantly abolished. From jts connections with various of the cranial nerves, we should
expect it to play an important part in the movements of the face, in deglutition, in the
action of the heart and of various glands, etc., important points which will be fully con-
sidered in their appropriate place. Its most striking function, however, is in connection
with respiration.

Connection of the Medulla Oblongata with Respiration. — In 1809, Legallois made a
number of experiments upon rabbits, cats, etc., in which he showed that respiration
depends exclusively upon the medulla oblongata and not upon the brain, and he farther
located the part which presides over this function at the site of origin of the pneumogastric
nerves. Flourens, in his elaborate experiments upon the nerve-centres,, extended the
observations of Legallois, and limited the respiratory centre in the rabbit, between the
upper border of the roots of the pneumogastrics and a plane situated about a quarter of
an inch below the lowest point of origin of these nerves ; these limits, of course, varying
with the size of the animal. Following these experiments, Longet has shown that the
respiratory nervous centre does not occupy the whole of the medulla included between
the two planes indicated by Flourens, but that it is confined to the gray matter of the
lateral tracts, or the intermediary fasciculi. This was demonstrated by the fact that
respiration persists in animals after division of the anterior pyramids and the restiform
bodies. Subsequently, Flourens still farther restricted the limits of the respiratory centre
and fully confirmed the observations of Longet.

The portion of the medulla oblongata above indicated presides over the movements
of respiration and is the true respiratory nerve-centre. Nearly all who have repeated
the experiments of Flonrens have found that the spinal cord may be divided below the
medulla oblongata, and that all of the encephalic ganglia above may be removed, re-

FUNCTIONS OF THE MEDULLA OBLONGATA.

727

spiratory movements still persisting. It is a very common thing in vivisections to kill an
animal by breaking up the medulla. In a dog, for example, we grasp the head firmly
with the left hand, flex it forcibly upon the neck, and penetrate with a stylet a little behind
the occipital protuberance, entering between the atlas and the skull. By
a rapid lateral motion of the instrument, the medulla is broken up, and
the animal instantly ceases to breathe. There are no struggles, no mani-
festations of the distress of asphyxia; the respiratory muscles simply
cease their action, and the animal loses instantly the sense of want of
air. A striking contrast to this is presented when the trachea is tied or
when all of the respiratory muscles are paralyzed without touching the
medulla.

In another chapter, we have insisted upon the mechanism of the
respiratory acts. We have conclusively shown by experiments, that an
impression is made upon the respiratory nervous centre, which is due to
want of oxygen and not necessarily to an irritation produced by car-
bonic acid ; and that this impression gives rise to the movements of
respiration. If this impression be abolished, there are no respiratory
movements ; and if the medulla, the sole centre capable of receiving this
impression and of generating the stimulus sent to the respiratory mus-
cles, be destroyed, respiration instantly ceases, without any sensation of
asphyxia.

Vital Point (so called). — Since it has been definitely ascertained that
destruction of a restricted portion of the gray substance of the medulla
produces instantaneous and permanent arrest of the respiratory move-
ments, Flourens and others have spoken of this centre as the vital knot,
destruction of which is immediately followed by death. With our
present knowledge of the properties and functions of the different tissues
and organs of which the body is composed, it is almost unnecessary to
present any arguments to show the unphilosophical character of such a
sweeping proposition. We can hardly imagine such a thing as instan-
taneous death of the entire organism ; still less can it be assumed that
any restricted portion of the nervous system is the one essential, vital
point. Probably, a very powerful electric discharge passed through the
entire cerebro-spinal axis produces the nearest approach to instantaneous
death of any thing of which we have any knowledge ; but, even here, it
is by no means certain that some parts do not for a time retain their so-
called vital properties. In apparent death, the nerves and the heart may
be shown to retain their characteristic properties; the muscles will con-
tract under stimulus, and will appropriate oxygen and give off" carbonic acid, or respire;
the glands may be made to secrete, etc. ; and no one can assume that, under these con-
ditions, the entire organism is dead. We really know of no such thing as death, except
as the various tissues and organs which go to make up the entire body become so altered
as to lose their physiological properties beyond the possibility of restoration ; and this
never occurs for all parts of the organism in an instant. A person drowned may be to all
appearances dead, and would certainly die without measures for restoration : yet. in
such instances, restoration may be accomplished, the period of apparent death l>ein:r
simply a blank, as far as the recollection of the individual is concerned. It is as utterly
impossible to determine the exact instant when the vital principle, or whatever it may
be called, leaves the body in death, as to indicate the time when the organism becomes
a living being. Death is nothing more than a permanent destruction of so-called vital
physiological properties ; and this occurs successively, and at different periods, for differ-
ent tissues and organs.

FIG. 230. — Stylet
forbreitkiny up
I nil a 00-
/(»it/(tta. (Ber-
nard.)

728 NERVOUS SYSTEM.

When we see that frogs will live for weeks, and sometimes for months, after destruc-
tion of the medulla oblongata, and that, in mammals, by keeping up artificial respiration,
we can prolong many of the most important functions, as the action of the heart, for
hours after decapitation, we can understand the physiological absurdity of the proposition
that there is any such thing as a vital point, in the medulla or in any part of the nervous
system.

Connection of the Medulla Ollongata with Various Reflex Acts. — There are numerous
reflex phenomena that are completely under the control of the medulla oblongata as a
nerve-centre. Among these are the various acts connected with respiration, as yawning,
coughing, crying, sneezing, etc. It also presides over the coordination of the muscles
concerned in expression, and the act of vomiting. We have seen, in treating of the
pneumogastric nerves, that their galvanization arrests the action of the heart in diastole.
The same result follows galvanization of the medulla at the point of origin of these nerves.
We have also fully discussed the influence of the medulla upon sugar-formation in the
liver, as illustrated by the striking experiments of Bernard, in which he produced diabetes
in animals by irritating the floor of the fourth ventricle, and the influence of this centre
upon the quantity and the composition of the urine.

There is very little to be said concerning certain ganglia and other parts of the brain
that we have not yet considered. The olfactory bulbs, or ganglia, preside over olfaction
and will be treated of fully in connection with the special senses. The pineal gland and
the pituitary body, in their structure, present a certain resemblance to the ductless glands,
and their anatomy has been considered in another chapter. Passing over the purely
theoretical views of the older writers, who had very indefinite ideas of the functions of
any of the encephalic ganglia, we have only to say that the uses of the pineal gland and
pituitary body in the economy are entirely unknown. The same remark applies to the
corpus callosum, the septum lucidum, the -ventricles, hippocampi, and various other minor
parts that are necessarily described in anatomical works. It is useless to discuss the
early or even the recent speculations with regard to the functions of these parts, which
are entirely unsupported by experimental or pathological facts and which have not ad-
vanced our positive knowledge. Most of the parts just enumerated have no physiological
history.

Rolling and Turning Movements following Injury of Certain Parts of the

Eneephalon.

The remarkable movements of rolling and turning, produced by section or injury of
certain of the commissural fibres of the encephalon, are not very important in their bearing
upon the functions of the brain, and they are rather to be classed among the curiosities of
experimental physiology. These movements follow unilateral lesions and are dependent,
to a certain extent, upon a consequent inequality in the power of the muscles on one side,
without actual paralysis. Vulpian enumerates the following parts, injury of which, upon
one side, in living animals, may determine movements of rotation :

" 1. Cerebral hemispheres;

" 2. Corpora striata ;

" 3. Optic thnlami (Flourens, Longet, Schiff);

" 4. Cerebral peduncles (Longet) ;

" 5. Pons Varolii ;

" 6. Tubercula quadrigemina or bigemina (Flourens) ;

" 7. Peduncles of the cerebellum, especially the middle, and the lateral portions of the
•erebellum (Magendie) ;

" 8. Olivary bodies, restiform bodies (Magendie) ;

" 9. External part of the anterior pyramids (Magendie) ;

ROLLING AND TURNING MOVEMENTS. 709

'' 10. Portion of the medulla from winch the facial nerve arises (Brown-Sequard) ;

" 11. Optic nerves ;

" 12. Semicircular canals (Flourens) ; auditory nerve (Brown-Sequard)."

To the parts above enumerated, Vulpian adds the upper part of the cervical portion
of the spinal cord.

The movements which follow unilateral injury of the parts mentioned above are of
two kinds; viz., rolling of the entire body on its longitudinal axis, and turning, always in
one direction, in a small circle, called by the French the movement of manege. A capital
point to determine in these phenomena is, whether these movements be due to paralysis
or enfeebleraent of certain muscles upon one side of the body, to a direct or reflex irrita-
tion of the parts of the nervous system involved, or to both of these causes combined. The
experiments of Brown-Sequard and others conclusively show that the movements may be
due to irritation alone, for they occur when parts of the encephalon and the upper por-
tions of the cord are simply pricked, without section of fibres. When there is extensive
division of fibres, it is probable that the effects of the enfeeblement of certain muscles are
added to the phenomena produced by simple irritation. The most satisfactory explana-
tion of these movements is the one proposed by Brown-Sequard, who attributes them to
a more or less convulsive action of muscles on one side of the body, produced by irrita-
tion of the nerve-centres. He regards the rolling as simply an exaggeration of the turn-
ing movements, and places both in the same category.

We do not propose to enter into an elaborate discussion of the above experiments, for
the reason that they do not seem to have advanced our positive knowledge of the func-
tions of the nerve-centres. In some of them, the movements have been observed toward
the side operated upon, and in others, toward the sound side. These differences probably
depend upon the fact that, in certain experiments, the fibres are involved before their
decussation, and in others, after they have crossed in the median line. In some instances,
the movements may be due to a reflex action, from stimulation of afferent fibres, and in
others, the action of the irritation may be direct. Judging from the fact that most of the
encephalic commissural fibres are apparently insensible and inexcitable under direct
stimulation, it is probable that the action is generally reflex.

In concluding the physiological history of the encephalon, we have only to refer to
the general properties of certain of the peduncles. Longet found that direct irritation of
the superior and the inferior peduncles of the cerebellum, in rabbits, produced pain, but
the disturbance consequent upon exposure of the parts did not allow of any accurate
observations upon the movements. He says nothing of the general properties of the mid-
dle peduncles or of the peduncles of the cerebrum.

CHAPTER XXII.

SYMPATHETIC NERVOUS SYSTEM-SLEEP.

General arrangement of the sympathetic system— Peculiarities in the intimate structure of the sympathetic ganglia
and nerves— General properties of the sympathetic ganglia and nerves— Functions of the pympatht -tic M^nn—
Vaso-motor nerves— Reflex phenomena operating through the sympathetic system— Trophic centres and nerves
(so called)— Sleep— General considerations— Condition of the organism during sleep— Dreams— R. -tlex mental phe-
nomena during sleep— Condition of the brain and nervous system during sleep— Theories of sleep— Anaesthesia
and sleep produced by pressure upon the carotid arteries— Differences between natural sleep and stupor or
coma— Regeneration of the brain-substance during sleep— Theory that sleep is due to a want of oxygen— Condi-
tion of the various functions of the organism during sleep.

WHILE there are certain points in the physiology of the sympathetic nervous system
that are perfectly well established, it must be admitted that its functions are, in many
respects, obscure, and that our positive knowledge of its general properties and its rela-

730 NERVOUS SYSTEM.

tions to the functions of nutrition, secretion, movements, etc., amounts to comparatively
little. The very name, sympathetic, is some indication of our indefinite ideas with regard
to its functions ; but we have adopted this name, for the reason that it is the one most
generally in use, although it has no very exact relation to the peculiar functions of the
system. It is sometimes called the ganglionic nervous system ; but this name is inappro-
priate, as it implies that it alone possesses ganglia. The name of the system of organic,
or vegetative life is more in accordance with its general functions ; but this is not so com-
monly used as that of sympathetic system. The older anatomists and physiologists called
the great cord of this system the nervus intercostalis.

As far as we know, there is no account of the sympathetic system, even in the most
recent works upon physiology or in special treatises, a careful study of which does not con-
vey the idea that there is little else in the literature of the subject than controversial
questions of priority, etc., in minor details, and a few observations, some of them quite
unsatisfactory, with regard to the effects of the division or galvanization of sympathetic
filaments upon the functions of circulation, secretion, and animal heat. It is unfortunate
that well-ascertained facts, which might be stated in a very few pages, should be so
largely overshadowed by a mass of purely historical details of no great interest. Still, we
must take the physiological data as we find them and endeavor not to limit the knowledge
to be looked for in the future, by adopting theories upon insufficient positive evidence.

There are certain important anatomico-physiological questions, more or less definitely
determined, that have a direct bearing upon the functions of the sympathetic system.
These are the following: Is the sympathetic anatomically and physiologically dependent
upon its connections with the cerebro-spinal nerves ? What are the general properties
of the sympathetic nerves as regards motion and sensation? Do the sympathetic ganglia
act as independent reflex nerve-centres? To what extent and in what way do the sym-
pathetic ganglia and nerves influence the functions of the various organs and tissues to
which their filaments are distributed ? A solution of these questions involves a careful
and critical study of the results of experiments upon living animals and of pathological
facts ; and it is evident that very little information is to be derived from observations
made anterior to the discovery of the properties and functions of the most important
parts of the cerebro-spinal system. We shall begin the study of these points with an
account of the general arrangement and the peculiarities of structure Of the sympathetic
ganglia and nerves.

General Arrangement of the Sympathetic System.

Like the cerebro-spinal system, the sympathetic is composed of centres and nerves,
at least as far as we can judge from its anatomy. The centres contain nerve-cells, most
of which differ but little from the cells of the encephalon and spinal cord. The nerves
are composed of fibres, the greater part of which are nearly identical in structure with the
ordinary motor and sensory fibres. The fibres are connected with the nerve-cells in the
ganglia, and the ganglia are connected with each other by commissural fibres. These
ganglia constitute a continuous double chain, on either side of the body, beginning above,
by the ophthalmic ganglia, and terminating below, in the ganglion impar. It is important
to note, however, that the chain of sympathetic ganglia is not independent, but that each
ganglion receives motor and sensory filaments from the cerebro-spinal nerves, and that
some filaments pass from the Sympathetic to the cerebro-spinal system. The general dis-
tribution of the sympathetic filaments is to mucous membranes — and possibly to integu-
ment— to non-striated muscular fibres, and particularly to the muscular coat of the
arteries. As far as we have been able to learn from anatomical investigations, there are
no fibres derived exclusively from the sympathetic which are distributed to striated
muscles, except those which pass to the muscular tissue of the heart. Near the terminal
filaments of the sympathetic, in most of the parts to which these fibres are distributed,
there exist numerous ganglionic cells.

GENERAL ARRANGEMENT OF THE SYMPATHETIC SYSTEM. 731

The general arrangement of the sympathetic ganglia and the distribution of the nerves
may be stated, sufficiently for our purposes, very briefly ; still, a knowledge of certain
anatomical points is indispensable as an introduction to an intelligent study of the physi-
ology of this system.

In the cranium, are four ganglia; the ophthalmic, the spheno-palatine, the otic, and
the submaxillary. In the neck, are the three cervical ganglia; the superior, middle, and
inferior. In the chest, are the twelve thoracic ganglia, corresponding to the twelve ribs.
The great semilunar ganglia, the largest of all, sometimes called the abdominal brain, are
in the abdomen, by the side of the crcliac axis. In the lumbar region, in front of the
spinal column, are the four, and sometimes five, lumbar ganglia. In front of the sacrum,
are the four or five sacral, or pelvic ganglia ; and in front of the coccyx, is a small, single
ganglion, the last of the chain, called the ganglion impar. Thus, the sympathetic cord,
as it is sometimes called, consists of from twenty-eight to thirty ganglia on either side,
terminating below in a single ganglion.

Cranial Ganglia. — The ophthalmic, lenticular, or ciliary ganglion is situated deeply
in the orbit, is of a reddish color, and about the size of a pin's-head. It receives a motor
branch from the third pair, and sensory filaments from the nasal branch of the ophthal-
mic division of the fifth. It is also connected with the cavernous plexus and with
Meckel's ganglion. Its so-called motor and sensory roots from the third and the fifth
pair have already been described in connection with these nerves. Its filaments of dis-
tribution are the ten or twelve short ciliary nerves, which pass to the ciliary muscle and
the iris. A very delicate filament from this ganglion passes to the eye with the central
artery of the retina, in the canal in the centre of the optic nerve.

The functions of the ophthalmic ganglion are connected exclusively with the action
of the ciliary muscle and iris ; and we shall here merely indicate its anatomical relations,
leaving its physiology to be taken up under the head of vision.

The spheno-palatine ganglion was first described by Meckel and is known as Meckel's
ganglion. This is the largest of the cranial ganglia. It is of a triangular shape, reddish
in color, and is situated in the spheno-maxillary fossa, near the spheno-palatine foramen.
It receives a motor root from the facial, by the Vidian nerve. Its sensory roots are the
two spheno-palatine branches from the superior maxillary division of the fifth. Its
branches of distribution are quite numerous. Two or three delicate filaments enter the
orbit and go to its periosteum. Its other branches, which it is unnecessary to describe
fully in detail, are distributed to the gums, the membrane covering the hard palate, the
soft palate, the uvula, the roof of the mouth, the tonsils, the mucous membrane of the
nose, the middle auditory meatus, a portion of the pharyngeal mucous membrane, and
the levator palati and azygos uvulee muscles. It is probable that the filaments sent to
these two striated muscles are derived from the facial nerve and do not properly belong
to the sympathetic system. The ganglion also sends a short branch, of a reddish-gray
color, to the carotid plexus.

The otic ganglion, sometimes called Arnold's ganglion, is a small, oval, reddish-gray
mass, situated just below the foramen ovale. It receives a motor filament from the
facial, and sensory filaments from branches of the fifth and the glosso-pharyngeal. Its
filaments of distribution go to the mucous membrane of the tympanic cavity and Eusta-
chian tube and to the tensor tympani and tensor palati muscles. Reasoning from the
general mode of distribution of the sympathetic filaments, those going to the striated
muscles are derived from the facial. It also sends branches to the carotid pU.-xus.

The submaxillary ganglion, situated on the submaxillary gland, is small, roumK-d,
and of a reddish-gray color. It receives motor filaments from the chorda tympad and
sensory filaments from the lingual branch of the fifth. Its filaments of distribution go to
Wharton's duct, to the mucous membrane of the mouth, and to the submaxillary gland.

Cervical Ganglia.— The three cervical ganglia are situated opposite the third, fifth,

732

NERVOUS SYSTEM.

FIG. 231 (A).— Cervical and thoracic portion of the sympathetic. (Sappey.)

1, 1, 1, right pneumogastric; 2, glosso-pharyngeal ; 3, spinal accessory • 4, divided trunk of the sublingnal;
5, 5, 5, chain of ganglia of the sympathetic ; 6, superior cervical ganglion ; 7, branches from this ganglion to
the carotid ; 8, nerve of Jacobson ; 9, two filaments from the facial, one to the spheno-palatine and the other
to the otic ganglion ; 10, motor oculi externus ; 11, ophthalmic ganglion, receiving a motor filament from
the motor oculi cpmmunis and a sensory filament from the nasal branch of the fifth ; 12, spheno-palatine
ganglion; 13, otic ganglion; 14, lingual branch of the fifth nerve; 15, submaxillary ganglion ; 16, 17,
superior laryneeal nerve; 18, external laryngeal nerve; 19, 20, recurrent laryngeal nerve; 21, 22, 23,
anterior branches of the upper four cervical nerves, sending filaments to the superior cervical sympathetic
ganglion ; 24, anterior branches of the. fifth and sixth cervical nerve, sending filaments to the middle cervical
ganglion ; 25, 26, anterior branches of the seventh and eighth cervical and the first dorsal nerves, sending fila-
ments to the inferior cervical ganglion ; 27, middle cervical ganglion ; 28, cord connecting the two ganglia;
29, inferior cervical ganglion ; 30, 31, filaments connecting this with the middle ganglion ; 32, superior car-
diac nerve ; 33, middle cardiac nerve ; 34, inferior cardiac nerve • 35, 35, cardiac plexus ; 36, ganglion of
the cardiac plexus ; 37, nerve following the right coronary artery ; 38, 38, intercostal nerves, with their two
filaments of communication with the thoracic ganglia ; 39, 40, 41, great splanchnic nerve ; 42. lesser splanchnic
nerve; 43, 43, solar plexus ; 44, left pneumogastric ; 45, risrht pneumoiraptric ; 46, lower end of the phrenic
nerve ; 47, section of the right bronchus ; 48, arch of the aorta ; 49, right auricle ; 50, right ventricle ; 51,
52, pulmonary artery; 53, right half of the stomach; 54, section of the diaphragm.

GENERAL ARRANGEMENT OF THE SYMPATHETIC SYSTEM. 733

and the seventh cervical vertebrae respectively. The middle ganglion is sometimes want-
ing, and the inferior is occasionally fused with the first thoracic ganglion. These ganglia
are connected together by the so-called sympathetic cord. They have numerous fila-
ments of communication above, with the cranial and the cervical nerves of the cerebro-
spinal system. Branches from the superior ganglion go to the internal carotid, to form
the carotid and the cavernous plexus, following the vessels as they branch to their dis-
tribution. Branches from this ganglion pass to the cranial ganglia. There are also
branches which unite with filaments from the pneumogastric and the glosso-pharyngeal
to form the pharyngeal plexus, and branches which form a plexus on the external carotid,
the vertebral, and the thyroid artery, following the ramifications of these vessels.

From the cervical portion of the sympathetic, the three cardiac nerves arise and pass
to the heart, entering into the formation of the cardiac plexus. The superior cardiao
nerve arises from the superior ganglion ; the middle nerve, the largest of the three,
arises from the middle ganglion, or from the sympathetic cord, when this ganglion is want-
ing; and the inferior nerve arises from the inferior cervical ganglion or the first thoracic.
These nerves present numerous communications with various of the adjacent cerebro-
spinal nerves, penetrate the thorax, and form the deep and the superficial cardiac plexus
and the posterior and the anterior coronary plexus. In these various plexuses, are found
numerous ganglioform enlargements ; and, upon the surface and in the substance of the
heart, are numerous collections of nerve-cells connected with the fibres.

Thoracic Ganglia. — The thoracic ganglia are situated in the chest, beneath the pleura,
and rest on the heads of the ribs. They are usually twelve in number, but occasionally
two are fused into one. They are connected together by the sympathetic cord. They
each communicate by two filaments with the cerebro-spinal nerves. One of these is
white, like the spinal nerves, and probably passes to the sympathetic, and the other, of
a grayish color, is thought to contain the true sympathetic filaments. From the upper
six ganglia, filaments pass to the aorta and its branches. The branches which form the
posterior pulmonary plexus arise from the third and fourth ganglia. The great splanchnic
nerve arises mainly from the seventh, eighth, and ninth ganglia, receiving a few filaments
from the upper six ganglia. This is a large, white, rounded cord, which penetrates the
diaphragm and passes to the semilunar ganglion, sending a few filaments to the renal
plexus and the suprarenal capsules. The lesser splanchnic nerve arises from the tenth
and eleventh ganglia, passes into the abdomen, and joins the coeliac plexus. The renal
splanchnic nerve arises from the last thoracic ganglion and passes to the renal plexus.
The three splanchnic nerves present numerous anastomoses with each other.

Ganglia in the Abdominal and the Pelvic Cavity. — The semilunar ganglia on the two
sides send off radiating branches to form the solar plexus. They are situated by the side
of the cceliac axis and near the suprarenal capsules. These are the largest of the sym-
pathetic ganglia. From these arise numerous plexuses distributed to various parts in
the abdomen, as follows : The phrenic plexus follows the phrenic artery and its branches
to the diaphragm. 'The cceliac plexus subdivides into the gastric, hepatic, and splenic
plexuses, which are distributed to organs as their names indicate. From the solar pi.
different plexuses are given off, which pass to the kidneys, the suprarenal capsules, the
testes in the male, and the ovaries in the female, the intestines (by the superior and the
inferior mesenteric plexuses), the upper part of the rectum, the abdominal aorta, and the
vena cava. The filaments follow the distribution of the blood-vessels in the solid viscera.

The lumbar ganglia, four in number, are situated in the lumbar reirion, upon the
bodies of the vertebra. They are connected with the pnnglia above and below and with
each other by the sympathetic cord, receiving, like the other pmirlin, filaments from the
spinal nerves. Their branches of distribution form the aortic lumbar plexus and the
hypogastric plexus and follow the course of the blood-vessels.

734

NERVOUS SYSTEM.

The four or five sacral ganglia and the ganglion impar are situated by the inner side
of the sacral foramina and in front of the coccyx. These are connected with the ganglia
above and with each other, and receive filaments from the sacral nerves, there being

FIG. 231 (B).—Lnmbar and sacral portions o the ^i:tn pathetic. (Sappey.)

1, section of the diaphragm; 2, lower end of the (esophagus; 3, left half of the stomach; 4, small intestine; 5, sig-
moid flexure of the colon; 6, rectum; 7, bladder; 8, prostate; 9, lower end of the left pneumogastric; 10, lower
end of the right pneumogastric; 11, solar plexus; 12, lower end of the (treat splanchnic nerve ; 13, lou-er end
of the lesser splanchnic nerve; 14, 14, last two thoracic ganglia; 15, li>,thefour lumbar ganglia; 16, 16, 17,

generally two branches of communication for each ganglion. The filaments of distribu-
tion go to all of the pelvic viscera and the blood-vessels. The inferior hypogastric, or
pelvic plexus is a continuation of the hypogastric plexus above, and receives a few fila-
ments from the sacral ganglia. The most interesting branches from this plexus are the

GENERAL ARRANGEMENT OF THE SYMPATHETIC SYSTEM. 735

uterine nerves, which go to the uterus and the Fallopian tubes. In the substance of the
uterus, the nerves are connected with small collections of ganglionic cells. The sympa-
thetic filaments are undoubtedly prolonged into the upper and lower extremities, follow-
ing the course of the blood-vessels and distributed to their muscular coat.

According to the latest researches, the filaments of the sympathetic, at or near their
termination, are connected with ganglionic cells, not only in the heart and the uterus,
but in the blood-vessels, lymphatics, coccygeal gland, the submucous and the muscular
layer of the entire alimentary canal, the salivary glands, pancreas, excretory ducts of
the liver and pancreas, the larynx, trachea, pulmonary tissue, bladder, ureters, the entire
generative apparatus, suprarenal capsules, thyrnus, lachrymal canals, ciliary muscle, and
the iris. In these situations, nerve-cells have been demonstrated by various observers,
and it is probable that they exist everywhere in connection with the terminal filaments
of this system of nerves.

Peculiarities in the Intimate Structure of the Sympathetic Ganglia and Nerves. — The
peculiarities in the structure of the cells and fibres of the sympathetic system are not
numerous, nor do they possess very great physiological importance. The free communi-
cations between the sympathetic ganglia and the cerebro-spinal nerves, and the differ-
ences in the general appearance of certain of these anastomosing branches, lead to the
important question of their origin. As a rule, the sympathetic nerves are softer and
more grayish in color than the spinal nerves. When there are two branches of commu-
nication between a ganglion and a spinal nerve, one of them is white and the other is
grayish, and we might infer from this that one, the white, is derived from the spinal
system, and the other, from the sympathetic ; but this is a point not yet settled by micro-
scopical investigations. It has been conclusively shown, however, that the communi-
cating fibres pass in both directions.

While the branches of the sympathetic contain a large number of the ordinary medul-
lated fibres, such as are found in the cerebro-spinal nerves, they also present numerous
fibres of Remak, and fine fibres, from 10^06 to ^-gVs °f an inch in diameter, which are
regarded by Kolliker as true efferent fibres from the sympathetic ganglia. With regard
to the fibres of Remak, we have nothing to add to what we have already stated under

FIG. 232.— Sympathetic gangUon with multipolar cells ; highly magnified. (Leydig.)

the head of the general structure of the nervous system. These points, with the fact
that most of the terminal filaments of the sympathetic are connected with nerve-cells in
the substance of the different tissues, constitute the most important anatomical pecu-
liarities of the sympathetic nerve-fibres.

With regard to the cells, which constitute the characteristic anatomical element of
the sympathetic ganglia, we shalV have little to say, as their peculiarities at present Beera

736 NERVOUS SYSTEM.

to be of purely anatomical interest. They are generally rounded, ovoid, or pear-shaped,
with a nucleus, generally clear, and a distinct nucleolus. They present a nucleated cap-
sule, probably composed of connective tissue, which is sometimes lined on its inner sur-
face with a single layer of flattened, polygonal epithelium. Some of the cells are unipolar,
some are bipolar, and some are multipolar. In frogs, Beale and Arnold have described a
peculiar appearance in certain cells, there being a single, straight prolongation, sur-
rounded by a fine, spiral fibre. These have not been demonstrated in the human subject,
and it is not necessary to enter into a discussion of the probable origin and nature of the
spiral fibre. The connection between the cells and fibres of the sympathetic is probably
the same as in the cerebro-spinal centres and is represented in the 'accompanying dia-
gram, taken from Leydig. (See Fig. 233.)

General Properties of the Sympathetic Ganglia and Nerves.

The older writers had no definite ideas with regard to the functions of the sympa-
thetic system, and they were divided, even on the simple question of its sensibility, some
assuming that the ganglia were absolutely insensible, while others noted distinct evi-
dences of pain following their irritation in living animals. The sensibility of the ganglia,
though distinct, is dull as compared with that of the ordinary sensory nerves. "We have
also noted a dull but well-marked sensibility of the cervical ganglia in rabbits. In view
of the decided and uniform results of the most careful recent experiments upon this point,
there can be no doubt of the existence of a certain degree of sensibility in the ganglia of
the sympathetic system.

As regards excitability, recent experiments are quite satisfactory. Mtiller exposed
the intestines and the semilunar ganglia in rabbits ; and, having waited until the intes-
tines, which generally present movements upon first opening the abdomen, had ceased their
contractions, the peristaltic movements " were immediately renewed with extraordinary
activity " by touching the ganglia with caustic potash. The experiments of Longet show
that a feeble continued galvanic current applied to the great splanchnic nerves produces
contractions of the muscular coat of the intestines when they contain alimentary mat-
ters, but that no contractions occur when they are empty. On the other hand, Pfliiger
has observed that galvanization of the splanchnic nerves produces a passive condition of
the small intestine ; that is, arrest of its movements without persistent contractions of
its muscular coat. More recently, in a series of very elaborate experiments, by Legros
and Onimus, it has been shown that the induced galvanic current applied to the splanch-
nic nerves does not produce peristaltic movements, but that these movements are excited
by the constant current.

Taking into consideration the most reliable direct observations upon the sympathetic
ganglia and nerves, the fact that their stimulation induces movements in the non-striated
muscles to which they are distributed can hardly, be doubted. This action is particularly
well marked in the muscular coat of the blood-vessels; but here, the function of the
nerves is so important, that it merits special consideration and will be treated of fully
under the head of the vaso-motor nerves. The mechanism of these movements, however, is
peculiar. The action does not immediately follow the stimulation, as it does in the case
of the cerebro-spinal nerves and the striated muscles, but it is induced gradually, begin-
ning a few seconds after the irritation and enduring for a time, and it is more or less
tetanic. This mode of action is peculiar to the sympathetic nerves and the non-striated
muscular fibres.

When we remember the invariable connection of the sympathetic ganglia with the
cerebro-spinal nerves, we see at once the importance of the question of the derivation of
the motor and sensory properties of the ganglionic system. Are the sympathetic ganglia
independent nerve-centres, or do they derive their properties from the cerebro-spinal
system ? This question may be satisfactorily answered by two kinds of experimental

FUNCTIONS OF THE SYMPATHETIC SYSTEM. 737

facts : In the first place, section or irritation of the spinal cord and certain of the en-
cephalic centres is capable of influencing the vaso-motor system, a fact which will be dwelt
upon more fully in another connection. In the second place, the experiments of Bernard
upon the submaxillary ganglion and its influence on the secretion of the submaxillary
gland have demonstrated, in the most conclusive manner, that this ganglion is the centre
presiding immediately over the reflex phenomena of secretion by the gland; but it has
also been shown that, when all of the connections of the submaxillary ganglion with the
cerebro-spinal system are divided, after a few days, this ganglion loses its power as a
reflex nervous centre. In the chapters upon secretion, we have given numerous examples
of reflex action through the sympathetic system. The experiments just cited from Ber-
nard show that individual ganglia belonging to this system may act independently for a
time, but that this action cannot continue indefinitely, after the cerebro-spinal branches
have been divided. It remains, however, to apply these experiments to other sympa-
thetic ganglia; but, in the case of the submaxillary, they are very satisfactory, from the
facility with which the parts may be operated upon and the certainty with which the
ganglion may be separated from its connections with the cerebro-spinal system. As
regards the explanation of the final loss of power over the functions of the submaxillary
gland, the experiments of Waller seem to have escaped the attention of the eminent
physiologist whom we have quoted. There is no experimental fact more conclusively
demonstrated than that of the anatomical degeneration and consequent loss of physio-
logical function of nerve-fibres in a few days after they have been separated from their
centres of origin. After division of a cerebro-spinal nerve-trunk, the tubes soon lose
their anatomical characters and will no longer respond to a galvanic stimulus. In the
case of the fibres operating upon the submaxillary gland, the question of their degenera-
tion after division of the cerebro-spinal roots was not submitted to microscopical investi-
gation. If these fibres had undergone the degeneration which has so frequently been
observed in experiments upon other nerves, their galvanization would not have produced
any effect ; which was precisely the result obtained by Bernard. In the absence of
direct observations upon this point, it is the most reasonable view to adopt, that the
fibres from the cerebro-spinal nerves had lost their function, as a natural consequence of
separation from their centres, and that this was the cause of the absence of effect upon
the gland following their galvanization. The observation of Bernard shows, however,
that filaments may pass to special organs from the cerebro-spinal centres through the
sympathetic ganglia.

Functions of the Sympathetic System.

In the early part of the last century (1712 and 1725), Pourfour du Petit demonstrated
that the influence of the sympathetic nerve in the neck (the great sympathetic was fre-
quently called the nervus intercostalis) was propagated from below upward toward the
head, and not from the brain downward. This may be taken as the starting-point of our
definite knowledge of the functions of the sympathetic system, though the experiments
of Petit showed only the influence of the cervical portion upon the eye. In 181G, Dupuy
removed the superior cervical ganglia in horses, with the effect of producing injection of
the conjunctiva, increase of temperature in the ear, and an abundant secretion of sweat
upon one side of the head and neck. These experiments showed that the sympathetic
has an important influence upon nutrition, calorification, and secretion. In 1851, Bernard
repeated the experiments of Pourfour du Petit, dividing the sympathetic in the neck on
one side in rabbits, and noted, on the corresponding side of the la-ad and the ear, in-
creased vnscularity, and an elevation in temperature, amounting to from 7° to 11° Fahr.
This condition of increased heat and vascularity continues for several months after divi-
sion of the nerve. In 1852, Brown-Sequard repeated these experiments and attributed
the elevation of temperature directly to an increase in the supply of blood to the parts
affected. He made a most important advance in the history of the sympathetic, by
47

738 NERVOUS SYSTEM.

demonstrating that its section paralyzed the muscular walls of the arteries, and, farther,
that galvanization of the nerve in the neck caused the vessels to contract. This was the
discovery of the vaso-motor nerves, concerning which so much has been written within
the past few years, and it belongs without question to Brown-Sequard, who published
his observations in August, 1852. A few months later, in the same year, Bernard made
analogous experiments and presented the same explanation of the phenomena observed.

The above embraces all that is important with regard to the history of experimental
observations upon the sympathetic. It is evident that we could know nothing of the
functions of this system before the time of Pourfour du Petit, when the prevailing opin-
ion was that the nerve originated from the encephalon, and that its influence was propa-
gated downward ; and writings anterior to the experiments of Bernard and of Brown-
Sequard present interesting suggestions and theories, but they contain little that bears
upon our positive knowledge.

The important points developed by the first experiments of Bernard and of Brown-
S6quard were, that the sympathetic system influences the general process of nutrition,
and that many of its filaments are distributed to the muscular coat of the blood-vessels.
Before these experiments, it had been shown that filaments from this system influenced
the contractions of the muscular coats of the alimentary canal. Leaving, for the present,
the action of the vaso-motor nerves, we shall briefly recapitulate some of the facts with
regard to the influence of the sympathetic upon animal heat and secretion.

When the sympathetic is divided in the neck, the local increase in temperature is
always attended with a very great increase in the supply of blood to the side of the head
corresponding to the section. The increased temperature is due to a local exaggeration
of the nutritive processes, apparently dependent directly upon the hypersemia; and it is
not probable that there are any nerves to which the name of calorific, as distinguished
from vaso-motor, can justly be applied. There are numerous instances in pathology of
local increase in temperature attending increased supply of blood to restricted parts. In
a recent experiment by Bidder, after excising about half an inch of the cervical sympa-
thetic in a half-grown rabbit, the ear on that side, in the course of about two weeks,
became distinctly longer and broader than the other.

The experiment of dividing the sympathetic in the neck, especially in rabbits, is so
easily performed, that the phenomena observed by Bernard and Brown-S6quard have
been repeatedly verified. We have often done this in class-demonstrations. A very
striking experiment is the following, suggested by Bernard : After dividing the sympa-
thetic and exhibiting the increase in the temperature and the vascularity of the ear on
one side in the rabbit, if both ears be cut off just above the head with a sharp knife, the
artery on the side on which the sympathetic has been divided will frequently send up a
jet of blood to the height of several feet, while, on the sound side, the jet is always
much less forcible, and it may not be observed at all. This experiment succeeds best in
large rabbits.

It is very easy to observe the effects of dividing the sympathetic in the neck, but
analogous phenomena have been noted in other parts. Among the most striking of these
•experiments are those reported by Samuel, who noted an intense hyperaBmia of the
mucous membrane of the stomach and intestines following extirpation of the coeliac
.plexus. By comparative experiments, it was shown that this did not result from the
;peritonitis produced by the operation.

As regards secretion, the influence of the sympathetic is very marked. When the
•sympathetic filaments distributed to a gland are divided, the supply of blood is very much
increased, and an abundant flow of the secretion follows. This point we have already
discussed in another chapter, where we have referred particularly to the experiments of
Bernard upon the salivary glands. In some recent experiments by Peyrani, it has been
shown that the sympathetic has a remarkable influence upon the secretion of urine.
When the nerves are galvanized in the neck, the amount of urine and urea is increased,

VASO-MOTOR NERVES. 739

and this increase is greater with the induced than with the constant current. When the
sympathetic is divided, the quantity of urine and urea sinks to the minimum.

Dr. Moreau has recently published a series of observations on the influence of the
sympathetic nerves upon the secretion of liquid by the intestinal canal, which are pecul-
iarly interesting in their bearing upon the sudden occurrence of watery diarrhcea. In
these experiments, the abdomen was opened in a fasting animal, and three loops of intes-
tine, each from four to eight inches long, were isolated by two ligatures. ' All of the
nerves passing to the middle loop were divided, taking care to avoid the blood-vessels.
The intestine was then replaced, and the wound in the abdomen was closed with sutures.
The next day the animal was killed. The two loops with the nerves intact were found
empty, as is normal in fasting animals, and the mucous membrane was dry ; but the loop
with the nerves divided was found filled with a clear, alkaline liquid, colorless or slightly
opaline, which precipitated a few flocculi of organic matter on boiling.

Vaso-Motor Nerves.

The experiments which we have already cited demonstrate beyond a doubt the exist-
ence of nerves distributed to the muscular coats of the blood-vessels and capable of
regulating their caliber and the quantity of blood sent to different parts. These are the
vaso-motor nerves, discovered by Brown-Sequard, in 1852. The importance of nerves
apable of regulating what we may call the local circulations is sufficiently apparent.
The glands, for example, require at certain times an immense increase in their supply of
blood, and the same is probably true of the muscles, brain, and other parts. It has been
shown, by direct experiments upon living animals, that local variations in the circulation,
independent of the action of the heart, actually take place, and that they are of great
importance in special functions ; and there are numerous instances of such action, which
can only take place through the nervous system. The phenomena of blushing and pallor,
from mental emotions, are familiar examples.

There can be no doubt of the fact that the sympathetic branches contain filaments
capable of modifying the caliber of the blood-vessels, .and that the cerebro-spinal nerves
also contain elements possessing analogous properties ; but when we reflect upon the
extensive anastomoses, in both directions, between the sympathetic and the ordinary
motor and sensory nerves, we can appreciate the importance of determining the exact
origin and course of these vaso-motor fibres. The first important question is, whether the
vaso-rnotor filaments be derived from the sympathetic ganglia or from the cerebro-spinal
centres.

All experiments upon the question just proposed tend to show that the vaso-motor
nerves are derived exclusively from the cerebro-spinal system and do not originate in
the sympathetic ganglia. Without citing the numerous confirmatory observations of dif-
ferent physiologists, it is sufficient to state that Schiff has experimentally demonstrated,
in the most conclusive manner, that the vaso-motor nerves are derived from the cerebro-
spinal centres and not from the sympathetic ganglia. There is now no difference of
opinion among physiologists upon this point, the only question being the exact location
of the vaso-motor centres.

As a summary of our present knowledge of the origin of the vaso-motor nerves in the
cerebro-spinal axis, we may cite the following remarks, from a review of the experiments
of Schiff, by Brown-Sequard : "1. That if there are vaso-motor elements which deoo*
sate in the spinal cord, their number is excessively small. 2. That the facts <>1 .-erven1 by
M. Schiff, on this subject, admit of a more simple explanation. 3. That a number of the
vaso-motor elements stop in the spinal cord. 4. That a tolerably large number of \
motor elements, coming from different points in the body, ascend as far as the tuber
annulare, and some as far as the cerebellum and to other parts of the enrophalon. 5.
That, consequently, the medulla oblongata is not the sole source of the vaso-motor ele-

740 NERVOUS SYSTEM.

ments." These statements express pretty much all that we know of the origin of the
vaso-motor elements and their decussation, as far as their direct action is concerned ; but
some important points have been developed by observations upon reflex vaso-motor phe-
nomena, involving a transmission of impressions to the centres through the nerves of
general sensibility.

Reflex Phenomena operating through the Sympathetic System. — We shall not discuss,
in this connection, the reflex phenomena of secretion, as these have already been consid-
ered with sufficient minuteness, nor again treat of reflex action, through the sympathetic,
upon the general circulatory system, which has been taken up fully under the head of the
depressor-nerve of the circulation, but we shall here describe certain reflex acts, involv-
ing vaso-motor phenomena, which we thus far have touched upon very briefly.

As regards animal heat, the phenomena of which are intimately connected with the
supply of blood to the parts, we may mention the observations of Brown-Sequard and
Lombard, who found that pinching of the skin on one side was attended with a diminu-
tion in the temperature in the corresponding member of the opposite side, and that some-
times, when the irritation was applied to the upper extremities, changes were produced
in the temperature of the lower limbs. Tholozan and Brown-S6quard found, 'also, that
lowering the temperature of one hand produced a^considerable depression in the heat of
the other hand, without any notable diminution in the general heat of the body. Brown-
Sequard showed that, by immersing one foot in water at 41° Fahr., the temperature of the
other foot was diminished about 7° Fahr. in the course of eight minutes. These facts
show that certain impressions made upon the sensory nerves affect the animal heat by
reflex action. As section of the sympathetic filaments increases the heat in particular
parts, with an increase in the supply of blood, and their galvanization reduces the quan-
tity of blood and diminishes the temperature, it is reasonable to infer that the reflex action
takes place through the vaso-motor nerves. If we assume that the impression is conveyed
to the centres by the nerves of general sensibility, and that the vessels are modified in
their caliber and the heat is affected through the sympathetic fibres, we have only to
determine the situation of the centres which receive the impression and generate the
stimulus. These centres, as we have already seen, are not situated in the sympathetic
ganglia, but in the cerebro-spinal axis.

The existence of vaso-motor nerves and their connection with centres in the cerebro-
spinal axis are now sufficiently well established. It is certain, also, that centres presiding
over particular functions may be distinctly located, as the genito-spinal centre, in the spinal
cord opposite the fourth lumbar vertebra, and the cilio-spinal centre, in the cervical region
of the cord. A stimulus generated in these centres, sometimes as the result of impressions
received through the nerves of general sensibility, produces contraction of the non-striated
muscular fibres of the iris, vasa deferentia, etc., including the muscular walls of the blood-
vessels. The contraction of the muscular walls of the vessels is tonic ; and, when their
nerves are divided, relaxation takes place, and the vessels are dilated by the pressure of
blood. By this action, the local circulations are regulated in accordance with impressions
made upon sensory nerves, the physiological requirements of certain parts, mental emotions,
etc. Secretion, the peristaltic movements of the alimentary canal, the movements of the
iris, etc., are influenced in tjiis way. This action is also illustrated in cases of reflex pa-
ralysis, in inflammations as the result of "taking cold," and in many pathological condi-
tions, of which it is not our province to treat. The facts already noted with regard to
the excito-motor action of the spinal cord in the functions of animal life have their anal-
ogy in the vaso-motor reflex system. When the centres are destroyed, when the sensory
nerves are paralyzed by anaesthetics, or when the true vaso-motor nerves are divided,
reflex vaso-motor action is abolished.

The vaso-motor filaments are not confined to the branches of the sympathetic, but
they exist as well in the ordinary cerebro-spinal nerves. Bernard has demonstrated this

TROPHIC CENTRES AND NERVES. 741

fact in the most conclusive manner. He divided the fourth, fifth, sixth, seventh, and
eighth pairs of lumbar nerves on one side in a dog, at the spinal column, and paralyzed
motion and sensation in the leg of that side, but the temperature of the two sides remained
the same. He afterward exposed and divided the sciatic nerve on that side, and then
noted a decided increase of temperature. This experiment, which is only one of a large
number, shows conclusively that the ordinary mixed nerves contain vaso-motor fibres,
which are entirely independent of the nerves of motion and sensation, a fact which is
admitted by all physiologists and has frequently been illustrated in cases of disease in the
human subject.

It only remains to show that the phenomena following section of the sympathetic in
animals are illustrated in certain cases of disease or injury in the human subject. It is
excessively rare to observe traumatic injury confined to the sympathetic in the neck. A
single case, however, apparently of this kind, has lately been reported by Mitchell. A
man received a gunshot-wound in the neck. Among the phenomena observed a few-
weeks after, were, contraction of the pupil on the side of the injury, and, after exercise,
flushing of the face upon that side. There was no difference in the temperature upon
the two sides, during repose, but no thermometric observations were made when half of
the face was flushed by exercise. Dr. Bartholow has reported several cases of unilateral
sweating of the head (two observed by himself), in several of which there was probably
compression of the sympathetic from aneurism. In those cases in which the condition
of the eye was observed, the pupil was found contracted in some and dilated in others.
In none of these cases were there any accurate thermometric observations. In a series
of observations by Wagner, upon the head of a woman, eighteen minutes after decapita-
tion, powerful galvanization of the sympathetic produced great enlargement of the pupil.
In such a case as this, it would not be possible to make any observations on the influence
of the sympathetic upon the temperature.

Trophic Centres and Nerves (so called).

We have deferred the consideration of the so-called trophic nerves until we had
treated of the functions of the sympathetic system, because the vaso-motor nerves, by
their influence upon the circulation, are evidently connected with the phenomena of
nutrition. It is not necessary to dwell very minutely upon this point; but cases of
disease, as well as experiments upon the inferior animals, show that, when a muscle is
paralyzed, as a result of the abolition of nervous influence and consequent disease, it
becomes atrophied, its fibres lose their characteristic structure and finally become inca-
pable of contracting under a stimulus. As we have seen that the cerebro-spinal
nerves, in addition to their motor and sensory fibres, contain vaso-motor elements, it
becomes a question whether the muscles be supplied with special nerves — aside from those
of motion and sensation and the vaso-motor nerves — which preside over their nutrition.
Such could properly be called trophic nerves. Many pathologist*, relying upon the
presence of certain lesions of cells in the cord, in connection with cases of progressive
muscular atrophy, admit the existence of trophic cells and nerves. It must be admitted,
however, that these views rest upon pathological facts alone and have not been demon-
strated by physiological experiments or observations.

After what we have said, it is evident that proper nutrition of the muscular system
depends upon its exercise and the integrity of its motor nerves. In the second place, the
history of monsters shows that the muscular system may be developed independently of
the cerebro-spinal centres. In the admirable work of Brachet, upon the gamrlionir s\>.trm,
numerous cases of anencephalic monsters are detailed, in which the muscular system was
found more or less perfectly developed. In some of these, the f.i-tus was delivered at
term and lived for several hours. When we consider the great number of cases of this
kind on record, a few of which only are cited by Brachet, it is evident that the cerebro-

742 NERVOUS SYSTEM.

spinal centres are not absolutely necessary to development in utero. Some of the cases
reported presented spasmodic movements of certain muscles.

While it is certain that a foetus may become developed in utero, when there is reason
to suppose that the cerebro-spinal influence is wanting and the chief nervous operations
are effected through the ganglionic system, direct experiments upon the sympathetic in
animals do not positively show any influence upon nutrition, except as this system of
nerves affects the supply of blood to the parts. When we divide a sympathetic nerve,
there is an apparent exaggeration of the nutritive processes in particular parts, and there
may be inflammatory phenomena, but atrophy of muscles is not observed. Indeed, we
only have atrophy of muscles following division of cerebro-spinal nerves, or, as recently-
observed cases of disease have shown, after disorganization of cells belonging to what we
recognize as motor centres. As regards the latter condition, there can be no doubt of
the fact that progressive muscular atrophy is attended with disorganization of certain of
the motor cells of the spinal cord.

Without fully discussing this subject, which belongs to pathology, the facts may be
briefly stated as follows : We may have progressive atrophy of certain muscles, which
may be uncomplicated with paralysis except in so far as there is weakness of these mus-
cles, due to partial and progressive destruction of their contractile elements. The only
pathological condition in these cases, aside from the changes in the muscular tissue, is
destruction of certain cells in the antero-lateral portions of the cord, with more or less
atrophy of the corresponding anterior roots of the nerves. No one has pretended to
have demonstrated cells in the cord, presenting anatomical peculiarities by which they
may be distinguished from the ordinary motor or sensory elements, but the fact of the
degeneration of certain cells, others remaining normal, and this fact alone, has led to the
distinction, by certain writers, of trophic cells ; and, of course, these must be connected
with the muscles by trophic nerves.

We shall now study the phenomena of progressive muscular atrophy from a physio-
logical point of view, and see if they afford any positive evidence of the existence of
special cells and nerves presiding over the nutrition of the muscular system, or whether
the phenomena observed cannot be explained by the partial degeneration of the ordinary
motor cells and nerves.

There can be no doubt of the fact that the cells of the antero-lateral columns of the
spinal cord preside over motion, and that the stimulus generated in these cells is con-
veyed to the muscles by the anterior roots of the spinal nerves. It is a fact, no less
definite, that, when a muscle or a part of a muscle is deprived of the motor stimulus by
which it is brought into action, its fibres atrophy, become altered in structure, and lose
their contractility. Starting with these two well-defined physiological propositions, and
assuming that a few of the ordinary motor cells of the cord are destroyed — we will not
call them trophic cells — what are the phenomena to be expected as a consequence of
such a lesion ? Reasoning from what we know of the physiology of the nervous system,
we should expect to find the following conditions :

The destruction of certain motor nerve-cells would certainly produce degeneration of
the fibres to which they give origin. This has been observed; for, in this condition, the
anterior roots arising from the diseased portions of the cord are atrophied. This occurs
when any motor nerves are separated from their cells of origin, and it involves no neces-
sity of assuming the existence of special trophic cells or nerves.

If a few of the motor cells be affected with disease, and if the degeneration be gradual
and progressive, we should expect progressive and partial paralysis of the muscles to
which their nerves are distributed. This paralysis, confined to a limited number of
fibres of particular muscles or sets of muscles, would give the idea of progressive weak-
ening of the muscles, and the phenomena would not be those observed in complete
paralysis produced by section of the motor nerves. These are precisely the phenomena
observed in progressive muscular atrophy, preceding the paralysis which is the final

SLEEP. 743

result of the disease; and these do not involve the action of any special centres or
nerves.

As regards the muscular atrophy itself, if the nervous stimulus he progressively de-
stroyed, the muscular tissue will necessarily undergo progressive degeneration and
atrophy.

"With the above considerations, we leave the trophic cells and nerves to the patholo-
gist ; and we can only admit the existence of centres and nerves specially and directly in-
fluencing the nutrition of the muscular system, when it has been demonstrated that there
are lesions of particular structures in the nervous system, which produce phenomena that
cannot he explained by our knowledge of the action of ordinary motor and sensory nerves
and of the vaso-motor system.

We have thus endeavored to represent what is actually known concerning the sym-
pathetic system, but it is evident that we have much to learn with regard to its physi-
ology. The great sympathetic ganglia may have functions of which we have no definite
idea ; and we are better prepared to advance our knowledge in this direction, by admit-
ting our ignorance, than by attempting to supply the deficiencies in our positive infor-
mation by theories unsupported by facts.

Sleep.

When we remember that about one-third of our existence is passed in sleep, and that,
at this time, voluntary motion, sensation, the special senses, and various of the functions
of the organism, are greatly modified, the importance of a physiological study of this
condition is sufficiently apparent. The subject of sleep is most appropriately considered
in connection with the nervous system, for the reason that the most important modifica-
tions in function are observed in the cerebro-spinal axis and nerves. Repose is as neces-
sary to the nutrition of the muscular system as proper exercise ; but repose of the mus-
cles relieves the fatigue due to exercise, without sleep. It is true that, after violent and
prolonged exertion, there is frequently a desire for sleep, but simple repose will often
restore the muscular power. After the most violent effort, a renewal of muscular vigor
is most easily and completely effected by rest without sleep, a fact familiar to all who are
accustomed to athletic exercises. The glands engaged in the production of the true secre-
tions need certain intervals of repose ; but this does not necessarily involve sleep. After
prolonged and severe mental exertion, however, or after long-continued muscular effort
which involves an excessive expenditure of the so-called nerve-force, sleep becomes an
imperative necessity. If the nervous system be not abnormally excited by effort, sleep
follows moderate exertion as a natural consequence, and it is the only physiological means
of complete restoration ; but the two most important muscular acts, viz., those con-
cerned in circulation and respiration, are never completely arrested, sleeping or waking,
although they undergo certain modifications.

In infancy and youth, when the organism is in process of development, sleep is more
important than in adult life or old age. The infant does little but sleep, eat. :m<l <!!
In adult life, under perfectly physiological conditions, we require about eight hours of
sleep ; some persons need less, but very few require more. In old age, unless after
extraordinary exertion, less sleep is required than in adult life. Each individual learns
by experience how much sleep is necessary for perfect health, and there is nothing which
more completely incapacitates one for mental or muscular effort, especially the former,
than loss of rest.

Sleeplessness is one of the most important of the predisposing causes of certain forms
of brain-disease, a fact which is well recognized by practical physicians. ( >ne ot the
most refined and exquisite methods of torture is long-continued deprivation of sleep; and
persons have been known to sleep when subjected to acutely painful iinpn. ssions. Severe
muscular effort, even, may be continued during sleep. In forced marches, rcirinieiits have

744 NERVOUS SYSTEM.

been known to sleep while walking ; men have slept soundly in the saddle ; persons will
sometimes sleep during the din of battle ; and other instances illustrating the imperative
demand for sleep after prolonged vigilance might be cited. It is remarkable, also, how
noises to which we have become accustomed may fail to disturb our natural rest. Those
who have been long habituated to the endless noise of a crowded city frequently find
difficulty in sleeping in the oppressive stillness of the country. We must have sleep;
and this demand is so imperious, that we soon accommodate ourselves to the most un-
favorable surrounding conditions. It is remarkable, also, that prolonged exposure to
intense cold induces excessive somnolence, and, if this be not resisted, the sleep passes
into stupor, the power of resistance to cold becomes rapidly diminished, and death is the
inevitable result. Intense heat often produces drowsiness, but, as is well known, is not
favorable to natural sleep. We generally sleep less in summer than in winter, though in
summer, perhaps, we are less capable of protracted mental and physical exertion.

Sleep is preceded by an indescribable feeling of drowsiness, an indisposition to mental
or physical exertion, and a general relaxation of the muscular system. It then requires
a decided eifort to keep awake ; and, if we yield to the soporific tendency, the voluntary
muscles cease to act, the lids are closed, we cease to appreciate the ordinary impressions
of sound, and we sometimes pass into a dreamless condition, in which we lose all knowl-
edge of existence. We say sometimes, because the mind is not generally inactive during
what we may regard as normal sleep. We may have dreams which are not due, as far
as can be ascertained, to impressions from the external world received during sleep.
Ideas in the form of dreams may be generated in the brain from impressions previously
received while awake, or trains of thought may be gradually extended from the moments
immediately preceding sleep into the insensible condition.

There may be, during sleep, mental operations of which we have no consciousness or
recollection, unconscious cerebration, as it is called by Carpenter. It is well known that
we vividly remember dreams immediately on awakening, but that the recollection of
them rapidly fades away, unless they be brought to mind by an effort to remember and
relate them. Whatever be the condition of the mind in sleep, if the sleep be normal,
there is a condition of repose of the cerebro-spinal system and an absence of voluntary
effort, which restore the capacity for mental and physical exertion.

The impressionability and the activity of the human mind are so great, most of the
animal functions are so subordinate to its influence, and we are so subject to unusual
mental conditions, that it is difficult to determine with exactness the phenomena of sleep
that are absolutely physiological, and to separate those that are slightly abnormal. We
cannot assert, for example, that a dreamless sleep, in which our existence is, as it were,
a blank, is the only normal condition of repose of the system ; nor can we determine
what dreams are due to previous trains of thought, to impressions from the external
world received during sleep, and are purely physiological, and what are due to abnormal
nervous influence, disordered digestion, etc. We may assume that an entirely refreshing
sleep is normal, and that is all.

That reflex ideas originate during sleep, as the result of external impressions, there
can be no doubt ; and we have already alluded to this point under the head of reflex
action. The most remarkable experiments upon the production of dreams of a definite
character, by subjecting a person during sleep to peculiar influences, are those of Maury.
The hallucinations produced in this way are called hypnagogic, and they occur when
the subject is not in a condition favorable to sound sleep. The experiments made by
Maury upon himself are so curious and interesting, that we quote the most striking of
them in full :

FIEST OBSERVATION. — " I was tickled with a feather successively on the lips and
inside of the nostrils. I dreamed that I was subjected to a horrible punishment, that a
mask of pitch was applied to my face, and then roughly torn off, tearing the skin of the
lips, the nose, and the face.

SLEEP. 745

SECOND OBSERVATION.—" A pair of pincers is held at a little distance from my ear,
and rubbed with a steel scissors. I dreamed that I heard the ringing of bells ; this soon
became the tocsin, and I imagined myself in the days of June, 1848.

THIRD OBSERVATION. — " I was caused to inhale Cologne- water. I dream that I am
in a perfumer's shop, and the idea of perfumes doubtless awakens the idea of the East : I
am in Cairo, in the shop of Jean Farina. Many extravagant adventures follow, the con-
nection of which escapes me.

FOURTH OBSERVATION. — " I am caused to smell a burning match. I dream that I am
at sea (remark that the wind was then blowing in through the windows), and that the
Saint-Barbe blew up.

FIFTH OBSERVATION.—" I am slightly pinched on the nape of the neck. I dream that
a blister is applied, which recalls the recollection of a physician who had treated me in
my infancy.

SIXTH OBSERVATION. — " A piece of hot iron is held to my face, keeping it far enough
removed, so that the sensation of heat should be slight. I dream of chauffeurs, who enter
houses and force the inmates, by putting their feet to the fire, to reveal where their money
was. The idea of the chauffeurs immediately suggests that of the Duchess d'Abrantes,
who, I suppose in my dream, has taken me as secretary. I had, indeed, long ago read in
the memoirs of this intelligent woman certain details concerning the chauffeurs.

SEVENTH OBSERVATION. — " The word parafagaramus is pronounced in my ear. I hear
nothing, and awake, having had rather a vague dream. The experiment is repeated
when I am asleep in my bed, and the word maman is pronounced many times in suc-
cession. I dream of different things, but in this dream I heard the humming of bees.
The same experiment, repeated several days after, when I was scarcely asleep, was more
conclusive. The words Azor, Castor, Leonore, were pronounced in my ear ; on awaking,
I recollected that I had heard the last two words, which I attributed to one of the per-
sons who had conversed with me in my dream.

"Another experiment of the same kind likewise showed that the sound of the word,
and not the idea attached to it, had been perceived. The words chandelle, haridelle,
were pronounced in my ear many times in succession. I awoke suddenly of my own
accord, saying, Jest elle. It was impossible for me to recall what idea I attached to this
answer.

EIGHTH OBSERVATION. — " A drop of water is allowed to fall on my forehead. I dream
that I am in Italy, that I am very warm, and that I am drinking the wine of Orviette.

NINTH OBSERVATION. — "A light, surrounded with a red paper, is many times in suc-
cession passed before my eyes. I dream of a tempest of lightning, and all the remem-
brance of a violent storm which I had encountered in the English Channel, in going from
Morlaix to Havre, is present in ray mind."

As regards dreams due to external impressions, it is a curious fact, which has been
noted by many observers and is one which accords with the personal experience of all who
have reflected upon the subject, that trains of thought and imaginary events, which seem
to pass over a long period of time in our dreams, actually occur in the brain within a few
seconds. A person is awakened by a certain impression, which undoubtedly gives rise
to a dream that seems to occupy hours or days, and yet the period of time between the
impression and the awakening is hardly more than a few seconds ; and persons will drop
asleep for a very few minutes, and yet have dreams with the most elaborate details ami
apparently of great length. It is unnecessary to cite the numerous accounts of literary
compositions of merit, the working out of difficult mathematical problems in dreams, etc.,
some of which are undoubtedly accurate. If it be true, that the mind is capable of form-
ing consecutive ideas during sleep— which can hardly be doubted— there is no ir«.<.d iva-on
why these phenomena should not occur, and the thoughts should not be remembered and
noted immediately on awakening. In most dreams, however, the mind is hardly in a
normal condition, and the brain generally loses the power of concentration and of accu-

746 NERVOUS SYSTEM.

rate reasoning. We sometimes commit atrocious crimes in our dreams, without appre-
ciating their enormity, and we are often placed in the most absurd and impossible condi-
tions, without any idea, at the time, of their extraordinary and unnatural character.
This is a fact sufficiently familiar to every one and is one which does not admit of satis-
factory explanation.

We have made no attempt to offer an explanation of the curious psychological phe-
nomena presented during sleep, and, indeed, we know little enough of the action of the
mind at any time ; but we have merely given the above as examples of what we may call
reflex mental phenomena. Somnambulism, general anaesthesia, sleep from hypnotics, the
so-called magnetic sleep, ecstasy, catalepsy, trance, etc., are abnormal conditions, which
we shall only consider in so far as they resemble natural sleep.

Condition of the Brain and Nervous System during Sleep.

As we have already seen, during sleep, the brain may be in a condition of absolute
repose — at least, as far as we have any subjective knowledge of mental operations — or we
may have more or less connected trains of thought. There is, also, as a rule, absence of
voluntary effort, although movements may be made to relieve discomfort from position or
external irritation, without awakening. The sensory nerves retain their properties,
although the general sensibility is somewhat blunted ; and the same may be said of the
special senses of hearing, smell, and probably of taste. The peculiar dreams induced
in the case of Maury by red lights show that the sense of sight is not entirely lost.
There is every reason to believe, however, that the functions of the sympathetic system
are not disturbed or affected by sleep, if we except the action of the vaso-motor nerves
upon the circulation in the brain.

Two opposite theories have long been in vogue with regard to the immediate cause
of sleep. In one, this condition is attributed to venous congestion and increased presssure
of blood in the brain, and this view probably had its origin in the fact that cerebral
congestion induces stupor or coma. Stupor and coma, however, are entirely distinct
from natural sleep ; for here, the functions of the brain are suspended, there is no con-
sciousness, no dreaming, and the condition is manifestly abnormal. In animals rendered
comatose by opium, the brain may be exposed and is found deeply congested with venous
blood. The same condition often obtains in profound anaesthesia from chloroform, but a
state of the brain very nearly resembling normal sleep is observed in anaesthesia from
ether. These facts have been positively demonstrated by experiments upon living ani-
mals, and have been observed in the human subject, in cases of injury of the head.
When opium is administered in large doses, the brain is congested during the condition
of stupor or coma, but this congestion is relieved when the animal passes, as sometimes
happens, from the effects of the agent into a natural sleep. In view of these facts and
others which will be stated hereafter, it is unnecessary to discuss the theory that sleep
is attended with or is produced by congestion of the cerebral vessels.

The idea that the circulation in the brain is diminished during sleep has long been
entertained by certain physiologists ; but, until within a few years, it has rested chiefly
upon theoretical considerations.

Passing over arguments by the older writers for and against this theory of sleep, we
come to the researches of Durham, in 1860, in which it seemed to be demonstrated that
the supply of blood to the brain is always greatly diminished during sleep. These experi-
ments were made upon dogs. A piece of the skull, about the size of a shilling, was
removed with a trephine, and a watch-glass was accurately fitted to the opening and
cemented at the edges with Canada balsam. When the animals operated upon in this
way were awake, the vessels of the pia mater were seen moderately distended, and the
circulation was active ; but, during perfectly natural sleep, the brain retracted and became
pale. " The contrast between the appearances of the brain during its period of func-

CONDITION OF THE BRAIN, ETC., DURING SLEEP. 747

tional activity and during its state of repose or sleep was most remarkable." There
can be hardly any doubt, from these experiments, that the circulation in the cerebral
substance is more active when we are awake than during sleep ; but the question has
been raised by Dr. Cappie, in a very interesting little work upon the causation of sleep,
whether, during a state of diminished activity of the capillary circulation in the brain-
substance, the veins be not congested, and sleep be immediately due to pressure from
these distended vessels on the gray matter. This point is one very difficult to decide,
and it has not been made the subject of experimental inquiry. Dr. Cappie accepts, in
the main, the experiments of Durham as accurate, but he regards his observations as ap-
plying only to the circulation in the arteries and capillaries. His view is that, when the
capillary circulation in the brain-substance is diminished in sleep, the nervous matter is
more or less collapsed, and that the veins are necessarily congested. At present, how-
ever, we can only accept the experimental results of Durham, that the circulation in the
brain is notably diminished in sleep.

The influence of diminished supply of blood to the brain has been illustrated by com-
pression of both carotid arteries. In an experiment performed upon his own person, Dr.
Fleming produced immediate and profound sleep in this way, and this result invariably
followed in subsequent trials upon himself and others. We have, however, the observa-
tions of Waller, who produced anaesthesia in patients by pressure upon both pneumogas-
tric nerves ; but the nerves are so near the carotid arteries that they could hardly be
compressed, in the human subject, without interfering with the current of blood, and
such experiments do not positively show whether the loss of sensibility be due to
pressure upon the nerves or upon the vessels. In some rare cases, in which both carotid
arteries have been ligatured in the human subject, it has been stated that there is an
unusual drowsiness following the necessary diminution in the activity of the cerebral
circulation; but this result is by no means constant, and the morbid conditions in-
volving so serious an operation are usually such as to interfere with their value as facts
bearing upon the question under consideration. As far as the human subject is concerned,
the most important facts are the results of compression of both carotids in healthy per-
sons. These, as well as experiments on animals, all go to show that the supply of blood
to the brain is very much diminished during natural sleep, and that sleep may be induced
by retarding the cerebral circulation by compressing the vessels of supply. When the
circulation is interfered with by compressing the veins, congestion is the result, and we
have stupor or coma.

If diminished flow of blood through the cerebral vessels be the cause of natural sleep,
it becomes important to inquire how this condition of physiological anrcmia is brought
about. It must be that, when the system requires sleep, the vessels of the brain contract
in obedience to a stimulus received through the sympathetic system of nerves, diminish-
ing the supply of blood, here, as in other parts under varied physiological conditions.
The vessels of the brain are provided with vaso-motor nerves, and it is sufficient to have
noted that the arteries are contracted during sleep, the mechanism of this action bcintr
well established by observations upon other parts of the circulatory system. Contraction
of the vessels of the pia mater has been observed, although there is some discussion with
regard to its exciting cause.

It must be acknowledged that we know but little of the intimate nature of tin- pro-
cesses of nutrition of the brain during its functional activity and in repose-; but there
can be no doubt of the fact that there is more or less cerebral action at all times when
we are awake. Although the mental processes are much less active durinir sleep, e?en at
this time, the operations of the brain are not always suspended. It is c<|u;illy well est-il.-
lished, that exercise of the brain is attended with physiological waste- of nervous sub-
stance, and, like other parts of the organism, its tissue requires periodic ivp,»e to allow
of the regeneration of the substance consumed. Analogies to this are to be found in
parts that are more easily subjected to direct observation. The muscles require repose

748 NERVOUS SYSTEM.

after exertion, and the glands, when not actively engaged in discharging their secretions,
present intervals of rest. As regards the glands, during the intervals of repose, the sup-
ply of blood to their tissue is very much diminished. It is probable, also, that the mus-
cles in action receive more blood than during rest; but it is mainly when these parts are
not active, and when the supply of blood is smallest, that the processes of regeneration
of tissue seem to be most efficient. As a rule, the functional activity of parts, while it is
attended with an increased supply of blood, is a condition more or less opposed to the
process of repair, the hyperremia being, apparently, a necessity for the marked and
powerful manifestations of their peculiar functions. When the parts are in active func-
tion, the blood seems to be required to keep at the proper standard the so-called irri-
tability of the tissues and to increase their power of action under proper stimulus.
Exercise increases the power of regeneration and favors full development, in the repose
which follows ; but, during rest, the tissues have time to appropriate new matter, and
this does not seem to involve a large supply of blood. A muscle is exhausted by pro-
longed exertion ; and the large quantity of blood passing through it carries away carbonic
acid, urea, and other products of disassimilation, which are all increased in amount, until
it gradually uses up its capacity for work. Then follows repose ; the supply of blood is
reduced, but, under normal conditions, the tissue repairs the waste which has been
excited by action, the blood furnishing nutritive matter and carrying away a compara-
tively small amount of effete products.

"VVe may safely assume that processes analogous to those just decribed take place in
the brain. By absence of voluntary effort, we allow the muscles time for rest and for the
repair of physiological waste, and their active function is for the time suspended. As
the activity of the brain involves consciousness, volition, the generation of thought, and,
in short, the mental condition observed while awake, complete repose of the brain is
characterized by the opposite conditions. It is true that we rest the brain without sleep,
by abstaining from mental effort, by the gratification of certain of the senses, and by men-
tal distraction of various kinds, and that the mind may work to some degree during sleep ;
but, during the period of complete repose — that condition which is so necessary to perfect
health and full mental vigor — we lose consciousness and volition, there is no thought,
and the brain, which does not receive blood enough to stimulate it to action, is simply
occupied in the insensible repair of its substance and is preparing itself for future work.
The exhaustion of the muscles produces a sense of fatigue of the muscular system, indis-
position to muscular exertion, and a desire for rest, not necessarily involving drowsiness.
Fatigue of the brain is manifested by indisposition to mental exertion, dulness of the
special senses, and a desire for sleep. Simple repose will relieve physiological fatigue of
muscles; and, when a particular set of muscles has been used, the fatigue disappears
when these muscles alone are at rest, though others be brought into action. Sleep, and
sleep alone, relieves fatigue of the brain. When the sleep has continued long enough for
the rest of the brain and the repair of its tissue, we awake, prepared for new effort.

We have now only to refer to a new theory of sleep, proposed by Sommer. Taking
as a basis the researches of Pettenkofer and Voit upon respiration, Sommer advances the
idea that, when the brain is active, or while we are awake, the system appropriates but
a small quantity of oxygen in respiration and eliminates a relatively large proportion of
carbonic acid; after a time, the oxygen thus appropriated is consumed, and the system
demands a new supply ; and, during sleep, the organism appropriates oxygen largely and
eliminates a relatively small amount of carbonic acid. When the elimination of carbonic
acid at the expense of the oxygen stored up reaches a certain point, the necessity for a
farther supply of oxygen induces sleep ; and when, during sleep, oxygen has been appro-
priated in sufficient quantity, the system awakes, prepared for a new period of activity
of the animal functions.

By reference to the researches of Pettenkofer and Voit, we find that these observers,
in experiments upon a man confined in a chamber in which the interchanges of gases in

CONDITION OF THE BRAItf, ETC., DURING SLEEP. 749

respiration could be estimated, noted, in twenty-four hours, that the subject of the observa-
tion, awake but in a condition of complete repose, appropriated sixty-seven per cent, of
the entire amount of oxygen of the twenty-four hours during the night, and thirty-three
per cent, during the day, while he eliminated fifty-eight per cent, of the entire amount
of carbonic acid excreted, during the day, and forty-two per cent., during the night.
When the subject of the experiment worked during the day, by turning a heavy wheel,
the appropriation of oxygen was thirty-one per cent, for the day, and sixty-nine per cent,
for the night ; and the elimination of carbonic acid was sixty-nine per cent, for the day, and
thirty-one per cent, for the night. According to these observations, the system stores up
oxygen at night for use during the day, at this time eliminating a relatively small quan-
tity of carbonic acid ; and, during the day, it excretes more carbonic acid than during
sleep, appropriating then a relatively small amount of oxygen.

This theory of sleep seems to rest upon observations too restricted to be adopted
without reserve. It is stated, indeed, that the first experiments of Pettenkofer and Voit
were not confirmed in other observations made upon the same person. It is hardly pos-
sible, with our present information, to assume that sleep is due simply to want of oxygen,
and it is more in accordance with well-established physiological facts to attribute it to a
necessity for the general regeneration of the nervous tissue, though into this, the neces-
sity for oxygen may enter as one element in the physiological repair.

During sleep, nearly all of the functions, except those directly under the control of the
sympathetic nervous system, are diminished in activity. The circulation is slower, and
the pulsations of the heart are less frequent, as well as the respiratory movements. These
points have already been considered under the heads of circulation and respiration. "We
have but little positive information with regard to the relative activity of the processes
of digestion, absorption, and secretion, during sleep. The drowsiness which many per-
sons experience after a full meal is probably due to a determination of blood to the ali-
mentary canal and a consequent diminution in the supply to the brain.

CHAPTER XXIII.

SPECIAL SENSES-TOUCH, OLF ACTION, AND GUSTATION.

General characters of the special senses— Muscular sense (so called)— Appreciation of weight— Sense of touch— Varia-
tions in tactile sensibility in different parts — Table of variations measured by the aesthesiometer — Connection
between the variations in tactile sensibility and the distribution of the tactile corpuscles— Titillation— Appnria-
tion of temperature — Venereal sense — Olfaction — Nasal fossae — Schneiderian and olfactory membrane— Physio-
logical anatomy of the olfactory nerves— Olfactory bulbs— Olfactory cells and terminations of the olfactory n. r\t
fibres— Properties and functions of the olfactory nerves—Mechanism of olfaction— Relations of olfaction to tho
sense of taste — Reflex acts through the olfactory nerves— Gustation — Savory substances — Relations between
gustation and olfaction — Taste and flavor — Modifications of the sense of taste — Nerves of taste— Chorda tympani
—Facial paralysis with impairment of taste— Paralysis of general sensibility of the tongue without impairment of
taste— Glosso-pharyngeal nerve (first division of the eighth)— Physiological anatomy— General properties of the
glosso-pharyngeal— Relations of the glosso-pharyngeal nerves to gustation— Mechanism of gustation— Physiolo-
gical anatomy of the organ of taste— Papillae of the tongue— Taste-buds, or taste-beakers— Connections of tho
nerves with the organs of taste.

OUR study of the nervous system thus far has involved simply motion and what is
known as general sensibility; and almost all our positive knowledge of these properrk-s
has been derived from experiments upon the inferior animals. As roirards sensation, tho
experiments have referred to impressions recognized as painful ; and we have seen that
these are conveyed to the centres by nerve-filaments, anatomically as well as physiologi-
cally distinct from those which convey to the contractile parts the stimulus that giv«l
to motion. As far as we have studied the sensory nerves, we have alluded to simple im-

750 SPECIAL SENSES.

pressions only ; but it is evident that the filaments of peripheral distribution of these
nerves are capable of receiving a variety of impressions, by which we determine, to a cer-
tain extent, the form, size, character of surface, density, and temperature of objects. We
also have a general appreciation of heat and cold ; a sense of resistance, which gives an
idea of weight ; and, finally, there are nerves of peculiar properties, terminating in organs
calculated to receive the impressions of smell, taste, sight, and hearing.

The senses of olfaction, gustation, vision, and audition, belong to peculiar organs, pro-
vided with nerves of special properties, which are usually not endowed with general sen-
sibility. These nerves have been omitted in our general study of the nervous system ;
and the accessory organs to which they are distributed are so important and intricate in
their structure as to demand extended description.

The senses of touch, titillation, temperature, and pain are all conveyed to the nerve-
centres by what we have described as ordinary sensory nerves ; the touch being perfected
in certain parts by peculiar arrangements of the terminal nerve-fibres. Although it be
possible that each one of these impressions may be transmitted by special and distinct
fibres, this has not yet approached a positive demonstration. The so-called muscular
sense, by which we appreciate weight, resistance, etc., undoubtedly depends, to a great
extent if not entirely, upon the muscular nerves.

Muscular Sense (so called).

It is difficult to define exactly what is meant by the term muscular sense, as it is used
by many physiologists. In all probability, the sense which enables us to appreciate the
resistance, immobility, and elasticity of substances that are grasped, on which we tread,
or which, by their weight, are opposed to the exertion of muscular power, is immensely
modified by education and habit. Still, it is undoubtedly true that the general sensibility
regulates the action of muscles to a very great extent. If, for example, the lower extremi-
ties be paralyzed as regards sensation, the muscular power remaining intact, the person
affected frequently cannot walk, unless he be able to see the ground. This difficulty
occurs for the simple reason that the limbs have lost the sense of contact with the ground,
which is nothing more nor less than loss of general sensibility. Many curious examples
of this kind are to be found in works upon diseases of the nervous system. One of the
most striking is a case communicated to Sir Charles Bell by Dr. Ley. The patient was
afflicted with partial loss of sensibility upon one side of the body, " without, however,
any corresponding diminution of power in the muscles of volition, so that she could hold
her child in the arm of that side so long as her attention was directed to it ; but, if sur-
rounding objects withdrew her from the notice of the state of her arm, the flexors grad-
ually relaxed, and the child was in hazard of falling." This is like certain of the phe-
nomena observed in cases of locomotor ataxia. In this disorder, there is disease of the
posterior columns of the spinal cord, involving, sometimes, the posterior roots of the
spinal nerves, with more or less impairment of general sensibility, the muscular power,
in some instances, being intact. Patients affected in this way are frequently unable to
walk or stand without the aid of the sight. One of the most characteristic phenomena
is inability to stand when blindfolded; although, with the aid of the sight, the muscles
can be made by the will to act with great power.

Without entering into a full discussion of the various arguments used for and against
the existence of a special " muscular sense," it is sufficient to state that, in those cases
in which general sensibility is lost or seriously impaired, the brain has no exact apprecia-
tion of the action of the muscles, except as regards the sense of fatigue. This question
is of great importance in connection with the pathology of the nervous system ; and it
seems that the weight of evidence is decidedly in favor of the view that there is no dis-
tinct perception of muscular action, aside from general sensibility, that can properly be
called a muscular sense.

SENSE OF TOUCH. 751

Habit and education enable us to appreciate with great nicety differences in weight ;
but this is chiefly due to the sense of resistance to muscular effort and has link- depeiid-
ence upon the sense of touch. In the elaborate and classical experiments of Weber, this
point was very strikingly illustrated. The observations of this physiologist upon the
sense of touch and general sensibility were very varied and extensive ; and, among the
most important of the results with regard to the appreciation of pressure and weight,
are the following :

In general, those parts which are most sensitive to the impressions of touch, as the
fingers, enable us to appreciate differences in pressure and weight with the greatest accu-
racy. The sense of simple pressure, unaided by the estimation of weight by muscular
effort, is generally more acute upon the left side, probably because the integument of the
left hand is thinner than that of the right hand. Differences in weight can be accurately
distinguished, when they amount to only one-sixteenth, by employing muscular effort in
lifting, as well as the sense of pressure; but the sense of pressure alone enables us to
appreciate a difference of not less than one-eighth. When weights are tested by lifting
with the hand, the appreciation of slight differences is more delicate when the weights
are successively tested with the same hand than when two weights are placed, one on
either hand. When the interval between the two trials amounts to more than forty sec-
onds, slight differences in weight — the difference between fourteen and a half and fifteen
ounces, for example — cannot be accurately appreciated. In such trials, it is necessary
to have the metals used of the same temperature, for cold metals seem heavier than
warm.

These observations formularized some of the facts, sufficiently evident to every one,
relating to the appreciation of slight differences in weight. It is well known that experts
acquire, in this regard, wonderful delicacy and accuracy. Those who are in the daily
habit of handling coins not only count with astonishing rapidity, but are able to detect
and throw out a light piece instantly and with unerring certainty.

Sense of Touch.

We have already considered, in connection with the nervous system, the modes of
termination of the sensory nerves ; and, in many instances, it is possible to explain, by
the anatomical characters of the nerves, the great differences that have been observed in
the delicacy of tlie tactile sensibility in different parts — differences which are exceedingly
important, pathologically as well as physiologically, and which have been studied by
Weber, Valentin, and others, with great minuteness.

Variations in the Tactile Sensibility in Different Parts. — In certain parts of the cuta-
neous surface, the general sensibility is much more acute than in others. For example,
a sharp blow upon the face is more painful than a similar injury to other parts; and the
eye, as is well known, is most exquisitely sensitive. The appreciation of temperature also
varies in different parts, this probably depending to a great extent upon habitual exposure.
Some parts, as the soles of the feet or the axilla, are peculiarly sensitive to titillution.
The sense of touch, however, by which we appreciate the size, form, character of the
surface, consistence, etc., of objects, is developed to a greater degree in some parts than
in others; a fact which can be very readily explained, in some instances, by the ana-
tomical arrangements of the peripheral sensory nerves. When we wish to ascertain
those properties of objects revealed by the sense of touch, we generally employ the lin-
gers. This sense is capable of education and is almost always extraordinarily developed
in persons who are deprived of other special senses, as sight or hearing. The blind learn
to recognize individuals by feeling of the face. A remarkable instance of this is quoted
in works on physiology, of the blind sculptor, Giovanni Gonelli. who *«fl sii.l to model
the most striking likenesses entk'ely by the sense of touch. Other ii:~ t his kihd

753 SPECIAL SENSES.

are on record. The blind have been known to become proficients in conchology and
botany, guided simply by the sense of touch. It is related of a blind botanist, that he
was able to distinguish ordinary plants by the fingers and by the tip of the tongue. It
is well known that the blind learn to read with perfect facility, by passing the fingers
over raised letters but little larger than the letters in an ordinary folio Bible. Kudolphi
cites the remarkable faculty acquired by Baczko, of distinguishing the colors of fabrics by
the sense of touch alone.

An exceedingly ingenious and accurate method of determining the relative delicacy
of the tactile sensibility of different portions of the cutaneous surface was devised a
number of years ago (1829) by E. H. Weber, whose researches upon this subject, which
have been repeatedly confirmed by other observers, are still the most careful and reliable
on record. This method consists in the application to the skin, of two fine but blunt
points, separated from each other by a known distance. The individual experimented
upon should be blindfolded, and the points applied to the skin simultaneously. By care-
fully adjusting the distance between the points, a limit will be reached where the two
impressions upon the surface are appreciated as one ; i. e., by gradually approximating
them, the subject will suddenly feel both points as one, when, an instant before, with the
points a little farther removed from each other, he distinctly felt two impressions. This
gives a very accurate measure of the delicacy of the tactile as distinguished from the
general sensibility of different parts, and it has lately been found a most important guide
in the investigation of diseases of the nervous system attended with partial anesthesia
of the surface. Of course, the instrument used may be very simple (a pair of ordinary
dividers will answer), but it is convenient to have some ready means of ascertaining the
distances between the points. An instrument, consisting simply of a pair of dividers,
with a graduated bar giving a measure of the separation of the points, is the best, as it
combines simplicity, convenience of use, and portability. This instrument is called the
sesthesiometer.

The experiments of Weber were made upon his own person, and, of course, they do not
show the variations that may occur in different individuals in health, a point of consider-
able importance in estimating the extent of anesthesia in disease. His observations also
showed some slight variations with the direction of the line of the two points, but these
are not important. Valentin repeated the experiments of Weber, and, in addition, took
the maximum, minimum, and mean, in six persons. Aside from these observations, the
repetition of Weber's experiments has done little more than confirm the original facts.
The table upon the next page, taken from the article on "Touch " by Dr. W. B. Carpen-
ter in the Cyclopedia of Anatomy and Physiology, London, 1849-1852, vol. iv., part ii.,
p. 1169, gives the results obtained by Weber and by Valentin.

If we note the distribution of the tactile corpuscles in connection with this table, it
will be seen that the sense of touch is most acute in those situations in which the cor-
puscles are most abundant. In the space of about one-fiftieth of a square inch on the
palmar surface of the third phalanx of the index-finger, Meissner counted the greatest
number of corpuscles, viz., one hundred and eight. In this situation, the tactile sensi-
bility is more acute than in any other part of the skin, the mean distance indicated by
the sesthesiometer being 0'603 of a line. In the same space on the second phalanx, forty
corpuscles were counted, the esthesiometer marking 1-558 line, this part ranking next in
tactile sensibility after the red surface of the lips. We can readily understand how the
tactile corpuscles, embedded in the amorphous substance of the cutaneous papilla?, might
increase the power of appreciation of delicate impressions by presenting hard surfaces
against which the delicate nerve-filaments can be pressed.

As regards those portions of the general cutaneous surface in which no tactile corpus-
cles have been demonstrated, it is not easy to connect the variations in the tactile sen-
sibility with the nervous distribution, as we know little or nothing of the comparative
richness of the terminal nervous filaments in these situations.

SENSE OF TOUCH.

753

Table of Variations in the Tactile Sensibility of Different Portions of the
Skin (Weber and Valentin).

The tactile sensibility is measured by the greatest distance between two points at which they convey a single
impression when applied simultaneously. The measurements are given in lines (t\ of an inch).

PART OF SURFACE.

WEBEK.

VALENTIN.

Tip of the ton°Tie ...

0-50
1-00

Max.
0-50
1-00
1-00
1-00
1-00
1-00
2-00
2-00
2-00
1-75
4-00
8-00
4-00
8-00
4-00
4-00
3-00
5-00
4-50
5-00
5-00
5-50
5-50
5-50
5-50
5-50
6-00
9-00
5-00
7-00
7-00
6-00
8-00

10-00

7-00

10-00

14-00
12-00
15-00

10-00

14-00
15-00
16-00
20-00
18-00
14-00
18-00
24-00
18-00
18-00
18-00
18-00
20-00
18-00
80-00
80-00
80-00
24-00
24-00
80-00

Min.
0-40
0-50
0-87
0-60
0-50
0-50
0-50
0-50
1-25
1-50
1-50
1-75
1-50
0-50
1-50
1-50
1-75
3-00
2-00
2-50
8-00
2-75
2-75
2-75
2-50
2-75
2-00
2-0(1
8-25
8-00
4-00
4-00
. 8-25
3-00
5-00
4-00
8-50
6 00
8-00
8-00
3-00
6-50
6-00

»*oo

7-50
12-00
7-00
8-00
9-00

10-00

6-00
7-50
8-00
10-50
8-75
9-00
7-00
11-00
11-50
11-00

Mean.
0-488
0-608
0-706
0-723
0-725
0-788
1-500
1-520
1-558
1-650
1-916
2-125
2-i08
2-250
2-478
2-500
2 6-25
3-250
8-333
8-888
8-883
8-893
8-8<J8
8-900
8-943
3-971
4-042
4-125
4-541
4-620
4-917
5-100
5-250
5-286
5-875
6-000
6-966
8-292
8-2<:2
9-000
9-200
9-588
10-208
12-066
12-525
18-000
18-292
18-292
18-708
18-850
13-SSrt
14-958
15-875
16-625
17-088
17-688
18-542
19-000
19-912
24-208

Relative
acuteneu,.

i-ooo

0-889
0-686

0-669
0-667
0-659
0-322
0-818
0-810
0-298
0-252
0-227
0-219
0-215
0-195
0-198
0-184
0-149
0-145
0-126
0-126
0-124
0-124
0-124
0-122
0-121
0-120
0-117
0-106
0-105
0-098
0-095
0-092
0-091
0-082
0-081
0-069
0-058
0-058
0-054
0-052

o-oto

0-047
0-040
0-089
0-087
0*084
0-061
0-085
0-084
0-084
0-081
0-080
0*029
0-028
0-027
0-OM
0-025
0-091
0-020

i Relative
obtuse neu.

1-000

1-461
1-41)6
1-500
1-517
8-180
8-145
8-228
8-414
8-964

4-568
4-6T5
5-127
6-172
5-481
6-724
6-8l>6

7-930
S-054
8-054
8-069
8-158
8-216
8-868
8-585
9-895
9-559
10-178
WMfl
10-862
10-986
12-155
12-414
14-41-2
17-156

IT-IM;

18-621
19-080
19-887

21-120
24-964
25-914

L'TTxil
27-501
28-861
28-f55
88*688
:;o-!>4^

84-897
86-M4
86*481

88-861

89-810
44-758
M-086

Palmar surface of third phalanx of forefinger

do. do. middle finger

do. do. ring-finger

do. do. thumb. . . '

do. do. little finger

Eed surface of under lip

2-00

do. upper lip

Palmar surface of second phalanges of fingers

2-00

do. first do.

Middle of the dorsum of the tongue.

4-00
3-00
4-00
8-00

Dorsal surface of the third phalanges of fingers

Portion of the lips not red

Tip of the nose

Edge of the tongue an inch from the tip

Lateral surface of the dorsum of the tongue

Palmar surface of the metacarpus

8-00
5-00
4-00
5-00
5-00
6-00

End of the great-toe

Metaca'rpal joint of tlie thumb

External surface of the eyelids

Palm of the hand

Dorsal surface of second phalanx of thumb

do. do. forefinger

do. do. middle finger

do. do. little finger '.

do. do. ring-finger

Centre of the hard palate

6-00
9-00
5-00
7-00
7-00

Mucous membrane of lips close to the gum

Skin of the cheek over buccinator

do. over anterior part of malar bone

Dorsal surface of first phalanges of fingers.

Prepuce

Dorsal surface of heads of metacarpal bones . .

8-00

10-00

Skin of cheek over posterior part of malar bone

Plantar surface of metacarpal bone of great-toe

Lower part of forehead

10-00

14-00
12-00
15-00

10-00

Back of the hand

Lower part of hairy scalp in occipital region

Surface of the throat beneath lower jaw

Back of the heel

Pubcs

Crown of the head

15-00
16-00

Areola around ninple

Dorsum of foot near the toes.

18-00

Axilla

Upper and lo\ver extremities of forearm

18-00
24-00
18-00
18-00
18-00
18-00
20-00
18-00
80-00
80-00
80-00
24-00
24-00
80-00

Back of the neck near the occiput

Upper and lower extremities of leg

Penis

Acromion and upper part of arm

Gluteal region and neighboring part of thigh

Middle of forearm where its circumference is greatest —
Middle of thi-h do.
Middle of cervical vertebrae.

Five upper dorsal vertebrae

Lower part of thorax and over lumbar vertebrae.

Middle of dorsal vertebrae

Titillation.—TliG sensation experienced when certain parts of the general surface are
subjected to titillation cannot easily be described, although it is sufficiently familiar. This
sensation is due simply to delicate impressions made in unusual situations and is remark-
able chiefly on account of the reflex movements which it occasions. If the soles of the
feet be tickled, it is almost impossible to avoid movements of the limbs. Tin-so are not
due entirely to the peculiar sensation appreciated by the brain, for the same stimulus, in
persons suffering from complete paralysis of sensation and voluntary motion of the lowir
extremities, may produce even violent action of the paralyzed muscles. The peculiar
48

754 SPECIAL SENSES.

nature of the sensation is due to the unusual character of the impression, and it does not
involve the action of special nerve-fibres as conductors.

Appreciation of Temperature. — It is not known that the sense of temperature, either
of the surrounding medium or of bodies applied to different parts of the skin, is appreci-
ated through any nerves other than those of general sensibility, or that there is any special
arrangement of the terminations of certain of the nerves connected with this sense. As
regards the general temperature, the sense is relative and is much modified by habit.
This statement needs no explanation. As is well known, what is cold for an inhabitant
of the torrid zone would be warm for one accustomed to an excessively cold climate.
Habitual exposure also modifies the sense of temperature. Many persons not in the habit
of dressing warmly suffer but little in extremely cold weather. Those who habitually
expose the hands, or even the feet, to cold, render these parts quite insensible to tempera-
ture ; and the same is true of those who often expose the hands, face, etc., to heat.

The variations in the sensibility of different parts of the surface to temperature depend,
as we have just indicated, to a great extent upon habit, exposure, etc., but also upon
special properties of the parts themselves. The differences, however, are not so marked
as to be of any great importance, and the experiments made upon tbis point are simply
curious. It is remarkable, however, to note the exquisite sensibility to variations in tem-
perature sometimes presented by those who are deprived of other senses. The example
is quoted by Dunglison, of Dr. Saunderson, formerly Professor of Mathematics at Cam-
bridge, England, who, " when some of his pupils were engaged in taking the altitude of
the sun, could tell, by the slight modification in the temperature of the air, when very
light clouds were passing over the sun's disk."

The experiments of Weber show conclusively that the skin is the main organ for the
appreciation of temperature, if we except the mouth, palate, vagina, and rectum, by which
the difference between warm and cold substances is readily distinguished. In several
instances in which large portions of the skin were destroyed by burns and other injuries,
experiments have been made by applying spatulas of different temperatures. At one thre
a spatula plunged in water at from 48° to 55° Fahr. was applied to a denuded surface,
and again, a spatula at from 113° to 122° Fahr. When the patient was requested to tell
which was the warmer, the answers were as frequently incorrect as they were correct ;
but the discrimination was easy and certain when the applications were made to the sur-
rounding healthy skin. When applications at a higher temperature were made to the
denuded part, the patient suffered only pain.

The venereal sense, which we shall not attempt to describe, is unlike any other sensa-
tion, and is general, as well as referable to the organs of generation. In this connection,
however, it is interesting to note that the tactile sensibility of the palmar surface of the
third phalanx of the fingers, measured by the sssthesiometer, compared with the sensi-
bility of the penis, is as 0'802 to 0-034, or between twenty-three and twenty-four times
greater.

Olfactory Nerves.

The nerves directly connected with the senses of olfaction, vision, and audition, are
but slightly if at all endowed with general sensibility. As regards the olfactory nerves,
the parts to which they are distributed are so fully supplied with branches from the fifth,
that it is difficult to determine the fact of their sensibility or insensibility to ordinary
impressions. The olfactory nerves, however, are distributed to the mucous membrane
of that portion of the nasal cavity endowed with the special sense of smell. Before
taking up their physiological anatomy, we shall describe briefly the parts to which the
olfactory sense is probably confined.

Nasal Fossce. — The two irregularly-shaped cavities in the middle of the face, opening
in front by the anterior nares and connected with the pharynx by the posterior nares,

OLFACTORY NERVES. 755

are called the nasal fossae. The membrane lining these cavities is generally called the
Schneiderian mucous membrane, and sometimes, particularly by the French, the pituitary
membrane. This membrane is closely adherent to the fibrous coverings of the bones
and cartilages by which the nasal fossae are bounded, and it is thickest over the turbinated
bones. It is continuous with the membrane lining the pharynx, the nasal duct and lach-
rymal canals, the Eustachian tube, the frontal, ethmoidal, and sphenoidal sinuses, and
the antrum. There are openings leading from the nasal fossae to all of these cavities.

The essential organ of olfaction is the mucous membrane lining the upper half of the
nasal fossae. Not only has it been shown anatomically that this part only of the mem-
brane receives the terminal filaments of the olfactory nerves, but physiological experi-
ments have demonstrated that it is the only part capable of receiving odorous impressions.
If a tube be introduced into the nostril, placed horizontally over an odorous substance so
that the emanations cannot penetrate its caliber, no odor is perceived, though the parts
below the end of the tube might receive the emanations ; but, if the tube be now directed
toward the odorous substance, so that the emanations can penetrate to the upper portion
of the nares, the odor is immediately appreciated.

That portion of the lining of the nasal fossae properly called the olfactory membrane
extends from the cribriform plate of the ethmoid bone downward a little less than an
inch. It is exceedingly soft and friable, very vascular, thicker than the rest of the
Schneiderian membrane, and, in man, has rather a yellowish color. It is covered by
long, delicate, columnar cells, nucleated, each one provided with from three to eight cili-
ary processes, their movement being from before backward. The mucous glands of the
olfactory membrane are numerous, long, and racemose. They secrete a fluid which keeps
the surface moist, a condition essential to the accurate perception of odorous impressions.

Physiological Anatomy of the Olfactory Nerves.— The apparent origin of the olfactory
nerve is by three roots, from the inferior and internal portion of the anterior lobe of the

FIG. 233.— Olfactory ganglion and nerves. (Hirschfeld.)

FIG. '283. — Olfactory ganglion ana nerves, ^mrscnieiu.;

1, olfactory ganglion and nerves; 2, branch of the nasal nerve; 8, spheno-palatine jranplion : 4. 7. l.rruiohrs »f th,-
great palatine nerve; 5, posterior palatine nerve; 6, middle palatine nerve; 8, 9, branches from tin- >,,!,
tine rangSon; 10, 11, 12, Vidian nerve and its branches; 18, external carotid branch from the supi-n-.r

trqncriirm

ganglion.

cerebrum, in front of the anterior perforated space. The three roots are an external and
an internal white root, and a middle root composed of gray matter. The external white
root is long and delicate, passing outward across the fissure of Sylvius to the middle lobe
of the cerebrum. The internal white root is thicker and shorter than the external root,

756

SPECIAL SENSES.

and it arises from the most posterior portion of the anterior lobe. The middle, or gray
root arises from a little eminence of gray matter situated on the posterior and inner por-
tion of the inferior surface of the anterior lobe.

The deep origin of these three roots of the olfactory nerves is still a matter of discus-
sion. The external root is stated by various anatomists to originate from the corpus
striatum, the optic thalamus, the anterior commissure, and the island of Reil; but
researches upon this point have been by no means satisfactory. The same uncertainty
exists with regard to the deep origin of the internal white root and the gray root.

The three roots of the olfactory converge to form a single nervous cord at the inner
boundary of the fissure of Sylvius. This passes forward and slightly inward in a deep
groove between two convolutions on the under surface of the anterior lobe, covered by
the arachnoid membrane, to the ethmoid bone. This portion of the nerve is exceedingly
soft and friable. It is composed of both white and gray matter, the proportions being
about two-thirds of 'the former to one-third of the latter. The gray substance, derived
from the gray root, is situated at the upper portion of the nerve, the white substance
occupying the inferior and the lateral portions.

By the side of the crista galli of the ethmoid bone, the nerve-trunk expands into an
oblong ganglion, called the olfactory bulb. This is grayish in color, excessively soft, and
contains the ordinary ganglionic elements. From the olfactory bulb, from fifteen to
eighteen nervous filaments are given off, which pass through the foramina in the cribriform
plate of the ethmoid bone. These filaments are composed entirely of nerve-fibres and are
quite resisting, owing to fibrous elements prolonged from the dura mater. It is strictly

proper, perhaps, to regard these as the true olfactory
nerves, the cord leading from the olfactory bulb to the
cerebrum being more properly a commissure. Having
passed through the cribriform plate, the olfactory nerves
are distributed to the olfactory membrane in three groups :
an inner group, distributed to the mucous membrane of
the upper third of the septum ; a middle group, to the
upper portion of the nasal fosses ; and an outer group, to
the mucous membrane covering the superior and middle
turbinated bones and a portion of the ethmoid.

The mode of termination of the olfactory nerves differs
from that of the ordinary sensory nerves, and is peculiar
and characteristic, as it is in the other organs of special
sense. According to recent observations, the olfactory
mucous membrane contains peculiar terminal nerve-cells,
FIG. ^.-Terminal filaments of the called the olfactory cells, which are situated between the
olfactory nerves; magnified 30 cells of epithelium. These are long, delicate, spindle-

diameters. (Kolliker.)

i, from the frog.-o, epithelial cells of shaped structures, varicose, each one containing a clear,
the olfactory region; b, olfactory round nucleus. The appearance of these, which are con-
ceils. 2. small branch of the olfac- . ,

tory nerve of the ftopr, separating at sidered as the true olfactory organs, is represented m Fig.

fibril"! S&to£Su of thveaehe°ep! 234. In the frog, there is a fine, hair-like process projecting
from each cell beyond the mucous membrane, which has

not been obsetved in man or the mammalia. The great delicacy of the structures enter-
ing into the composition of the olfactory membrane renders the investigation of the ter-
mination of its nervous filaments exceedingly difficult.

Properties and Functions of the Olfactory Nerves. — It is almost certain that the olfac-
tory nerves possess none of the general properties of the ordinary nerves belonging to the
cerebro-spinal system, but that they are endowed with the special sense of smell alone.
As far as we know, no one has exposed and operated upon the filaments coming from the
olfactory bulbs and distributed to the pituitary membrane in living animals ; but experi-

OLFACTORY KERVES. 757

inents upon the nerves behind the olfactory bulbs show that they are entirely insensible
to ordinary impressions. Attempts have been made to demonstrate, in the human sub-
ject, the special properties of these nerves, by passing a galvanic current through the
nostrils ; but the situation of the nerves is such that these observations are of necessity
indefinite and unsatisfactory. On one or two occasions, in witnessing surgical operations
upon the upper part of the nasal fossre, we have been struck with the exceedingly dull
sensibility of its mucous membrane.

The question as to whether or not the olfactory nerves endow the membrane of the
nasal fossa) with the sense of smell hardly demands discussion at the present day. Jt
must be evident to any one who reads the experiments of Magendie, in which he at-
tempted to show that the sense of smell was retained after division of these nerves, that
he confused the general sensibility of the parts with the peculiar impressions of odors;
and the cases, especially the one reported by Bernard, in the human subject, in which it
was supposed that the olfactory sense existed notwithstanding congenital absence of the
olfactory nerves and bulbs, are by no means satisfactory, in view of the numerous in-
stances in which precisely the opposite has been observed.

Among the numerous experiments upon the higher orders of animals, in which the
olfactory nerves have been divided, we may cite, as open to no objections, those of Vul-
pian and Philipaux, upon dogs. It is well known that the sense of smell is usually very
acute in these animals. Upon dividing or extirpating the olfactory bulbs, " after the
animal had completely recovered, it was deprived of food for thirty-six or forty-eight
hours ; then, in its absence, a piece of cooked meat was concealed in a corner of the
laboratory. Animals, successfully operated upon, then taken into the laboratory, never
found the bait ; and nevertheless, care had been taken to select hunting-dogs." This
experiment is absolutely conclusive ; more so than those in which animals deprived of
the olfactory bulbs were shown to eat faBces without disgust, for this sometimes occurs in
dogs that have not been mutilated.

Comparative anatomy shows that the olfactory bulbs are generally developed in pro-
portion to the acuteness of the sense of smell. Pathological facts also show, in the
human subject, that impairment or loss of the olfactory sense is coincident with injury
or destruction of these ganglia. Numerous cases have been reported in which the sense
of smell was lost or impaired from injury to the olfactory nerves. In nearly all of the
cases on record, the general sensibility of the nostrils was not affected. In 1864, we had
an opportunity of examining the following very remarkable case of gunshot wound of the
head, in which, among other injuries, the sense of smell was destroyed :

The patient was a soldier, twenty-three years of age, who was shot through the head
with a rifle-ball, May 3, 1863. The ball entered on the left side, 1£ inch behind and £
of an inch below the outer canthus of the eye, emerging at nearly the corresponding
point on the opposite side. Small pieces of bone were discharged from time to time for
three months from openings in the posterior nares and the throat. He was examined
May 10, 1864, when the wounds had healed with falling in of the face over the left
malar and nasal bones. He had then entirely lost the power of distinguishing odors.
Upon applying acetic acid to the nostrils, he stated that he felt a prickling sensation, but
no odor. Dilute ammonia produced a warm sensation. Chloroform gave no sensation,
lie had no sensation from the emanations of flowers. There was loss of pi-m-i-al seii>i-
bility of the nasal mucous membrane on the left side, with diminished sensibility on the
right side. He had a sensation, not very definite, when in water-closets, where (as he
was told) the odor was very offensive, but he experienced no sensation unless the emana-
tions were very powerful. Before entering the army, he was a photographer l»y trade
and was familiar with the odors of acetic acid and ammonia. In this rase, it is almost
certain that the olfactory nerves had been divided, although other injuries undoubtedly
existed.

758 SPECIAL SENSES.

\

Mechanism of Olfaction.

There can be no doubt at the present day with regard to the mechanism of the sense
of smell. Substances endowed with odorous properties give off material emanations,
which must come in contact with the olfactory membrane before their peculiar odor is
appreciated. As we have seen, this membrane is situated high up in the nostrils, is
peculiarly soft, is provided with numerous glands, by the secretions of which its surface
is kept in proper condition, and it possesses the peculiar nerve-terminations of the olfac-
tory filaments.

In experimenting upon the sense of smell, it has been found quite difficult to draw the
exact line of distinction between impressions of general sensibility and those which attack
the special sense, or, in other words, between irritating and odorous emanations ; and
the vapors of ammonia, acetic acid, nitric acid, etc., undoubtedly possess irritating
properties which greatly overshadow their odorous qualities. It is unnecessary, in this
connection, to discuss the different varieties of odors recognized by some of the earlier
writers, as the fragrant, aromatic, fetid, nauseous, etc., distinctions sufficiently evident
from their mere enumeration ; and it is plain enough that there are emanations, like
those from delicately-scented flowers, which are easily recognizable by the sense of
smell while they make no impression upon the ordinary sensory nerves. The very
marked individual differences in the delicacy of the olfactory organs in the human sub-
ject and in different animals is an evidence of this fact. Hunting-dogs recognize odors
to which we are absolutely insensible ; and certain races of men are said to possess a
wonderful delicacy of the sense of smell. Like all of the other special senses, olfaction
may be cultivated by attention and practice, as is exemplified in the delicate discrimina-
tion of wines, qualities of drugs, etc., by experts.

After what we have said concerning the situation of the true olfactory membrane in
the upper part of the nasal fossa3 and the necessity of particles impinging upon this mem-
brane in order that their odorous properties may be appreciated, it is almost unnecessary
to state that the passage of odorous emanations to this membrane by inspiring through
the nostrils is essential to olfaction, so that animals or men, after division of the trachea,
being unable to pass the air through the nostrils, are deprived of the sense of smell. The
act of inhalation through the nose, when we wish to appreciate a particular odor, is an
illustration of the mechanism by which the odorous particles may be brought at will in
contact with the olfactory membrane.

It is a curious point to determine whether the sense of smell be affected by odors
passing from within outward through the nasal fossae. Persons who have offensive ema-
nations from the respiratory organs usually are not aware, from their own sensations,
of any disagreeable odor. This fact is explained by Longet on the supposition that the
olfactory membrane becomes gradually accustomed to the odorous impression, and there-
fore it is not appreciated. This is an apparently satisfactory explanation, for we could
hardly suppose that the direction of the emanations, provided they came in contact with
the membrane, could modify their effects. He cites a case of cancer of the stomach,
in which the vomited matters were exceedingly fetid. At first, the patient, when he
expired the gases from the stomach through the nostrils, perceived a disagreeable odor at
each expiration ; but little by little this impression disappeared.

Relations of Olfaction to the Sense of Taste. — The relations of the sense of smell to
gustation are very intimate. In the appreciation of delicate shades of flavor, it is well
known that the sense of olfaction plays so important a part, that it can hardly be sepa-
rated from gustation. The common practice of holding the nose when disagreeable
remedies are swallowed is another illustration of the connection between the two senses.
In most cases of anosmia, there is inability to distinguish delicate flavors ; and patients
can distinguish by the taste only sweet, saline, acid, and bitter impressions.

GUSTATION. 759

It is undoubtedly true that we lose the delicacy of the sense of taste when the sense
of smell is abolished. The experiment of tasting wines blindfolded and with the nostrils
plugged, and the partial loss of taste during a severe coryza, are sufficiently familiar illus-
trations of this fact. In the great majority of cases, when there is complete anosmia, the
taste is sensibly impaired; and, in cases in which this does not occur, it is probable
that the savory emanations pass from the mouth to the posterior portion of the nasal
fossae, and that here the mucous membrane is not entirely insensible to special impres-
sions.

It is unnecessary, in this connection, to describe fully the reflex phenomena which fol-
low impressions made upon the olfactory membrane. The odor of certain sapid sub-
stances, under favorable conditions, will produce an abundant secretion of saliva and even
of gastric juice, as has been shown by experiments upon animals. Other examples of the
effects of odorous impressions of various kinds are sufficiently familiar.

Gustation.

The special sense of taste enables us to appreciate what is known as the savor of cer-
tain substances introduced into the mouth; and this sense exists, in general terms, in
parts supplied by filaments from the lingual branch of the fifth and the glosso-pliaryngeal
nerves.

It is somewhat difficult to define precisely what is meant by savory substances. The
word savory is frequently used so as to include the quality of odor ; and, indeed, the
senses of gustation and olfaction are quite closely connected. Almost all substances that
affect the sense of taste possess a certain odor, and taste and smell are thus simultaneously
impressed. Medicinal articles of a disagreeable taste may sometimes be swallowed with-
out making a very disagreeable impression, if the nares be closed. Again, when the
nares are closed or when the sense of smell is rendered obtuse by an affection of the
Schneiderian membrane, it is difficult to distinguish delicate shades of flavor, as the differ-
ences in wines. This is a matter of common observation and remark. There are, also,
certain articles which have a repulsive odor, the taste of which is not disagreeable, such
as some varieties of old cheese. As a rule, however, ' articles agreeable to the taste pos-
sess an agreeable odor, and the senses of taste and smell are not'easily separated from
each other. These facts have led to a distinction — which cannot, however, be always
made with accuracy — between true tastes and flavors. It is assumed by some physiolo-
gists, that the true tastes are quite simple, presenting the qualities which we recognize as
sweet, acid, saline, and bitter ; while the more delicate shades of what are called flavors
nearly always involve olfactory impressions, which it is difficult to separate entirely from
gustation.

If we apply the term savor exclusively to the quality which makes an impression upon
the sense of taste, we recognize that the sensation is special in its character and different
from the tactile sensibility of the parts involved and from the sensation of temperature.
The terminal filaments of the gustatory nerves are impressed by the actual contact of
savory substances, which must, of necessity, be soluble. To a certain extent, there is a
natural classification of savors, some of which are agreeable, and others disagreeable ; but
even this distinction is modified by habit, education, and various other circumstances.
Articles that are unpleasant in early life often become agreeable in later years. Inasmuch
as the taste is, to some extent, an expression of the nutritive demands of the system, it is
found to vary under different conditions. Chlorotic females, for example, frequently
crave the most unnatural articles, and these morbid tastes may disappear under appro-
priate treatment. Inhabitant ; of the frigid zones seem to crave fatty articles and will
even drink rancid oils with avidity. Patients often become accustomed to the most dis-
agreeable remedies and take them without repugnance. Again, the most savory dishes
may even excite disgust, when the sense of taste has become cloyed, while abstinence

760 SPECIAL SENSES.

sometimes lends a delicious flavor to the simplest articles of food. The taste for certain
articles is certainly acquired, and this is almost always true of tobacco, now so largely
used in civilized countries.

Any thing more than the simplest classification of savors is difficult, if not impossible.
We recognize that certain articles are bitter or sweet, empyreumatic or insipid, acid or
alkaline, etc., but, beyond these simple distinctions, the shades of difference are closely
connected with olfaction and are too delicate and numerous for detailed description.
Many persons are comparatively insensible to nice distinctions of taste, while others recog-
nize with facility the most delicate differences. Strong impressions may remove, for a
time, the appreciation of less powerful and decided flavors. The tempting of the appetite
by a proper gradation of gustatory and odorous impressions is illustrated in the modern
cuisine, which aims at an artistic combination and succession of dishes and wines, so that
the agreeable sensations are prolonged to the utmost limit. This may often be regarded
as a violation of strictly hygienic principles, but it none the less exemplifies the cultiva-
tion of the sense of taste.

In discussing the physiology of taste, we shall avoid an elaborate and artificial classi-
fication of savory articles, arid shall use the terms sweet, acid, bitter, etc., as they are
commonly understood. We shall first describe the physiological anatomy and properties
of the gustatory nerves, and then consider the mechanism of gustation, the special organs
of taste, and the probable mode of connection between the organs of taste and the nerves.

Nerves of Taste. — Two nerves, the chorda tympani and the glosso-pharyngeal, preside
over the sense of taste. These nerves seem to be distributed to distinct portions of the
gustatory apparatus and to have somewhat different functions. The chorda tympani has
already been referred to as one of the branches of the facial ; the glosse-pharyngeal, one
of the nerves of the eighth pair, has not yet been described.

Chorda Tympani. — In the description we have given of the facial, the chorda tympani
is spoken of as the fourth branch. It passes through the tympanum, between the ossicles
of the ear, and joins the inferior maxillary division of the fifth, at an acute angle, between
the two pterygoid muscles, becoming so closely united with it that it cannot be followed
farther by ordinary dissection. (See Fig. 202, p. 622.) It is impossible to determine with
certainty from what root the filaments of this branch derive their origin, whether from
the main trunk or the intermediary nerve of Wrisberg; but experiments have shown that
it possesses functions entirely distinct from those of the other branches of the facial. The
lingual branch of the inferior maxillary division of the fifth has been called the gustatory
branch ; but this is an error ; for, as we shall see, the fifth has nothing to do with gusta-
tion, except that it is joined with filaments of the chorda tympani, which reach the tongue
through the lingual branch.

As regards the course of the filaments of the chorda tympani after this nerve has joined
the fifth, there can be no doubt, both from the effect upon taste and the alteration cf
the nerve-fibres following its division. Vulpian and Prevost, by the so-called Wallerian
method, after dividing the chorda tympani, found degenerated fibres at the terminations
of the lingual branch of the fifth in the mucous membrane of the tongue, the fibres being
examined ten days or more after the section. It is well known that, a number of days
after the section of a nerve, its fibres of distribution undergo change, and these observa-
tions leave no doubt of the fact that the chorda tympani is really distributed to the lingual
mucous membrane. Observations upon the sense of taste show that the chorda tympani
is distributed to about the anterior two-thirds of the tongue.

The general properties of the chorda tympani have only been ascertained by observa-
tions made after its paralysis or division. All experiments in which excitation has been
applied directly to the nerve in living animals have been negative in their results.
Longet states that, when the nerve has been isolated as completely as possible and all
reflex action is excluded, its galvanization produces no movement in the tongue.

GUSTATION. 761

It is now established beyond question that, in cases of facial palsy in which the lesion
affects the root so deeply as to involve the chorda tympani, there is loss of taste in the
anterior two-thirds of the tongue, tactile sensibility being unaffected; and numerous
cases illustrating this fact have been cited by various authors. Aside from cases of
paralysis of the facial with impairment of taste, in which the general sensibility of the
tongue is intact, numerous instances are on record of affections of the fifth pair, in \vhk-h
the tongue is absolutely insensible to ordinary impressions, the sense of taste being pre-
served. A number of such cases have been reported, which show conclusively that the
fifth pair presides over general sensibility only, and that it is not a gustatory nerve, except
by virtue of filaments derived from the chorda tympani.

Passing from the consideration of pathological cases to experiments upon living ani-
mals, the results are equally satisfactory. Although it is somewhat difficult to observe
impairment of taste in animals, Bernard and others have succeeded in training dogs and
cats so as to observe the effects of colocynth and various sapid substances applied to the
tongue. In a great number of experiments of this kind, it has been observed that, after
section of the chorda tympani or of the facial so as to involve the chorda tympani, the
sense of taste is abolished in the anterior two-thirds of the tongue on the side of the sec-
tion. However this result may be explained, the fact remains, that section of the nerve
in the lower animals is followed by the same results as those observed in pathological
observations. In a remarkable case reported by Moos, the introduction of an artificial
membrana tympani was followed by loss of taste upon the corresponding side of the
tongue, and upon both sides, .when a membrane was introduced into each ear. This dis-
appeared when the membranes were removed, and the phenomena were referred to
pressure upon the chorda tympani. Experimenters are somewhat at variance with
regard to the effects observed upon animals, some asserting that the sensations of taste
are simply delayed in their manifestation ; but we must remember the difficulty of such
observations, and we are to rely mainly upon the unmistakable phenomena noted in
cases of affection of the chorda tympani in the human subject.

It seems tolerably certain, first, that the gustatory filaments of the lingual branch of
the fifth are derived exclusively from the chorda tympani ; second, that the chorda tym-
pani, viewed as a gustatory nerve, is really a branch of the facial ; third, that many cases
of paralysis of the entire large root of the fifth, in the human subject, present loss of
general sensibility in the tongue and no alteration of taste ; and fourth, that paralysis ot
the facial, behind the origin of the chorda tympani, is attended with loss of taste in the
anterior two-thirds of the tongue, without any affection of the general sensibility of this
organ.

As a summary of our knowledge regarding the gustatory properties of the anterior
two-thirds of the tongue, certainly in the human subject, it may be stated without
reserve, that these properties depend upon the chorda tympani, its gustatory filaments
being derived from the facial and taking their course to the tongue with the lingual
branch of the inferior maxillary division of the fifth. In addition, the lingual branch of
the fifth contains filaments, derived from the largo root of this nerve, which endow the
mucous membrane with general sensibility.

Glosso-Pharyngeal Nerve (First Division of tJie Eighth).— The plosso-ph.-iryn.
distributed to those portions of the gustatory mucous membrane not supplied by filaments
from the chorda tympani. It is undoubtedly a nerve of taste; and the .pn-Mion of its
other functions will be fully considered in connection with its general properties as well
as the differences between this nerve and the chorda tympani. We have mentioned this
nerve in another chapter as the first division of the eighth pair according to the classifi-
cation of Willis, but we have to treat of its physiological anatomy in this connection, as
its most important function is in connection with gustation.

Physiological Anatomy of the Glosso-Pharyngeal.—Wiz apparent origin of the _
pharyngeal is from the groove between the lateral tracts of the medulla oblongata and

762

SPECIAL SENSES.

the inferior peduncle of the cerebellum, between the roots of the auditory nerve above
and the pneumogastric below. A number of its filaments of origin come from the
medulla and a portion from the peduncle. The deep origin is nearly the same as that of
the pneumogastric, its filaments arising primarily from the gray substance of the medulla
oblongata. From this origin, the filaments pass forward and outward to the posterior
foramen lacerum, which the nerve enters in company with the pneumogastric, the spinal
accessory, and the internal jugular vein. At the upper portion of the foramen, is a small
ganglion, the jugular ganglion, including only a portion of the root. Within the foramen,
is the main ganglion, including all of the filaments of the trunk, called the petrous gan-
glion, or the ganglion of Andersch, after the anatomist by whom it was first described.

At or near the ganglion of Andersch, the glosso-pharyngeal usually receives a delicate
filament from the pneumogastric. This communication is sometimes wanting. The
same may be said of a small filament passing to the glosso-pharyngeal from the facial,
which is not constant. Branches from the glosso-pharyngeal go to the otic ganglion and
to the carotid plexus of the sympathetic.

FIG. <%&.— Glosso-pharyngeal nerve, (Sappey.)

1. large root of the fifth nerve : 2, ganglion of Gasser ; 3, ophthalmic division of the fifth ; 4, superior maxillary division ;
5, inferior maxillary division ; 6, 10, lingual branch of the fifth, containing the filament* of the chorda tym-
pani ; 7, branch from the sublingual to the lingual branch of the fifth ; 8, chorda tympani ; 9, inferior dental
nerve; 11, submaxillary ganglion; 12, mylo-hyoid branch of the inferior dental nerve; 13, anterior belly of the
digastric muscle ; 14, section of the mylo-hyoid muscle ; 15, 18, glosso-pharyngeal nerve; 16, ganglion of An-
dersch; 17, brandies from the glosso-pharyngeal to the stylo-glossus and the sti/lo-pharyngeus muscles;
19, 19, pneumogastric; 20, 21, ganglia of the pneumogastric ; 22, 22, superior laryngeal nerve ; 23, spinal accessory ;
24, 25, 26, 27, 28, sublingual nerve and branches.

The distribution of the glosso-pharyngeal is quite extensive. The tympanic branch,
the nerve of Jacobson, arises from the anterior and external part of the ganglion of
Andersch, and enters the cavity of the tympanum, where it divides into six branches.
Of these six branches, two posterior are distributed to the mucous membrane of the
fenestra rotunda and the membrane surrounding the fenestra ovalis ; two anterior are

GUSTATION. 763

distributed, one to the carotid canal, where it anastomoses with a branch from the supe-
rior cervical ganglion, and the other to the mucous membrane of the Eustachian tube ;
two superior branches are distributed to the otic ganglion and, as is stated by some anat-
omists, to the spheno-palatine ganglion.

A little below the posterior foramen lacerum, the glosso-pharyngeal sends branches
to the posterior belly of the digastric and to the stylo-hyoid muscle. There is also a
branch which joins a filament from the facial to the stylo-glossus.

Opposite the middle constrictor of the pharynx, three or four branches join branches
from the pneumogastric and the sympathetic to form together the pharyngeal plexus.
This plexus contains numerous ganglionic points, and filaments of distribution from the
three nerves go to the mucous membrane and to the constrictors of the pharynx. Prob-
ably, the mucous membrane is supplied by the glosso-pharyngeal. As we have stated in
another chapter, it is probable that the muscles of the pharynx are supplied by filaments
from the pneumogastric, which are originally derived from the spinal accessory.

Near the base of the tongue, branches are sent to the raucous membrane covering the
tonsils and the soft palate.

The lingual branches penetrate the tongue about midway between its border and
centre and are distributed to the mucous membrane at its base, being probably connected
with the papillae.

General Properties of the Glosso- Pharyngeal. — As in the case of other sensory nerves
emerging from the cranial cavity, it is important, in studying the general properties of
the glosso-pharyngeal, to make our observations under certain conditions. First, it must
be remembered that this nerve contracts anastomoses a short distance from its origin.
As we desire to know the properties of the original filaments of the nerve, we must
operate upon it before it has received communicating fibres. Next, in irritating sensory
nerves, we are liable to produce reflex contractions. To avoid this, the nerve must be
divided, when the reflex contractions will only follow stimulation of the central end. It
is probably from a neglect of these essential experimental conditions, that the results of
direct observation have been so discordant in the hands of different physiologists.

To begin with, we shall assume that the glosso-pharyngeal nerve must be irritated be-
tween its origin and the ganglion of Andersch, in order to avoid anastomosing filaments
from motor nerves, and that the nerve must be divided and irritation be applied to its
peripheral end, to avoid reflex movements. Assuming these conditions as essential, we
can discard most of the earlier experiments, as open to the objections we have mentioned.
Longet, operating upon horses and dogs, after removal of the cerebral lobes and division of
the glosso-pharyngeal, found that galvanization of the peripheral extremity of the nerve
did not produce movements of the palate or pharynx; and, from these experiments, ho
concludes that the nerves are exclusively sensory at their roots, or, at least, that they do
not contain motor filaments. In another chapter, under the head of movements of the
palate and uvula, we have cited in detail a series of experiments which illustrate tho
reflex movements of the velum palati through the facial, produced by galvanization of
the glosso-pharyngeal. As a complement to the first experiments of Longet, just cited,
the same observer noted contractions of the pharyngeal muscles following galvanization
of the peripheral end of the divided nerve in the neck, which could only be produced by
the action of motor anastomosing filaments.

As regards general sensibility, there can be no doubt of the fact that tho g
pharyngeal is sensory, although its sensibility is somewhat obtuse. In tho experiment! in
which the nerve has seemed to be insensible to ordinary impressions, it is ].r«.bal»le that
the animals operated upon had been exhausted more or less by pain and loss of blood in
the operation of exposing the nerve, which, it is well known, abolish the sensibility of
some of the nerves. Longet states distinctly that, unless the animals (dogs) IK- aliva.ly
oxhausted by resistance during the operation, they have always appeared to sutler pain
on pinching or dividing the glosso-pharyngeal.

764 SPECIAL SENSES.

Experiments upon the glosso-pharyngeal are not very definite and satisfactory in their
results as regards the general sensibility of the base of the tongue, the palate, and the
pharynx. The sensibility of these parts seems to depend chiefly upon brandies of the fifth
passing to the mucous membrane through Meckel's ganglion. Experiments show, also,
that the reflex phenomena of deglutition take place mainly through these branches of the
fifth, and that the glosso-pharyngeal has little or nothing to do with the process. In fact,
after division of both glosso-pharyngeal nerves, deglutition does not seem to be affected.

With these remarks, we dismiss the functions of the glosso-pharyngeals as nerves of
general sensibility and shall consider in detail their relations to the sense of taste.

Relations of the Glosso-Pharyngeal Nerves to Gustation. — Eelying upon experiments
on the inferior animals, particularly dogs, it seems pretty certain that there are two
nerves presiding over the sense of taste : The chorda tympani gives this sense to the
anterior portion of the tongue exclusively, probably the anterior two-thirds ; the glosso-
pharyngeal supplies this sense to the posterior portion of the tongue ; the chorda tympani
seems to have nothing to do with general sensibility ; while the glosso-pharyngeal is an
ordinary sensory nerve, as well as a nerve of special sense.

Where there are such differences in the delicacy of the sense of taste as exist usually
in different individuals, it must be difficult to describe with accuracy delicate shades of
savor, particularly in alimentary substances ; but the distinct impressions of acidity or
bitter quality are easily recognizable. It is certain, however, that saline, acid, and styptic
tastes are best appreciated through the chorda tympani, and that sweet, alkaline, bitter,
and metallic impressions are received mainly by the glosso-pharyngeal.

Mechanism of Gustation.— The mode in which sapid substances are brought in con-
tact with the organ of taste is so simple, that we need only allude to it, before we study
the anatomy of the parts directly concerned and their connections with the terminal
filaments of the gustatory nerves. In the first place, the articles which make the special
impression are in solution; introduced into the mouth, they increase the flow of saliva,
the reflex action involving chiefly the submaxillary and sublingual glands ; there is usu-
ally more or less mastication, which increases the flow of the parotid saliva ; and, during
the acts of mastication and the first stages of deglutition, the sapid substances are dis-
tributed over the gustatory membrane, so much so, indeed, that it is difficult to exactly
locate the seat ot the special impression. In this way, by the movements of the tongue,
aided by an increased flow of saliva, the actual contact of the savory articles is rapidly
effected. The thorough distribution of these substances over the tongue and the mucous
membrane of the general buccal cavity leads to a certain amount of confusion in our
appreciation of the special impressions ; and, in order to ascertain if different portions
of the membrane possess different properties, it is necessary to make careful experiments,
limiting the points of contact as closely as possible. This has been done, with the result
of showing that the true gustatory organ is quite restricted in its extent, and, as such, it
demands special anatomical description.

Physiological Anatomy of the Organ of Taste. — Recent anatomical and physiological
researches have shown that, at least in the human subject, the organ of taste is probably
confined to the dorsal surface of the tongue. When we examine the structure of the
mucous membrane of the mouth, tongue, and palate, we find that the upper surface of
the tongue presents numerous papillae, called, in contradistinction to the filiform papilla,
fungiform and circumvallate. These are not found on its under surface or anywhere
except on the superior portion. It is now pretty well established that the circumvallate
and fungiform papillae alone are the organs of taste. Camerer, in some recent experi-
ments upon the gustatory organs by the application of solutions to different parts through
fine glass tubes, concluded that the parts around a papilla have no gustatory sensibility, but
that different savors can be distinguished when a single papilla is touched. These obser-
vations give a new importance to the peculiar papillae of the tongue, and we therefore
present a description of their arrangement and structure.

GUSTATION.

765

In Fig. 236, which represents the dorsal surface of the tongue, the large, circumvallate
papillae, which usually number from seven to twelve, are seen in the form of a V, occu-
pying the base of the tongue. The fungiform papillae are scattered over the surface but
are most numerous at the point and near the borders. Both of these varieties of papillae
are distinguishable by the naked eye.

The circumvailate papilloe are simply enlarged fungiform papillae, each one surrounded
by a circular ridge, or wall, and covered by numerous small, secondary papillae. The
fungiform papillee have a short, thick pedicle and enlarged, rounded extremities. Accord-

FIG. 236.— Papillae, of the tongue. (Sappey.)

1, 1, circumvallate papilla; 2, median circumvallate papilla, which entirely fills the foramen caecum; 8, 8, 8, 8, fungi-
form papilla; 4, 4, filiform papillae; 5, 5, vertical folds and furrows of the border of the tongue; C, 6, 6, 6, glands at
the base of the tongue ; 7, 7, tonsils; 8, epiglottis; 9, median glosso-epiglottidean fold.

ing to Sappey, from one hundred and fifty to two hundred of these can easily he counted.
These, also, present secondary papilla) on their surface. When the mucous membrane of
the tongue is examined with a low magnifying power, particularly after maceration in
acetic or dilute hydrochloric acid, their structure is readily observed. They are abun-
dantly supplied with blood-vessels and nerves.

Taste- Buds, or Taste-Beakers.— A few years ago, Lov6n and, a little later, Schwalbo
described, under these names, peculiar structures, which are supposed to be the true

766

SPECIAL SENSES.

organs of taste. They are found on the lateral slopes of the circumvallate papilla and
occasionally on the fungiform papill®. The structure of these organs is very simple.
They consist of flask-like collections of spindle-shaped cells, which are received into little
excavations in the epithelial covering of the mucous membrane, the bottom resting upon
the connective-tissue layer. Their form is ovoid, and, at the neck of the flask, is a

FIG. 237. FIG. 238.

Varieties of papillae of the tongue. (Sappey.)

Fig. 237. — Medium-sized circumvallate papilla: 1, papilla, the base only being apparent: it is seen that the base is
covered with secondary papillae ; 2, groove between the papilla and the surrounding wall ; 3, 3, wall of the papilla.
Fig. 2-38. — Fungiform, filiform, and hemispherical papilla? : 1, 1, two fungiform papillae, covered with secondary pa-
pillae; 2, 2, 2, filiform papilla? ; 8, a filiform papilla, the prolongations of which are turned outward; 4. a filiform
papilla, with vertical prolongations ; 5, 5, small filiform papillae, with the prolongations turned inward ; 6, 6, fili-
form papilla?, with striations at their bases ; 7, 7, hemispherical papilla?, slightly apparent, situated between the
fungiform and the filiform papillae.

rounded opening, called the taste-pore. Their length is from -g-^ to -5^-5-, and their trans-
verse diameter, about -$±-$ of an inch. The cavity of the taste-beakers is filled with cells,
of which two kinds are described. The first variety, the outer cells, or the cover-cells,
are spindle-shaped, and curved to correspond to the wall of the beaker. These come to
a point at the taste-pore. In the interior of the beaker, are elongated cells, with large,
clear nuclei, which are called taste-cells. It is supposed that nerve-fibrils are connected

directly with these cells. As far as we

can learn, the only reason why these
structures are connected with the physi-
ology of gustation is on account of their
anatomical relations to the gustatory
papillas.

It now remains only to note the ulti-
mate distribution of the nerves in the-
gustatory organ. Upon this point, ana-
tomical researches are not entirely sat-
isfactory. However, the following de-
scription, by Elin, may be regarded as
probably correct, although the facts
have not been absolutely demonstrated.
According to this authority, from the submucous tissue, small nerve-branches pass per-
pendicularly to the upper layer of the membrane. These fibres have a varicose appear-
ance. In the most superficial layer of the mucous membrane, there is a net-work of fine,
non-medullated fibres ; and, from this net- work, branches follow the blood-vessels into the
papillss and penetrate the epithelium. Sometimes, though more seldom, they pass into
the epithelium lying between the papilla. In this layer, there are branches which end,
some in nerve-cells, and some taking a winding course and passing into neighboring

FIG. 239.— Taste-buds from the lateral taste-organ of the
rabbit. (Engelmann.)

PHYSIOLOGICAL ANATOMY OF THE OPTIC NERVES. 767

fibres. These descriptions are from preparations made with chloride of gold ; but the
plates by which they are illustrated are somewhat unsatisfactory.

According to the views of those who have described the so-called taste-beakers, sapid
solutions find their way into the interior of these structures through the taste-pores and
come in contact with what have been called the taste-cells, these structures being directly
connected with the terminal filaments of the gustatory nerves.

CHAPTER XXIV.

VISION.

General considerations— Physiological anatomy and general properties of the optic nerves— Physiological anatomy of
the eyeball — Sclerotic coat— Cornea — Membrane of Descemet, or of Demours — Ligamentum iridis pectinatum —
Choroid coat — Ciliary processes — Ciliary muscle — Iris — Pupillary membrane — Retina — Crystalline lens — Aqueous
humor — Chambers of the eye — Vitreous humor— Summary of the anatomy of the globe — The eye as an optical
instrument— Laws of refraction, dispersion, etc., bearing upon the physiology of vision— Theories of light— Re-
fraction by lenses— Myopia and hypermetropia— Formation of images in the eye— Mechanism of refraction in the
eye — Astigmatism — Movements of the iris — Direct action of light upon the iris — Action of the nervous system upon
the iris — Mechanism of the movements of the iris — Accommodation of the eye to vision at different distances —
Changes in the crystalline lens in accommodation— Action of the ciliary muscle— Changes in the iris in accom-
modation—Erect impressions produced by images inverted upon the retina— Single vision with both eyes— Cor-
responding points — The horopter — Appreciation of distance and of the form of objects — Mechanism of the stereo-
scope— Duration of luminous impressions— Irradiation — Movements of the eyeball — Muscles of the eyeball — Parts
for the protection of the eyeball— Eyelids— Muscles which open and close the eyelids— Conjunctival mucous
membrane — Lachrymal apparatus — Composition of the tears.

THE chief important points to be considered in the physiology of vision are the fol-
lowing :

1. The physiological anatomy and the general properties of the optic nerves.

2. The physiological anatomy of the parts essential to correct vision.

3. The laws of refraction, diffusion, etc., bearing upon the physiology of vision.

4. The action of the different parts of the eye in the production and appreciation of
correct images.

5. Binocular vision.

6. The physiological anatomy and the functions of accessory parts, as the muscles
which move the eyeball.

7. The physiological anatomy and the functions of the parts which protect the eye, as
the lachrymal glands, eyelids, etc.

Physiological Anatomy of the Optic Nerves. — The optic nerves, or optic tracts, take
their origin, each by two principal roots of white matter and a few filaments from what is
described as the gray root, chiefly from the tubercula quadrigemina, but in part from
those portions of the encephalon over which the nerves pass to go to the eyes. The
internal white root arises from the posterior, and the external white root, which is the
larger, from the anterior tuberculum. The gray root is situated in front of and above
the optic commissure and is a dependence of the gray matter which eovers the internal
surface of the optic thalamus. It arises from the gray matter which constitute- tin.- ante-
rior floor of the third ventricle, in the form of delicate filaments which join the optic
nerves at this point.

The apparent origin of the optic nerves is from the tubercula quadripeniina, receiving
filaments from the corpora geniculata, the optic thalami, the peduncles of the cerebrum,
the anterior substantia perforata, the tuber cinereum, and the lamina terminalis. It has
thus far been found impossible to trace all these roots to their true origin in the cerebral
substance ; but experiments upon the lower animals, in which it has been shown that

768

SPECIAL SENSES.

the sense of sight is completely abolished by destruction of the angular convolution of
the cerebrum, show that the true origin of the filaments that preside over vision is, in all
probability, from this portion of the cerebral hemispheres.

The two principal roots of the optic nerves unite
above the external corpus geniculatum, forming a
flattened band, which takes an oblique course around
the under surface of the crus cerebri to the optic
commissure. This is usually called the optic tract,
in contradistinction to the optic nerve, which is de-
scribed as arising from the optic commissure.

The optic commissure, or chiasm, is situated just in
front of the corpus cinereum, resting upon the olivary
process of the sphenoid bone. As its name implies,
this is the point of union between the nerves of the
two sides. At the commissure, the fibres from the
optic tracts take three directions ; and, in addition,
the commissure contains filaments passing from one
eye to the other, which have no connection with the
optic tracts. The four sets of fibres in the optic
commissure are the following :

1. Decussating fibres, passing from the optic
tract upon either side to the eye of the opposite
side. The greatest part of the fibres take this direc-
tion. Their relative situation is internal.

2. External fibres, much fewer than the preced-
ing, which pass from the optic tract to the eye upon
the same side.

3. Fibres, situated on the posterior boundary of
the commissure, which pass from one optic tract to
the other and do not go to the eyes. These fibres
are scanty and are sometimes wanting.

4. Fibres, situated on the anterior border of the commissure, greater in number than the
preceding, which pass from one eye to the other and which have no connection with the
optic tracts.

It is probable, reasoning chiefly from cases of cerebral injury or disease, that the fila-
ments from the optic tracts upon the two sides are connected with distinct portions of
the retina ; and two pathological cases have lately been reported by Drs. Keen and

Thomson, of Philadelphia, which go to show that this is
the fact, and which illustrate certain interesting points
in connection with the decussation of the nerves. One
was a case of gunshot-wound of the head, with severe
injury of the brain-substance. This case presented, im-
mediately after the injury, unconsciousness and partial
paralysis of the right arm and right leg, which lasted two
or three months. About a year after, the paralysis had
almost entirely disappeared, but the memory was some-
what impaired. Upon careful examination of the eyes, it
was ascertained that the field of vision was divided in
each eye by a vertical line passing through its centre.
In the right eye, the inner half of the retina, beginning on
a line with the inner border of the macula lutea, was entirely insensible to light. In
the left eye, the outer half of the retina, beyond the macula, was insensible to light. No
pathological appearances were observed upon examining the retina) with the ophthalmo-

FIG. 240.— Optic tracts, commissure, and
nemes. (Hirschfeld.)

1, infundibulum ; 2, corpus cinerewn ; 3,
corpora albicantia; 4, cerebral pedun-
cle ; 5, tuber annulare ; 6, optic tracts
and nerves, decussating at the commis-
sure, or chiasm; 7, motor oculi com-
munis ; 8, patheticus ; 9, fifth nerve ; 10,
motor oculi externus ; 11, facial nerve ;
12, auditory nerve; 13, nerve of Wris-
berg; 14, glosso-pharyngeal nerve; 15,
pnemnogastric ; 10, spinal accessory; 17,
sublingual nerve.

FIG. 241. — Diagram of the decussation

at the optic commissure.
The dotted lines show the four direc-
tions of the fibres.

GENERAL PROPERTIES OF THE OPTIC NERVES. 769

scope. The second case, reported by Dr. "W. Thomson, presented the same condition
following partial hemiplegia, the result of sunstroke. The peculiar affection of vision in
these cases, called hemiopsia, especially as illustrated in the first case, reported by Dr.
Keen, can be explained by assuming the following as the course of the decussating fibres
of the optic tracts : From the left side of the encephalon, visual fibres pass to the right
eye, supplying the inner mathematical half of the retina, from a vertical line passing
through the macula lutea. Visual fibres also pass to the left eye, supplying the outer
half of the retina, beginning at the macula lutea. The macula lutea, then, and not the
point of entrance of the optic nerve, is in the line of division of the visual field. The
outer half of the left and the inner half of the right retina are supplied by fibres from the
left side ; and the outer half of the right and the inner half of the left retina are sup-
plied from the right side. Although this anatomical arrangement has not been actually
demonstrated, it is rendered exceedingly probable by pathological cases like those just
cited. In the case reported by Dr. Keen, the left side of the brain was injured, as the
paralysis occurred in the right leg and arm.

With the exception of the few filaments derived from what have been described as the
gray roots, the fibres of the optic tracts and the optic nerves are of the medullated variety,
and they present no differences in structure from the ordinary cerebro-spinal nerves.

The optic commissure is covered with a fibrous membrane and is consequently more
resisting than the optic tracts. From its anterior and outer border, arise the optic nerves,
which take a curved direction to the eyes. The nerves are rounded and are enclosed in
a double fibrous sheath derived from the dura mater and the arachnoid. They pass into
the orbit upon the two sides by the optic foramina and penetrate the sclerotic at the
posterior, inferior, and internal portion of the globe. As the nerves enter the globe, they
lose their coverings from the dura mater and arachnoid. The sheath derived from the
dura mater is adherent to the periosteum of the orbit at the foramen opticum, and, when
it reaches the globe, it fuses with the sclerotic coat. Just before the nerves penetrate the
globe, they each present a well-marked constriction. At the point of penetration, there
is a thin but strong membrane, presenting numerous perforations for the passage of the
nervous filaments. This membrane, the lamina cribrosa, is in part derived from the
sclerotic, and in part, from the coverings of the individual nerve-fibres, which lose their
investing membranes at this point. In the interior of each eye, there is a little, mammil-
lated eminence, formed by the united fibres of the nerve. The retina, with which the
optic nerve is connected, will be described as one of the coats of the eye.

In the centre of the optic nerve, is a minute canal, lined by fibrous tissue, in which are
lodged the central artery of the retina and its corresponding vein, with a delicate nervous
filament from the ophthalmic ganglion. The vessels penetrate the optic nerve a short
distance (from $ to £ of an inch) behind the globe. The central canal does not exist
behind these vessels.

General Properties of the Optic Nerves.— There is very little to be said regarding the
general properties of the optic nerves, except that they are undoubtedly the only nerves
capable of conveying to the cerebrum the special impressions of sight, and that they are
not endowed with general sensibility.

That the optic nerves are the only nerves of sight, there can be no doubt. Their
division or injury always involves loss or impairment of vision, directly ooTBWpOBding
with the lesion. It is interesting, however, to note that they are absolutely insensible to
ordinary impressions. "We can, in a living'animal, pinch, cauterize, cut, destroy in any
way the optic nerve without giving rise to the slightest painful sensation ; whether it be
taken before or after its decussation, it seems completely insensible in its entire length.'"
(Longet.)

Not only are the optic nerve and retina insensible to pain, but any irritation produce
the impression of light. This wa» stated in the remarkable paper, Idea of a '»my

49

770

SPECIAL SENSES.

of the Erain, printed by Charles Bell, in 1811. A few years later, Magendie, in operating
for cataract, passed the needle to the bottom of the eye and irritated the retina, in two
persons. The patients experienced no pain but merely an impression of flashes of light.
The insensibility of the optic nerves has also been repeatedly noted in surgical operations
in which the nerves have been exposed. If a current of galvanism be passed through the
optic nerves, a sensation of light is experienced. The same phenomenon is observed when
the eyeball is pressed upon or contused, a fact which is sufficiently familiar.

Physiological Anatomy of the Eyeball.

The eyeball is a spheroidal body, partially embedded in a cushion of fat in the orbit,
protected by the surrounding bony structures and the eyelids, its surface bathed by the
secretion of the lachrymal gland, and movable in various directions by the action of cer-
tain muscles. When the axis of the eye is directed forward, the globe has the form of a
sphere in its posterior five-sixths, with the segment of a smaller sphere occupying its
anterior sixth. The segment of the smaller sphere, bounded externally by the cornea, is
more prominent than the rest of the surface.

The eyeball is made up of several coats enclosing certain refracting media. The exter-
nal coat is the sclerotic, covering the posterior five-sixths of the globe, which is continuous
with the cornea, covering the anterior sixth. This is a dense, opaque, fibrous membrane,
for the protection of the inner coats and the contents of the globe. The cornea is dense,
resisting, and perfectly transparent. The muscles that move the globe of the eye are
attached to the sclerotic coat.

Were it not for the prominence of the cornea, the eyeball would present very nearly
the form of a perfect sphere, as will be seen by the following measurements of its various
diameters; but the prominence of its anterior sixth gives the greatest diameter in the
antero-posterior direction.

The form and dimensions of the globe are subject to considerable variations after
death, by evaporation of the humors, emptying of vessels, etc., and there is no way in
which the normal conditions can be restored. The most exact measurements are those
made by Sappey. As an illustration of the post-mortem changes in the eye, Sappey men-
tions comparative measurements made three hours and twenty-four hours after death, the
results of which presented very considerable differences.

In measurements made by Sappey, apparently with great care and accuracy, from one
to four hours after death, bf the eyes of twelve adult females and fourteen adult males of
different ages, the following mean results were obtained :

Subjects examined.

Diameters (inch).

Ant. -post.

Transverse.

Vertical.

Oblique.

Mean of 12 females, from 18 to 81 years of age

0-941
0-968

0'911
0-941

0-905
0-925

0-987
0-949

Mean of 14 males, from 20 to 79 years of age

From these results, it is seen that all the diameters are less in the female than in the
male. The antero-posterior diameter is the greatest of all, and the vertical diameter is
the shortest. The measurements at different ages, not cited in the table just given, show
that the excess of the antero-posterior diameter over the others is diminished by age.

Sclerotic Coat. — The sclerotic is the dense, opaque, fibrous covering of the posterior
five-sixths of the eyeball. Its thickness is different in different portions. At the point
of penetration of the optic nerve, it measures -fa of an inch. It is thinnest at the middle
portion of the eye, measuring about -^ of an inch, and is a little thicker again near the
cornea. This membrane is composed chiefly of bundles of ordinary connective tissue.

PHYSIOLOGICAL ANATOMY OF THE EYEBALL. 771

The fibres are slightly wavy, and arranged in flattened bands, which are alternately longi-
tudinal and transverse, giving the membrane a lamellated appearance, although it cannot
be separated into distinct layers. Mixed with these bands of connective-tissue fibres, are
numerous small fibres of elastic tissue. The vessels of the sclerotic are scanty. They are
derived from the ciliary vessels and the vessels of the muscles of the eyeball. The tissue
of the sclerotic yields gelatine on boiling.

Cornea. — The cornea is the transparent membrane which covers about the anterior
sixth of the globe of the eye. As before remarked, this is the most prominent portion of
the eyeball. It is in the form of a segment of a sphere attached by its borders to the
segment of the larger sphere formed by the sclerotic. The thickness of the cornea is
about gV of an inch in its central portion, and about -^ of an inch near its periphery. Its
substance is composed of transparent fibres, arranged in incomplete layers, something like
the layers of the sclerotic. It yields chondrine, instead of gelatine, on boiling.

Upon the external, or convex surface of the cornea, are several layers of delicate,
transparent, nucleated epithelium. The most superficial cells are flattened, the middle
cells are rounded, and the deepest cells are elongated and arranged perpendicularly.
These cells become slightly opaque and whitish after death. Just beneath the epithelial
covering of the cornea, is a very thin, transparent membrane, described by Bowman
under the name of the " anterior elastic lamella." This membrane, with its cells, is a
continuation of the conjunctiva.

The proper corneal membrane is composed of excessively pale, flattened bundles of
fibres, interlacing with each other in every direction. Their arrangement is lamellated,
although they cannot be separated into complete and distinct layers. Between the bun-
dles of fibres, lie a great number of stellate, anastomosing, connective-tissue corpuscles.
In these cells and in the intervals between the fibres, there is a considerable quantity of
transparent liquid. The fibres constituting the substance of the cornea are continuous
with the fibrous structure of the sclerotic, from which they cannot be separated by
maceration. At the margin of the cornea, the opaque fibres of the sclerotic abruptly
become transparent. The corneal substance is very tough, and it will resist a pressure
sufficient to rupture the sclerotic.

Upon the posterior, or concave surface of the cornea, is the membrane of Descemet,
or of Demours. This is elastic, transparent, structureless, rather loosely attached, and
covered with a single layer of regularly polygonal, nucleated epithelium. At the circum-
ference of the cornea, a portion of this membrane passes to the anterior surface of the
iris, in the form of numerous processes which constitute the ligamentum iridis pectinatum,
a portion passes into the substance of the ciliary muscle, and a portion is continuous
with the fibrous structure of the sclerotic.

In the adult, the cornea is almost without blood-vessels, but in foetal life it presents
a rich plexus extending nearly to the centre. These disappear, however, before birth,
leaving a very few delicate, looped vessels at the extreme edge.

A great deal of anatomical interest has lately been attached to the cornea, from
researches showing the termination of the fine nerve-fibres in the nuclei of the posterior
layer of the epithelium of its convex surface and the investigation of the " lymph-spaces"
by the use of certain reagents, the demonstration of the so-called " wandering cells"
etc., points that we do not propose to consider. It is well known that the surface of the
cornea is exquisitely sensitive.

Choroid Coat.— Calling the sclerotic and the cornea the first coat of the cyrl.all, the
second is the choroid, with the ciliary processes, the ciliary muscle, and the iris,
was called by the older anatomists the uvea, a name which was later applied, sometimes
to the entire iris, and sometimes to its posterior, or pigmentary layer. Wo shall describe,
however, the choroid and ciliary processes together as the second coat, and then take up
the ciliary muscle and the iris.

772 SPECIAL SENSES.

The choroid is distinguished from the other coats of the eye by its dark color and its
great vascularity. It occupies that portion of the eyeball corresponding to the sclerotic.
It is perforated posteriorly by the optic nerve and is connected in front with the iris.
It is very delicate in its structure and is composed of two or three distinct layers. Its
thickness is from yfg- to ^ of an inch. Its thinnest portion is at about the middle of the
eye. Posteriorly it is a little thicker. Its thickest portion is at its anterior border.

The external surface of the choroid is connected with the sclerotic by vessels, nerves
(the long ciliary arteries and the ciliary nerves), and very loose connective tissue. This
is sometimes called the membrana fusca, although it can hardly be called a distinct layer.
It contains, in addition to the vessels, nerves, and fibrous tissue, a few irregularly-shaped
pigment-cells.

FIG. 242.—C1ioroid coat of the eye. (Sappey.)

1, optic nerve ; 2, 2, 2, 2, 3, 3, 3, 4, sclerotic coat, divided and turned back to show the choroid ; 5, 5, 5, 5, the cornea,
divided into four portions and turned back ; 6, 6, canal of Schlemm ; 7, external surface of the choroid, traversed
by the ciliary nerves and one of the long ciliary arteries ; 8, central vessel into which open the vasa vorticosa; 9,
9, 10, 10, choroid zone ; 11. 11. ciliary nerves; 12, long ciliary artery ; 13, 13, 13, 13, anterior ciliary arteries ; 14, iris ;
15, 15, vascular circle of the iris ; 16, pupil.

The rest of the choroid is composed of two distinct layers ; viz., an external, vascular,
and an internal, pigmentary layer. The vascular layer consists of numerous arteries, veins,
and capillaries, arranged in a peculiar manner. The layer of capillary vessels, which is
internal, is sometimes called the middle layer of the choroid, or the tunica Ruyschiana.
The arteries, which are derived from the posterior short ciliary arteries and are connected
with the capillary plexus, lie just beneath the pigmentary layer. The plexus of capilla-
ries is closest at the posterior portion of the membrane. The veins are external to the
other vessels. They are very numerous and are disposed in curves converging to four
trunks. This arrangement gives the veins a very peculiar appearance, and they have
been called the vasa vorticosa. The pigmentary portion is composed, over the greatest
part of the choroid, of a single layer of regularly polygonal cells, somewhat flattened,
measuring from ^-^ to y^Vs- of an mcn in diameter. These cells are filled with pig-
mentary granulations of uniform size, and they give to the membrane its characteristic
dark-brown or chocolate color. The pigmentary granules in the cells are less numerous
near their centre, where a clear nucleus can readily be observed. In the anterior por-
tion of the membrane, in front of the anterior limit of the retina, the cells are smaller,
more rounded, more completely filled with pigment, and present several layers. Beneath
the layer of hexagonal pigment-cells, the intervascular spaces of the choroid are occupied
by stellate pigment-cells.

PHYSIOLOGICAL ANATOMY OF THE EYEBALL.

773

Ciliary Processes. — The anterior portion of the choroid is arranged in the form of
folds or plaits projecting internally, called the ciliary processes. The largest of these
folds are about TV of an inch in length. They are from sixty to eighty in number. The
larger folds are of nearly uniform size and are regularly arranged around the margin of
the crystalline lens. Between these folds, which constitute about two-thirds of the entire
number, are smaller folds, lying, without any regular alternation, between the larger.
Within the folds, are received corresponding folds of the thick membrane, continuous an-
teriorly with the hyaloid membrane of the vitreous humor, called the zone of Zinn.

The ciliary processes present blood-vessels, which are somewhat larger than those of
the rest of the choroid. The pigmentary cells are smaller and are arranged in several
layers. The anterior border of the processes is free and contains little or no pigment.

Ciliary Muscle. — This muscle, formerly known as the ciliary ligament and now
sometimes called the tensor of the choroid, is almost universally recognized by physi-

FIG. 243.— Ciliary muscle ; magnified 10 diameters. (Sappey.)

1, 1, crystalline lens ; 2, hyaloid membrane; 8, zone of Zinn; 4, iris; 5, 5, one of the ciliary pp
' 'fibres of the ciliary muscle; 7, section of the circular portion of the ciliary muscle; b. wnous Pfe"***"*""]
process; I), 10, sclerotic coat; 11, 12, cornea ; 13, epithelial layer of 'the conu-a ; 4. nu-i.il.ran.; •••
figamentum iri.lis pectinatuin; 16. epithelium of the membrane of Descemet; 17, union of the
with the cornea ; IS, section of the canal of Schlemm.

ologists as the agent for the accommodation of the eye to vision at different distances.
Under this view, the ciliary muscle is an organ of great importance, and i
in the study of accommodation, to have an exact idea of its relations' to the coats
eye and to the crystalline lens. For this reason, we shall describe its arrangemen
exactly as possible.

The form and situation of the ciliary muscle are as follows : It surrounds
margin of the choroid, in the form of a ring about | of an inch wide and ft o1
in thickness at its thickest portion, which is its anterior border. It becomes

774 SPECIAL SENSES.

from before backward, until its posterior border apparently fuses with the fibrous struct-
ure of the choroid. It is semitransparent and of a grayish color. Its situation is just
outside of the ciliary processes, these processes projecting in front of its anterior border
about ^V °f an inch. Regarding the anterior border of this muscle as its origin and the
posterior border as its insertion, it arises in front from the circular line of junction of the
cornea and sclerotic, from the border of the membrane of Descemet, and the ligarnentum
iridis pectinatuin. Its fibres, which are chiefly longitudinal, pass backward and are
lost in the choroid, extending somewhat farther back than the anterior limit of the
retina. In addition, a net-work of circular muscular fibres has been described lying over
the anterior portion of the ciliary body, at the periphery of the iris, beneath the longitu-
dinal fibres. Some of these fibres have an oblique direction.

Although there was formerly considerable discussion with regard to the structure of
the ciliary ligament, or muscle, there can now be scarcely any doubt of the fact that it is
composed mainly of muscular fibres. These fibres, anatomically considered, belong to the
non-striated, or involuntary variety. They are pale, present a number of oval, longi-
tudinal nuclei, and have no striae.

It is evident, from the arrangement of the fibres of the ciliary muscle, that its action
must be to approximate the border of connection of the sclerotic and cornea and the cir-
cumference of the choroid, compressing the vitreous humor and relaxing the suspensory
ligament of the crystalline lens. We shall see farther on that this action enables the lens
to change its form, and probably it adapts the curvature of the lens to vision at different
distances. The nerves of the ciliary muscle are derived from the long and the short
ciliary.

Iris. — The iris corresponds to the diaphragm of optical instruments, except that its
orifice is capable of dilatation and contraction. It is a circular membrane, situated just
in front of the crystalline lens, with a round perforation, the pupil, near its centre. It is
called the uvea by some anatomists, a name that was formerly applied to the iris and
choroid together.

The attachment of the greater circumference of the iris is to the line of junction of
the cornea and sclerotic, near the origin of the ciliary muscle, the latter passing back-
ward to be inserted into the choroid, and the former passing directly over the crystalline
lens. The diameter of the iris is about half an inch. The pupil is subject to considerable
variations in size. When at its medium of dilatation, the diameter of the pupil is from %
to £ of an inch. The pupillary orifice is not in the mathematical centre of the iris but is
situated a little toward the nasal side. The thickness of the iris is a little greater than
that of the choroid, but it is unequal in different parts, the membrane being thinnest at
its great circumference and its pupillary border, and thickest at about the junction of its
inner third with the outer two-thirds. It slightly projects anteriorly and divides the space
between the lens and the cornea into two chambers, anterior and posterior, the anterior
chamber being much the larger. Taking advantage of a property of the crystalline lens,
called fluorescence, which enables us, by concentrating upon it a blue light, to see the
boundaries in the living eye, Helmholtz has demonstrated that the posterior surface of
the iris and the anterior surface of the lens are actually in contact, except, perhaps, for a
certain distance near the periphery of the iris. This being the case, the posterior cham-
ber is very small and only exists near the margins of the lens and the iris.

The color of the iris is very different in different individuals. Its anterior surface is
generally very dark near the pupil and presents colored radiations toward its periphery.
Its posterior surface is of a dark-purple color and is covered with pigmentary cells.

The entire iris presents three layers. The anterior layer is continuous with the mem-
brane of the aqueous humor. At the great circumference, it presents little fibrous pro-
longations, forming a delicate dentated membrane, called the ligamentum iridis pectina-
tum. The membrane covering the general anterior surface of the iris is extremely thin

PHYSIOLOGICAL ANATOMY OF THE EYEBALL. 775

and is covered by cells of tessellated epithelium. Just beneath this membrane, are a
number of irregularly-shaped pigmentary cells.

The posterior layer of the iris is very thin, easily detached from the middle layer, and
contains numerous small cells exceeding rich in pigmentary granules. Some anatomists
recognize this membrane only as the uvea.1

The middle layer constitutes by far the greatest part of the substance of the iris. It
is composed of connective tissue, muscular fibres of the non-striated variety, numerous
blood-vessels, and, probably, nerve-terminations. From a physiological point of view,
the arrangement of the muscular fibres is the most interesting. Directly surrounding
the pupil, forming a band about -fa of an inch in width, is a layer of non-striated muscu-
lar fibres, called the sphincter of the iris. The existence of these fibres is admitted by
all anatomists. It is different, however, for the radiating muscular fibres. Most anato-
mists describe, in addition to the sphincter, fibres of the same variety, which can be
traced from near the great circumference of the iris almost to its pupillary border, lying
both in front of and behind the circular fibres, which are, as it were, enclosed between
them. A few observers deny that these fibres are muscular ; but they recognize a thick
muscular layer surrounding the arteries of the iris. This is merely a question of observa-
tion ; but the weight of anatomical authority is greatly in favor of the existence of the
radiating fibres, and their presence explains certain of the phenomena of dilatation of
the iris which would otherwise be difficult to understand.

The blood-vessels of the iris are derived from the arteries of the choroid, from the
long posterior ciliary, and from the anterior ciliary arteries. The long ciliary arteries are
two branches, running along the sides of the eyeball between the sclerotic and choroid, to
form, finally, a circle surrounding the iris. The anterior ciliary arteries are derived from
the muscular branches of the ophthalmic. They penetrate the sclerotic a little behind
the iris and join the long ciliary arteries in the vascular circle. From this circle, the
vessels branch and pass into the iris, to form a smaller arterial circle around the pupil.
The veins from the iris empty into a circular sinus situated at the junction of the cornea
with the sclerotic. This is sometimes spoken of as the circular venous sinus, or the canal
of Schlemm.

The nerves of the iris are the long ciliary, from the fifth cranial, and the short ciliary,
from the ophthalmic ganglion.

Pupillary Membrane. — At a certain period of foetal life, the pupil is closed by a mem-
brane connected with the lesser circumference of the iris, called the pupillary membrane.
This is not distinct during the first months ; but, between the third and the fourth months,
it is readily seen. It is most distinct at the sixth month. The membrane is thin and trans-
parent, and it completely separates the anterior from the posterior chamber of the eye. It
is provided with vessels derived from the arteries of the iris, anastomosing with each
other and turning back in the form of loops near the centre. At about the seventh
month, it begins to give way at the centre, gradually atrophies, and generally scarcely a
trace of it can be seen at birth.

Retina. — The retina is described by anatomists as the third tunic of the eye. It is
closely connected with the optic nerve, and the most important structures entering into
its composition are probably continuous with prolongations from the nerve-colls. This
is the membrane endowed with the special sense of sight, the other structures in the eye
being accessory.

If the sclerotic and choroid be removed from the eye under water, the retina is seen,
in perfectly fresh specimens, in the form of an exceedingly delicate and trunspaivnt ini-in-
brane covering the posterior portion of the vitreous humor. A short time after death, it
becomes slightly opaline. It extends over the posterior portion of the eyeball to a dis

i The name uvea was applied, at one time, to the choroid with the iris, again to the iris alone, and again to the
posterior, or pigmentary layer of the iris. To avoid confusion, this term will not be again used.

776 SPECIAL SENSES.

tance of about ^ of an inch behind the ciliary processes. "When torn from its anterior
attachment, it presents a finely-serrated edge, called the ora serrata. This edge adheres
very closely, by mutual interlacement of fibres, to the zone of Zinn. In the middle of
the membrane, its thickness is about -^ of an inch. It becomes thinner near the ante-
rior margin, where it measures only about -^ of an inch. Its external surface is in con-
tact with the choroid, and its internal, with the hyaloid membrane of the vitreous humor.

The optic nerve penetrates the retina about % of an inch within and T^ of an inch be-
low the antero-posterior axis of the globe, presenting, at this point, a small, rounded
elevation upon the internal surface of the membrane, perforated in its centre for the pas-
sage of the central artery of the retina. At from ^ to £ of an inch external to the point
of penetration of the nerve, is an elliptic spot, its long diameter being horizontal, about
£ of an inch long and ^ of an inch broad, called the yellow spot of Sommerring, or the
macula lutea. In the centre of this spot, is a depression, called the fovea centralis. This
depression is exactly in the axis of distinct vision. The yellow spot exists only in man
and the quadrumana.

The structures in the retina which present the greatest physiological interest are the
external layer, formed of rods and cones, the layer of nerve-cells, and the filaments which
connect the rods and cones with the cells. These are the only anatomical elements of
the retina, as far as we know, that are directly concerned in the reception of optical im-
pressions, and they will be described rather minutely, while the intermediate layers will
be considered more briefly.

Most modern anatomists recognize eight distinct layers in the retina, as follows :

1. An external layer, situated next the choroid, called Jacob's membrane, the bacillar
membrane, or the layer of rods and cones.

2. The external granule-layer.

3. The inter-granule layer (cone-fibre plexus, of Hulke).

4. The internal granule-layer.

5. The granular layer.

6. The layer of nerve-cells (ganglion-layer).

7. The expansion of the fibres of the optic nerve.

8. The limitary membrane.

The layer of rods and cones is composed of rods, or cylinders, extending through its
entire thickness, closely packed, and giving to the external surface a regular, mosaic ap-
pearance ; and, between these, are a greater or less number of flask-shaped bodies, the
cones. This layer is about ¥^ of an inch in thickness at the mid,dle of the retina; ¥^
of an inch, about midway between the centre and the periphery ; and, near the periphery,
about -fjr-Q of an inch. At the macula lutea, the rods are wanting, and the layer is com-
posed entirely of cones, which are here very much elongated. Over the rest of the mem-
brane, the rods predominate, and the cones become less and less numerous toward the
periphery.

The rods are regular cylinders, their length corresponding to the thickness of the
layer, terminating above in truncated extremities, and below in points, which are prob-
ably continuous with the filaments of connection with the nerve-cells, though they have
been actually traced only into the external granule-layer. Their diameter is about T^TJ-^
of an inch. They are clear, of rather a fatty lustre, soft and pliable, but somewhat brittle,
and so alterable that they are with difficulty seen in a natural state. They should be
examined in perfectly fresh preparations, moistened with liquid from the vitreous humor
or with serum. Their intimate structure, as well as that of the cones, has recently
been very closely studied, especially by German anatomists. When perfectly fresh, it
is difficult to make out any thing but an entirely homogeneous structure ; but, shortly after
death, each rod seems to be divided by a delicate line into an outer and an inner segment,
the outer being a little the longer. At the upper extremity of the inner segment, is a
hemispherical body, with its convexity presenting inward, called the lentiform body (lin-

PHYSIOLOGICAL ANATOMY OF THE EYEBALL.

777

FIG. 244.-£0</0 of the retina.

(Schultze.)

From the monkev. — A. Eods, after ma-
ceration in iodized serum, the outer
segment (&) truncated, the inner
segment (a) coagulated, granular,
and somewhat swollen ; c, filament
of the rods; d, nucleus. B. Eods
from the frog: 1. Fresh, magnified
500 diameters; a, inner segment;
&, outer segment ; c, lentiform body ;
d, nucleus. 2. Treated with di-
lute acetic acid and broken up into
plates.

aenformiger Kdrper}. The entire inner segment is somewhat granular, and it often pre-
sants a granular nucleus at its inner extremity. The outer segment apparently differs
in its constitution from the inner segment and is not similarly affected by reagents.
Treated with dilute acetic acid, the outer segment becomes
broken up transversely into thin disks. These points in
the anatomy of the rods are referred to particularly, for
the reason that they have lately been used as an anatomi-
cal basis for a theory of the perception of colors. They
can be readily understood by reference to Fig. 244.

The cones are probably of the same constitution as the
rods, but that portion called the inner segment is pyri-
form. The straight portion above (the outer segment) is
sometimes called the cone-rod. The entire cones are
about half the length of the rods and occupy the inner
portion of the layer. The outer segment is, in its consti-
tution, precisely like the outer segment of the rods. The
inner segment is slightly granular and contains a nucleus.
The cones are connected below with filaments passing
into the deeper layers of the retina. The arrangement of
the rods and cones is seen in Fig. 245, which shows the
different layers of the retina.

At the fovea centralis, the external layer is composed
entirely of immensely - elongated cones, with no rods.
These are slightly increased in thickness at the macula
lutea, but are diminished again in thickness, by about
one-half, at the fovea centralis. At the fovea, the optic
nerve-fibres are wanting; and the ganglion-cells, which exist in a single layer over
other portions of the retina, here present from six to eight layers, except at the very
centre, where there are but three layers. Of the layers between the cones and the
ganglion -cells, the external granule-layer and the inter-granule layer (cone-fibre plexus)
remain, in the fovea, while the internal granule-layer' and the granular (molecular) layer
are wanting. At the fovea, indeed, those elements of the retina which may be regarded
as purely accessory seem to disappear, leaving only the structures that are concerned
directly in the reception of visual impressions.

The external granule-layer is composed of large granules, looking like cells, which are
each nearly filled with a single nucleus. These are connected with the filaments from the
rods and cones. They are rounded or ovoid and measure from y^nr to Tznnr of an inch
in diameter. The inter-granule layer (cone-fibre plexus) is composed apparently of mi-
nute fibrilhe and a few nuclei. The internal granule-layer is composed of cells nearly
like those of the external granule-layer, but a little larger, and probably connected with
the filaments of the rods and cones. The granular (molecular) layer is situated next the
layer of ganglion-cells.

The layer of ganglion-cells is composed of multipolar cells, like those in the brain,
measuring from ^Vc" to TTG °f an incn *n diameter. In the centre of the retina, at the
macula lutea, the cells present eight layers, and they diminish to a single layer near the
periphery. The smaller cells are situated near the centre, and the larger, near the periph-
ery. Each cell sends off several filaments (from two to twenty-five) probably going to
the layer of rods and cones, and a single filament, which becomes continuous with one
of the filaments of the optic nerve.

The layer formed by the expansion of the optic nerve is composed of pale, transparent
nerve-fibres, from -^^ to 25^00 of an inch in diameter. These do not call for spei-ul
description.

The limitary membrane is a delicate structure, with fine stria) and nuclei, composed

778

SPECIAL SENSES.

of connective-tissue elements. It is about 84%00 of an inch in thickness. From this
membrane, connective-tissue elements are sent into the various layers of the retina,
where they form a framework for the support of the other structures.

As we before remarked, the retina becomes progressively thinner from the centre to
the periphery. The granular layers and the nervous layers rapidly disappear in the
anterior half of the membrane.

FIG. 245 (A).— Vertical section of the retina. FIG. 245 (B).— Connection of the rods and cones
(H. Miiller.) of the retina with the nervous elements.

(Sappey.)

FIG. 245 (A).— 1, 1, layer of rods and cones ; 2, rods ; 3, cones ; 4, 4, 5, 6, external granule-layer; 7, inter-granule layer
(cone-fibre plexus); 8, internal granule-layer; 9, 10, finely granular gray layer; 11, layer of nerve-cells; 12, 12,
12, 12, 14, 14, fibres of the optic nerve ; 18, membrana limitans.

FIG. 245 (B).— 1, 1, 2, 3, rods and cones, front view ; 4, 5, 6, rods, side view ; 7, 7, 8, 8, cells of the external and internal
granule-layers ; 9, cell, connected by a filament with subjacent cells ; 10, 13, nerve-cells, connected with cells of the
granule-layers ; 11, 21, filaments connecting cells of the external and internal granule-layers (12 is not in the figure) ;
14, 15, 16, 17, 18, 19, 20, 22, 28, 24, 25, 26, a rod and a cone, connnected with the cells of the granule-layers, with the
nerve-cells, and with the nerve-fibres.

The connection between the rods and cones and the ganglion -cells may be readily
understood if we accept the following explanation: The filaments from the bases of the
rods and cones pass inward, presenting, in their course, the corpuscles which we have
described in the granule-layers, and finally become, as is thought, directly continuous
with the poles of the ganglion-cells. The cells, in their turn, send filaments to the layer
formed by the expansion of the optic nerve, which are continuous with the nerve-fibres.
This arrangement is shown in Fig. 245 (B).

Dr. E. Gr. Loring, of New York, has kindly furnished the following description of the
blood-vessels of the retina, with Fig. 246, which was drawn by himself from nature:

" The arteries and veins of the retina are subdivisions of the arteria and vena centralis.
The larger branches run in the nerve-fibre layer and are immediately beneath the limitary

PHYSIOLOGICAL ANATOMY OF THE EYEBALL. 779

membrane. The vessels lie so superficially that, in a cross-section examined with the
microscope, they are seen to project above the general level of the retina, toward the
vitreous humor. While the large vessels are in the plane of the inner surface of the
retina, the smaller branches penetrate the substance of the retina to the inter-granule
layer. They do not extend, however, as far as the external granule-layer and the layer
of rods and cones. These two layers, therefore, have no blood-vessels.

" The ramifications of the vessels present a beautifully arborescent appearance when
seen with the ophthalmoscope. The manner in which the vessels are distributed and the
way in which the circulation is carried on can be better understood by a study of Fig.
246 than by any detailed description. The figure represents the ophthalmoscopic appear-
ance of a normal eye in young adult life. The darker vessels are the veins, and the
lighter vessels, the arteries. The dotted oval line is diagrammatic and marks the position
and extent of the macula lutea. It is seen that this oval space contains a number of fine

Fia. m.-Blood-vetael* of the retina; magnified 7* diameters. (E. Q. Loring.)

vascular twigs which, coming from above and below, extend toward the spot in the cen-
tre of the oval which marks the position of the fovea centralis. In opposition, then, to
the general opinion, which is that the macula lutea has no blood-vessels, it is the spot of
all others in the retina which is most abundantly supplied with minute vascular branches.
These vessels can be distinctly seen even with the ophthalmoscope ; and microscopical
examination shows that the capillary plexus in the macula lutea is closer and richer than
in any other part of the retina. According to Nettleship, the area surrounding the fmva
centralis is the part which is most abundantly supplied with arteries, capillaries, and
veins. The fovea centralis itself, however, has no blood-vessels."

The arteries of the retina send branches to the periphery, where they supply a
plexus of very small capillaries in the ora serrata. These capillaries empty fa to an mco
plete venous circle, branches from which pass back by the sides of the arteries
vena centralis.

780

SPECIAL SENSES.

Crystalline Lens. — The crystalline is a double-convex lens, transparent, and exceed-
ingly elastic. It has a function in the refraction of the rays of light analogous to the ac-
tion of convex lenses in optical instruments. When we come to study its exact structure,
however, we shall find many points that are still undetermined and somewhat obscure ;
but, fortunately, these are not, as far as we know, of much physiological importance.

The lens is situated behind the pupil, in what is called the hyaloid fossa of the vitre-
ous humor, which is exactly moulded to its posterior convexity. In the foetus, the cap-
sule of the lens receives a branch from the arteria centralis, but it is non-vascular in the
adult. The anterior convexity of the lens is just behind the iris, and its borders are in
relation with what is known as the suspensory ligament. The convexities do not present
regular curves, and they are so subject to variations after death that the measurements,
post mortem, are of little value. During life, however, they have been measured very
exactly in the various conditions of accommodation. The diameters of the lens in the
adult are about ^ of an inch transversely and ^ of an inch antero-posteriorly. The con-
vexity is greater on its posterior than on its anterior surface. In foetal life, the convexi-

FIG. 24T.— Crystalline lens anterior view. (Babuchin.)

ties of the lens are much greater than in the adult and its structure is much softer. In
old age, the convexities are diminished and the lens becomes harder and less elastic.
The substance of the lens is made up of layers of fibres of different degrees of density,
and the whole is enveloped in a delicate membrane, called the capsule.

The capsule of the lens is an exceedingly thin, transparent membrane which is very
elastic. This membrane is generally from -^^ to y^ of an inch thick; but it is very
thin at the periphery, measuring here only -^^ of an inch. Its thickness is increased in
old age. On the anterior portion, the capsule is lined on its inner surface with a layer
of exceedingly delicate, nucleated epithelial cells. The posterior half of the capsule has
no epithelial lining. The cells are regularly polygonal, measuring from -gfaf to T1?Vff
of an inch in diameter, with large, round nuclei. After death they are said to break
down into a liquid, known as the liquid of Morgagni, though by some this liquid is sup-
posed to be exuded from the substance of the lens. At all events, the cells disappear
soon after death.

If the lens be viewed entire with a low magnifying power, it presents, upon either of

PHYSIOLOGICAL ANATOMY OF THE EYEBALL.

781

its surfaces, a star with from nine to sixteen radiations extending from the centre to
about half or two-thirds of the distance to the periphery. The stars seen upon the two
surfaces are not coincident, the rays of one being situ-
ated between the rays of the other. In the foetus, the
stars are more simple, presenting only three radiations
upon either surface. These stars are not fibrous, like
the rest of the lens, but are composed of a homogene-
ous substance, which extends, also, between the fibres.

The greatest part of the substance of the lens is
composed of very delicate, soft, and pliable fibres,
which are transparent, but perfectly distinct. These
fibres are flattened, six-sided prisms, closely packed
together, so that their transverse section presents a
regularly-tesselated appearance. They are from ^^
to -g^nr of an inch broad and from ^-^-^ to -^-^ of an
inch in thickness. Their flat surfaces are parallel
with the surface of the lens. The direction of the
fibres is from the centre and from the rays of the stel-
late figures to the periphery, where they turn and pass
to the star upon the opposite side. The outer layers
of fibres, near the equator, or circumference of the
lens, are provided with exceedingly distinct, oval nu-
clei, with one or two nucleoli. These become smaller
as we pass deeper into the substance of the lens, and
gradually they disappear.

The regular arrangement of the fibres of the lens makes it possible to separate its sub-
stance into laininaa, which have been compared by anatomists to the layers of an onion;
but this separation is entirely artificial, and the number of apparent layers depends upon
the dexterity of the manipulator. It is to be noted, however, that the external portions
of the lens are soft, even gelatinous, and that the central layers are
much harder, forming a sort of central kernel, or nucleus.

The lens is composed of a peculiar organic nitrogenized sub-
stance, very analogous to globuline, called crystalline, combined
with various inorganic salts. One of the peculiar constituents of
this body is cholesterine. In an examination of four fresh crystal-
line lenses of the ox, we found cholesterine, in the proportion of
0*907 of a part per 1,000. In some cases of cataract, cholesterine
exists in the lens in a crystalline form ; but, under normal condi- FlG>
tions, it is united with the other constituents.

FlG- ^--

1, crystalline lens; 2. 2, vit-
reous humor ; 8, 8. zone
of Zinn ; 4, 4, posterior
portion of tho zone of
Zinn. thrown into folds;
o. fi. 6. anterior and mid-
dle portions of the zone
ofZinu.

Suspensory Ligament of the Lens (Zone of Zinn). — When we come
to the description of the vitreous humor, we shall see that it occu-
pies about the posterior two-thirds of the globe, and is enveloped in
a delicate capsule, called the hyaloid membrane. In the region ot
the ora serrata of the retina, this membrane divides into two layers. The posterior layer
lines the depression in the vitreous humor into which the lens is received. The anterior
layer passes forward toward the lens and divides into two secondary layers, one of which
passes forward to become continuous with the anterior portion of the capsule of the lens,
while the other passes to the posterior surface of the lens to become continuous with this
portion of its capsule. The anterior of these layers is corrugated, or thrown into folds
which correspond with the ciliary processes, with which it is in contact. This corru-
gated portion is called the zone of Zinn. The two layers thus surround the lens and i
properly called its suspensory ligament. As the two layers of the suspensory ligament

782 SPECIAL SENSES.

separate at a certain distance from the lens, one passing to the anterior and the other
to the posterior portion of the capsule, there remains a triangular canal, about -^ of an
inch wide, surrounding the border of the lens, called the canal of Petit. Under natural
conditions, the walls of this canal are nearly in apposition and it contains a very small
quantity of clear liquid.

As we have already remarked in describing the retina, this membrane is closely con-
nected, at the ora serrata, by a mutual interlacement of fibres, with the suspensory liga-
ment. It is important to appreciate clearly the relations of the suspensory ligament, in
order to understand the mechanism of accommodation of the lens to vision at different
distances. The ciliary muscle being in repose, during what is termed the indolent
condition of the eye, when it is adapted to vision at long distances, the tension of the
parts flattens the lens ; but, in the effort of accommodation for near objects, the ciliary
muscle contracts, compresses the contents of the globe, relaxes the suspensory ligament,
and the inherent elasticity of the lens renders it more convex. It is by a delicate use of
this muscle, that the proper adaptation of the curvatures of the lens is obtained.

The membrane forming the suspensory ligament is composed of pale longitudinal and
transverse fibres of rather a peculiar appearance, which are much less affected by acetic
acid than the ordinary fibres of connective tissue.

Aqueous Humor. — The space bounded in front by the cornea, posteriorly by the crys-
talline lens and the anterior face of its suspensory ligament, and, at its circumference, by
the tips of the ciliary processes, is known as the aqueous chamber. This contains a clear
liquid, called the aqueous humor. The iris separates this space into two divisions, which
communicate with each other through the pupil ; viz., the anterior chamber, situated be-
tween the anterior face of the iris and the cornea, and the posterior chamber, between the
posterior face of the iris and the crystalline. It is evident, from the position of the iris,
that the anterior chamber is much the larger ; and, indeed, the posterior surface of the
iris and the anterior surface of the lens are in contact, except, perhaps, near their periph-
ery or when the iris is very much dilated. The liquid filling the chambers of the eye is
said to be secreted by the blood-vessels of the ciliary processes; at all events, it is rapidly
reproduced after it has been evacuated, as occurs in many surgical operations upon the eye.

The aqueous humor is colorless and transparent, faintly alkaline, of a specific gravity
of about 1005, and possesses the same index of refraction as the cornea and the vitreous
humor. It contains a small quantity of an albuminoid matter, but it is not rendered
turbid by heat or other agents which coagulate albumen. Various inorganic salts (the
chlorides, sulphates, phosphates, and carbonates) exist in this liquid, in small proportion.
It contains also traces of urea and glucose.

Vitreous Humor. — The vitreous humor is a clear, glassy substance, occupying about
the posterior two-thirds of the globe. It is enveloped in an exceedingly delicate, struct-
ureless capsule, called the hyaloid membrane, which is about ^^ of an inch in thick-
ness. This membrane adheres pretty strongly to the limitary membrane of the retina.
In front, at the ora serrata, as we have already seen, the hyaloid membrane is thickened
and becomes continuous with the suspensory ligament of the lens.

The vitreous humor itself is gelatinous, of feeble consistence, slightly alkaline in its
reaction, with a specific gravity of about 1005. Upon section, there oozes from it a
watery fluid of a slightly mucilaginous consistence. This humor is not affected by heat
or alcohol, but it is coagulated by certain mineral salts, especially the acetate of lead.
When thus solidified, it presents regular layers, like the white of an egg boiled in its
shell ; but these are artificial. In the embryon, the vitreous humor is divided into
many little cavities and contains cells and leucocytes. It is also penetrated by a branch
from the central artery of the retina, which passes through its centre to ramify upon
the posterior surface of the crystalline lens. This structure, however, is not found in the

SUMMARY OF THE ANATOMY OF THE GLOBE OF THE EYE. 783

adult, the vitreous humor being then entirely without blood-vessels. The vitreous humor
is divided into compartments formed by delicate membranes radiating from the point of
penetration of the optic nerve to the anterior boundary where the hyaloid membrane
is in contact with the capsule of the lens. In this way, the humor is divided up, some-
thing like the half of an orange, by about one hundred and eighty membranous processes
of extreme delicacy, which do not interfere with its transparency.

Summary of the Anatomy of the Globe of the Eye.

In this summary, we propose simply to show the relations of the various parts, giving
at the same time a brief statement of their physiological importance, in connection with

11-41. -\ . \\C

Cod

R.

FIG. 250.— Section of the human eye, copied from Helmholts and slightly modified.

Fig. 250, which represents a section of the human eye and shows the relations of its
various coats, humors, etc.

The eyeball is nearly spherical in its posterior five-sixths, its anterior sixth being
formed of the segment of a smaller sphere, which is slightly projecting. In its posterior
five-sixths, it presents the following coats, indicated in the figure:

S. The sclerotic ; a dense, fibrous membrane, chiefly for the protection of the more
delicate structures of the globe, and giving attachment to the muscles which move the
eyeball. Attached to the sclerotic, are the tendons of R, R, the recti muscles.

Cor. The cornea; a transparent structure, forming the anterior, projecting sixth of
the globe ; dense and resisting, allowing, however, the passage of light ; covered, on its
convex surface, with several layers of transparent epithelial cells.

Clio. The choroid coat, lining the sclerotic and extending only as far forward as the
cornea ; connected with the sclerotic by loose connective tissue, in which ramify blood-
vessels and nerves, and presenting an external, vascular layer and an internal pigmentary
layer, which latter gives its characteristic dark-brown color.

C. P., C. P. The ciliary processes; peculiar folds of the choroid, which form its ante-
rior border, and which embrace the folds of the suspensory ligament of the lens.

784 SPECIAL SENSES.

C. K, C. M. The ciliary muscle, situated just outside of the ciliary processes, arising
from the circular line of junction of the sclerotic with the cornea, passing over the cili-
ary processes, and becoming continuous with the fibrous tissue of the choroid. The
action of this muscle is to tighten the choroid over the vitreous humor and to relax the
ciliary processes and the suspensory ligament of the lens, when the lens, by virtue of its
elasticity, becomes more convex. This action is shown by the dotted lines in the figure.

I., I. The iris ; dividing the space in front of the lens into two chambers occupied by
the aqueous humor: (A) The anterior chamber is much the larger. The iris, in its cen-
tral portion surrounding the pupil (P), is in contact with the lens. Its circumference is
just in front of the line of origin of the ciliary muscle.

Eet., Ret. The retina; a delicate, transparent membrane, lining the choroid and ex-
tending to about -5*5- of an inch behind the ciliary processes, the anterior margin forming
the ora serrata. 0. The optic nerve penetrating the retina a little internal to and below
the antero-posterior axis. The layer of rods and cones is situated externally next the
choroid. Internal to the layer of rods and cones, are the four granular layers; next, the
layer of nerve-cells ; next, the expansion of the fibres of the optic nerve ; and next, in
apposition with the hyaloid membrane of the vitreous humor, is the limitary membrane.

C. The crystalline lens ; elastic, transparent, enveloped in its capsule and surrounded
by S. L., S. L., the suspensory ligament.

S. L., S. L. The suspensory ligament ; the anterior layer connected with the anterior
portion of the capsule of the lens, and the posterior, with the posterior portion of the
capsule. The folded portion of this ligament, which is received between the folds of the
ciliary processes, is called the zone of Zinn. The triangular canal between the anterior
and the posterior layers of the suspensory ligament and surrounding the equator of the
lens is called the canal of Petit.

V. The vitreous humor; enveloped in the structureless hyaloid membrane, which
membrane is continuous in front with the suspensory ligament of the lens.

Refraction in the Eye.

It is simply impossible to obtain a clear idea of the physiology of vision without hav-
ing carefully studied the physiological anatomy of the visual organs ; and, for this rea-
son, we have been as exact as possible and somewhat minute in our description of the
structure of the eye. If the student will carefully study the anatomy of the parts, a
very succinct statement of some of the well-established laws of refraction will render
the physiology so simple that it will follow almost without explanation.

In applying the laws of the refraction of light to the transparent media of the eye,
it is necessary to bear in mind certain general facts with regard to vision, that have as
yet been referred to either very briefly or not at all.

The eye is not by any means a perfect optical instrument, looking at it from a purely
physical point of view. This statement, however, should not be understood as implying
that the arrangement of the organs of vision is not such as to adapt them perfectly to the
functions which they have to perform in connection with the proper appreciation of
visual impressions. By physical tests, it can be demonstrated that the eye is not entirely
achromatic ; but, in ordinary vision, the dispersion of colors is not appreciated. There
is but a single point in the retina, the fovea centralis, where vision is absolutely distinct ;
and it is upon this point that images are made to fall when the eye is directed toward
any particular object.

It is curious to note, however, that the refracting apparatus is not exactly centred, a
condition so essential to the satisfactory performance of our most perfect optical instru-
ments. For example, in a compound microscope or a telescope, the centres of the differ-
ent lenses entering into the construction of the instrument are all situated in a straight
line. Were the eye a perfect optical instrument, the line of vision would coincide ex-

REFRACTION IN THE EYE. 735

actly with the axis of the cornea; but this is not the case. The visual line (aline drawn
from an object to its image on the fovea centralis) deviates from the axis of the cornea,
in normal eyes, to the nasal side. The visual line, therefore, forms an angle with the
axis of the cornea. This is known as the angle alpha. This deviation of the visual
line from the mathematical centre of the eye is observed both in the horizontal and in
the vertical planes. " The horizontal deviation varies from two to eight degrees (Schuer-
man), the vertical, from one to three degrees (Mandtbtamm)." Of course, this want of
exact centration of the optical apparatus, in normal eyes, does not practically affect dis-
tinct vision, for, when the eyes are directed toward any object, this object is brought in
the line of the visual axis ; but the angle alpha is an important element to be taken into
account in various mathematical calculations connected with the physics of the eye.

The field, or area of distinct vision, is quite restricted ; but, were it larger, it is proba-
ble that the mind would become confused with the extent and variety of the impressions,
and that we should be unable so easily to observe minute details and fix the attention
upon small objects.

While we see certain objects with absolute distinctness in a restricted field, the angle
of vision is very wide, and rays of light are admitted from an area equal nearly to the
half of a sphere. Such a provision is eminently well adapted to our requirements. We
direct the eyes to a particular point and see a certain object distinctly, getting the advan-
tage of an image in the two eyes exactly at the points of distinct vision ; the rays com-
ing from without the area of distinct vision are received upon different portions of the
surface of the retina and produce an impression more or less indistinct, not interfering
with the observation of the particular object to which the attention is for the moment
directed ; but, even while looking intently at any object, the attention may be attract-
ed by another object of an unusual character, which might, for example, convey an idea
of danger, and the point of distinct vision can be turned in its direction. Thus, while
we see distinctly but few objects at one time, the area of indistinct vision is immense ;
and our attention may be readily directed to unexpected or unusual objects that may
come within any portion of the field of view. The small extent of the area of distinct
vision, especially for near objects, may be readily appreciated if we watch a person
attentively reading a book, when the eyes will be seen to follow the lines from one side
of the page to the other with perfect regularity. When we consider that, in addition to
these remarkable qualities, which are never thought of in artificial optical instruments,
the eye may be accommodated at will, with the most exquisite nicety, to vision at differ-
ent distances, and that we possess correct appreciation of form, etc., by the use of the
two eyes, it is evident that the organ of vision gains rather than loses in comparison with
the most perfect instruments that have ever been or probably ever will be constructed.

Laws of Refraction, Dispersion, etc., bearing upon the Physiology of Vision. — In
the present state of physiological science, we have little to do with the theory of
light, except as regards the modifications of luminous rays in passing through the re-
fracting media of the eye. It will be sufficient to state that nearly ail physicists of the
present day agree in accepting what is known as the theory of undulation, rejecting in
toto the emission-theory proposed by Newton. It is necessary to the theory of undula-
tion to assume that all space and all transparent bodies are permeated with what has been
called a luminiferous ether; and that light is propagated by a vibration or an undulation
of this hypothetical substance. This theory assimilates light to sound, in tin- mechanism
of its propagation; but, in sound, the waves are supposed to be longitudinal, or to fol-
low the line of propagation, while in light the particles are supposed to vibrato trans-
versely, or at right angles to the line of propagation. It must be remembered, however,
that the undulatory theory of sound is capable of positive demonstration, and that the
propagation of sound by waves can only take place through ponderable matter, the
vibrations of which can always be observed; while luminous vibrations involve the
50

786 SPECIAL SENSES.

existence of an imponderable and a purely hypothetical ether. It is possible, indeed, that
scientific facts may, in the future, render the existence of such an ether improbable or its
supposition unnecessary ; but, at present, all we can say is that the theory of luminous
undulation is entirely in accord with the optical phenomena that have thus far been rec-
ognized.

The different calculations of physicists with regard to the velocity of light have been
remarkably uniform in their results. The lowest calculations put it at about 185,000
miles in a second, and the highest, at about 195,000 miles. The rate of propagation is
usually assumed to be about 192,000 miles.

The intensity of light is in proportion to the amplitude of the vibrations. The inten-
sity diminishes as the distance of the luminous body increases, and is in inverse ratio to
the square of the distance.

In the theory of the colors into which pure white light may be decomposed by prisms,
it is assumed, as a matter of demonstration, that the waves of the different colors of the
solar spectrum are not of the same length. The decomposition of light is produced by
differences in the refrangibility of the different colored rays as they pass through a denser
medium, than the air. The differences in the wave-lengths for different colors is very
simply set forth by Tyndall as follows :

" The color of light is determined solely by its wave-length. The ether-waves grad-
ually diminish hi length from the red to the violet. The length of a wave of red light is
about ^^ of an inch ; that of the wave of violet light is about ^-^ of an inch. The
waves which produce the other colors of the spectrum lie between these extremes.

"The velocity of light being 192,000 miles in a second, if we multiply this number
by 39,000, we obtain the number of waves of red light in 192,000 miles ; the product is
474,439,680,000,000. All of these waves enter the eye in a second. In the same inter-
val 699,000,000,000,000 waves of violet light enter the eye. At this prodigious rate is
the retina hit by the waves of light.

"Color, in fact, is to light, what pitch is to sound. The pitch of a note depends
solely on the number of aerial waves which strike the ear in a second. The color of
light depends on the number of ethereal waves which strike the eye in a second.
Thus the sensation of red is produced by imparting to the optic nerve four hundred and
seventy-four millions of millions of impulses per second, while the sensation of violet is
produced by imparting to the nerve six hundred and ninety-nine millions of millions per
second/' In this way the scale of colors in the solar spectrum is compared to the scale
of musical notes and intervals. Indeed, Helmholtz has constructed a theoretical scale
of colors to correspond with musical tones and semitones.

The analysis of white light into the different colors of the spectrum shows that it is
compound ; and, by synthesis, the colored rays may be brought together, producing
white light. Colors may be obtained by decomposition of light by transparent bodies,
the different colored rays being refracted, or bent by a prism at different angles. It is
not in this way, however, that the colors of different objects are produced. Certain
objects have the property of reflecting the rays of light. A perfectly smooth, polished
surface, like a mirror, may reflect all of the rays ; and the object then has no color, the
reflected light only being appreciated by the eye. Certain other objects do not reflect
all of the rays of light, some of them being lost to view or absorbed. When an object
absorbs all of the rays, it has no color and is called black. When an object absorbs the
rays equally and reflects a portion of these rays without decomposition, it is gray or
white. There are many objects, however, that decompose white light, absorbing certain
rays of the spectrum and reflecting others. The rays not absorbed, but returned to
the eye by reflection, give color to the object. Thus, if an object absorb all of the rays
of the spectrum except the red, the red rays strike the eye, and the color of the object
is red. So it is with objects of different shades, the colors of which are given simply
by the unabsorbed rays.

REFRACTION IN THE EYE. 737

It is a curious fact that the mixture of different colors in certain proportions will
result in white. Two colors, which, when mixed, result in white, are called complemen-
tary. The following colors of the spectrum bear such a relation to each other :

Red and greenish-blue.

Orange and cyanogen-blue.

Yellow and indigo-blue.

Greenish-yellow and violet.

The fact that impressions made upon the retina persist for an appreciable length of
time enables us to illustrate the law of complementary colors. If a disk, presenting
divisions with two complementary colors, be made to revolve so rapidly that the impres-
sions made by the two colors are blended, the resulting color is white.

It is almost useless, with our present knowledge, to speculate with regard to the prob-
able mechanism of the appreciation of colors in vision. The facts just stated are suffi-
ciently clear, showing that the number of ethereal vibrations is different for different
colors ; but it is by no means determined that differences in the amplitude of the vibra-
tions are in direct relation with the arrangement of the disks of the rods and cones in
different portions of the retina, a theory lately proposed by Zenker. The curious phe-
nomena of color-blindness depend upon an abnormal condition of the visual apparatus.
Persons possessing this peculiarity — called sometimes Daltonism, after the celebrated
English chemist, who described this infirmity as it existed in his own person — although
vision may be normal in other respects, cannot distinguish certain colors, will mistake red
for green, etc., and some can only distinguish black and white. It is a curious fact, also,
that persons affected with color-blindness (Daltonism, or achromatopsia) are sometimes
incapable of distinguishing different musical tones. Although often congenital and irre-
mediable, it is now known that color-blindness is sometimes produced by the excessive
use of alcohol and tobacco, exposure to cold and wet, etc., and is amenable to treatment.

Refraction ~by Lenses. — A ray of light is an imaginary pencil, so small as to present
but a single line ; and the light admitted to the interior of the eye by the pupil is sup-
posed to consist of an infinite number of such rays. In studying the physiology of
vision, it is important to recognize the laws of refraction of rays by transparent bodies
bounded by curved surfaces, with particular reference to the action of the crystalline lens.

Fm. 251.— Refraction by prism*.

The action of a double-convex lens, like the crystalline, in the refraction of liirht.
maybe readily understood if we simply apply the well-known laws of ivfrartion 1,
prisms. A ray of light falling upon the side of a prism at an angle is deviated toward
a line perpendicular to the surface of the prism. As the ray passes from the prisn to

788 SPECIAL SENSES.

the air, it is again refracted, but then the deviation is from the perpendicular of the sec-
ond surface of the prism. If we imagine two prisms placed together, as in Fig. 251, the
ray A B will be bent toward the perpendicular G B to M. As it passes from the prism,
it will be refracted from the perpendicular H M and take the direction M I. Correspond-
ing refraction takes place in the ray 1ST O falling upon the lower prism. These two rays
will cross each other at the point L.

A circle is supposed to be equivalent to a polygon with an infinite number of sides.
A regular double-convex lens is a transparent body bounded by portions of a sphere, and
it may be assumed to be composed of an infinite number of prisms. The action of a con-
vex lens is to converge the rays of light falling upon different portions of their surface so
that they cross at a certain distance behind the lens. If we imagine the lens A B (Fig.
252) to be free from spherical aberration, the rays C D and C E, from the point C, will

FIG. 252.— Refraction T>y convex lenses.

be refracted and brought to a focus at the point F. In the same way. the rays from the
point K will be brought to a focus at the point L, the two sets of rays crossing at G.
The same is true for all the rays from the object C K, which strike the lens at an angle ;
but the ray H I, which is perpendicular to the lens, is not deviated. The line H I is
called the axis of the lens. These facts may be applied to the crystalline lens. The rays
from an object C K fall upon the lens and are brought to a focus so as to produce the
image L F. The retina is supposed to be at such a distance from the lens that the rays
are brought to a focus exactly at its surface. Inasmuch as the rays cross each other at
the point G, the image is always inverted.

Supposing the crystalline lens to be free from spherical and chromatic aberration, the
formation of a perfect image depends upon the following conditions :

The object must be at a certain distance from the lens. If the object be too near, the
rays, as they strike the lens, are too divergent and are brought to a focus beyond the
plane L I F, or behind the retina ; and, as a consequence, the image is confused. In
optical instruments, the adjustment is made for objects at different distances by moving
the lens itself. In the eye, however, the adjustment is effected by increasing or dimin-
ishing the curvatures of the lens, so that the rays are always brought to a focus at the
visual surface of the retina. The faculty of thus changing the curvatures of the crys-
talline lens is called accommodation. This power, however, is restricted within certain
well -defined limits.

In some individuals, the antero-posterior diameter of the eye is too long, and the
rays, for most objects, come to a focus before they reach the retina. This defect may be
remedied by placing the object very near the eye, so as to increase the divergence of the
rays as they strike the crystalline. Such persons are said to be near-sighted (myopic),
and objects are seen distinctly only when very near the eye. This defect may be reme-

REFRACTION IN THE EYE. 739

died for distant objects by placing concave lenses before the eyes, by which the rays
falling upon the crystalline are diverged. The opposite condition, in which the antero-
posterior diameter is too short (hypermetropia), is such that the rays are brought to a
focus behind the retina. This is corrected by converging the rays of incidence by plac-
ing convex lenses before the eyes. In old age, the crystalline lens becomes flattened, its
elasticity is diminished, and the power of accommodation is lessened; conditions which
also tend to bring the rays to a focus behind the retina. This condition is called pres-
byopia. To render near vision, as in reading, distinct, objects are placed farther from
the eye than under normal conditions. The defect may be remedied, as in hypermetro-
pia, by placing convex lenses before the eyes, by which the rays are converged before
they fall upon the crystalline lens.

The mechanism of accommodation will be fully considered in connection with the
physiology of the crystalline lens ; and at present, it is sufficient to state that, in looking at
distant objects, the rays, as they fall upon the lens, are nearly parallel. The lens is then
in repose, or u indolent." It is only when an effort is made to see near objects distinctly,
that the agents of accommodation are called into action ; and then, very slight changes
in the curvature of the lens are sufficient to bring the rays to a focus exactly on the
visual surface of the retina.

Spherical Aberration. — In a convex lens, with its surfaces consisting of portions of a
perfect sphere, the rays of light from any object are not converged to a uniform focus,
and the production of an absolutely distinct image is impossible. For example, if we
suppose the crystalline lens to present regular curvatures, the rays refracted by its periph-
eral portion would be brought to a focus in front of the retina ; the focus of the rays
converged by the lens near its centre would be behind the retina ; a few, only, of the
rays would have their focus at the retina itself; and, as a consequence, the image would
appear confused. This is illustrated in imperfectly-corrected lenses and is called spherical
aberration. For example, in examining an object with an imperfectly-corrected objec-
tive under the microscope, it is evident that the field of view is not uniform, and that
there is a different focal adjustment for the central and the peripheral portions of the
lens. In the construction of optical instruments, this difficulty may be in part corrected
if the rays of light be cut off from the periphery of the lens by a diaphragm, which is
an opaque screen with a circular perforation allowing the rays to pass to a restricted por-
tion of the lens near its centre. The iris corresponds to the diaphragm of optical instru-
ments, and it corrects the spherical aberration of the crystalline in part, by eliminating a
portion of the rays that would otherwise fall upon its peripheral portion. But this cor-
rection is not sufficient tfor high magnifying powers; and it is only by the more or less
perfect correction of this kind of aberration by other means, that powerful lenses have
been rendered available in optics.

The spherical aberration of lenses which diverge the rays of li.irht is precisely opposite
to the aberration of converging lenses. If, therefore, we construct a compound lens, it
is possible to fulfil the conditions necessary to the convergence of all the incident rays to
a focus on a uniform plane, so that the image produced behind the lens is not distorted.
Given, for example, a double-convex lens, by which the rays are brought to innumerable
focal points situated in different planes. The fact that but a few of these focal point* arc-
in the plane of the retina renders the image indistinct. If we place behind this eonvx
lens a concave lens, by the action of which the rays are more or less diverged, tin- ine-
quality of the divergence by different portions of the second lens will have the following
effect: As the angle of divergence gradually increases from the centre toward the periph-
ery, the rays near the periphery, which are most powerfully converged by the coim-x
lens, will be most widely diverged by the peripheral portion of the concave lens; so that,
if the opposite curvatures be accurately adjusted, the aberrant rays may be blended,
is evident that, if all of the rays were equally converged by the convex lens and equally

790 SPECIAL SENSES.

diverged by the concave lens, the action of the latter would be simply to elongate the
focal distance ; and it is equally evident that, if the aberration of the one be exactly oppo-
site to the aberration of the other, there will be perfect correction. Mechanical art has
not enabled us to effect correction of every portion of very powerful convex lenses in this
way ; but, by a combination of lenses and diaphragms together, highly-magnified images,
nearly perfect, have been produced.

It is evident that, for distinct vision at different distances, the crystalline lens must be
nearly free from spherical aberration. This is not effected by a combination of lenses, as
in ordinary optical instruments, but by the curvatures of the lens itself, and by certain
differences in the consistence of different portions of the lens, which will be fully con-
sidered hereafter.

Chromatic Aberration. — We have already alluded to the fact that a refracting medium
does not act equally upon the different colored rays into which pure white light may be
decomposed ; in other words, as the pure ray falling upon the inclined surface of a glass
prism is bent, it is decomposed into the colors of the spectrum. As a convex lens is
practically composed of an infinite number of prisms, the same effect would be expected.
Indeed, a simple convex lens, even if the spherical aberration be corrected, always
produces more or less decomposition of light. The image formed by such a lens will
consequently be colored ; and this defect in simple lenses is called chromatic aberration.
At the same time, it is evident that the centre of the different rays from an object will be
composed of all the colors of the spectrum combined, producing the effect of white light ;
but, at the borders, the different colors will be separate and distinct, and an image pro-
duced by a simple convex lens will thus be surrounded by a circle of colors like a rain-
bow.

In prisms, the chromatic dispersion may be corrected by allowing tbe colored rays
from one prism to fall upon a second prism, which is inverted, so that the colors will be
brought together and produce white light. Two prisms thus applied to each other con-
stitute, in fact, a flat plate of glass, and the rays of light pass without deviation. If this
law be applied to lenses, it is evident that the dispersive power of a convex lens may be
exactly opposite to that of a concave lens. By the convex lens, the colored rays are
separated by convergence and cross each other ; while, in the concave lens, the colored
rays are dispersed in the opposite direction. If, then, we combine a convex with a con-
cave lens, the white light decomposed by the one will be recomposed by the other, and
the chromatic aberration will thus be corrected. But, in using a convex and a concave
lens composed of the same material, the convergence by the one will be neutralized by
the dispersion of the other, and there will be no amplification ofrthe object.

In the construction of optical instruments, the chromatic aberration is corrected, with
but slight diminution in the amplification, by combining lenses made of different material,
as of flint-glass and crown-glass. Flint-glass has a much greater dispersive power than
crown-glass. If, therefore, we use a convex lens of crown-glass combined with a concave
lens of flint-glass, the chromatic aberration of the convex lens may be corrected by a con-
cave lens with a curvature which will take but little from the magnifying power. A com-
pound lens, with the spherical aberration of the convex element corrected by the curvature
of a concave lens, and the chromatic aberration corrected by the curvature, in part, and
in part by the superior refractive power of flint-glass over crown-glass, will produce
a perfect image.

Although the eye is not absolutely achromatic, the dispersion of light is not sufficient
to interfere with distinct vision. We can understand how the chromatic aberration is
practically corrected in the crystalline lens, when we remember that its various layers
are of different consistence and of different refractive power.

FORMATION OF IMAGES IN THE EYE. 791

Formation of Images in the Eye.

It is only necessary to call to mind the general arrangement of the different structures
in the eye and to apply the simple laws of refraction, to comprehend precisely how images
are formed upon the retina.

The eye corresponds to a camera obscura. Its interior is lined with a dark, pigment-
ary membrane (the choroid), the function of which is to prevent the confusion of images
by internal reflection. The rays of light are admitted through a circular opening (the
pupil), the size of which is regulated by the movements of the iris. The pupil is contracted
when the light striking the eye is intense and is dilated as the amount of light is dimin-
ished. In the accommodation of the eye, the pupil is dilated for distant objects and con-
tracted for near objects ; for, in looking at near objects, the aberrations of sphericity and
achromatism in the lens are more marked, and the peripheral portion is cut off by the
action of this movable diaphragm, thus aiding the correction. The rays of light from an
object pass through the cornea, the aqueous humor, the crystalline lens, and the vitreous
humor, and they are refracted with so little spherical and chromatic aberration, that the
image formed upon the retina is practically perfect. The layer of rods and cones of the
retina is the only portion of the eye endowed directly with special sensibility, the impres-
sions of light being conveyed to the brain by the optic nerves. This layer is situated
next the choroid, but the other layers of the retina, through which the light passes to
reach the rods and cones, are perfectly transparent.

It has been positively demonstrated that the rods and cones are the only structures
capable of directly receiving visual impressions, by the following interesting experiment,
first made by Purkinje: We concentrate upon the sclerotic, with a convex lens of short
focus, an intense light, at a point as far as possible removed from the cornea. This passes
through the translucent coverings of the eye at this point, and the image of the light
reaches the retina. If we then look at a dark surface, we have the field of vision present-
ing a reddish-yellow illumination, with a dark, arborescent appearance produced by the
shadow of the large retinal vessels ; and, as we move the lens slightly, the shadow of the
vessels moves with it. Without going: elaborately into the mechanism of this remarkable
phenomenon, it is sufficient to state that Heinrich Mtiller has arrived at an absolute mathe-
matical demonstration that the shadows of the vessels are formed upon the layer of rods
and cones, and that this layer alone is capable of receiving impressions of light. His ex-
planation is accepted by all writers at the present day and is regarded as positive proof
of the peculiar sensibility of this portion of the retina. In carefully-conducted observa-
tions of this kind, a spot is seen in which no vessels appear, which corresponds to the
fovea centralis. When the experiment is prolonged, the vessels disappear, as the sensi-
bility of the retina becomes diminished by fatigue.

Theoretically, an illuminated object placed in tho angle of vision would form upon the
retina an image, diminished in size and inverted. This fact is capable of actual demon-
stration by means of the ophthalmoscope. With this instrument, the retina and the im-
ages formed upon it may be seen during life with perfect distinctness.

All parts of the retina, except the point of entrance of the optic nerve, are sensitive to
light ; and the arrangement of the cornea and pupil is such, that the field of vision is, at
the least estimate, equal to the half of a sphere. If a ray of light fall upon the border of
the cornea at a right angle to the axis of the eye, it is refracted by its surface and will
pass through the pupil to the border of the retina upon the opposite side. Above and
below, the circle of vision is cut off by the overhanging arch of the orbit and the malar
prominence; but externally the field is free. With the two eyes, therefore, tho lateral
field of vision must be equal to at least one hundred and eighty degrees. It is easy to
demonstrate, however, by the ophthalmoscope, as well as by taking cognizance of the
impressions made by objects far removed from the axis of distinct vision, that images
formed upon the lateral and peripheral portions of the retina are confused and imperfect.

792 SPECIAL SENSES.

We have a knowledge of the presence and an indefinite idea of the general form of large
objects situated outside of the area of distinct vision ; but, when we wish to note such
objects exactly, the eyeball is turned by muscular effort, so as to bring them at or very
near the axis of the globe. This tact, with what we know of the mechanism of refraction
by the cornea and lens, makes it evident that the area of the retina upon which images
are formed with perfect distinctness is quite restricted. A moment's reflection is sufficient
to convince any one that, in order to see any object distinctly, we must look at it, or
bring the axis of the eye to bear upon it directly. Let us see, now, how far this fact is
capable of positive demonstration.

If we examine the bottom of the eye with the ophthalmoscope, we can see the yellow
spot with the fovea centralis, apparently free from blood-vessels, and composed, as we
know, chiefly of those elements of the retina which are sensitive to light. If, at the
same time, we examine an image for which the eye is perfectly adjusted, it will be seen
that this image is perfect only at the fovea centralis ; and, if the object be removed from
the axis of vision, we see a confused image upon the retina removed from the fovea, at
the same time that the subject is conscious of indistinct vision. In the words of Helm-
holtz, " It is only in the immediate vicinity of the ocular axis that the retinal image pos-
sesses entire distinctness ; beyond this, the contours are less defined. It is in part for
this reason that in general we see distinctly in the field of vision, only the point that we
fix. All the others are seen vaguely. This lack of distinctness in indirect vision, in
addition, depends also upon diminished sensibility of the retina : at a slight distance from
the fixed point, the distinctness of vision has diminished much more than the objective
distinctness of retinal images."

At the point of penetration of the optic nerve, the retina is insensible to luminous
impressions ; at least, its sensibility is here so obtuse as to be entirely inadequate for
the purposes of vision. This point is called the punctum caecum ; and its want of
sensibility was demonstrated many years ago (1668) by Mariotte. The classical ex-
periment by which this important fact was positively ascertained, which is gener-
ally known to physiologists as Mariotte's experiment, is so curious that we quote it
verbatim :

"I fasten'd on an obscure Wall about the hight of my Eye, a small round paper, to
serve me for a fixed point of Vision ; and I fastened such an other on the side thereof
towards my right hand, at the distance of about 2. foot ; but somewhat lower than the
first, to the end that it might strike the Optick Nerve of my Right Eye, whilst I kept my
Left shut. Then I plac'd myself over against the First paper, and drew back by little
and little, keeping my Right Eye fixt and very steddy upon the same ; and being about
10. foot distant, the second paper totally disappear'd."

In this experiment, the rays of light from the paper which has disappeared from view
are received upon the punctnm ccecum, at the point of entrance of the optic nerve. If
the observer withdraw himself still farther, the second circle will reappear, as the rays
are removed from the punctum cascum. With the ophthalmoscope, the point of penetra-
tion of the optic nerve may be readily seen in the living eye. If the image of a flame
be directed upon this point, the sensation of light is either not perceived or it is very
faint and indefinite, and it is then probably due to diffusion to other portions of the
retina.

The relative sensibility of different portions of the retina has been accurately meas-
ured by Volkmann and has been found to be in an inverse ratio equal to about the square
of the distance from the axis of most perfect vision. This observer calculated the dis-
tance between the sensitive elements of the retina at which he supposed that two par-
allel lines would appear as one. In the axis of vision, the distance was 0-00029", and, at
a deviation inward of 8°, it was 0'03186", a diminution of acuteness of more than a hun-
dred times.

MECHANISM OF REFRACTION IN THE EYE. 793

Retinal Red. — In 1876, Prof. F. Boll published a short account of a discovery which
may possibly revolutionize our ideas of the mechanism of the appreciation of images
formed upon the retina. He discovered in the outer segments of the rods a peculiar red
or purple color, which disappeared after ten or twelve seconds of exposure to light. This
was first observed by Boll in the retina of frogs that had been kept for a certain time in
the dark. From his preliminary researches, Boll concluded that this coloration of the
retina exists only during life and persists but a few moments after death ; that it is con-
stantly destroyed during life by the action of light and reappears in the dark ; and finally
that it plays an important part in the act of vision. Kiihne and others have since con-
firmed and extended the original observations of Boll ; and the " retinal red " has been
noted in the mammalia and in man. It has been extracted from the retinas of frogs and
dissolved in a five-per-cent. solution of crystallized ox-gall, still presenting in solution its
remarkable sensitiveness to light. Finally it has been found possible to fix images of
simple objects, such as strips of black paper pasted upon a plate of ground glass, upon
the retina, by a process very like that of photography. These observations constitute
one of the most remarkable of recent discoveries ; but they are as yet too incomplete for
extended discussion in this connection.1

Mechanism of Refraction in the Eye.

A visible object sends rays from every point of its surface to the cornea. If the
object be near, the rays from each and every point are divergent as they strike the eye.
Rays from distant objects are practically parallel. It is evident that the refraction for
diverging rays must be greater than for parallel rays, as a necessity of distinct vision ; in
other words, the eye must be accommodated for vision at different distances. Leaving,
however, the mechanism of accommodation for future consideration, we shall endeavor
to show how the rays of light as they penetrate the eye are refracted and brought to a
focus at the retina. The important agents in refraction in the eye are the surfaces of the
cornea and the crystalline lens. Careful calculations have shown that the index of
refraction of the aqueous humor is sensibly the same as that of the substance of the cor-
nea, so- that, practically, the refraction is the same as if the cornea and the aqueous hu-
mor were one and the same substance. The index of refraction of the vitreous humor ig
practically the same as that of the aqueous humor, both being about equal to the index of
refraction of pure water. Refraction by the crystalline lens, however, is more complex
in its mechanism; depending, first, upon the curvatures of its two surfaces, and, again
upon the differences in the consistence of different portions of its substance. In view o
these facts, we may simplify the conditions of refraction in the eye by assuming tl
lowing arrangement :

The cornea presents a convex surface upon which the rays of light are receded At
a certain distance behind its anterior border, is the crystalline, a double convex lens,
corrected sufficiently for all practical purposes, both for spherical and ehromatio a
tion. This lens is practically suspended in a liquid with an index of refraet.on o,,ua o
that of pure water, as both the aqueous humor in front and the *^'£"T*"
have the same refractive power. Behind the lens, in its „,. and esactl;
which the ravs of li-ht are brought to a focus by the action of the cornea and i
SSS^SS£, which is the centre of distinct vision The an—a 1 clon,,, s ;
the fovea are capable of receiving visual impressions, wh.ch are conveyed to
by the optic nerves. All impressions made upon other portion, of t
pLatively indistinct; and the point of entrance of the ont.c nerve "••»
Inasmuch as the punctum ctecum is situated in either eye upon the nas

^^^

July, 1878, p. 190.

794 SPECIAL SENSES.

in normal vision, rays from the same object cannot fall upon both points at the same time.
Thus, in binocular vision, the insensibility of the punctum caecum does not interfere with
sight ; and the movements of the globe prevent any notable interference in vision, even
with one eye. The sclerotic coat is for the protection of its contents and for the inser-
tion of muscles. The iris has an action similar to that of the diaphragm in optical instru-
ments. The suspensory ligament of the lens, the ciliary body, and the ciliary muscle, are
for the fixation of the lens and its accommodation to distinct vision at different distances.
The choroid is a dark membrane for the absorption of light, preventing confusion of vision
from reflection within the eye.

Refraction by the cornea is effected simply by its external surface. The rays of light
from a distant point are deviated by its convexity so that, if they were not again refracted
by the crystalline lens, they would be brought to a focus at a point situated about T\ of
an inch behind the retina. Without the crystalline lens, therefore, distinct, unaided
vision is generally impossible, although the sensation of light is appreciated. In cases of
extraction of the lens for cataract, the crystalline is supplied by a convex lens placed
before the eye.

The rays of light, refracted by the anterior surface of the cornea, are received upon
the anterior surface of the crystalline lens, by which they are still farther refracted.
Passing through the substance of the lens, they undergo certain modifications in refrac-
tion dependent upon the differences in the various strata of the lens. These modifica-
tions have not been accurately calculated ; but it is sufficient to state that they contribute
to the accuracy of the formation of the retinal image and to the production of an image
practically free from chromatic dispersion. As the rays pass out of the crystalline lens,
they are again refracted by its posterior curvature and are brought to a focus at the area
of distinct vision.

The rays from all points of an object distinctly seen are brought to a focus, if the
accommodation of the lens be correct, upon a restricted surface in the macula lutea ; but
the rays from different points cross each other before they reach the retina, and the
image is consequently inverted. This is a fact capable of actual demonstration, as we
have shown in treating of the formation of images in the eye.

Calculating the curvatures of the refracting surfaces in the eye and the indices of
refraction of its transparent media, it has been pretty clearly shown, by mathematical
formula, that the eye, viewed simply as an optical instrument, and not practically, as the
organ of vision, presents a certain degree of spherical and chromatic aberration; but with
these formulae we have little to do in our purely physiological consideration of vision.

In most calculations of the size of images, the positions of conjugate foci, etc., in nor-
mal and abnormal eyes, a schematic eye reduced by Bonders, after the example of List-
ing, is regarded as sufficiently exact for all practical purposes. This simple scheme
represents the eye as reduced to a single refracting surface, the cornea, and a single liquid
assumed to have an index of refraction equal to that of pure water. The distance between
what are called the two nodal points and between the two principal points of the dioptric
system of the eye is so small, amounting to hardly T£7 of an inch, that it can be neglected.
In this simple eye, we assume a radius of curvature of the cornea of about £ of an inch,
and have a single optical centre situated ^ of an inch back of the cornea, the " principal
point " being in the cornea, at the axis of vision. The posterior focal distance, that is,
the focus, at the bottom of the eye, for rays that are parallel in the air, is about -f of an
inch. The anterior focal distance, that is, for rays parallel in the vitreous humor, is about
-f of an inch. The measurements in this simple schematic eye can be easily remembered
and used in calculations.

Astigmatism.

We have already alluded to an important peculiarity in the optical apparatus; which
is that the visual line does not coincide exactly with the axis of the eye. There is still

ASTIGMATISM.

795

another normal deviation from mathematical exactness in the refraction of rays by the
cornea and the crystalline lens, which is of considerable importance. If we place before
the eyes two threads crossing each other at right angles in the same plane, one of these
threads being vertical, and the other, horizontal, when the optical apparatus is adjusted
so that one line is seen with perfect distinctness, the other is not well defined. In other
words, when we accommodate for the vertical thread, the horizontal is indistinct, and
vice versa. If the horizontal line be seen distinctly, in order to see the vertical without
modifying the accommodation, it must be removed to a greater distance. This depends
chiefly upon a difference in the vertical and the horizontal curvatures of the cornea, so
that the horizontal meridian has a focus slightly different from the focus of the vertical
meridian. A condition opposite to that observed in the cornea usually exists in the
crystalline lens ; that is, the difference which exists between the curvatures of the lens
in the vertical and the horizontal meridians is such that the deepest curvature in the lens
is situated in the meridian of the shallowest curvature of the cornea. In this way, in
normal eyes, the aberration of the lens has a tendency to correct the aberration in the
cornea ; but this correction is incomplete, and there still remains, in all degrees of tension
of accommodation, a marked difference in the vision as regards vertical and horizontal
lines.

The condition just described is known under the name of normal, regular astigmatism ;
but the aberration is not sufficiently great to interfere with distinct vision. The degree
of regular astigmatism presents normal variations -in different eyes. In some eyes there
is no astigmatism ; but this is rare. According to Bonders, if the astigmatism amount to
^5- or more, it is to be considered abnormal ; which simply means that, beyond this point,
the aberration interferes with distinct vision.

From the mere definition of regular astigmatism, it is evident that this condition and
the degree to which it exists may easily be determined by noting the differences in the
foci for vertical and horizontal lines, and it may be exactly corrected by the application
of cylindrical glasses of proper curvature. Indeed, the curvature of a cylindrical glass
which will enable a person to distinguish vertical and horizontal lines with perfect dis-
tinctness at the same time is an exact indication of the degree of aberration. Regular
astigmatism, such as we have described, may be so exaggerated as to interfere very
seriously with vision, when it becomes abnormal. This kind of aberration, however,
which is dependent upon an abnormal condition of the cornea, is remediable by the
use of properly-adjusted cylindrical glasses.

Irregular astigmatism, excluding cases of pathological deformation, opaque spots, etc.,
in the cornea, depends upon irregularity in the different sectors of the crystalline lens.
Instead of a simple and regular aberration, consisting in a difference between the depth
of the vertical and the horizontal curvatures of the cornea and lens, we have irregular
variations in the curvatures of different sectors of the lens. As a consequence of this,
when the irregularities are very great, there is impairment of the sharpness of vision.
The circles of diffusion, which are regular in normal vision, become irregularly radiated,
and single points appear multiple, an irregularity described under the name of polyopia
monocularis. Accurate observations have shown that this condition exists to a very
moderate degree in normal eyes ; but it is so slight as not to interfere with ordinary vision.
In what is called normal, irregular astigmatism, the irregularity depends entirely upon
the crystalline lens. If we place before the eye a card with a very small opening, ami
move this before the lens, so that the pencil of light falls successively upon diffcivnt
tors, it can be shown that the focal distance is different for different portions. The radi-
ating lines of light observed in looking at remote luminous points, as the fixed stars, are
produced by this irregularity in the curvatures of the different sectors of the lens.

While regular astigmatism, both normal and abnormal, may bo perfectly corrected
by placing cylindrical glasses before the eyes, it is impossible, in the great majority of
cases, to construct glasses which will remedy the irregular form.

796 SPECIAL SENSES.

Movements of the Iris.

The movements of the iris are sufficiently simple, as well as the physiological con-
ditions under which they take place ; and it is only when we come to study the exact
mechanism of the production of these movements through the nervous system, that the
subject becomes complex, and, to a certain extent, obscure. As regards the movements
themselves, the simple facts are as follows :

There are two physiological conditions under which the size of the pupil is modified :
The first of these depends upon the amount of light to which the eye is exposed. When
the quantity of light is small, the pupil is widely dilated, so as to admit as much as pos-
sible to the retina. When the eye is exposed to a bright light, the retina is protected by
contraction of the iris. The muscular action by which the iris is contracted is character-
istic of the smooth muscular fibres, as can be readily seen by exposing an eye, in which
the pupil is dilated, to a bright light. Contraction does not take place instantly, but an
appreciable interval elapses after the exposure, and a more or less gradual diminution in
the size of the pupil is observed. This is seen both in solar and in artificial light. The
second of these conditions depends, indirectly, upon the voluntary action of muscles.
We have already seen, in connection with the physiology of the third pair of nerves, that
the effort of converging the axes of the eyes by looking at a very near object contracts
the pupils. We shall see, also, that the effort of accommodation of the eye for near
objects produces the same effect, even when the eyes are not converged. This action
will be fully considered under the head of accommodation.

One point relating to the anatomy of the iris is of great importance in connection with
the physiology of its movements ; and that is the question of the existence of dilator
fibres. Upon this point there is some difference of opinion ; but, as we stated in treating
of the structure of the eye, the weight of anatomical authority is decidedly in favor of
the existence of radiating fibres.

Direct Action of Light upon the Iris. — The variations in the size of the pupil under
different physiological conditions are effected almost exclusively through the nervous
system, either by reflex action from variations in the intensity of light, or by a direct
influence, as in accommodation for distances ; but it is nevertheless true that the muscu-
lar tissue of the iris will respond directly to the stimulus of light. Earless noted, in sub-
jects dead of various diseases, from five to thirty hours after death, that the iris con-
tracted under the stimulus of light ; and he justly remarks that this is probably due to
direct action upon its muscular tissue, and that it is not reflex, for the reason that the
irritability of the nerves in warm-blooded animals disappears certainly in twenty hours
after death. The experiments of Harless were made upon the two eyes, one being
exposed to the light, while the other was closed. The contraction, however, took place
very slowly, requiring an exposure of several hours. This mode of contraction is very-
different from the action of the iris during life, but it is precisely like the contraction
observed after division of the motor oculi communis, which is slow and gradual and
undoubtedly depends upon the direct action of light upon the muscular fibres.

Action of the Nervous System upon the Iris.— This subject, as far as it relates to the
third pair, has been pretty fully considered in connection with the physiology of these
nerves ; and it is unnecessary to refer again in detail to the experiments which have
already been cited. The reflex phenomena observed are sufficiently distinct. WThen light
is admitted to the retina, the pupil contracts, and the same result follows mechanical
irritation of the optic nerves. When the third pair of nerves has been divided, no such
reflex phenomena are observed. It is well known, also, that division of the third nerves
in the lower animals or their paralysis in the human subject produces permanent dilata-
tion of the pupil, the iris responding, only in the slow and gradual manner already indi-
cated, to the direct action of light.

MOVEMENTS OF THE IRIS. 797

Taking all the experimental facts into consideration, it is certain that the third ncrvo
has an important influence upon the iris. Filaments from the ophthalmic ganglion animate
the circular fibres, or sphincter, and these filaments derive their power from the third
cranial nerve. If this nerve be divided, the iris becomes permanently dilated and is im-
movable, except that it responds very slowly to the direct action of light. The reflex
action by which the pupil is contracted under the stimulus of light operates through the
third nerve, and no such action can take place after this nerve has been divided. In view
of these facts, there can be no doubt with regard to the nervous action upon the sphincter
of the pupil, this muscle being animated exclusively by filaments from the motor oculi
communis, coming through the ophthalmic ganglion.

We admit, with most modern anatomists, the existence of radiating muscular fibres in
the iris, the action of which is antagonistic to the circular fibres, and which dilate the
pupil. That these fibres are subjected to nervous influence is rendered certain by experi-
ments upon the sympathetic system.

The effects of division of the sympathetic in the neck have been treated of fully in
connection with the general functions of these nerves. It will be sufficient for our present
purposes to state, in a general way, the influence of these nerves upon the movements of
the iris. There can be no doubt that the action of the sympathetic upon the pupil is
directly antagonistic to that of the third pair, the former presiding over the radiating, or
dilating muscular fibres ; and the only question to determine is the course taken by the
sympathetic filaments to the iris. Experiments on the influence of the fifth pair upon the
pupil have been somewhat contradictory in different animals. In rabbits, section of this
nerve in the cranial cavity produces contraction of the pupil ; but in dogs and cats the
same operation produces dilatation. In the human subject, of course, it is impossible to
determine this point by direct experiment ; and the varying results obtained in observa-
tions upon different animals probably depend upon differences in the anatomical relations
of the nerves. It is probable, however, that the filaments of the sympathetic which ani-
mate the dilator fibres join the fifth nerve near the ganglion of Gasser and from this
nerve pass to the iris.

There seem to be two distinct nerve centres corresponding to the two sets of nerves
which regulate the movements of the iris. One of these centres presides over the reflex
contractions of the iris, and the other is the centre of origin of the nervous influence
through which the pupil is dilated.

The mechanism of reflex contraction of the iris under the stimulus of light is suffi-
ciently simple. An impression is made upon the retina, which is conveyed by the optic
nerves to the centre of vision, and, in obedience to this impression, the sphincter of the
iris contracts. If the optic nerves be divided, so that the impression cannot be conveyed
to the centre, or if we divide the third pair, through which the motor stimulus is con-
veyed to the muscular fibres, no movements of the iris can take place. The centres
which preside over these reflex phenomena are situated in the tubercula qua3rigemina,
In the remarkable experiments of Flourens upon the encephalic centres, it was shown
that the iris loses its mobility after destruction of the tubercula. This fact has been
repeatedly confirmed by later experimenters. In birds, in which the decussation of the
optic nerves is complete, this action is crossed, destruction of the tubercle upon one side
producing immobility of the iris upon the opposite side ; but in man, where the anatomi-
cal relations of the optic nerves upon the two sides are more complex, the crossed action
is probably not so complete. In man, the axes of both eyes are habitually brought
to bear upon objects, and it is well known that there is a physiological unity in the
action of the two eyes in ordinary vision. We also observe that, when one i-yc only
is exposed to light, the pupil becoming contracted under this stimulus, the pupil ot
the other eye also contracts. There is, indeed, a direct contraction and dilatation
of the pupil of the eye which is exposed to the light, and an indir.-ct. or "OOB
sual" movement of the iris upon the opposite side. The oonaensnal contraction occurs

798 SPECIAL SENSES.

about | of a second later than the direct action, and the consensual dilatation, about \
of a second later. (Bonders.)

Budge and Waller have shown that the filaments of the sympathetic which produce
dilatation of the pupil take their origin from the spinal cord. In the spinal cord, between
the sixth cervical and the second thoracic nerves, is situated the inferior cilio-spinal
centre. When the spinal cord is stimulated in this situation, both pupils become dilated.
If the cord be divided longitudinally and the two halves be separated from each other by
a glass plate, stimulation of the right half produces dilatation of the right pupil, and mce
versa. This does not occur when the sympathetic in the neck has been divided. In
addition to the inferior cilio-spinal centre, there is a superior centre, which is in com-
munication with the superior cervical ganglion and is situated near the sublingual nerve.
The influence of this centre over the pupil cannot be demonstrated by direct stimulation,
because it is too near the origin of the fifth, irritation of which has an influence over the
iris; but it is shown by division of its filaments of communication with the iris.

Section and galvanization of the different nerves which regulate the movements of the
iris have a certain influence upon its vascularity ; and, indeed, it has been thought that
contraction is in a measure due to congestion of its vessels, and dilatation, to an opposite
condition. This view is adopted by some of those who deny the existence of the radi-
ating muscular fibres of the iris. Assuming that the size of the pupil is, to a certain
extent, affected by the condition of the vessels, it is evident that the more extensive move-
ments of the iris are due mainly to muscular action. It has been also shown that the
changes in the iris produced by injection of its vessels are not to be compared in their
extent with its physiological movements. The changes in vascularity produced by divid-
ing or galvanizing the sympathetic do not differ from the phenomena noted in experi-
ments upon other portions of the sympathetic system.

Accommodation of the Eye to Vision at Different Distances.

The mechanism by which the eye is adjusted for distinct vision at different distances
is one of the most interesting and important points connected with the physiology of the
sight. At the present day, this point may be regarded as definitely settled, particularly
since the variations in the thickness and the curvatures of the crystalline lens have been
so accurately measured by Helmholtz. We shall have little to say with regard to the
various theories of accommodation advanced by the older physiologists, except to indicate,
in a very general way, the most plausible views that have been adopted from time to time
by physiological writers. In the first place, we shall note certain physical laws and their
application to the eye, which show the necessity for accommodation.

Supposing the eye to be adapted to vision at an infinite distance, in which the rays
from an object, as they strike the cornea, are practically parallel, it is evident that the
foci of the rays, as they form a distinct image upon the retina, are all situated at the
proper plane. Under these conditions, in a perfectly normal eye, the image, appreciated
by the individual or seen by means of the ophthalmoscope, is perfectly clear and distinct.
If the foci be situated in front of the retina, the rays, instead of coming to a focus upon a
point in the retina, will cross, and, from their diffusion or dispersion, will produce indis-
tinct vision. Under these circumstances, a distinct point is not perceived, but every point
in the image is surrounded by an indistinct circle. These are called " circles of diffusion."
If, now, the eye, adjusted for vision at an infinite distance, be brought to bear upon &
near object, the rays from which are divergent as they strike the cornea, the image will
be no longer distinct, but will be obscured by circles of diffusion. It is the adjustment by
which these circles of diffusion are removed that constitutes accommodation. This fact
has been demonstrated by Helmholtz by means of the ophthalmoscope. " If the eye be
adjusted to the observation of an object placed at a certain distance, it is found that the
image of a flame, placed at the same distance, is produced with perfect distinctness upon

ACCOMMODATION OF THE EYE.

799

the retina, and, at the same time, upon the illuminated plane of the image, the vessels and
the other anatomical details of the retina are seen with equal distinctness. But, when
the flame is brought considerably nearer, its image becomes confused, while the details
of the structure of the retina remain perfectly distinct."

It is evident that there is a certain condition of the eyes adapted to vision at an infi-
nite distance, and that, for the distinct perception of near objects, the transparent media
must be so altered in their arrangement or in the curvatures of their surfaces, that the
refraction will be greater; for, without this, the rays would be brought to a focus be-
yond the retina.

The changes in the eye by which accommodation is effected are now known to con-
sist mainly in an increased convexity of the lens for near objects ; and the only points in
dispute are a few unimportant details in the mechanism of this action. The simple facts
to be borne in mind in studying this question are the following :

When the eye is accommodated to vision at an infinite distance, the parts are passive.

In the adjustment of the eye for near objects, the convexities of the lens are increased
by muscular action.

In accommodation for near objects, the pupil is contracted; but this action is merely
accessory and is not essential.

The ordinary range of accommodation varies between a distance of about five inches
and infinity.

Changes in the Crystalline Lens in Accommodation. — It is important to determine
first the extent and nature of the changes of the lens in accommodation ; and, by the
ingenious experiments of the German physiologists, particularly those of Helmholtz,
these changes have been accurately measured in the living subject. As the general result
of these measurements, it was ascertained that the lens becomes increased in thickness
in accommodation for near objects, chiefly by an increase in its anterior curvature, by
which this surface of the lens is made to project toward the cornea. As the iris is in
contact with the anterior surface of the lens, this membrane is made to project in the act
of accommodation. The posterior curvature of the lens is also increased, but this is slight
as compared with the increase of the curvature of its anterior surface. . The distance
between the posterior surface of the lens and the cornea is not sensibly altered. It is
unnecessary to describe minutely the methods employed in making these calculations,
and it is sufficient for our purposes to state that it is done by accurately measuring the
comparative size of images formed by reflection from the anterior surface of the lens.
The results obtained by Helmholtz in observations upon three different persons are as
follows :

Persons examined.

Eadius of curvature of the anterior surface
of the lens.

Displacement of the pupil in accommodation
for near objects.

Distant vision.

Near vision.

0. II.
B. P.
J. H.

0-4641 of an inch.
0-3432 "
0-4056 "

0-3354 of an inch.
0-2701 "

0-0140 of an inch.
0-0172

The mechanism of the changes in the thickness and in the curvatures of the lens in
accommodation can only be understood by keeping clearly in mind the physical proper-
ties of the lens itself and its anatomical relations. In situ, in what has been called the
indolent state of the eye, the lens is adjusted to vision at an infinite distance and is flat-
tened by the tension of its suspensory ligament. After death, indeed, it i> • pro-
duce changes in its form by applying traction to the zone of Zinn. If we remember,

800

SPECIAL SENSES.

now, the exact relations of the suspensory ligament, the ciliary muscle, and the lens, and
keep in mind the tension within the globe, it is evident that, when the ciliary muscle is in
repose, the capsule will compress the lens, increasing its diameter and diminishing its
convexity. It is in this condition that the eye is adapted to vision at an infinite distance.
It is evident, also, that very slight changes in the convexity of the lens will be sufficient
for the range of accommodation required. If we fix with the eye any near object we are
conscious of an effort, and the prolonged vision of near objects produces a sense of fatigue.
This may be illustrated by the very familiar experiment of looking at a distant object
through a gauze. When the object is seen distinctly, the gauze is scarcely perceived ;
but by an effort we can bring the eye to see the meshes of the gauze distinctly, when the
impression of the distant object is either lost or becomes very indistinct.

Our knowledge of the action of the ciliary muscle is only to be arrived at theoretically
and by studying the effects produced upon the lens. This muscle, it will be remembered,
arises from the circular line of junction of the cornea and sclerotic, wrhich is undoubtedly
its fixed point, passes backward, and is lost in the tissue of the choroid, extending as far
back as the anterior border of the retina. Most of the fibres pass directly backward, but
some become circular or spiral. When this muscle contracts, the choroid is drawn for-
ward, with, probably, a slightly spiral motion of the lens, the contents of the globe situ-
ated posterior to the lens are compressed, and the suspensory ligament is relaxed. The
lens itself, the compressing and flattening action of the suspensory ligament being dimin-
ished, becomes thicker and more convex, by virtue of its own elasticity, in the same way
that it becomes thicker after death when the tension of the ligament is artificially dimin-
ished.

FIG. 253. — Section of the lens, etc., showing the mechanism of accommodation. (Fick.)

The left side of the figure (F) shows the lens adapted to vision at infinite distances ; the right side of the figure (N)
shows the lens adapted to the vision of near objects, the ciliary muscle being contracted and the suspensory liga-
ment of the lens consequently relaxed.

This is, in brief, the mechanism of accommodation. Near objects are seen distinctly
by a voluntary contraction of the ciliary muscle, the action of which is adapted to the
requirements of vision with exquisite nicety. In early life, the lens is soft and elastic,
and the accommodating power is at its maximum ; but in old age the lens becomes flat-
tened, harder, and less elastic, and the power of accommodation is necessarily diminished.

Changes in the Iris in Accommodation. — The size of the pupil is sensibly diminished
in accommodation of the eye for near objects. Although the movements of the iris are
directly associated with the muscular effort by which the form of the lens is modified,
the contraction of the pupil is not one of the essential conditions of accommodation.
Helmholtz cites a case in which the iris was completely paralyzed, the power of accom-
modation remaining perfect ; and he mentions another case, reported by Yon Graefe, in
which accommodation was not disturbed after loss of the entire iris.

We have already noted the fact that the pupil contracts when the eyes are made to
converge by the action of the muscles animated by the third pair of nerves ; and it is evi-

ERECT IMPRESSIONS PRODUCED BY INVERTED IMAGES. 801

dent that convergence of the eyes always occurs in looking at very near objects. It
becomes a question, then, whether the contraction of the pupil in accommodation for near
objects be associated with the action of the third nerves, or with filaments from the
ophthalmic ganglion, which supplies the nervous influence to the ciliary muscle. This
seems to have been definitively settled by Donders, who demonstrated two important
points : First, that increased convergence of the visual lines without change of accommo-
dation makes the pupil contract, as is easily proven by simple experiments with prismatic
glasses. Second, that when accommodation is effected without converging the visual
axes, "each stronger tension is combined with contraction of the pupil."

The action of the iris, as is evident from the facts just stated, is to a certain extent
under the control of the will ; but it cannot be disassociated, first, from the voluntary
action of the muscles which converge the visual axes, and second, from the action of the
ciliary muscle. Donders states that, by alternating the accommodation for a remote and
a near object, he could voluntarily contract and dilate the pupil more than thirty times
in the minute. Brown-Sequard, in discussing the voluntary movements of the iris, men-
tions a case in which " the pupil could be contracted or dilated without changing the
position of the eye or making an effort of adaptation for a long or a short distance."
As a farther evidence of the connection of accommodation with muscular action, cases
are cited in works on ophthalmology, in which there is paralysis of the ciliary mus-
cle as well as cases in which the act of accommodation is painful.

An interesting phenomenon connected with accommodation is observed in looking at
a near object through a very small orifice, like a pinhole. The shortest distance at
which we can see a small object distinctly is about five inches ; but, if we look at the
same object through a pinhole in a card, it can be seen distinctly at the distance of about
one inch, and it then appears considerably magnified. In this experiment, the card serves
as a diaphragm with a very small opening, so that the centre of the lens only is used ;
and the apparent increase in the size of the object is probably due to the fact that its dis-
tance from the eye is many times less than the distance at which distinct vision is possible
under ordinary conditions. It is well known that myopic persons, by being able to bring
the eye nearer to objects than is possible in ordinary vision, can see minute details with
extraordinary distinctness.

Erect Impressions produced by Images inverted upon the Retina.

If we have become thoroughly acquainted with the mechanism of the formation of
images upon the retina and the physiological action of the different parts of the optical
apparatus, it will be sufficient to note the action of both eyes, as contrasted with the
action of one, in normal vision, without discussing fully the multitude of curious observa-
tions made with the stereoscope ; and we can readily comprehend the action of muscles by
which the axis of vision is directed toward different objects, without entering into a discus-
sion of abstruse mathematical calculations with regard to the exact centre of rotation, the
law of torsions, and other points connected with physiological optics. These are ques-
tions, however, of great interest to ophthalmologists and are fully discussed in elaborate
special treatises.

We shall allude briefly, in this connection, to a question which has long engaged the
attention of physiologists, and one which, we cannot but think, has been made the sub-
ject of much unprofitable speculation. It is a matter of positive demonstration that the
images of objects seen are inverted as they appear upon the retina. "W liy is it. however,
that objects are appreciated as erect, when their images are thus in \vrtrd ? With a
knowledge of the fact that the appreciation of impressions made upon tin- 0
special sense is capable of education and is corrected by experien. ifl hardly

necessary to enter into an elaborate discussion of this point. We appreciate with accu-
racy the density of objects, the direction of sounds, differences in musical tones, the
51

802 SPECIAL SENSES.

taste of sapid substances, odors, etc., as the result, to a great degree, of education. In
the same way, probably, we acquire the power of noting the position of objects in vision ;
but even this supposition is not necessary to explain the phenomenon of direct vision by
means of inverted images. The following paragraph, quoted from Giraud-Teulon, is a
simple expression of facts and shows the absurdity of the elaborate theoretical explana-
tions made by many of the earlier writers :

" If the objects seen mark their image upon the retina, each one in a proper second-
ary axis ; if, on the other hand, the retina appreciates these, independently of ourselves,
in these same secondary axes, which all cross at the same point, it is evident that an
exact or erect sensation, as well as the object which produces it, should necessarily corre-
spond to an inverted or reversed image. But it is neither habit, education, nor informa-
tion derived from the sense of touch, that enables us, as it is said, to see objects erect
by means of reversed images. The retina sees or localizes objects where they are ; that is
what we call 'erect.' If the picture be reversed, it is a mere matter of geometry."

In discussing the same question, Helmholtz says that " our natural consciousness is
completely ignorant even of the existence of the retina and of the formation of images :
how should it know any thing of the position of images formed upon it? "

Binocular Vision.

"We have thus far considered the mechanism of the eye and its action as an optical instru-
ment, in simple, or monocular vision. It is evident, however, that we habitually use both
eyes, and that their axes are practically parallel in looking at distant objects and are con-
verged when objects are approached to the nearest point at which we have distinct vision.
In fact, an image is formed simultaneously upon the retina of each eye, but it is neverthe-
less appreciated as a unit. If the axis of one eye be slightly deviated by pressure upon
the globe, so that the images are not formed upon corresponding points upon the retina
of each eye, our vision is more or less indistinct and is double. In strabismus, when this
condition is recent, temporary, or periodical, as in recent cases of paralysis of the exter-
nal rectus muscle, when both eyes are normal, there is double vision. When the strabis-
mus is permanent and has existed for a long time, double vision may not be observed,
unless the subject direct the attention strongly to this point. As it is usual, in such
cases, for one eye to be much superior to the other in acuteness of vision, an object is
fixed with the better eye, and its image is formed upon the fovea. The image formed
upon the retina of the other eye is indistinct, and in many instances it is habitually disre-
garded ; so that, practically, the subject uses but one eye, and presents the errors of
appreciation which attend monocular vision, such as a want of accurate estimation of
the solidity and distance of objects. It is stated as the rule that, when strabismus of
long standing is remedied, as far as the axes of the eyes are concerned, by an operation,
binocular vision is not restored ; but the experiments necessary to the accurate determi-
nation of this point are exceedingly delicate and must be made with great care. This is
explained upon the supposition that the functional power of the retina of the affected
eye has been gradually and irrecoverably lost from disuse. In normal binocular vision,
the images are formed upon the fovea centralis of each eye ; that is, upon corresponding
points, which are, for each eye, the centres of distinct vision.

It is hardly necessary to speculate with regard to the reason why two images, one
upon each retina, convey the impression of a single object. We appreciate a sound with
both ears ; the impression of a single object is received by the sensory nerves of two or
more fingers ; the olfactory nerves upon the two sides are simultaneously concerned in
olfaction ; and, in the same way, when we look at a single object with both eyes, the
brain appreciates a single image. We shall see, however, that the concurrence of both
eyes is necessary to the exact appreciation of distance and form ; and, when the two images
are formed upon corresponding points, the brain receives a correct impression of a single

BINOCULAR VISION. 803

object. When our vision is perfectly normal, the sensation of the situation of any single
object is referred to one and the same point ; and we cannot receive the impression of a
double image unless the conditions of vision be abnormal.

Corresponding Points. — While it requires no argument, after the statements we have
just made, to show that an image must be formed upon the fovea of each eye in order
to produce the effect of a single object, it becomes important to ascertain how far it is
necessary that the correspondence of points be carried out in the retina. This leads to
considerations of very great interest and importance. It is almost certain that, for abso-
lutely perfect, single vision with the two eyes, the impressions must be made upon ex-
actly corresponding points, even to the ultimate sensitive elements of the retina. We
may suppose, indeed, that each rod and each cone of one eye has its corresponding rod
and cone in the other, situated at exactly the same distance in corresponding directions
from the visual axis. When the two images of an object are formed upon these correspond-
ing points, they appear as one ; but, when the images do not correspond, the impression
is as though the images were formed upon different points in one retina, and, of neces-
sity, they appear double.

The effect of a slight deviation from the corresponding points may be illustrated by
the following experiment : We fix a small object, like a lead-pencil, held at a distance of
a few inches, with the eyes, and see it distinctly as a single object ; we hold in the same
line, a few inches farther removed, another small object ; when the first is seen distinctly,
the second appears double ; we fix the second with the eyes, and the first appears double.
It is evident here, that, when the axes of the eyes bear upon one of these objects, the
images of the other must be formed at a certain distance from the corresponding retinal
points.

The Horopter. — The above-mentioned experiment enables us to understand the situa-
tion of the horopter. If we fix both eyes upon any object directly in front and keep
them in this position, a similar object moved to one side or the other, within a certain
area, may be seen without any change in the direction of the axis of vision ; but the dis-
tance from the eye at which we have single vision of this second object is fixed, and, at
any other distance, the object appears double. The explanation of this is, that, at a cer-
tain distance from the eye, the images are formed upon corresponding points in the retina;
but, at a shorter or longer distance, this cannot occur. This illustrates the fact that there
are corresponding points throughout the sensitive layer of the retina, as well as in the
fovea centralis. By these experiments, the following facts have been ascertained : With
both eyes fixed upon an object, another object moved to one side or the other can be
distinctly seen only when it is carried in a certain curved line. On either side of this line,
the object appears double. This line, or area, for the line may have any direction, is
called the horopter. It was supposed at one time to be a regular curve, a portion of a
circle drawn through the fixed point and the points of intersection of the rays of light in
each eye. Although it has been ascertained that the line varies somewhat from a regular
curve, and also varies in different meridians, this is due to differences in refraction, etc.,
and the principle is not altered.

It is undoubtedly true that education and habit have a great deal to do with the cor-
rection of visual impressions and the just appreciation of the size, form, and distance of
objects. If we may credit the account of the remarkable case of Caspar Ilaiiscr. who is
said to have been kept in total darkness and seclusion, from the iviv of live months until
he was nearly seventeen years old, the appreciation of size, form, and distance is acquired
by correcting and supplementing the sense of sight by experience, even in binocular ril
This boy at first had no idea of the form of objects, or of distance, until he had teamed
by touch, by walking, etc., that certain objects were round, others square, and had actually

804 SPECIAL SENSES.

traversed the distance from one object to another. At first, all objects appeared to be, as
it were, painted upon a screen. Such points as these it would be impossible for us to
accurately observe in infants ; but we have all seen young children grasp at remote
objects, apparently under the impression that they were within reach. It must be ad-
mitted, however, that the case of Casper Hauser is rather indefinite ; but it is certain
that, even in the adult, education and habit enable us to greatly improve the faculty of
estimating distances.

The important questions for us now to determine relate to the differences between
monocular and binocular vision in the adult. We may see an object distinctly with
one eye ; but are we able, from an image made upon one retina, to appreciate all its
dimensions and its exact locality ?

Accurate observations bearing upon this question leave no doubt of the fact that
monocular vision is incomplete and inaccurate, and that it is only when two images are
formed, one upon each retina, that vision is perfect. We cannot better illustrate the
truth of this proposition and the exact condition of our positive knowledge upon this
important point, than by quoting in full the facts and arguments advanced by Giraud-
Teulon :

" Monocular vision only indicates to us immediately visual direction, and not precise
locality. At whatever distance a luminous point may be situated in the line of direction,
it forms its image upon the same point in the retina.

" In the physiological action of a single eye, in order to arrive at an idea of the dis-
tance of a point in a definite direction, we have only the following elements :

" 1. The consciousness of an effort of accommodation.

" 2. Our own movement in its relations to the point observed.

" 3. Facts brought to bear from recollection, education, our acquired knowledge with
regard to the form and size of objects : in a word, experience.

" 4. The geometric perspective of form and position.

" 5. Aerial perspective.

" All these are elements wanting in precision and leaving the problem without a
decisive solution.
• " And, indeed :

" We place before one of our eyes, the other being closed, the excavated mould of a
medallion : we do not hesitate, after a few seconds, to mistake it for the relief of the
medallion. This illusion ceases at the instant that both eyes are opened.

" Or again :

" A miniature, a photograph, a picture, produces for a single eye a perfect illusion ;
but, if both eyes be open, the picture becomes flat, the prominences and the depressions
are effaced.

" We may repeat the following experiment described by Malebranche : 'Suspend by
a thread a ring, the opening of which is not directed toward us ; step back two or three
paces ; take in the hand a stick curved at the end ; then, closing one eye with the hand
endeavor to insert the curved end of the stick within the ring, and we shall be surprised
at being unable to do in a hundred trials what we should believe to be very easy. If,
indeed, we abandon the stick and endeavor to pass one of the fingers through the ring,
we shall experience a certain amount of difficulty, although it is very near. This diffi-
culty ceases at the instant that both eyes are opened.'

" As regards precision, exactitude of information concerning the relative distance
of objects, that is to say, the idea of the third dimension or of depth, there is then a
notable difference between binocular vision and that which is obtained by means of one
eye alone."

It is evident that an accurate idea of the distance of near objects cannot be obtained
except by the use of both eyes, and this fact will explain, in part, the errors of monocu-
lar vision, when we look with one eye upon objects in relief ; for, under these conditions,

BINOCULAR VISION. 805

we cannot determine with accuracy whether the points in relief be nearer or farther
from the eye than the plane surface. This will not fully explain, however, the idea of
solidity of objects which we obtain by the use of both eyes ; for the estimation of dis-
tance is obtained by bringing the axes of both eyes to bear upon a single object, be it
near or remote. The fact is, as was distinctly stated by Galen, in the second century
that, when we look at any solid object not so far removed as to render the visual axes,
practically parallel, we see with the right eye a portion of the surface which is not seen
with the left eye, and vice versa. The two impressions, therefore, are not identical for
each retina ; the image upon the left retina including a portion of the left side of the
object not seen by the right eye, the right image in the same way including a portion of
the right surface not seen by the left eye. These slightly dissimilar impressions are
fused, as it were, produce the impression of a single image, when vision is perfectly
normal, and this gives the idea of relief or solidity, enabling us to appreciate exactly the
form of objects, when they are not too remote.

The fact just stated is of course a mathematical necessity in binocular vision for near
objects ; but the actual demonstration of the fusion of two dissimilar images and the con-
sequent formation of a single image giving the impression of solidity was made by the
invention of the stereoscope, by Wheatstone. The principle of this instrument is very
simple. Two pictures are made, representing a solid object, one viewed slightly from
the right side, and the other, slightly from the left, so as to imitate the differences in
the images formed upon the two retina3. These pictures are so placed in a box that the
image of one is formed upon the right retina, and the other, upon the left. When these
conditions are accurately fulfilled, we see but a single image, and this conveys to the
mind the perfect illusion of a solid object. Experiments with the stereoscope are so
familiar that they need hardly be dwelt upon. With most persons, an apparatus is
necessary to shut off disturbing visual impressions ; but some individuals are able to
fuse two images in this way, placed in proper position, without the aid of an instrument,
by a simple effort of the will.

The invention of the stereoscope has led to many curious and interesting experiments,
especially since the art of photography has enabled us to produce pictures in any position
with absolute accuracy ; but a simple statement of the principle upon which the instru-
ment is constructed illustrates the mechanisrn of binocular vision in the appreciation of
the form of objects. Experience, the aid of the sense of touch, etc., enable persons with
but one eye to get a notion of form, but the impressions are never entirely accurate in
this regard, although, from habit, this defect occasions little or no inconvenience. A
striking illustration of these points is afforded by the' binocular microscope, which,
especially with low magnifying powers, produces a startling impression of relief.

As we have just remarked, the stereoscope affords a satisfactory explanation of the
mechanism of the eye in the appreciation of the form of objects ; but, notwithstanding
this, a theory has been proposed, and is adopted by some writers, that we obtain an idea
of form by rapidly and insensibly directing the eyes successively toward different points
on the surface of objects. It is difficult to understand how the eye can make these rapid
movements, but the question is definitively settled by a very simple fact demonstrated
by Dove, Helmholtz, and others. In an article on visual perception, by Helinholtz, it is
stated that stereoscopic effect is recognized when two pictures are seen illuminated by
an electric spark, the duration of which does not amount to the four-thousandth part of
a second, so short, indeed, that a falling body appears absolutely motionless. Under
these conditions, displacement of the line of vision would seem to be impossible.

We shall conclude our discussion of binocular vision and the stereoscope with a brief
account of some experiments upon the binocular fusion of colors, which are very curious,
although they have no very important bearing upon the physiology of the eye in ordinary
vision. Though an opposite opinion is held by some experimenter*, Helmholtz, with
many others, states that, when one color is seen with one eye and another color with the

806 SPECIAL SENSES.

other eye, in the stereoscope, the impression is not of a single color resulting from the
combination of the two. It is true that there is an imperfect mingling of the two colors,
but this is very different from the resulting color produced by the actual fusion of the
two. There is, in other words, a sort of confusion of colors, without the complete com-
bination with which we are familiar in ordinary experiments. One additional point of
interest, however, is that the binocular fusion of two pictures, unequally illuminated or
of different colors, produces a single image of a peculiar lustre, even when both surfaces
are dull. This may be very strikingly shown by making a stereoscopic combination of
images of crystals, one with black lines on a white ground, and the other with white lines
on a black ground. The resulting image has then the appearance of dark, brilliant crys-
tals, like graphite.

Duration of Luminous Impressions.

The time necessary for vision is exceedingly short ; so short, indeed, that it almost
passes our powers of comprehension. Taking advantage of the very delicate methods of
chronometric observations now employed by physicists, it has been shown by Prof. Rood,
of New York, that the letters on a printed page are distinctly seen when illuminated by
an electric spark, the duration of which was measured and found to be not more than
forty billionths of a second. Inasmuch as the waves of light strike the eye at the rate of
over five hundred millions of millions in a second, it is evident that, even in the period
indicated by Prof. Rood, an immense number of waves have time to impinge upon the
retina.

We have long been familiar with the fact that an impression made upon the retina
endures for a length of time that can readily be measured, and that its duration bears a
certain degree of relation to the intensity of the luminous excitation. If, after looking
fixedly at a very bright object, we suddenly produce complete obscurity, the object is
more or less distinctly seen after the rays have ceased to pass to the eye, and the image
fades away gradually. When we produce a rapid succession of images, they may be, as
it were, fused into one, as the spokes of a rapidly-revolving wheel are indistinct and
produce a single impression. This is due to the persistence of the successive retinal
impressions; for, if a revolving wheel, or even a falling body, be illuminated for the brief
duration of an electric spark, it appears absolutely stationary, as the period of time neces-
sary for perfectly distinct vision and the duration of the illumination are so short, that
there is no time for any appreciable movement of the object. The familiar experiments
made with revolving disks strikingly illustrate these points. In a disk marked with
alternate radiating lines of black and white, the rays become entirely indistinguishable
during rapid revolution, and the disk appears of a uniform color, such as would be pro-
duced by a combination of the black and white. Very beautiful effects of artificial com-
bination of colors may be produced in this way, the resultant color appearing precisely
as if the individual colors had been ground together. It is also interesting, in this con-
nection, to note that the duration of retinal impressions varies considerably for the
different colors. According to Emsmann, the duration for yellow is 0*25 of a second;
for white, 0;25 of a second ; for red, 0-22 of a second ; and for blue, 0'21 of a second.

It is unnecessary to describe farther in detail the well-known phenomena which
illustrate the point under consideration. The circle of light produced by rapidly revolving
a burning coal, the track of a meteor, and other illustrations, are sufficiently familiar, as
well as many scientific toys producing optical illusions of various kinds.

Irradiation. — It has been observed that luminous impressions are not always confined
to the elements of the retina directly involved, but are sometimes propagated to those
immediately adjacent. This gives to objects a certain degree of amplification, which is
generally in proportion to their brightness. An illustration of this is afforded by the
simple experiment of looking at two circles, one black on a white ground, and the other

MOVEMENTS OF THE EYEBALL. 807

white on a black ground. Although the actual dimensions of the two circles are iden-
tical, the irradiation of rays from the white circle makes this appear the larger. In a
circle with one half black and the other white, the white portion will appear larger, for
the same reason. This deception increases sensibly when we look steadily at the object.
These phenomena are due to what has been called by physiologists irradiation ; and their
explanation is very simple. It is probable that luminous impressions are never confined
absolutely to those parts of the retina upon which the rays of light directly impinge, but
that the sensitive elements immediately contiguous are always more or less involved.
In looking at powerfully-illuminated objects, the irradiation is considerable, as compared
with objects which send fewer luminous rays to the eye.

In experiments analogous to those just described, made with strongly colored objects,
it has been observed that the border of irradiation takes a color complementary to that
of the object itself. This is particularly well marked when the objects are steadily looked
at for some time. Illustrations of this point also are very simple. If we looked fixedly
at a red spot or figure on a white ground, we soon see surrounding the red object a faint
areola of a pale green ; or, if the image be yellow, the areola will appear pale blue.
These appearances have been called accidental areolae.

Movements of the Eyeball.

The eyeball nearly fills the cavity of the orbit, resting, by its posterior portion,
upon a bed of adipose tissue, which is never absent, even in extreme emaciation. Out-
side of the sclerotic, is a fibrous membrane, the tunica vaginalis oculi, or capsule of
Tenon, which is useful in maintaining the equilibrium of the globe. This fibrous mem-
brane surrounds the posterior two-thirds of the globe and is loosely attached to the
sclerotic. It is perforated by the optic nerve posteriorly, and by the tendons of the
recti and oblique muscles of the eyeball in front, being reflected over these muscles. It
is also continuous with the palpebral ligaments and is attached by two tendinous bands
to the border of the orbit at the internal and the external angles of the lids.

The muscles which move the globe are six in number for each eye. These are, the
external and internal recti, the superior and inferior recti, and the two oblique muscles.
The four recti muscles and the superior oblique arise posteriorly from the apex of the
orbit. The recti pass directly forward by the sides of the globe and are inserted by
short, tendinous bands into the sclerotic, at a distance of from one-fourth to one-third of
an inch from the margin of the cornea. The superior oblique, or trochlearis muscle
passes along the upper and inner wall of the orbit to a point near the inner angle. It
here presents a rounded tendon, which passes through a ring, or pulley of fibro-cartilage ;
and it is from this point that its action is exerted upon the globe. From the pulley, or
trochlea, the tendon becomes flattened, passes outward and backward beneath the supe-
rior rectus, and is inserted into the sclerotic, about midway between the superior and the
external rectus and just behind the equator of the globe. The inferior oblique muscle
arises just within the anterior margin of the orbit, near the inner angle of the eye, and
passes around the anterior portion of the globe, beneath the inferior m-tus and between
the external rectus and the eyeball, taking a direction outward and slightly backward.
Its tendon is inserted into the sclerotic, a little below the insertion of the superior
oblique. The general arrangement of these muscles is shown in Fi.ir. 'J.VI.

The various movements of the eyeball are easily understood by a study of the asso-
ciated movements of the muscles just enumerated, at least, as far as is necessary to tlu>
comprehension of the mechanism by which the eyes are directed toward any ptrtkulai
object. We have already seen that the centre of exact vision is in the fovra : and r
evident that, in order to see any object distinctly, it is necessary to bring it within the
axes of vision of both eyes. As the globe is so balanced in the orbit as to be capable of
rotation, within certain limits, ki every direction, we have only to note the exact mode

808

SPECIAL SENSES.

of action of each of the muscles, in order to comprehend how the different movements
are accomplished ; and it is sufficient for our purposes to admit that, approximative^,
there is a common axis of rotation for each pair of muscles.

Under ordinary conditions, in the human subject, the action of the six ocular muscles
is confined to the movements of rotation and torsion of the globe. It is said that, in the
human subject, there is no such thing as protrusion of the eye from general relaxation
of these muscles, and that it is impossible, by a combined action of the four recti muscles
to retract the globe in the orbit ; but those who have operated upon the eyes assert posi-
tively that this statement is erroneous, and that the globe is almost always suddenly and
powerfully drawn within the orbit when a painful impression is made upon the cornea.
This is stated as a matter of common observation by ophthalmic surgeons.

FIG. 254.— Muscles of the eyeball. (Sappey.)

1, attachment of the tendon connected with the inferior rectus, internal rectus, and external rectus ; 2, external rectus
divided and turned downward to expose the inferior rectus ; 8, internal rectus ; 4, inferior rectus ; 5, superior
rectus ; b, superior oblique ; 7, pulley and reflected portion of the superior oblique ; 8, inferior oblique : 9, leva-
tor palpebri superioris; 10, 10, middle portion of the levator palpebri superioris ; 11, optic nerve.

The extent to which the line of vision may be turned by a voluntary effort varies in
different individuals, even when the eyes are perfectly normal. In myopic eyes, the centre
of rotation is deeper in the orbit than normal, and the extent of the possible deviation of
the visual line is correspondingly diminished. Helmholtz states that, in his own person,
with the greatest effort that he is capable of making, he can move the line of vision in
the horizontal plane to the extent of about fifty degrees, and, in the vertical plane, about
forty-five degrees ; but he adds that these extreme rotations are very forced, and that
they cannot be sustained for any length of time. It is probable that we seldom move the
eyeball in any direction to an angle of forty-five degrees, the direction of the visual line
being more easily accomplished by movements of the head.

Action of the Recti Muscles.— The action of the recti, particularly of the internal and
external, is quite simple.

The internal and the external recti rotate the globe upon a vertical axis, which is per-
pendicular to the axis of the eye. The isolated action of these muscles, particularly of the
external rectus, is often illustrated in certain forms of paralysis, which have been alluded
to in connection with the history of the cranial nerves.

The superior and the inferior recti rotate the globe upon a horizontal axis, which is

MOVEMENTS OF THE EYEBALL.

809

obt.

not at right angles with the axis of the eye, but is inclined from the nasal side slightly
backward. The line which serves as the axis of rotation for these muscles forms an angle
of about seventy degrees with the axis of the globe ; and, as a consequence of this arrange-
ment, their action is not so simple as that of the internal and external recti. The inser-
tion of the superior rectus is such, that, when it contracts, the pupil is directed upward
and inward, the inferior rectus directing the pupil downward and inward.

The above represents the simple, isolated action of each pair of recti muscles ; but it
is easy to see how, without necessarily involving the action of the oblique muscles, the
globe maybe made to perform an immense variety of rotations, and the line of vision may
be turned in nearly every direction, by the action of the recti muscles alone.

Action of the Oblique Muscles. — Although there has been considerable discussion con-
cerning the exact mode of action of the oblique muscles, their mechanism may now be
regarded as pretty well settled, at least as regards the human subject. In the first place,
it is sufficient for all practical purposes, to assume that the superior and the inferior
oblique muscles act as direct antagonists to each other. The next point to determine is
the direction of the axis of rotation of the globe with reference to the action of these
muscles. The most exact, recent measurements show that this axis is horizontal and
that it has an oblique direction from before backward and from without inward. The
angle formed by the axis of rotation of the oblique muscles with the axis of the globe is
thirty -five degrees; and the angle be-
tween the axis of the oblique muscles
and the axis of the superior and inferior
recti muscles is seventy-five degrees.

Given the direction of the axis of
rotation and the direction of the supe-
rior oblique muscle, it is easy to under-
stand the effects of its contraction. As
this muscle, passing obliquely backward
and forward over the globe, acts from
the pulley near the inner angle of the
eye to its insertion just behind the an-
terior half of the globe on its external
and superior surface (7, Fig. 254), it
must rotate the globe so as to direct the
pupil downward and outward.

The inferior oblique, passing outward
and slightly backward under the globe,
acts from its origin at the margin of the
orbit near the inner angle of the eye to
its insertion, which is just below the in-
sertion of the superior oblique. This
muscle rotates the globe so as to direct
the pupil upward and outward.

The action of the oblique muscles

seems to be specially connected with FIG. 255.- Diagram illustrating the action of the, mutclet of

Vie eyeball. (l<ick.)
jnt the muscles of the eychnll. and the

r.ext.

The dark lines represent the muscles of the e;

dotted lines, the axis of the superior and the inferior rectus
and the axis of the oblique muscles.

the movements of torsion of the globe.

It is necessary to distinct, single vision

with both eyes, that the images should

be formed upon exactly corresponding points on the retina, and that they shoul

for the two eyes, corresponding relations to the perpendicular. Thus it is

head is inclined to one side, the eyes are twisted upon an oblique, antcro-postenor axis;

as can be readily observed if we watch little spots upon the iris during these movements.

810 SPECIAL SENSES.

The superior oblique muscle is supplied by a single nerve, the patheticus. When this
muscle is paralyzed, the inferior oblique acts without its antagonist, and the eyeball is
immovable, as tar as the twisting of the globe, just described, is concerned. When
the head is moved toward the shoulder, the globe cannot rotate to maintain a position
corresponding to that of the other eye, and we have double vision. This point has
already been touched upon in connection with the physiology of the nerves of the eye-
ball and the situation of corresponding points in the retina.

Associated Action of the Different Muscles of the Eyeball.— -It is almost unneces-
sary to add, after the description just given of the actions of the individual muscles of
the globe, that their contractions may be associated, so as to produce an infinite variety
of movements. We have no consciousness, under ordinary circumstances, of the muscular
action by which the globe is rotated and twisted in various directions, except that, by an
effort of the will, we direct the visual line toward different objects. By a strong effort,
we can make the eyes converge by contracting both internal recti, and some persons can
produce extreme divergence by using both external recti ; but this is abnormal.

In looking at distant objects, the axes of vision are practically parallel. When we
look at near objects, the effort of accommodation is attended with the amount of con-
vergence necessary to bring the visual axes to bear upon identical points. In looking
around at different objects, we move the head more or less, rotating and twisting the
globes in various directions. In the movements of the globes vertically, the axes are
kept parallel, or at the proper angle, by the internal and external recti, and the superior
and inferior recti upon the two sides act together. In rotating the globe from one side
to the other, upon a vertical axis, the external rectus upon one side acts with the internal
rectus upon the other. In the movements of torsion upon an antero-posterior axis, there
must be an associated action of the oblique muscles and the recti. We quote from Longet
the following, as illustrative of this combination of action :

'l If the eyes be directed obliquely Upward and to the left, the vertical meridians of
the two eyes are parallel and inclined from left to right, for the left eye, outward, and for
the right eye, inward. The movement of the left eye upward and to the left, or outward,
necessitates a contraction of the superior rectus, the extern;,! rectus, and the inferior
oblique muscles. As regards the right eye, also directed upward and to the left, that is
to say, inward, this is moved by the simultaneous action of the superior rectus, the inter-
nal rectus, and the inferior oblique."

We have given the above quotation simply to illustrate a combination of action of
three muscles for each eye, the only difference in binocular vision being that in one eye
the external rectus is brought into play, while the internal rectus acts upon the opposite
side. Reversing this action of the internal and external recti, we have the action which
directs the pupil upward and to the right. If we substitute for the superior rectus and
the inferior oblique, the inferior rectus and the superior oblique, we have the pupil directed
downward, and either to the right or left, as the internal or external rectus upon either
side is brought into action.

One important point, never to be lost sight of in our study of the associated action
of the muscles of the globe, relates to the associated movements of the two eyes. We
have already seen that perfect binocular vision is possible only when impressions are
made upon exactly corresponding points in the retina of each eye. If one eye be deviated
in the horizontal plane, the points no longer correspond, and there is double vision, the
same as if two impressions were made upon one retina; for, when the impressions
exactly correspond, the two retinas act practically as a single organ. The same is true
in deviation of the globe in the vertical plane. If we suppose, for the sake of argument,
that the retina is square, it is evident that a torsion, or twisting of one globe upon an
antero-posterior axis must be attended with an analogous movement of the other globe,
in order to bring the visual rays to bear upon the corresponding points ; in other words,

PARTS FOR THE PROTECTION OF THE EYEBALL. 811

the obliquity of the assumed square of the retina must be exactly the same for the two
eyes, or the coincidence of the corresponding points would be disturbed and we should
have double vision. When we clearly understand that deviation of one eye in the hori-
zontal or the vertical plane disturbs the relation of the corresponding points, which is
sufficiently easy of comprehension, and that a deviation from exact coincidence of action
in torsion of the globes twists, as it were, the corresponding points, so that their rela-
tion is also disturbed, we can see that the varied movements of the globes, by the com-
bined action of the recti and oblique muscles, must correspond for each eye, in the move-
ments of torsion upon an antero-posterior axis, as well as in movements of rotation upon
the horizontal or the vertical axis.

Parts for the Protection of the Eyeball.

The orbit, formed by the union of certain of the bones of the face, receives the eyeball,
the ocular muscles, the muscle of the upper lid, blood-vessels, nerves, part of the lachry-
mal apparatus, and contains, also, a certain amount of adipose tissue, which latter never
disappears, even in extreme marasmus. The bony walls of this cavity protect the globe
and lodge the parts above enumerated. The internal, or nasal wall of the orbit projects
considerably beyond the external wall, so that the extent of vision is far greater in the
outward than in the inward direction. As the globe is more exposed to accidental injury
from an outward direction, the external wall of the orbit is strong, while the bones which
form its internal wall are comparatively fragile. The upper border of the orbit (the
superciliary ridge) is provided with short, stiff hairs (the eyebrows) which serve to shade
the eye from excessive light and to protect the eyelids from perspiration from the fore-
head.

The eyelids are covered by a very thin integument and are lined by the conjunctival
mucous membrane. The subcutaneous connective tissue is thin and loose and is entirely
free from fat. The skin presents numerous short papillae and small sudoriparous glands.
At the borders of the lids, are short, stiff, curved hairs, arranged in two or more rows,
called. the eyelashes or cilia. Those of the upper lid are longer and more numerous than
the lower cilia. The curve of the lashes is from the eyeball. They serve to protect the
globe from dust, and, to a certain extent, to shade the eye.

The tarsal cartilages are small, elongated, semilunar plates, extending from the edges
of the lids toward the margin of the orbit, between the skin and the mucous membrane.
Their length is about an inch. The central portion of the upper cartilage is about one-
third of an inch broad, and the corresponding part of the lower cartilage measures about
one-sixth of an inch. At the inner canthus, or angle of the eye, is a small, delicate liga-
ment, or tendon, the tendo palpebrarum, which is attached to the lachrymal groove
internally, passes outward, and divides into two lamellae, which are attached to the two
tarsal cartilages. At the outer canthus, the cartilages are attached to the malar bone by
the external tarsal ligament. The tarsal cartilages receive additional support from the
palpebral ligament, a fibrous membrane attached to the margin of the orbit and the con-
vex border of the cartilages and lying beneath the orbicularis muscle. This membrane is
strongest near the outer angle of the eye.

On the posterior surface of the tarsal cartilages, partly embedded in them and lyinjr
just beneath the conjunctiva, are the Meibomian glands. The structure and functions
of these glands have already been considered in connection with secretion. They pro-
duce an oily fluid, which smears the edges of the eyelids and prevents the overflow of
tears.

Muscles which open and close the Eyelids.— Leaving out the corrupitor snpereilii,
which draws the skin of the forehead downward and inward, we have the orbiculans
palpebrarum, which closes the lids, and the levator palpebrae supt-rinris. which raises the
upper lid. The tensor tarsi, called the muscle of Homer, is a very thin, delicate muscle,

81% SPECIAL SENSES.

which is regarded by some anatomists as a deep portion of the orbicularis. Considering
this as a distinct muscle, it consists of two delicate slips, which pass from either eyelid
behind the lachrymal sac, uniting here to go to its attachment at the posterior portion of
the lachrymal bone. When this acts with the orbicularis, it compresses the lachrymal sac.

The orbicularis palpebrarum is a broad, thin muscle, closely attached to the skin,
surrounding the free margin of the lids, and extending a short distance over the bones,
beyond the margin of the orbit. This muscle may be described as arising from the tendo
palpebrarum, the surface of the nasal process of the superior maxiliary bone, and the
internal angular process of the os frontis. From this origin at the inner angle of the
eye, its fibres pass elliptically around the fissure of the lids, as above indicated. Its
action is to close the lids. In the ordinary, moderate contraction of this muscle, only
the upper lid is moved ; but, in forcible contraction, the lower lid moves slightly and the
lids are drawn toward the nose. In facial palsy, or when the temporo-facial branch of
the portio dura of the seventh nerve is paralyzed, this muscle cannot act, and it is impos-
sible to close the eye.

The levator palpebrso superioris is situated within the orbit. It arises from a point
a little above and in front of the optic foramen at the apex of the orbit, passes forward
above the eyeball, and spreads into a thin tendon, which is inserted into the anterior
surface of the superior tarsal cartilage. Its evident action is to raise the upper lid. It is
animated by filaments from the third pair of cranial nerves ; and, when this nerve is
paralyzed, we have permanent falling of the upper lid, or blepharoptosis. This muscle
and its relations are shown in Fig. 254 (9, 10, 10), page 808.

In the act of opening the eyes, the levator muscles alone are brought into play.
Closing of the lids is accomplished by the orbicular muscles. Both of these sets of mus-
cles act to a great extent without the intervention of the will. The eyes are kept open
almost involuntarily, except in extreme fatigue ; although, when the will ceases to act,
the lids are closed. Nevertheless, we are hardly conscious of an effort in keeping the
eyes open, in our waking moments, and we require an effort to close the eyes. During
sleep, the eyes are closed and the globes are turned upward. The contractions of the
orbicular muscles which take place in winking are usually involuntary. This act occurs
at short intervals, and it is useful in spreading the lachrymal secretion over the exposed
portions of the globes. The action of both sets of muscles is usually simultaneous, although
we may educate them so as to close one eye while the other is kept open. The action
of the orbicularis is so far removed from the control of the will, that, when the surface
of the globe is touched or irritated or when the impression of light produces intense
pain, it is impossible to keep the eye open.

Conjunctive^ Mucous Membrane. — The entire inner surface of the upper and lower
eyelids is lined by a mucous membrane, which is reflected forward from the inner periph-
ery of the lids over the eyeball. The membrane lining the lids is called the palpebral
conjunctiva, and that covering the eyeball, the ocular conjunctiva. The latter presents
a sclerotic and a corneal portion. The membrane presents a superior and an inferior
fold, where it is reflected upon the globe. In the superior conjunctival fold, are numer-
ous glandular follicles, or accessory lachrymal glands, which secrete a certain portion of
the fluid which moistens the surface of the eyeball. These are generally described as
forming a part of the lachrymal gland. At the inner canthus, there is a vertical fold
(the plica semilunaris) with a reddish, spongy elevation at its inner portion, called the
caruncula lacrymalis. The caruncnla presents a collection of follicular glands, with a
few delicate hairs on its surface. The conjunctiva is continuous with the membrane of
the lachrymal ducts, of the puncta lacrymalia, and of the Meibomian glands. Beneath the
conjunctiva, except in the corneal portion, is a loose connective tissue.

The palpebral conjunctiva is reddish, thicker than the ocular portion, furrowed, and
presents small, isolated papillae near the borders of the lids, which increase in number

PARTS FOR THE PROTECTION OF THE EYEBALL.

813

and size toward the folds. This portion of the membrane presents large capillary blood-
vessels and lymphatics and is covered with a layer of cells of flattened epithelium. The
sclerotic portion is thinner, less vascular, and has no papillse. It is covered by conical
and rounded epithelial cells, which present from two to four layers. Over the cornea,
the epithelium of the sclerotic portion is continued in delicate, transparent layers, without
a distinct basement-membrane.

The Lachrymal Apparatus. — The eyeball is constantly bathed in a thin, watery fluid
which is secreted by the lachrymal gland, is spread over the globe by the movements of
the lids and of the eyeball, and is prevented, under ordinary conditions, from overflowing
upon the cheek, by the Meibomian secretion. The excess of this fluid is collected into
the lachrymal sac and is carried into the nose by the nasal duct. The lachrymal gland,
the lachrymal canals, duct, and sac, and the nasal duct, constitute the lachrymal appa-
ratus.

The lachrymal gland is an ovoid, flattened gland of the racemose variety, resembling
the salivary glands in its general structure. It is about the size of a small almond and is
lodged in a shallow depression in the bones of the orbit at its upper and outer portion.
It is closely attached to the periosteum by its upper surface and is moulded below to the
convexity of the globe. Its anterior portion is separated from the rest by a well-marked
groove, is comparatively thin, and adheres to the upper lid. It presents from six to eight
(usually seven) ducts, which form a row of openings into the conjunctival fold. Five or
six of these orifices are situated above the outer canthus and two or three open below.
In its minute structure, this gland presents no points of special physiological interest as
distinguished from the ordinary racemose glands. It receives nervous filaments from the
fifth cranial nerve and the sympathetic.

FIG. 256.— Lachrymal and Meibomian glands. (Sappey.)

1, 1, internal wall of the orbit; 2, 2, internal portion of the orbicularis palpebrarura ; 3. 3, attachment of this muscle to
the orbit; 4, orifice for the passage of the nasal artery; 5, muscle of Homer; C, 6. posterior surface of the eyelids,
with the Meibomian glands; 7, 7, 8, 8, 9, 9, 10, lachrymal gland and ducts; 11, openings of the lachrymal ducta.

The apparatus by which the excess of tears is conducted into the nose begins by two
little points, situated on the margin of the upper and the lower lid, near the inner canthu*,
called the puncta lacrymalia, which present each a minute orifice. These orifices open
respectively into the upper and the lower lachrymal canals, which together surround the
caruncula lacrymalis. At the inner angle, just beyond the ciinincula, tlio two canals
join, to empty into the lachrymal sac, which is the dilated upper extremity of the nasal
duct. The duct is about half an inch in length and empties into the inferior meatus of the
nose, taking a direction nearly vertical, and inclined slightly outward and backward. This

814

SPECIAL SENSES.

portion of the lachrymal apparatus is fibrous and is lined by a reddish mucous membrane,
which presents several well-marked folds. Near the puncta, are two folds, one for each
lachrymal canal. Another pair of folds exists near the horizontal portions of the canals.
At the opening of the duct into the nose, is an overhanging fold of the nasal mucous
membrane. These folds are supposed to prevent the reflux of fluid from the lachrymal
canals and the entrance of air from the nose. The mucous membrane of the lachrymal
canals is covered by a flattened epithelium, like that of the conjunctiva. The lachrymal
sac and duct are lined by a continuation of the ciliated epithelium of the nose. The dis-
position of the apparatus just described is shown in Fig. 257.

The Tears. — The secretion of the lachrymal glands is constant, although the quantity of
fluid may be increased under various conditions. The, actual amount of the secretion has
never been estimated. During sleep it is much diminished ;
and, when the eyes are open, the quantity is just sufficient to
moisten the eyeball, the excess being carried into the nose so
gradually that this process is not appreciated. That this drain-
age of the excess of tears takes place is shown by cases of ob-
struction of the nasal duct, when the liquid constantly over-
flows upon the cheeks, producing considerable inconvenience.

The mechanism of the action of the excretory lachrymal
apparatus is quite simple, though it has been the subject of a
good deal of discussion. It is probable that the openings at
the puncta lacrymalia take up the liquid like delicate pipettes,
this action being aided by the movements in winking, by
which, when the lids are closed, the points are compressed and
turned backward, opening and drawing in the tears when the
lids are opened. It is possible that the lachrymal sac is com-
pressed in the act of winking, by the contractions of the muscle
of Horner, and that this, while it empties the sac, may, in the
subsequent relaxation, assist the introduction of liquid from the
orbit.

We know very little with regard to the chemical compo-
sition of the tears, beyond the analysis made many years ago
by Frerichs. According to this observer, the following is the composition of the lachry-
mal secretion :

Fio. 257. — Lachrymal canals,
lachrymal sac, and nasal
canal, opened by their ante-
rior portion. (Sappey.)

1, walls of the lachrymal pas-
sages, smooth and adherent;
2, 2, walls of the lachrvmal sac,
presenting delicate folds of the
mucous membrane ; 3. a simi-
lar fold belongs to the nasal
mucous membrane.

Composition of the Tears.

Water

Epithelium.
Albumen. .

990-60 to 987-00
1-40 " 3-20

0-80 " 1-00

Chloride of sodium, "^
Alkaline phosphates, |
Earthy phosphates,
Mucus,
Fat,

7-20

8-80

1,000-00 1,000-00

The specific gravity of the tears has never been ascertained. The liquid is perfectly
clear, colorless, of a saltish taste and a feebly alkaline reaction. The albumen given in
the table is called by some authors, lachrymine, thrsenine, or dacryoline. This substance,
whatever it may be called, resembles mucus in many regards and is probably secreted by
the conjunctiva and not by the lachrymal glands. It differs from ordinary mucus in being
coagulated by water.

The secretion of tears is readily influenced through the nervous system. Aside from

AUDITORY NERVES. 815

the increased flow of this secretion from emotional causes, which probably operate through
the sympathetic, a hypersecretion almost immediately follows irritation of the mucous
membrane of the conjunctiva or of the nose. The same result follows violent muscular
effort, laughing, coughing, sneezing, etc. The secretion of tears under stimulation of the
mucous membrane is reflex.

CHAPTER XXV.

AUDITION.

Physiological anatomy of the auditory nerves— General properties of the auditory nerves— Topographical anatomy
of the parts essential to the appreciation of sound — The external ear — General arrangement of the parts composing
the middle ear — Anatomy ot the tympanum — Arrangement of the ossicles of the ear — Muscles of the middle ear
— Mastoid cells — Eustachian tube — Muscles of the Eustachian tube — Mucous membrane of the middle ear and of
the Eustachian tube— General arrangement of the bony labyrinth — Laws of sonorous vibrations— Noise and musi-
cal sounds — Intensity, pitch, and quality of musical sounds — Musical scale — Harmonics, or overtones— Resonators
of Helmholtz — Resultant tones— Summation tones — Harmony — Discord— Tones by influence (consonance) — Uses
of different parts of the auditory apparatus — Uses of the external ear— Structure of the membrana tyuipani— Uses
of the membrana tympani — Vibrations of the membrane by influence — Appreciation of the pitch of tones — Mech-
anism of the ossicles of the ear — Physiological anatomy of the internal ear — General arrangement of the mem-
branous labyrinth— Vestibule— Semicircular canals— Cochlea— Liquids of the labyrinth— Distribution of nerves in
the cochlea — Organ of Corti — Functions of different parts of the internal ear — Functions of the semicircular canals
— Functions of the parts contained in the cochlea — Summary of the mechanism of audition.

THE general considerations introductory to the study of vision are equally applicable
to the physiology of hearing. The impressions of sound are conveyed to the brain by
special nerves ; but, in order that these impressions shall reach these nerves so as to be
properly appreciated, a complex accessory apparatus is required, the integrity of which is
essential to perfect audition. The study of the arrangement and action of these accessory
parts is even more important and is far more intricate than the physiology of the auditory
nerves. The latter simply convey the impressions to the brain, by a mechanism analogous
to that of general nervous conduction, the essential character of which is not fully under-
stood. The auditory nerves conduct impressions of sound, as the optic nerves conduct
impressions of light; and this statement expresses the extent of our positive knowledge;
but there is an elaborate apparatus by which the waves are collected, conveyed to a
membrane capable of vibration, and finally carried to the nerves, by which we are enabled
to appreciate the intensity and the varied qualities of sound.

Our positive and definite knowledge of the structure and arrangement of the auditory
apparatus is by no means so complete as it is with regard to the eye, nor do we as yet
understand so clearly the physiological relations of many points developed by late ana-
tomical researches ; and, for this reason, it does not seem desirable to consider the struct-
ure of the ear as fully as we have the anatomy of the eye, restricting ourselves, as we
have done, to the physiological anatomy of parts. With this end in view, we shall take
up fully the following points:

1. The physiological anatomy and the general properties of the auditory nerves.

2. The physiological anatomy of the parts essential to the correct appreciation of
sound.

3. The laws of the propagation of sonorous vibrations, as far as they are applicable
to audition.

4. The physiological action of different parts of the auditory apparatus.

Physiological Anatomy of the Auditory Nerves.— The auditory nerve constitutes the
portio mollis of the seventh pair of Willis. The origin of this nerve can easily be traced
to the floor of the fourth ventricle, where it presents two roots. The external, or super-

816 SPECIAL SENSES.

ficial root, sometimes called the posterior root, can be seen usually without preparation.
This consists of from five to seven grayish filaments, which decussate in the median line,
and pass outward, winding from the fourth ventricle around the restiform body. The
deep root consists of numerous distinct filaments, arising from the gray matter of the
fourth ventricle, two or three of which pass to the median line to decussate with corre-
sponding filaments from the opposite side. This root passes around the restiform body
inward, so that this portion of the medulla is encircled, as it were, by the two roots.
Passing from the superior and lateral portion of the medulla oblongata, the trunk of the
nerve is applied to the superior and anterior surface of the facial. It then passes around
the middle peduncle of the cerebellum, and receives a process from the arachnoid mem-
brane, which envelops it in a common sheath with the facial. It then penetrates the
internal auditory meatus. In its course, it receives filaments from the restiform body,
and possibly from the pons Varolii. Within the meatus, the nerve divides into an ante-
rior and a posterior branch, the anterior being distributed to the cochlea, and the poste-
rior, to the vestibule and semicircular canals. The distribution of these branches will be
fully described in connection with the anatomy of the internal ear.

The color of the auditory nerves is grayish, and their consistence is soft, thus differing
from the ordinary cerebro-spinal nerves, and resembling, to a certain extent, the other
nerves of special sense. On the external, or superficial root, is a small ganglioform en-
largement, containing fusiform nerve-cells. According to the latest researches, the fila-
ments of the trunk of this nerve consist of very large axis-cylinders, surrounded by a
medullary sheath, but having no tubular membrane. In the course of these fibres, are
found small, nucleated ganglionic enlargements.

General Properties of the Auditory Nerves. — There can be no doubt, as regards the
portio mollis of the seventh, that it is the only nerve capable of receiving and conveying
to the brain the special impressions produced by waves of sound ; but it is an interesting
question to determine, whether this nerve be endowed also with general sensibility.
Analogy with most of the other nerves of special sense would indicate that the auditory
nerves are insensible to ordinary impressions ; and this view is sustained by direct experi-
ments, made many years ago.

The phenomena observed during the passage of galvanic currents through the audi-
tory nerves have, of late years, been the subject of much discussion. The old experiment
of Yolta, which was almost immediately confirmed by Hitter, is sufficiently familiar and
is often quoted as showing that galvanic stimulation of these nerves produces a sensation
of sound ; but the facts ascertained leave room for doubt with regard to the precise mode
of action of the current. A careful study of recent observations upon this point renders
the question even more obscure ; but, from a purely physiological point of view, we have
only to do with the effects of stimulating the auditory nerves in health. Leaving the
therapeutic and diagnostic uses of galvanism out of the question, we find that there is
considerable uncertainty with regard to the fact of direct stimulation of the auditory
nerves, in the recent experiments with the galvanic current. Brenner observed strong
sensations of sound with one of the poles of a battery in the auditory passage filled with
water and the other connected with different parts of the body. When the cathode was
placed in the ear, the sound was heard at the making of the current. With the anode in
the ear, there was no sound at the making of the current or during its passage, but a
slight sound was heard at the breaking of the current. These phenomena closely resem-
ble those produced by the galvanic current applied to ordinary motor nerves, in so far
as the action seemed to be most vigorous at the making of the circuit, with the direct
current, and at the breaking of the circuit, with the inverse current; for, when the
cathode is placed in the ear, the current is direct, following the course of the nerve from
the centre to the periphery, and vice versa. Without following out the discussion of this
question in detail, it seems only necessary to study the very clear and satisfactory experi-

THE EXTERNAL EAR: 817

ments of Wreden, to become convinced that the subjective auditory phenomena, attrib-
uted by Brenner and others to irritation of the auditory nerves, are due to contraction
of the muscles of the middle ear, particularly the stapedius. The facts, clinical and ex-
perimental, upon which this view is based, are the following: In cases of clonic spasm of
the stapedius, sensations of sound have been observed, exactly like those produced by an
induced current. In cases of complete facial paralysis from otitis, in which paralysis of
the auditory nerve could be positively excluded, it was not possible to produce subjective
auditory sensations, even by powerful galvanization by a catheter passed through the
Eustachian tube into the tympanic cavity, or by the external meatus. In addition, there
are other well-established clinical observations, mentioned by Wreden, which sustain the
theory of muscular contraction and are opposed to the idea of direct stimulation of the
auditory nerves.

The facts just stated show that there is no positive evidence of the production of im-
pressions of sound by galvanic stimulation of the auditory nerves ; while it appears from
experiments, that these nerves are not endowed with general sensibility. The results,
then, as regards the auditory nerves, are simply negative. Were it possible to subject
these nerves to mechanical or galvanic stimulation, in the human subject, without involv-
ing other parts, we might arrive at some definite conclusion ; but the difficulties in the
way of such an experiment, it must be admitted, have thus far proved insurmountable.

Topographical Anatomy of the Parts essential to the Appreciation of Sound.

Perfect audition requires the anatomical integrity of a very complex apparatus, which,
for convenience of anatomical description, may be divided into the external, middle, and
internal ear. A correct appreciation of the physiology of these parts demands, as a neces-
sary preparation, a knowledge of their physiological anatomy :

1. The external ear includes the pinna and the external auditory meatus, which is
closed internally by the membrana tympani.

2. The middle ear includes the cavity of the tympanum, or drum, with its boundaries.
The parts here to be described are, the membrana tympani, the form of the tympanic
cavity, its openings, its lining membrane, and the small bones of the ear, or ossicles, with
their ligaments, muscles, and nerves. The cavity of the tympanum communicates, by
the Eustachian tube, with the pharynx and also presents openings into the mastoid cells.

3. The internal ear contains the terminal filaments of the auditory nerve. It includes
the vestibule, the three semicircular canals, and the cochlea, which together form the
labyrinth.

The pinna and the external meatus simply conduct the waves of sound to the tym-
panum. The parts entering into the structure of the middle ear are accessory, and are
analogous in their functions to the refracting media of the eye. Structures contained
in the labyrinth constitute the true sensory organ ; and these bear the same relations to
the auditory apparatus as the retina to the eye.

The External Ear. — It is hardly necessary to our purpose to describe very minutely
the external ear. The pinna, or auricle is that portion projecting from the head, which
first receives the waves of sound. Beginning externally, we have the helix, which is the
outer ridge of the pinna. Just within this, is a groove, called the fossa of the helix. This
fossa is bounded anteriorly by a prominent but shorter ridge, called the nmilu-lix ; and
above the concha, between the superior portion of the antihelix and the anterior portion
of the helix, is a shallow fossa, called the fossa of the antihelix. The deep fossa, imme-
diately surrounding the opening of the meatus, is called the concha. A small lobe pro-
jects posteriorly, covering the anterior portion of the concha, which is called the trains;
and the projection at the lower extremity of the antihelix is called the antitragus. The
fleshy, dependent portion of the pinna is called the lobule of the ear.
52

818 SPECIAL SENSES.

The form of the pinna and its consistence depend upon the presence of fibro-cartilage,
which occupies the whole of the external ear except the lobule. This structure has
already been described in another chapter.

The integument covering the ear does not vary much from the integument of the
general surface. It is thin, closely attached to the subjacent parts, and possesses small,
rudimentary hairs, with sudoriparous and sebaceous glands.

The muscles of the ear are not important in the human subject ; and, excluding a
few exceptional cases, they are not under the control of the will. The extrinsic muscles
are the superior, or attollens, the anterior, or attrahens, and the posterior, or retrahens
aurem. In addition, there are the six small intrinsic muscles, situated between the ridges
upon the cartilaginous surface. The pinna is attached to the sides of the head by two
distinct ligaments and a few delicate ligamentous fibres.

The external auditory meatus is about an inch and a quarter in length and extends
from the concha to the membrana tympani. Its course is somewhat tortuous. Passing
from without inward, its direction is at first somewhat upward, turning abruptly over a
bony prominence near the middle, from which it has a slightly downward direction to
the membrana tympani. Its general course is from without inward and slightly forward.
The inner termination of the canal is the membrana tympani, which is quite oblique, the
upper portion being inclined outward, so that the inferior wall of the meatus is consid-
erably longer than the superior.

The walls of the external meatus are partly cartilaginous and fibrous, and partly bony.
The cartilaginous and fibrous portion occupies a little less than one-half of the entire
length and consists of a continuation of the cartilage of the pinna, with fibrous tissue.
About the lower two-thirds of this portion of the canal is cartilaginous, the upper third
being fibrous. The rest of the tube is osseous and is a little longer and narrower than
the cartilaginous portion. Around the inner extremity of the canal, with the exception
of its superior portion, is a narrow groove, which receives the greater portion of the
margin of the membrana tympani.

The skin of the external meatus is continuous with the integument covering the
pinna. It is very delicate, becoming thinner from without inward. In the osseous por-
tion, it adheres very closely to the periosteum, and, at the bottom of the canal, it is
reflected over the membrana tympani, forming its outer layer. In the cartilaginous and
fibrous portion, are numerous short, stiff hairs, with sebaceous glands attached to their
follicles, and the coiled tubes known as the ceruminous glands. The structure of these
glands and the properties and composition of the cerumen have already been described
under the head of secretion.

General Arrangement of the Parts composing the Middle Ear. — Without a very elabo-
rate and minute anatomical description, fully illustrated by plates, it is difficult to give a
clear idea of the structure and relations of the very complex apparatus of the middle and
the internal ear. Such a minute and purely anatomical description would be out of
place in this work, wl>ere it is desired only to give such an account of the anatomy as
will enable the student to comprehend the physiology of the ear, reserving for special
description certain of the most important structures. In beginning the difficult task of
describing the physiological anatomy of the middle and internal ear, it will be convenient
to give a general outline of the different parts, with their names. This, with a careful
study of Figs. 258, 259, 260, and 261, can hardly fail to greatly facilitate the closer in-
vestigation of the more important structures.

The arrangement of the parts constituting the external ear is sufficiently simple. The
middle ear presents a narrow cavity (Fig. 258, 11), of irregular shape, situated between
the external ear and the labyrinth, in the substance of the temporal bone. The general
arrangement of its parts is shown in Fig. 258. The outer wall of the tympanic cavity is
formed by the membrana tympani (Fig. 258, 6). This membrane is concave, its concav-

THE MIDDLE EAR. 819

ity looking outward, and oblique, inclining usually at an angle of forty-five degrees with
the perpendicular. This angle, however, varies considerably in different individuals.
The roof is formed by an exceedingly thin plate of bone. The floor is bony and is much
narrower than the roof. The inner wall, separating the tympanic cavity from the laby-
rinth, is irregular, presenting several small elevations and foramina. The fenestra ovalis,
an ovoid opening near its upper portion, leads to the cavity of the vestibule. This is

FIG. 258. — General view of the organ of hearing. (Sappey.)

1, pinna ; 2, cavity of the concha, on the walls of which are seen the orifices of a great number of sebaceous glands ;
3, external auditory meatus ; 4, angular projection formed by the union of the anterior portion of the concha
with the posterior wall of the auditory canal ; 5, openings of the ceruminous glands, the most internal of which
form a curved line which corresponds with the beginning of the osseous portion of the external meatus : f..
membrana tympani and the elastic fibrous membrane which forms its border; 7, anterior portion of the incus;
8, malleus ; 9, handle of the malleus applied to the internal surface of the membrana tympani, which it draws
inward toward the projection of the promontory ; 10, tensor tympani muscle, the tendon of which is reflected at
a right angle to become attached to the superior portion of the handle of the malleus ; 11, tympanic cavitv ; 1*2;
Eustachian tube, the internal, or pharyngeal extremity of which has been removed by a section perpendicular
to its curve ; 13, superior semicircular canal ; 14, posterior semicircular canal ; 15, ex'ternal semicircular canal,
16, cochlea; 17, internal auditory canal ; 18, facial nerve; 19, large petrosal branch, given off from the ganHio-
form enlargement of the facial and passing below the cochlea to go to its distribution ; 20, vestibular branch of
the auditory nerve ; 21, cochlear branch of the auditory nerve.

closed, in the natural state, by the base of the stapes and its annular ligament. Below,
is a smaller, ovoid opening, the fenestra rotunda, which leads to the cochlea. This is
closed, in the natural state, by a membrane, called the secondary membrana tympani.
In addition, the posterior wall presents several small foramina leading to the mastoid
cells, which are lined by a continuation of the mucous membrane of the tympanic
cavity. The tympanic cavity also presents an opening leading to the Eustachian tube,
and a small foramen, which gives passage to the tendon of the stapedius muscle. The
Eustachian tube extends from the upper part of the pharynx to the tympanum.

The small bones of the ear are three in number; the incus, the malleus, nnd the
stapes, forming a chain, connected together by ligaments (Fig. 259). These bone -
situated in the upper part of the tympanic cavity. The handle of the malleus (A. •_>.
Fig. 259) is closely attached to the membrana tympani, and the long process (A, 3, !
259) is attached to the Glasscrian fissure of the temporal bone. The malleus is articu-
lated with the incus. The incus (B, Fig. 259) is connected with the posterior wall
of the tympanic cavity, near the openings of the mastoid cells. It is articulated with
the malleus, and, by the extremity of its long process (B, 2, Fig. 259), with the stapes.
The stapes (0, Fig. 259) is the most internal bone of the middle car. It is articulated

820

SPECIAL SENSES.

by its smaller extremity with the long process of the incus. Its base is oval (0*, Fig.
259) and, with its annular ligament, is applied to the fenestra ovalis. The direction of

the stapes is nearly at a right angle with the
long process of the incus in the natural state
(8, Fig. 260).

There are three well-defined muscles con-
nected with the middle ear. Of these, two are
attached to the malleus, and one, to the stapes.
The largest of the three muscles is the tensor
tympani, called sometimes the internal muscle
of the malleus. Its fibres arise from the carti-
laginous portion of the Eustachian tube, the
spinous process of the sphenoid bone, and the
adjacent portion of the temporal. From this
origin, it passes backward, almost horizontally,
to the tympanic cavity. In front of the fenes-
tra ovalis, it turns, nearly at a right angle, over
'a bony process, and its tendon is inserted into
the handle of the malleus at its inner surface
near the root. The tendon is very delicate,
and the muscular portion is about half an inch
in length (10, Fig. 258). The muscle and its
tendon are enclosed in a distinct fibrous sheath.
The action of this muscle is to draw the handle
of the malleus inward, pressing the base of the
stapes against the membrane of the fenestra ovalis and producing tension of the mem-
brana tympani. The fibres of this, and of all the muscles of the middle ear, are of the
striated variety. The tensor tympani is supplied with motor filaments from the otic
ganglion, which are probably derived from the facial nerve.

FIG. 259.— Ossicles of the tympanum of the right
side ; magnified 2 diameters. (Arnold.)

A, malleus; 1, its head; 2, the handle; 3, long, or
slonder process ; 4, short process ; B, incus ; 1, its
body ; 2, the long process with the orbicular pro-
cess; 3, short, or posterior process; 4, articular
surface receiving the head of the malleus ; <J,
stapes; 1, head; 2, posterior crus; 3. anterior
crus ; 4, base ; C*. base of the stapes ; D, the three
bones in their natural connection aa seen from the
outside ; a, malleus ; 6, incus ; c, stapes.

FIG. 260.— The right temporal lone, the petrosal portion removed, showing the ossicles seen from within. From

a photograph. (Kiidinger.)

4, the incus, the short process of which is directed nearly in an horizontal direction backward ; 5, the long process of the

incus, free in the tympanic cavity, articulated with the stapes; 6, the malleus, articulated with the incus; 7, the

long process of the malleus in the Glasserian fissure ; 8. the stapes, articulated with the incus. This is drawn

somewhat outward ; otherwise, the base of the stapes alone would be visible. This figure shows the handle of

* the malleus attached to the membrana tympani.

The laxator tympani, the external muscle of the malleus, arises from the spinous pro-
cess of the sphenoid bone and, by a few filaments, from the cartilaginous portion of the

THE MIDDLE EAR. 821

Eustachian tube. It passes backward, through the Glasserian fissure, to be inserted into
the neck of the malleus, being enclosed, in its course, in a fibrous sheath. The laxator
tympani is generally believed to be muscular, though some authorities deny that it is
composed of true muscular fibres. Its action would be to draw the malleus forward and
outward, producing relaxation of the membrana tympani. It is not definitely known from
what nerve this muscle derives its motor filaments.

The stapedius muscle is situated in the descending portion of the aqueductus Fallopii
and in the cavity of the pyramid on the posterior wall of the tympanic cavity. Its ten-
don emerges from a foramen at the summit of the pyramid. In the canal in which this
muscle is lodged, its direction is upward and vertical. At the summit of the pyramid, it
turns at nearly a right angle, its tendon passing horizontally forward to be attached to
the head of the stapes. Like the other muscles of the ear, this is enveloped in a fibrous
sheath. Its action is to draw the head of the stapes backward, relaxing the membrana
tympani. This muscle receives filaments from the facial nerve by a distinct branch, the
tympanic.

The posterior wall of the tympanic cavity presents several foramina which open
directly into numerous irregularly-shaped cavities, communicating freely with each other,
in the mastoid process of the temporal bone. These are called the mastoid cells. They
are lined by a continuation of the mucous membrane of the tympanum. There is, under
certain conditions, a free circulation of air between the pharynx and the cavity of the
tympanum through the Eustachian tube, and from the tympanum to the mastoid cells.

The Eustachian tube (12, Fig. 258) is partly bony and partly cartilaginous. Following
its direction from the tympanic cavity, it passes forward, inward, and slightly downward.
Its entire length is about an inch and a half. Its caliber gradually contracts from the
tympanum to the spine of the sphenoid, and from this constricted portion it gradually
dilates to its opening into the pharynx, the entire canal presenting the appearance of two
cones. The osseous portion extends from the tympanum to the spine of the sphenoid bone.
The cartilaginous portion is an irregularly triangular cartilage, bent upon itself above,
forming a furrow, with its concavity presenting downward and outward. The fibrous
portion occupies about half of the tube beyond the osseous portion, and completes the
canal, forming its inferior and external portion. In' its structure, the cartilage of the
Eustachian tube is intermediate between the hyaline and the fibro-cartilage.

The circumflexus, or tensor palati muscle, which has already been described in connec-
tion with deglutition, is attached to the anterior margin, or the hook of the cartilage. The
attachments of this muscle have lately been accurately described by Rudinger, who calls
it the dilator of the tube. The following excellent summary of the action of the muscles
upon the tube is taken from the report on otology, by Dr. J. Orne Green, contained in
the Transactions of the American Otological Society, 1870 :

"The tensor palati muscle is a dilator of the tube; it is inserted along the whole
length of the hook of the cartilage, passing forward, inward, and slightly downward, and
its fibres spread out along the edge of the soft palate and on the side of the pharynx. In
contracting, it draws the hook of the cartilage forward and a little downward, thus en-
larging the caliber of the tube. The levator palati takes its origin from the temporal
bone just below the osseous tube, and passes along the floor of the tube, some of its fibres
arising from the lower end of the cartilage ; it is inserted in the uvula, and, in contracting
the belly of the muscle which lies along the floor of the tube, becomes thicker: the floor
of the tube is raised, and the fibres arising from the cartilage serve to draw the lower end
of this away from the opposite wall.

" The palato-pharyngens rises from the posterior part of the lower end of the cartilage,
passes backward, and is inserted on the posterior wall of the pharynx. Its action would
be to draw the posterior wall of the tube backward; but. as it is often but slightly de-
veloped, it probably only serves to fix the cartilage, so that the other muscles can act
more effectively.

822 NERVOUS SYSTEM.

" The opening of the tube is thus the result of the action of these three muscles: the
tensor palati, or dilator .tubse, draws the hook of the cartilage outward, the cartilage
becomes less curved and the tube is widened; the levator palati in contracting becomes
more horizontal, and draws the lower end of the cartilage inward and upward, thus
enlarging the pharyngeal orifice more than 3//;. As soon as these muscles cease acting,
the elasticity of the cartilage restores the canal to its former condition."

It is thus that the action of certain of the muscles of deglutition dilates the pharyngeal
opening of the Eustachian tube. If we close the mouth and nostrils and make several
repeated acts of deglutition, we draw the air from the tympanic cavity, and the atmos-
pheric pressure renders the membrane of the tympanum tense, increasing its concavity.
By one or two lateral movements of the jaws, we open the tube, the pressure of air is
equalized, and the ear returns to its normal condition. The nerves animating the dilator
tubas come from the pneumogastric and are derived from the spinal accessory.

A smooth mucous membrane forms a continuous lining for the Eustachian tube, the
cavity of the tympanum, and the mastoid cells. In all parts, it is closely adherent to the
subjacent tissues, and, in the cavity of the tympanum, it is very thin. In the cartilaginous
portion of the Eustachian tube, there are numerous mucous glands, which are most
abundant near the pharyngeal orifice, and gradually diminish in number toward the
osseous portion, in which there are no glands. Throughout the tube, the surface of the
mucous membrane is covered with conoidal cells of ciliated epithelium. The mucous
membrane of the tympanic cavity is very thin, consisting of little more than epithelium
and a layer of connective tissue. It lines the walls of the cavity, the inner surface of the
membrana tympani, is prolonged into the mastoid cells, and covers the ossicles and those
portions of the muscles and tendons which pass through the tympanum. On the floor of
the tympanic cavity and on its anterior, inner, and posterior walls, the epithelium is of
the conoidal, ciliated variety. On the promontory, roof, ossicles, and muscles, the cells
are of the pavement-variety and not ciliated, the transition from one form to the other
being gradual. The entire mucous membrane contains numerous lymphatics, a plexus
of nerve-fibres and nerve-cells, with some peculiar cells, the physiology of which is not
understood.

We have thus given a general sketch of the physiological anatomy of the middle ear,
and shall not find it necessary to treat more fully of the cavity of the tympanum, the
mastoid cells, or the Eustachian tube, except as regards certain points in their physiology.
The minute anatomy of the membrana tympani and the articulations of the ossicles can
be more conveniently considered in connection with the physiology of these parts.

General Arrangement of the Bony LalyrintTi. — The internal portion of the auditory
apparatus is contained in the petrous portion of the temporal bone. It consists of an
irregular cavity, called the vestibule, the three semicircular canals (13, 14, 15, Fig. 258),
and the cochlea (16, Fig. 258). The general arrangement of these parts in situ and their
relations to the adjacent structures are shown in Fig. 258. Fig. 261, showing the bony
labyrinth isolated, is taken from the beautiful photograph contained in Etidinger's atlas.

The vestibule is the central chamber of the labyrinth, communicating with the tympanic
cavity by the fenestra ovalis, which is closed in the natural state by the base of the stapes.
This is the central, ovoid opening shown in Fig. 261. The inner wall of the vestibule
presents a small, round depression (the fovea hemispherica) perforated by numerous small
foramina, through which pass nervous filaments from the internal auditory meatus.
Behind this depression, is the opening of the aqueduct of the vestibule. In the posterior
wall of the vestibule, are five small, round openings leading to the semicircular canals,
with a larger opening below, leading to the cochlea.

The general arrangement of the semicircular canals is shown in Fig. 261 (6, 7, 8, 9,
10, 11, 12).

The arrangement of the cochlea (the anterior division of the labyrinth) is shown in

THE INTERNAL EAR. 823

Fig. 261 (1, 3, 4). This is a spiral canal, about an inch and a half long, and one-tenth of
an inch wide at its commencement, gradually tapering to the apex, and making, in its
course, two and a half turns. Its interior presents a central pillar, around which winds
a spiral lamina of bone. The fenestra rotunda (2, Fig. 261), closed in the natural state
by a membrane (the secondary membrana tympani), lies between the lower portion of the
cochlea and the cavity of the tympanum.

FIG. 261.— T/ie left bony labyrinth of a new-born child, forward and outward view. From a photograph.

(Rudinger.)

1, thfcwide canal, the beginning of the spiral canal of the cochlea; 2, the feneotra rotunda: 8. the second turn of the
cochlea; 4, the final half-turn of the cochlea; 5, the border of the bony wall of the vestibule, situated l.ctwi-cn the
cochlea and the semicircular canals; 6, the superior, or sagi tal semicircular canal; 7, the portion of the superior
semicircular canal bent outward; 8, the posterior, or transverse semicircular caual; 9, the portion of the p«»trri<>r
connected with the superior semicircular canal; 10. point of junction of the superior and the posterior semicir'-u-
lar canal; 11, the ampulla ossea externa; 12, the horizontal, or external semicircular canal. The explanation of
this Figure has been modified and condensed from Rudinger.

What is called the membranous labyrinth is contained within the bony parts just
described. Its structure, and the ultimate distribution and connections of the auditory
nerve, which penetrates by the internal auditory meatus, involve some of the most intri-
cate and difficult points in the whole range of minute anatomy. Some of these ha\v
direct and important relations to the physiology of hearing, while many are of puivly
anatomical interest. Such facts as bear directly upon physiology will be considered fully
in connection with the functions of the internal ear.

Physics of Sound.

The sketch that we have given of the general anatomical arrangement of the auditory
apparatus conveys an idea of the uses of the different parts of the ear. The waves of
sound must be transmitted to the terminal extremities of the auditory IHTVO in the
labyrinth. These waves are collected by the pinna, are conducted to the moml.rana
tympani through the external auditory meatus, produce vibrations of the ID. ml.r.-uia
tympani, are conducted by the chain of ossicles to the opening in the labyrinth, and
are communicated through the fluids of the labyrinth to the ultimate nervous lilanu-nN.
The free passage of air through the external meatus and the communication* of the cavity
of the tympanum with the mastoid cells, and, by the Eustachian tube, with the pharynx,
are necessary to the proper vibration of the membrana tympani; the iiite.irrity of tho

824 SPECIAL SENSES.

ossicles and of their ligaments and muscles is essential to the proper conduction of sound
to the labyrinth ; the presence of liquid in the labyrinth is a condition essential to the
conduction of the waves to the filaments of distribution of the auditory nerves ; and,
finally, from the labyrinth, the nerves pass through the internal auditory meatus to the
brain, where the auditory impressions are appreciated.

Most of the points in acoustics which are essential to the comprehension of the physi-
ology of audition are definitely settled. The theories of the propagation of sound involve
wave-action, concerning which there is no dispute among physicists. For the conduc-
tion of sound, a ponderable medium is essential ; and it is not necessary, as in the case
of the undulatory theory of light, to assume the existence of an imponderable ether.
The human ear, although perhaps not so acute as the auditory apparatus of some of the
inferior animals, not only appreciates irregular waves, such as produce noise as distin-
guished from sounds called musical, but is capable of distinguishing regular waves, as in
simple musical sounds, and harmonious combinations.

In music, certain successions of regular sounds are agreeable to the ear and constitute
what we call melody. Again, we are able to appreciate, not only the intensity of sounds,
both noisy and musical, but we recognize pitch and different qualities, particularly in
music. Still farther, we find that musical notes may be resolved into certain invariable
component parts, such as the octave, the third, fifth, etc. These components of what
are usually supposed to be simple sounds — which may be isolated by artificial means, to
be described farther on — are called tones ; while the sounds themselves, produced by the
union of the different tones, are called notes, which may themselves be combined to form
chords.

The quality of musical sounds may be modified by the simultaneous production of
others which correspond to certain of the components of the predominating note. For
example, if we add to a single note, the third, fifth, and octave, we produce a major
chord, the sound of which is very different from that of a single note or of a note with
its octave. If we diminish the third by a semitone, we have a different quality, w^ich
is peculiar to minor chords. In this way, we can form an immense variety of musical
sounds upon a single instrument, as the piano. And still farther, by the harmonious
combinations of the notes of different instruments and of different registers of the
human voice, as in grand choral and orchestral compositions, shades of effect, almost
innumerable, may be produced. The modification of tones in this way constitutes har-
mony ; and an educated ear, not only experiences pleasure from these musical combina-
tions, but can distinguish their different component parts.

A chord may convey to the ear the sensation of completeness in itself or it may lead
to a succession of notes before this sense of completeness is attained. Different chords
of the same key may be made to follow each other, or we may, by transition-notes, pass
to the chords of other keys. Each key has its fundamental note, and the transition from
one key to another, in order to be agreeable to the ear, must be made in certain well-
defined and invariable ways. These regular transitions constitute modulation. The ear
becomes fatigued by long successions of notes always in one key, and modulation is essen-
tial to the enjoyment of elaborate musical compositions ; otherwise, the notes would not
only become monotonous, but their correct appreciation would be impaired, as the ap-
preciation of colors becomes less distinct after looking for a long time at an object pre-
senting a single vivid tint.

Laws of Sonorous Vibrations.

As we have already remarked, sound is produced by vibrations in a ponderable me-
dium. The sounds ordinarily heard are transmitted to the ear by means of vibrations
of the atmosphere. A simple and very common illustration of this fact is afforded by
the experiment of striking a bell carefully arranged in vacua. Although the stroke and
the vibration can readily be seen, there is no sound ; and, if air be gradually introduced,

LAWS OF SONOROUS VIBRATIONS. 825

the sound will become appreciable and progressively more intense as tlie surrounding
medium is increased in density.

If we produce a single sound, or shock, in a free atmosphere, we may suppose that
the waves are transmitted equally in every direction ; and this is accomplished in the
following manner : An imaginary sphere of air receives an impulse, or shock, from the
body which produces the sound. This shock is, in its turn, communicated to another
spherical stratum of air ; this, to a third, and so on. The elasticity of the air, however,
produces a recoil of each imaginary sphere of air, and it is a portion of the last stratum
which strikes the tympanum, throwing it into vibration. If but a single impulse be
given to the air, we may suppose that all of the different strata, after a single oscillation,
return to their original quiescent condition. The first stratum receives the shock, and
the last communicates the shock to the ear. The oscillations of sound, produced in this
way, are to and fro in the direction of the line of conduction and are said to be longi-
tudinal. In the undulatory theory of light, the vibrations are supposed to be at right
angles to the line of propagation, or transversal. A complete oscillation to and fro is
called a sound- wave.

It is evident that vibrating bodies may be made to perform and impart to the atmos-
phere oscillations of greater or less amplitude. The intensity of the sound is in propor-
tion to the amplitude of the vibrations. If we cause a tuning-fork to vibrate, the sound
is at first loud, or intense ; but the amplitude gradually diminishes, and the sound dies
away until it is lost. In a vibrating body capable of producing a definite number of
waves of sound in a second, it is evident that, the greater the amplitude of the wave, the
greater is the velocity of the particles thrown into vibration. It has been ascertained by
experiment, that there is an invariable mathematical relation between the intensity of
sound, the velocity of the conducting particles, and the amplitude of the waves ; and
this is expressed by the formula, that the intensity is proportional to the square of the
amplitude. It is evident, also, that the intensity of sound is diminished by distance, as
the amplitude of the waves and the velocity of the vibrating particles become weaker,
the farther we are removed from the sonorous body. The sound, as the waves recede
from the sonorous body, becomes distributed over an increased area. The propagation
of sound has been reduced also to the formula, that the intensity diminishes in propor-
tion to the square of the distance.

Sonorous vibrations are subject to many of the laws of reflection which we have
studied in connection with light. Sound may be absorbed by soft and non-vibrating
surfaces, in the same way that certain surfaces absorb the rays of light. It is in this way
that we explain the deadening of sound in apartments furnished with carpets, curtains,
etc., and its reflection from smooth, hard surfaces. By carefully-arranged convex sur-
faces, the waves of sound may be readily collected to a focus. These laws of the reflec-
tion of sonorous waves explain echoes and the conduction of sound by confined strata of
air, as in tubes. We thus explain the mechanism of speaking-trumpets, the collection of
the waves by the pavilion of the ear, and their transmission to the tympanum by the
external auditory meatus. To make the parallel between sonorous and luminous trans-
mission more complete, it has been ascertained that the waves of sound may be refracted
to a focus by being made to pass through an acoustic lens, as a balloon filled with car-
bonic-acid gas. The waves of sound may also be deflected around solid bodies, when
they produce what have been called by Tyndall, shadows of sound.

Any one observing the sound produced by the blow of an axe can note the important
fact that sound is transmitted with much less rapidity than light. At a short distance.
our view of the body is practically instantaneous; but there is a considerable intervjil
between the blow and the sound. This interval represents the velocity of the sonorous
conduction. This fact is also illustrated by the interval between a Hash of liglitninir and
the sound of thunder. The velocity of sound depends upon the density and elasticity of
the conducting medium. The rate of conduction of sound by atmospheric air at the

826 SPECIAL SENSES.

freezing-point of water is about 1,090 feet per second. This rate presents comparatively
slight variations for the different gases, but it is very much more rapid in liquids and in
solids. In ordinary water, it is 4,708 feet per second ; in iron or steel wire, about 16,000
feet ; and in most woods, in the direction of the fibre, about the same.

Noise and Musical Sounds. — There is a well-defined physical as well as an eesthetic
distinction between noise and music. Taking, as examples, single sounds, a sound be-
comes noise when the air is thrown into confused and irregular vibrations. A noise may
be composed of a few musical sounds, when these are not in accord with each other, and
sounds called musical are not always entirely free from discordant vibrations, as we shall
see in studying musical sounds, properly so called. A noise possesses intensity, varying
with the amplitude of the vibrations, and it may have different qualities, depending upon
the form of its vibrations. We may call a noise dull, sharp, ringing, metallic, hollow,
etc., thus expressing qualities that are readily understood. In percussion of the chest,
the resonance is called vesicular, tympanitic, etc., distinctions in quality that are quite
important. A noise may also be called sharp or low in pitch, as the rapid or slow vibra-
tions predominate, without answering the requirements of musical sounds. These expla-
nations, with the definition that a noise is a sound that is not musical, will be better
understood after we have described some of the characters of musical vibrations.

A pure and simple musical sound consists of vibrations following each other at regular
intervals, provided that the succession of waves be not too slow or too rapid. When the
vibrations are too slow, we have an appreciable succession of impulses, and the sound is
not musical. When they are too rapid, we recognize that the sound is excessively sharp,
but it is then painfully acute and has no pitch that can be accurately determined by the
auditory apparatus. Such sounds may be occasionally employed in musical compositions,
but, in themselves, they are not strictly musical.

In musical sounds, we recognize duration, intensity, pitch, and quality. The duration
depends simply upon the length of time during which the vibrating body is thrown into
action. The intensity depends, as we have already stated, upon the amplitude of the
vibrations, and it has no relation whatsoever to pitch. Pitch depends absolutely upon the
rapidity of the regular vibrations, and quality, upon the combinations of different tones
in harmony, the character of the harmonics of fundamental tones, and the form of the
vibrations.

Pitch of Musical Sounds. — In discussing the pitch of musical sounds, we shall leave
out of the question, for the present, the harmonics, which exist in nearly all musical notes
and affect their quality, and confine ourselves to the study of simple vibrations. Such
tones are those of great organ-pipes, which are deficient in harmonics and in overtones,
and are almost entirely pure.

Pitch depends upon the number of vibrations. A musical sound may be of greater or
less intensity; it may at first be quite loud and gradually die away; but the number of
vibrations in a definite tone is invariable, be it weak or powerful. The rapidity of the
conduction of sound does not vary with its intensity or pitch, and, in the harmonious
combination of the sounds of different instruments, be they high or low in pitch, intense
or feeble, it is always the same in the same conducting medium. Distinct musical notes
may present an immense variety of qualities, but all tones of the same pitch have abso-
lutely equal rates of vibration. Tones equal in pitch are said to be in unison. This fact,
though simple, has a most important physiological bearing. In the first place, an edu-
cated ear can, without difficulty, distinguish slight differences in pitch in ordinary musical
tones. Again, we ascertain by experiment that this power of appreciation of tones is
restricted within well-defined limits, which vary slightly in different individuals. With-
out citing all of the numerous observations upon this point, we may state that Helmholtz,
whose authority is the very highest, gives, as the range of sounds that can be legitimately

LAWS OF SONOROUS VIBRATIONS. 827

employed in music, those of from 40 to 4,000 vibrations in a second, embracing about
seven octaves. In an orchestra, the double bass gives the lowest note, which has 40-25
vibrations in a second, and the highest note, given by the small flute, has 4,752 vibrations.
In grand organs, there is a pipe which gives a note of 16 -5 vibrations, and the deepest
note of modern pianos has 27'5 vibrations ; but delicate shades of pitch in these low notes
are not appreciable to most persons. Sounds above the limits just indicated are painfully
sharp, and their pitch cannot be exactly appreciated by the ear. The physiological inter-
est connected with these facts is, that the limits of the appreciation of musical sounds are
probably due to the anatomical arrangement of the auditory apparatus, as we have a
limit to the acuteness of vision, which can be explained by the structure of the eye. This
fact is the basis of the accepted theories of the appreciation of musical sounds.

Musical Scale. — We have thus far considered musical sounds, without any reference
to the relations of different notes to each other. A knowledge of these relations lies at
the foundation of the science of music ; and, without a clear idea of certain of the funda-
mental laws of music, we cannot thoroughly comprehend the mechanism of audition.

It requires very little cultivation of the ear to enable us to comprehend the fact, that
the successions and combinations of tones must obey certain fixed laws; and, long before
these laws were the subject of mathematical demonstration, the relations of the different
notes of the scale were established, merely because certain successions and combinations
were agreeable to the ear, while others were discordant and apparently unnatural. Now
that we are pretty thoroughly acquainted with the laws of vibrations, we can study the
scale from a scientific, as well as from an esthetic point of view.

The most convenient notes for our study are those produced by vibrating strings, and
the phenomena here observed are essentially the same for all musical sounds; for it is
by means of vibrations communicated to the air that the waves of sound find their
way to the auditory apparatus. Let us take, to begin with, a string vibrating 24
times in a second. If this string be divided into two equal parts, each part will vibrate
48 times in a second. The note thus produced is the octave, or the 8th of the primary
note, called the 8th, because the natural scale, as we Shall see, contains eight notes, of
which the first is the lowest and the last, the highest. We may divide the half again,
producing a second octave, and so on, within the limits of our appreciation of musical
sounds. If we divide the string so that f of its length will vibrate, we have 36 vibrations
in a second, and this note is the 5th in the scale. If we divide the string again, so as to
leave f of its length, we have 30 vibrations, which gives the 3d note in the scale. These
are the most natural subdivisions of the note; and the 1st, 3d, 5th, and 8th, when sound-
ed together, make what is known as the common major chord. Three-fourths of the
length of the original string makes 32 vibrations, and gives the 4th note in the scale. If
we take f of the string, we have 27 vibrations, and the note is the 2d in the scale. Witli
| of the string, we have 40 vibrations in a second, or the 6th note in the scale. With -fa
of the string, we have 45 vibrations in a second, or the 7th note in the scale.

It will be observed that we have started with a note, which we may call C. This is
the key-note, or the tonic. In this scale, which is called the natural, or diatonic key, we
have a regular mathematical progression from the 1st to the 8th. This is called the
major key of 0. Melody consists in an agreeable succession of notes, which we may
assume, for sake of simplicity, to be pure. We cannot, in a simple im-lotly. sound any
note but one of those in the scale. When a different note is sounded, we pa.-s into a k«-y
which has a different fundamental note, or tonic, with a different succession of 3<K r>rhs,
etc. Every key, therefore, has its 1st, 3d, 5th, and 8th, as well as tlie inti-nneclijite
notes. If we substitute for the 3d a note formed by a string | the length <»f tin- tonic
instead of f, we have the key converted into the minor. The minor chord, consisting of the
1st, the diminished 3d, the 5th, and the 8th, is perfectly harmonious, but it lm> a quality
quite different from that of the major chord. The notes of a melody may progress in the

828 SPECIAL SENSES.

minor key as well as in the major. Taking the small numbers of vibrations merely for
convenience, the following is the mode of progression in the natural scale of 0 major:

1st. 2d. 3d. 4th. 5th 6th. 7th. 8th.

Note CDEFGABC

Lengths of the string 1 f £ f I 5 W 2

Number of vibrations 24 27 30 32 36 40 45 48

The intervals between the notes of the scale, it is seen, are not equal. The smallest,
between the 3d and 4th and the 7th and 8th, are called semitones. The other intervals
are either full perfect tones or small perfect tones. Although there are semitones, not
belonging to the key of 0, between 0 and D, D and E, F and G, G and A, and A and
B, these intervals are not all composed of exactly the same number of vibrations ; so
that, taking the notes on a piano, if we have D as the tonic, its 5th would be A. We
assume that D has 27 vibrations, and A, 40, giving a difference of 13. With C as the
tonic and G as the 5th, we have a difference of 12. It is on account of these differences
in the intervals, that each key in music has a peculiar and an individual character.

In tuning a piano, which is the single instrument most commonly used for accompani-
ment and the general interpretation of musical compositions, the ordinary method is by
the 5ths. We bring the 5th of 0 in exact accord with the tonic ; then the 5th of D ;
then the 5th of E, and finally the 5th of F. The 5th of E should be the octave of C,
but, by progressing in this way, the last note (C) is too sharp and is not the octave of
the lower 0. If this progression were continued higher and higher, the octaves would
become more and more out of tune ; and, to avoid this, the octaves are made perfect and
the 5ths and 3ds are tuned down, so that the inequality is distributed throughout the
scale. This is called tempering the scale, and, with this " temperament," the notes are
not exactly true ; still, musicians are accustomed to this, and they fail to recognize the
mathematical defect.

Even in melody, and still more in harmony, in long compositions, the ear becomes
fatigued by a single key, and it is necessary, in order to produce the most pleasing effects,
to change the tonic, by what is called modulation, returning afterward to the original key.

Quality of Musical Sounds. — By appropriate means, we can analyze or decompose
white light into prismatic colors ; and, in the same way, nearly all musical sounds, which
seem at first to be simple, can be resolved into certain well-defined constituents. There
are few absolutely simple sounds used in music. We may take an example, however, in
the notes of great stopped-pipes in the organ. These are simple, but are of an unsatis-
factory quality and wanting in richness. Almost all other musical sounds, however,
have a fundamental tone, which we recognize at once ; but this tone is accompanied
by harmonics caused by secondary vibrations of subdivisions of the sonorous body.
The number, pitch, and intensity of these harmonic, or aliquot vibrations affect what
is called the quality, or timbre of musical notes, by modifying the form of the sonorous
waves. This fact, which we shall discuss more elaborately farther on, requires little
argument for its support. If we suppose a string vibrating a certain number of times in
a second, the vibrations being perfectly simple, we should have, according to the laws
of vibrating bodies, a simple musical tone; but, if we suppose that the string subdivides
itself into different segments, one of which gives the 3d, another, the 5th, and so on, of the
fundamental tone, it is evident that the form of the vibrations must be considerably
modified. This is the fact ; and, with these modifications in form, the quality, or timbre
of the note is changed. We can illustrate this roughly on the piano. If we strike the
note 0, we have a certain quality of sound. We may assume, for sake of argument,
that this is a simple tone, although in reality it is complex. We now strike simultaneously
the fundamental note, its 3d, 5th, and 8th, making the common chord of 0 major. The
predominant note is still C, but the addition of the harmonious notes modifies its quality.

LAWS OF SONOROUS VIBRATIONS. 829

If we diminish the third by a semitone, we still have C for the predominant note, but
the quality of the chord is changed to the minor. In this rough illustration, the ear can
readily detect the harmonious tones ; but, in the note of a single string, this cannot be
done without practice and close attention. Still, in the notes of single strings, the ear
can distinguish the harmonics ; and, what is more satisfactory, the existence of harmon-
ics can be actually demonstrated in various ways.

From what we have just stated, it follows that nearly all musical tones consist, not
only of a fundamental sound, but of harmonic vibrations, subordinate to the fundamental
and qualifying it in a particular way. These harmonics may be feeble or intense ; cer-
tain of them may predominate over others ; some, that are usually present, may be
eliminated ; and, in short, there may be a great diversity in their arrangement, and thus
the timbre may present an infinite variety. This is one of the elements entering into the
composition of notes, and it affords a partial explanation of quality.

Another element in the quality of notes depends upon their reenforcement by reso-
nance. The vibrations of a stretched string, not connected with a resonant body, are
almost inaudible. In musical instruments, we have the sound taken up by some mechani-
cal arrangement, as the sound-board of the organ, piano, violin, harp, guitar, etc. In
the violin, for example, the sweetness of the tone depends chiefly upon the construction
of the resonant part of the instrument, and but little upon the strings themselves, which
are frequently changed. The same is true of the human voice, of wind-instruments, etc. ;
but we could not discuss these points elaborately, without giving a full description of the
various musical instruments in common use, which would be out of place in a work upon
physiology.

In addition to the harmonic tones of sonorous bodies, various discordant sounds are
generally present, which modify the timbre, producing, usually, a certain roughness,
such as the grating of a violin-bow, the friction of the columns of air against the angles
in wind-instruments, etc. All of these conditions have their effect upon the quality of
tones ; and these discordant sounds may exist in infinite number and variety. These
sounds are composed of irregular vibrations and are consequently inharmonious. Nearly
all notes that we speak of in general terms as musical are composed of musical, or har-
monic aliquot tones with the discordant elements to which we just alluded.

Aside from the relations of the various component parts of musical notes, the quality
depends largely upon the form of the vibrations. To quote the words of Helmholtz, u the
more uniformly rounded the form of the wave, the softer and milder is the quality of the
sound. The more jerking and angular the wave-form, the more piercing the quality.
Tuning-forks, with their rounded forms of wave, have an extraordinarily soft quality ;
and the qualities of sound generated by the zither and violin resemble in harshness the
angularity of their wave-forms."

Harmonics, or Overtones. — As we have stated in the foregoing discussion, nearly all
sounds are composite, but some contain many more aliquot, or secondary vibrations than
others. The notes of vibrating strings are peculiarly rich in harmonics, and these may
be used for illustration, remembering that the phenomena here observed have their analo-
gies in nearly all varieties of musical sounds. If a stretched string be made to vibrato.
the secondary tones, which qualify, as it were, the fundamental, are called harmonics, or,
in German, overtones, a term which is now much used by English writers.

While it is difficult at all times to distinguish by the ear the individual overtones of
vibrating strings, their existence can be demonstrated by a few simple experiments,
us suppose, for example, that we have a string, the fundamental tone of which is ('
damp this string with a feather at one-fourth of its length and draw a violin-how ,-icrr
the smaller section. We then sound, not only the fourth part of the string across which
the bow is drawn, but the remaining three-fourths; but, if we have placed little rulers
paper upon the longer segment, at distances equal to one-fourth the entire string, they

830 SPECIAL SENSES.

will remain undisturbed, while riders placed at any other portion of the string will be
thrown off. This experiment shows that the three-fourths of the string have been di-
vided, as we have sounded the second octave above the fundamental tone. This may be
illustrated by connecting one end of the string with a tuning-fork. When this is done,
and the string is brought to the proper degree of tension, it will first vibrate as a whole,
then, when a little tighter, will spontaneously divide into two equal parts, and, under
increased tension, into three, four, and so on. By damping a string with the light touch
of a feather, we suppress the fundamental tone and bring out the overtones, which exist
in all vibrating strings, but are usually concealed by the fundamental. The points which
mark the subdivisions of the string into segments of secondary vibrations are called
nodes. When we damp the string at its centre, we quench the fundamental tone and
have overtones an octave above ; damping it at a distance of one-fourth, we have the
second octave above, and so on. When we damp it at a distance of one-fifth from the
end, we have the four-fifths sounding the 3d of the fundamental, with the second octave
of the 3d. If we damp it at a distance of two-thirds, we have the 5th of the fundamen-
tal, with the octave of the 5th.

Every vibrating string possesses, thus, a fundamental tone and overtones. We have,
qualifying the fundamental, first, as the most^ simple, a series of octaves ; next, a series
of 5ths of the fundamental and their octaves ; and next, a series of 3ds. These are the
most powerful overtones, and they form the common chord of the fundamental ; but they
are so far concealed by the greater intensity of the fundamental, that they cannot be easily
distinguished by the unaided ear, unless the fundamental be quenched in some such way
as we have indicated. In the same way, the harmonic 5ths and 3ds overpower other
overtones; for we have the string subdividing again and again into overtones, which are
not harmonious like the notes of the common chord of the fundamental.

The presence of overtones, resultant tones, and additional tones, which latter will be
described hereafter, can be demonstrated, without damping the strings, by the resonators,
invented by Helmholtz. It is well known that, if a glass tube, closed at one end, which
^contains a column of air of a certain length, be brought near a resounding body emitting
V a note identical with that produced by the vibrations of the column of air, the air in the
tube will resound in consonance with the note. If, for example, we have a tube sounding
C, a tuning-fork of the same pitch sounded near the tube will throw the air in the tube
into action and will produce a powerful sound, while no other note will have this effect.
The resonators of Helmholtz are constructed upon this principle. A glass globe or tube
(Fig. 262) is constructed so as to produce a certain note. This has a larger opening (a)
and a smaller opening (b) which latter is fitted in the ear by warm sealing-wax, the other
ear being closed. When the proper note is sounded, it is reenforced by the resonator
and is greatly increased in intensity, while all other notes are heard very faintly. Sup-
pose, now, that we apply this to the detection of overtones. We fix in the ear a resonator
adjusted to G, and sound the fundamental (0). The fundamental (C) is imperfectly heard,
but the overtone (G) is reenforced, and we have a loud and distinct sound of the 5th. By
using resonators graduated to the musical scale, we can easily analyze a note and distin-
guish the overtones. In the same way, if we place in the ear a resonator tuned to a par-
ticular note and strike a succession of chords on the piano, the general sound is imper-
fectly heard ; but, whenever we strike the note of the resonator, this is clearly distin-
guished, to the practical exclusion of all others; and we can thus analyze complicated
chords into each of their constituent parts. This experiment shows the similarity between
chords, resolved into their constituent parts, and single notes, resolved into their harmonics,
or overtones. The resonators of Helmholtz, which are open at the larger extremity, are
infinitely more delicate than those in which this is closed by a membrane.

A very striking and instructive point in the present discussion is the following : All
the overtones are produced by vibrations of segments of the string included between the
comparatively still points, called nodes ; and, if we cause a string to vibrate by plucking

LAWS OF SONOROUS VIBRATIOXS.

831

or striking it at one of these nodal points, we abolish the overtones which vibrate from this
node at a fixed point. For example, if we pluck the string at its exact centre, we sound
the fundamental ; but we then have a dull tone, which is deficient in the overtones of the
octaves. Ws can demonstrate the fact that these overtones are absent, for, if we damp
the string at its centre, the fundamental is quenched, but we have no octaves, which are
always heard on damping the centre when the string is plucked at other points. In the
same way, by plucking the string at different points, we can abolish the overtones of

FIG. 2C2 a.

FIG. 262 b.
FIG. 262.— Resonators of Helmholte.

6ths, 3ds, etc. It is readily understood that, when a string is plucked at any point, it
will vibrate so vigorously at this point that no node can be formed. This fact has long
been recognized by practical musicians, although many are probably unacquainted with
its scientific explanation. Performers upon stringed instruments habitually attack the
strings near their extremities. In the piano, where the strings may be struck at almost
any point, the hammers are placed at from £ to | of their extremities ; and it has been
ascertained by experience that this gives the richest notes. The nodes formed at these
points would produce the 7ths and 9ths as overtones, which do not belong to the perfect
major chord, while the nodes for the harmonious overtones are undisturbed. The reason,
then, why the notes are richer and more perfect when the strings are attacked at this
point, is that the harmonious overtones are full and perfect, and certain of the discordant
overtones are suppressed.

When two harmonious notes are produced under favorable conditions, we can
hear, in addition to the two sounds, a sound differing from both and much lower than
the lower of the two. This sound is too low for an harmonic, and it has been called a
resultant tone. The formation of a new sound by combining two sounds of different
pitch is analogous to the blending of colors in optics, except that the primary sound-
not lost. The laws of the production of these resultant sounds are very simple. When
two notes in harmony are sounded, the resultant tone is equal to the difference between
the two primaries. For example, if we sound C, with 48 vibrations, and its 5th, with 7:2
vibrations in a second, the resultant tone is equal to the difference, which is -24 vibrations,
and it is consequently the octave below C ; or, if we sound C, with 48 vibrations, and its
•3d, with 60, we have a resultant tone two octaves below C, the number of vibrations
being 12.1 These resultant tones are very feeble as compared with the primary tones, and
* These numbers are used merely in illustration. A sound of 12 vibrations does not come within the musical scale.

832 SPECIAL SENSES.

they can be heard only under the most favorable experimental conditions. In addition to
these sounds, Helmholtz has discovered sounds, even more feeble, which he calls addi-
tional, or summation tones. The value of these is equal to the sum of vibrations of the
primary tones. For example, 0 (24) and its 5th (36) would give a summation tone of 60
vibrations, or the octave of the 3d ; and 0 (24) with its 3d (30) would give 54 vibrations,
the octave of the 2d. These tones can readily be distinguished by means of the reso-
nators already described.

It is thus seen that musical sounds are excessively complex. With single sounds, we
have an infinite variety and number of harmonics, or overtones, and in chords, which
will be treated of more fully under the head of harmony, we have a series of resultants,
which are lower than the primary tones, and a series of additional, or summation tones,
which are higher ; but both the resultant and the summation tones bear an exact mathe-
matical relation to the primary tones of the chord.

Harmony. — We have discussed the overtones, resultant tones, and summation tones
of strings rather fully, for the reason that, in the physiology of audition, we shall see that
the ear is capable of recognizing single sounds or successions of single sounds ; but, at
the same time, certain combinations of sounds are appreciated and are even more agree-
able than those which are apparently produced by simple vibrations. Combinations of
tones which thus produce an agreeable impression are called harmonious. They seem to
become blended with each other into a complete sound of peculiar quality, all of the dif-
ferent vibrations entering into their composition being simultaneously appreciated by the
ear. From what we have learned of overtones, it is evident that few musical sounds are
really simple, and that those which are simple are wanting in richness, while they are per-
fectly pure. The blending of tones which bear to each other a certain mathematical rela-
tion is called harmony ; but two or more tones, though each one be musical, are not neces-
sarily harmonious. The most prominent overtone, except the octave, is the 5th, with its
octaves, and this is called the dominant. The next is the 3d, with its octaves. The
other overtones are comparatively feeble. Reasoning, now, from our knowledge of the
relations of overtones, we might infer that the reenforcement of the 5th and 3d by other
notes bearing similar relations to the tonic would be agreeable. This is the fact, and it
was ascertained empirically long before the pleasing impression produced by such com-
binations was explained mathematically. We do not propose to enter into a full discus-
sion of the laws of harmony, but a knowledge of certain of these laws is essential to the
comprehension of the physiology of audition. These are very simple, now that we have
analyzed the sound of a single vibrating body.

It is a law in music, that the more simple the ratio between the number of vibrations
in two sounds, the more perfect is the harmony. The simplest relation, of course, is
1 : 1, when the two sounds are said to be in unison. The next in order is 1 : 2. If we
sound C and its 8th, we have, for example, 24 vibrations of one to 48 of the other.
These sounds can produce no discord, because the waves never interfere with each other,
and the two sounds can be prolonged indefinitely, always maintaining the same relations.
The combined impression is therefore continuous. The next in order is the 1st and 5th,
their relations being 2:3. In other words, with the 1st and 5th, for two waves of the
1st we have three waves of the 5th. The two sounds may thus progress indefinitely,
for the waves coincide for every second wave of the 1st and every third wave of the 5th.
The next in order, if we sound at the same time the 1st, 5th, and 8th, is the 3d. The 3d
of C has the 8th of C for its 5th, and the 5th of C for its minor 3d. The 1st, 3d, 5th,
and 8th form the common major chord ; and the waves of each tone blend with each
other at such short intervals of time that the ear experiences a continuous impression,
and no discord is appreciated. This explanation of the common major chord illustrates
the law that, the smaller the ratio of vibration between different tones, the more perfect
is their harmony. Sounded with the 1st, the 4th is more harmonious than the 3d ; but

LAWS OF SONOROUS VIBRATIONS. 833

its want of harmony with the 5th excludes it from the common chord. The 1st, 4th,
and 8th are harmonious, but to make a complete chord we must use the 6th. These dis-
cussions might be extended into the progression of chords and modulation ; but this is
not essential to our purpose, as we wish only to ascertain the laws of the vibrations of
sounds in harmony and the mechanism of discords.

Discords. — A knowledge of the mechanism of simple accords enables us to understand
more easily the rationale of discords, and vice versa. As in the case of harmony, the fact
that certain combinations of musical tones produce a disagreeable impression was ascer-
ained empirically, with no knowledge of the exact cause of the palpable dissonance.
Thanks to the labors of modern physicists, however, the mechanism of discords is now
pretty well settled. We shall, in our explanation, begin with a combination of tones
slightly removed from perfect unison.

Suppose, for example, that we have two tuning-forks giving precisely the same num-
bers of vibrations in a second ; the tones are then in perfect unison. We load one of the
forks with a bit of wax, so that its vibrations are slightly reduced, and start them both
in vibration at the same instant. Taking the illustration given by Tyndall, we assume
that one fork has 256, and the other, 255 vibrations in a second. While these two forks
are vibrating, we have one gradually gaining upon the other ; but, at the end of half a
second, one will have made 128 vibrations, while the other will have made 127£. At
this point the two waves are in direct opposition to each other ; they are moving in
exactly opposite directions ; and, as a consequence, the sounds neutralize each other, and
we have an instant of silence. The perfect sounds, as the two forks continue to vibrate,
are thus alternately reenforced and diminished, and we have what are known in music as
beats. As the difference in the number of vibrations in a second is one, we have the
instants of silence occurring once in a second ; and in this illustration the beats occur
once a second. Unison takes place when two sounds can follow each other indefinitely,
their waves blending perfectly ; dissonance is marked by successive beats, or pulses. If
we now load forks so that one will vibrate 240 times in a second, and the other 234, there
will be six times in a second when the interference will be manifest ; or, to make it
plainer, in £ of a second, one fork will make 40 vibrations, while the other is making
39. We shall then have 6 beats in a second. From these experiments, the law may
be deduced, that the number of beats produced by two tones not in harmony is equal
to the difference between the two rates of vibration. An analogous interference of un-
dulations is observed in optics, when waves of light are made to interfere and produce
darkness.

It is evident that the number of beats will increase as we sound two discordant tones
higher and higher in the scale. According to Helmholtz, the beats can be recognized up
to 132 in a second. Beyond that point they become confused, and we have only a sen-
sation of dissonance, or roughness. We can illustrate this point very satisfactorily by a
simple experiment upon the piano. Let us take two tones, the highest on the scale,
separated from each other by a semitone. When we strike these two notes together,
we have a disagreeable sensation of dissonance, but no appreciable beats, because, the
rate of vibration of each note being high, the difference is great and the beats are too
rapid to be appreciated as such. We strike, now, the two notes an octave below ; still
we have dissonance, less disagreeable, but no beats. Passing down, an octave at a time, as
the numbers of vibrations become smaller, the difference between them is less, and there
are fewer beats in a second, until they are readily appreciated as beats and can even be
counted. Beats, then, are due to interference of sound-waves, and the number in a second
is equal to the difference in the rate of vibrations. When these are too rapid to be appre-
ciated as beats, we have simply a sensation of discord. There is no interference of the
waves of tones in unison, provided the waves start at the same instant ; the intensity of
the sound being increased by reinforcement. The differences between the 1st and 8th,
53

834 SPECIAL SENSES.

the 1st and 5th, the 1st and 3d, and other harmonious combinations, is so great that we
have no beats and no discord, the more rapid waves reenforcing the harmonics of the
primary sound. It is important to remember, in this connection, that resultant tones are
equal to the difference in the rates of vibration of two harmonious tones. If we take a
note of 240 vibrations, and its 5th, with 360 vibrations, these two have a difference of
120, which is the lower octave of the 1st and is a harmonious tone.

It is evident that the laws which we have thus stated are equally applicable to
overtones, resultant tones, and additional tones, which have their beats and dissonances,
as well as the primary tones.

Tones ~by Influence (Comonince). — The term consonance is generally applied to the
harmonious combinations of two or more sounds, and is synonymous with accord, as it
is used in music. In this sense, it is opposed to dissonance, or discord. By some writers,
however, consonance is used to denote sounds produced in sonorous bodies by the influ-
ence of sounds in unison. If, for example, we have a bell tuned to a certain note and
bring near its opening a tuning-fork vibrating in unison with this note, the bell will
sound vigorously in unison, although it is influenced only by the vibrations in the air pro-
duced by the primary sound. We have already spoken of this under the head of reso-
nance ; and sounds produced in this way are properly called tones by influence. Some
physicists designate these as sympathetic vibrations. Dr. Elsberg, of New York, uses
the term co-vibration and co-sounding, as applied to these phenomena.

It is evident that the mechanism of the production of tones by influence cannot be
neglected in studying the physiology of audition. We have, as an important part of the
auditory apparatus, the membrane of the tympanum, capable of various degrees of ten-
sion, which is thrown into vibration in obedience to waves of sound conducted by the
atmosphere ; and it will be an important point to determine how far the vibrations of
this membrane are affected by the laws of the production of tones by influence.

After what we have learned of the laws of musical vibrations, it will be easy to com-
prehend the production of sounds by influence. We shall take first the most simple
example, applied to strings. If we gently touch the note 0 upon the piano, so as to raise
the damper but not sound the string, and then sing a note in unison, the string will
return the sound, by the influence of the sound-waves. The sound thus produced by
the string will have its fundamental tone and overtones ; but the series of overtones will
be complete ; for none of the nodes are abolished, as in striking or plucking the string
at any particular point. If, instead of the note in unison, we sing any of the octaves,
the string will return the note sung ; and the same is true of the 3d, 5th, etc. If we
now strike a chord in harmony with the undamped string, this chord will be exactly
returned by influence. In other words, a string may be made to sound by influence, its
fundamental tone, its harmonics, and harmonious combinations. To carry the observa-
tion still farther, the string will return, not only a note of its exact pitch and its harmon-
ics, but notes of the quality of the primary note. This is a very important point in its
applications to the physiology of hearing and can be readily illustrated. Taking iden-
tical notes in succession, produced by the voice, trumpet, violin, clarinet, or other musi-
cal instruments^ it can be easily noted that the quality of the note, as well as the pitch,
is rendered by a resounding string ; and the same is true of combinations of notes.

The above laws of tones by influence have been illustrated by strings merely for the
sake of simplicity ; but they have a more or less perfect application to all bodies capable
of producing musical tones, except that some are thrown into vibration with more diffi-
culty than others. An interesting application of these laws, however, particularly with
reference to the physiology of the ear, is in the case of stretched membranes; for this
brings to our mind the possible action of the membrana tympani.

If we have a thin membrane, like a piece of bladder or thin rubber, stretched over a
circular orifice, such as the mouth of a wide bottle, this can be tuned to a certain note.

USES OF DIFFERENT PARTS OF THE AUDITORY APPARATUS. 835

When arranged in this way, the membrane can be made to sound its fundamental note
by influence. In addition, the membrane, like a string, will divide itself so as to sound the
harmonics of the fundamental, and it will likewise be thrown into vibration by the 5th
3d, etc., of its fundamental tone, thus obeying the laws of vibrations of strings, though
the harmonic sounds are produced with greater difficulty.

Uses of Different Parts of the Auditory Apparatus.

The uses of the pavilion of the ear and of the external auditory meatus are sufficiently
apparent. The pavilion serves to collect the waves of sound, and probably it inclines them
toward the external meatus as they come from various directions. Although this action
is simple, it undoubtedly has a certain degree of importance, and the various curves of
the concavity of the pavilion tend more or less to concentrate the sonorous vibrations.
Sucli has long been the opinion of physiologists, and this seems to be carried out by
experiments in which the concavities of the external ear have been obliterated by wax.
There is, probably, no resonance or vibration of much importance until the waves of
sound strike the membrana tympani. The same remarks may be made with regard to
the external auditory meatus. We do not know precisely how the obliquity and the
curves of this canal affect the waves of sound, but we may suppose that the deviation
from a straight course protects, to a certain degree, the tympanic membrane from im-
pressions that might otherwise be too violent.

Structure of the Membrana Tympani. — The general arrangement of the membrana
tympani has already been described in connection with the topographical anatomy of the
auditory apparatus. This structure, which is of great importance in the physiology of
hearing, is delicate, elastic, about the thickness of ordinary gold-beater's skin, and is
subject to various degrees of tension, from the action of the muscles of the middle ear
and different conditions of atmospheric pressure within and without the cavity of the
tympanum. Its form is nearly circular. From a number of accurate measurements of
its diameter in the adult, by Sappey, we may assume that its ring measures a little more
than f of an inch vertically and about f of an inch antero-posteriorly. The excess of the
vertical over the horizontal diameter is about 7V of an inch. Notwithstanding the asser-
tion of some of the older anatomists, that the tympanic membrane presents one or two
small perforations, it is now almost universally regarded as forming a complete division,
without openings, between the external meatus and the middle ear ; or, if any openings
exist, they are exceedingly minute.

The periphery of the tympanic membrane is received into a little ring of bone, which
may be separated by maceration in early life, but which is consolidated with the adja-
cent bony structures in the adult. This bony ring is incomplete at its superior portion,
but, aside from this, it resembles the groove which receives the crystal of a watch. At the
periphery of the membrane, is a ring of condensed fibrous tissue, which is received into
the bony ring. This ring also presents a break at its superior portion.

The concavity of the membrana tympani presents outward, and it may be increased or
diminished by the action of the muscles of the middle ear. The point of greatest con-
cavity, where the extremity of the handle of the malleus is attached, is called the mnbo.
Upon the inner surface of the membrane are two pouches, or pockets. One is formed by
a small, irregular, triangular fold, situated at the upper part of its posterior half and con-
sisting of a process of the fibrous layer. This, which is called the posterior pocket. i< ..JTIJ
below and extends from the posterior upper border of the membrane to the handl
the malleus, which it assists in holding in position. u After it has been divided, the bone
is much more movable than before." (Troltsch.) The anterior pocket is lower and shorter
than the posterior. It is formed by a small bony process turned toward the n.-ck of the
malleus, by the mucous membrane, by the bony process of the malleus, by its anterior

836 SPECIAL SENSES.

ligament, the chorda tympani, and the anterior tympanic artery. The handle of the
malleus is inserted between the two layers of the fibrous structure of the membrana
tympani and occupies the upper half of its vertical diameter, extending from the periph-
ery to the umbo.

The membrana tympani, though thin and translucent, presents three distinct layers.
Its outer layer is an excessively delicate prolongation of the integument lining the exter-
nal meatus, presenting, however, neither papillae nor glands. The inner layer is a deli-
cate continuation of the mucous membrane lining the tympanic cavity and is covered by

FIG. 263. — Eight membrana tympani, teen from within. Trom a photograph, and somewhat reduced.

(Kudinper.)

1, head of the malleus, divided ; 2, neck of the malleus; 3, handle of the malleus, with the tendon of the tensor tym-
pani muscle; 4, divided tendon of the tensor tympani; 5, (5. portion of the malleus between the layers of the
membrana tympani ; 7, outer (radiating) and inner (circular) fibres of the membrana tympani ; 8, fibrous ring of
the membrana tympani; 9, 14, 15, dentated fibres, discovered by Gruber ; 10, posterior pocket; 11, connection
of the posterior pocket with the malleus ; 12, anterior pocket ; 13, chorda tympani nerve.

tessellated epithelial cells. The fibrous portion, or lamina propria, is formed of two
layers. The outer layer consists of fibres, radiating from the handle of the malleus to
the periphery. These are best seen near the centre. The inner layer is composed of
circular fibres, which are most abundant near the periphery and diminish in number
toward the centre.

The color of the membrana tympani, when it is examined with an aural speculum by
daylight, is peculiar, and it is rather difficult to describe, as it varies in the normal ear in
different individuals. Politzer describes the membrane, examined in this way, as trans-
lucent, and of a color which " most nearly approaches a neutral gray, mingled with a
weaker tint of violet and light yellowish-brown. This color is modified, in certain por-
tions of the membrane, by the chorda tympani and the bones of the ear, which produce
some opacity. The entire membrane in health has a soft lustre. In addition, there is

USES OF DIFFERENT PARTS OF THE AUDITORY APPARATUS. 837

seen, with proper illumination, a well-marked, triangular cone of light, with its apex at
the end of the handle of the malleus, spreading out in a downward and forward direc-
tion, and from T\ to T^ of an inch broad at its base. This appearance is regarded by
pathologists as very important, as indicating a normal condition of the membrane. It is
undoubtedly due to reflection of light, depending upon three factors, indicated by Roosa
as follows: "First, the inclination of the membrana tympani to the auditory canal;
second, the traction of the malleus, which renders it concave at the centre; third, its
polish or brilliancy." With this explanation, it is not admitted that the light spot is due
to a peculiar structure of that portion of the membrane upon which it is seen.

Uses of the Metnbfana Tympani. — It is unquestionable that the membrana tympani is
very important in audition. In cases of disease in which the membrane is thickened,
perforated, or destroyed, the acuteness of hearing is always more or less affected. That
this is in great part due to the absence of a vibrating surface for the reception of wavi-s
of sound, is shown by the relief which is experienced by those patients who can tolerate
the presence of an artificial membrane of rubber, when this is introduced. As regards
the mere acuteness of hearing, aside from the pitch of sounds, the explanation of the
action of the membrane is very simple. Sonorous vibrations are not readily transmitted
through the atmosphere to solid bodies, like the bones of the ear; and when they are
thus transmitted they lose considerably in intensity. "When, however, the aerial vibra-
tions are received by a delicate membrane, under the conditions of the membrana tym-
pani, they are transmitted with very little loss of intensity; and, if this membrane be
connected with solid bodies, like the bones of the middle ear, the vibrations are readily
conveyed to the sensory portions of the auditory apparatus. The parts composing the
middle ear are thus admirably adapted to the transmission of sonorous waves to the
auditory nerves. The membrane of the tympanum is delicate in structure, stretched to
the proper degree of tension, and vibrates under the influence of the waves of sound.
Attached to this membrane, is the chain of bones, which conducts its vibrations, like
the bridge of a violin, to the liquid of the labyrinth. The membrane is fixed at its
periphery and has air upon both sides, so that it is under the most favorable conditions
for vibration.

A study of the mechanism of the ossicles and muscles of the middle ear shows that
the membrana tympani is subject to certain physiological variations in tension, due to
contraction of the tensor tympani. It is also evident that this membrane may be drawn
in and rendered tense by exhausting or rarefying the air in the drum. If the mouth and
nose be closed and we attempt to breathe forcibly by expanding the chest, the external
pressure tightens the membrane. In this condition, the ear is rendered insensible to
grave sounds, but high-pitched sounds appear to be more intense. If the tension be re-
lieved, as may be done by an act of swallowing, the grave sounds are heard with normal
distinctness. This experiment, tried at a concert, produces the curious effect of aboli-h-
ing a great number of the lowest tones, while the shrill sounds are heard very acutely.
The same phenomena are observed when the external pressure is increased by descent in
a diving-bell.

Undoubted cases of voluntary contraction of the tensor tympani have been ol-
by otologists ; and in these, by bringing this muscle into action, the limit of the perception
of high tones is greatly increased. In two instances of this kind, recorded by Dr. Hlako,
of Boston, the ordinary limit of perception was found to bo three thousand single vibra-
tions; and, by contraction of the muscle, this was increased to five thousand >in-le vibra-
tions.

The membrana tympani undoubtedly vibrates by influence, when il
accord with a given note. In other words, this membrane obey< the Itwsof consonan.-
and vibrates strongly by the influence of sounds in unison or in harm. my with it
mental tone. The laws of vibrations by influence have already been fully discu*

838 SPECIAL SENSES.

and it remains for us now to determine how far these laws are applicable to the physi-
ology of the vibrations of the membrana tyinpani and the action of these vibrations in
the accurate perception of musical sounds.

There are certain phenomena of vibration of the membrana tympani that must occur,
as a physical necessity, under favorable conditions, which it is important to note in this
connection ; and these have hardly attracted sufficient attention at the hands of physio-
logical writers. In the first place, this membrane must obey the laws of vibration by
influence. It is undoubtedly thrown into vibration by irregular waves of noise, as contra-
distinguished from musical tones ; but, when a tone is sounded in unison with its funda-
mental tone, or when the tone sounded is one of the octaves of its fundamental, it must
undergo a vibration by influence, like an artificial membrane. If we suppose the mem-
brane to be tuned in unison with a certain note, it will not only return this note by influ-
ence, but it will repeat its quality. Not only this, when a combination of harmonious
tones is sounded, the combined sound will be returned, with all the shades in quality
which the combined tones produce. On account of its small size, the sound produced by
the exposed membrane itself cannot be heard ; but that the membrane does vibrate by
influence, has been proven by experiments with small particles of sand on its surface.

We are certainly justified in supposing that vibrations of the membrana tympani, too
delicate to be revealed to the eye or the ear in objective experiments, may be appreciated
by the auditory nerves as a subjective phenomenon. In other words, we can probably ap-
preciate vibrations in our own tympanic membrane, when these would be too delicate to
be observed by the eye or ear, in a membrane exposed and subjected to similar influences.
This point must be accepted as probable ; and it cannot be proven by direct experiment.
If this be true, the most complex combinations of sound produced by an orchestra might
be actually reproduced by the tympanic membrane, if this membrane were accurately
tuned to the fundamental tone.

The arrangement of the muscles and bones of the middle ear admits of the possibility
of tuning the membrana tympani with exquisite nicety. These muscles are sometimes so
far under the control of the will that we can tighten the membrane to its limit by a vol-
untary effort ; the muscles are of the striated variety, and are capable of rapid action ;
they are supplied with motor filaments from the cerebro-spinal system ; the ear is fatigued
by long attention to particular tones ; persons not endowed with what is termed a musical
ear cannot appreciate slight distinctions between different tones ; the ear is capable of
education in the appreciation of pitch and in following rapid successions of tones; and, in
short, there are many points in the mechanism of the transmission of musical sounds in
the ear that seem to involve muscular action. In the larynx, we nre conscious of differ-
ences in the tension of the vocal chords only from differences in the character and pitch
of the sounds produced ; in the eye, we are conscious of the contraction of 'the muscle of
accommodation from the fact that an effort enables us to see objects distinctly at differ-
ent distances; and it is not impossible that, under ordinary conditions, the consciousness
of contractions of the muscles of the middle ear may be revealed only by the fact of the
correct appreciation of certain musical tones. Some persons can educate the ear so as to
acquire what is called the faculty of absolute pitch; that is, without the aid of a tuning-
fork or any musical instrument, they can give the exact musical value of any given tone.
A possible explanation of this is that such persons may have educated the muscles of the
ear so as to put the tympanic membrane in such a condition of tension as to respond to
a given note and to recognize the position of this note in the musical scale. Finally, an
accomplished musician, in conducting an orchestra, can, by a voluntary effort, direct his
attention to certain instruments, and hear their notes distinctly, separating them, as it
were, from the general mass of sound, can distinguish the faintest discords, and immedi-
ately designate a single instrument making a false note.

The fact that rapid successions of notes are readily appreciated does not of necessity
argue against the possibility of following these notes with the muscles of the ear ; for the

USES OF DIFFERENT PARTS OF THE AUDITORY APPARATUS. 839

muscles of the larynx may act so as to produce successions of notes as rapidly as they can
be correctly appreciated. Nor does the fact that we must prepare the tympanic mem-
brane for certain notes militate against the theory we have just given, for musical com-
positions present melodious successions in a certain scale, the notes of which hear well-
defined harmonious relations to each other, and we immediately appreciate a change in
the key, which is simply a change in the fundamental. These changes in the key must
be made in accordance with the laws of modulation ; otherwise they are harsh and grat-
ing. Modulation in music is simply a mode of-passing from one key to another by certain
transition-notes or chords, which seem inevitably to lead to a certain key, and to no
other. Finally, the laws of vibration by influence show that a single vibrating membrane
returns the quality as well as the pitch of tones and of combinations of tones as well.

The theory we have just given of the possible action of the membrana tympani is an
elaboration of the view advanced by Everard Home. Unfortunately for the simplicity of
the mechanism of hearing and the idea of division and isolation of function in different
parts, which is so seductive to physiologists, there are certain faets and considerations
which may prevent some from adopting it absolutely and exclusively as an explanation
of the mechanism of the appreciation of musical sounds. These are the following :

Destruction of both membrane tympani does not necessarily produce total deafness,
although this condition involves considerable impairment of hearing. So long as there
is simple destruction of these membranes, the bones of the middle ear and the other
parts of the auditory apparatus being intact, the waves of sound are conducted to the
auditory nerves, though imperfectly. In a remarkable case reported by Sir Astley
Cooper, which is cited by most writers upon physiology, one membrana tympani was en-
tirely destroyed, and the other was nearly gone, there being some parts of its periphery
remaining. In this person, the hearing was somewhat impaired, although he could dis-
tinguish ordinary conversation pretty well. Fortunately, he had considerable musical
taste, and it was ascertained that his musical ear was not seriously impaired ; " for he
played well on the flute and had frequently borne a part in a concert. I speak this, not
from his authority only, but also from that of his father, who is an excellent judge of
music, and plays well on the violin : he told me, that his son, besides playing on the
flute, sung with much taste, and perfectly in tune." This single case, if its details be
accurate — which we have no reason to doubt — shows conclusively that the correct appre-
ciation of musical sounds may exist independently of the action of the membrana tym-
pani.

There is one consideration, of the greatest importance, that must be kept in view
in studying the functions of any distinct portion of the auditory apparatus, like the
membrana tympani. This, like all other parts of the apparatus, except the auditory
nerves themselves, has simply an accessory function. If the regular waves of a musical
tone be conveyed to the terminal filaments of the auditory nerves, these waves make
their impression and the tone is appreciated. It makes no difference, except as regards
intensity, how these waves are conducted ; the tone is appreciated by the impression
made upon the nerves, and the nerves only. The waves of sound are not like the waves
of light, refracted, decomposed, perhaps, and necessarily brought to a focus as they im-
pinge upon the retina; as far as the action of the accessory parts of the ear are concerned,
the waves of sound are unaltered ; that is, the rate of their succession remains ahsolutely
the same, though they be reflected by the concavities of the concha and repeated l>y the
tympanic membrane. Even if we assume that the membrane, under normal conditions,
repeats musical sounds by vibrations produced by influence, and that this membrane is
tuned by voluntary muscular action so that tones are exactly repeated, the position of
these tones in the musical scal^ is not and cannot be altered by the action of any of the
accessory organs of hearing. The fact that a person may retain his musical ear witli
both membranes destroyed is not really an argument against the view that the membrane
repeats tones by influence ; for, if musical tones or noisy vibrations be conducted to the

840 SPECIAL SENSES.

auditory nerves, the impression produced must of necessity be dependent exclusively
upon the character, regularity, and number of the sonorous vibrations. And, again, the
physical laws of sound, which are fixed and unchangeable, teach us that a membrane^
like the membrana tympani, must return or reproduce sounds which are in unison or are
harmonious with its fundamental tone, much more perfectly than discordant or irregular
vibrations. In a loud confusion of noisy sounds, we can readily distinguish pure melody
or harmony, even when the vibrations of the latter are comparatively feeble. In follow-
ing with the ear any piece of music, reasoning from purely physical considerations, it
must at times occur that the tones are in exact unison or in harmony with the funda-
mental tone of the membrana tympani. Supposing the fundamental tone of the mem-
brane to be constant and invariable, such tones would be heard much more distinctly
than others, as a physical necessity. Such a difference in the appreciation of certain
notes in melody does not occur ; and the only reasonable explanation of this is that the
tension of the membrane is altered. It is shown by anatomical researches that the ten-
sion can be altered by muscular action, and, as the muscles are striated, we may suppose
that it may be modified rapidly. Physiological observations show that such modifica-
tions in tension do occur ; and there are on record unquestionable instances in which the
membrana tympani is tightened by a voluntary contraction of the tensor tympani muscle.

Another important point to note in this connection is the following: Can it be
shown that the appreciation of the pitch of tones bears any relation to the degree of ten-
sion of the tympanic membrane ? We can answer this question unreservedly in the
affirmative. When the membrane is rendered tense, there is insensibility to low tones.
When the membrane is brought to the highest degree of tension by voluntary contrac-
tion of the tensor tympani, the limit of appreciation of high tones may be raised from
three thousand to five thousand vibrations. It is a fact in the physics of the membrana
tympani, that the vibrations are more intense the nearer the membrane approaches to a
vertical position. It has also been shown that the membrane has a strikingly vertical
position in musicians, and that the position is very oblique in persons with an imperfect
musical ear. This fact has a most important bearing upon the probable relation between
the membrana tympani and the correct appreciation of musical sounds.

In view of all facts and considerations for and against the theory which we have
given of the action of the tympanic membrane in the appreciation of musical sounds,
does it not seem probable that there are, acting upon this membrane, muscles of auditory
accommodation, analogous in their operation to the muscle of visual accommodation ?
We have carefully studied this subject in all its bearings, and, if the reader follow closely
our process of reasoning, it must seem probable that the muscles of the middle ear are
muscles of auditory accommodation ; but it should be remembered that the action of the
membrane is not absolutely essential, and that musical tones, however conducted, must
of necessity be correctly appreciated, whenever and however they find their way to the
auditory nerves.

Experiments have shown pretty conclusively that the tympanic membrane vibrates
more forcibly when relaxed than when it is tense. It is evident that the relaxed mem-
brane must undergo vibrations of greater amplitude than when it is under strong tension.
In certain cases of facial palsy, in which it is probable that the branch of the facial going
to the tensor tympani was affected, the ear became painfully sensitive to powerful impres-
sions of sound. This probably has no relation to pitch, and most sounds that are pain-
fully loud are comparatively grave. The tension of the membrane may be modified as a
means of protection of the ear, but the facts belonging to cases of facial palsy are all
that we have bearing upon this point. Artillerists are in danger of rupture of the mem-
brana tympani from sudden concussions. To guard against this injury, it is recom-
mended to stop the ear, draw the shoulder up against the ear most in danger, and parti-
cularly to inflate the middle ear after Valsalva's method. " This method consists in
making a powerful expiration, with the mouth and nostrils closed."

USES OF DIFFERENT PARTS OF THE AUDITORY APPAItA'ITS. 841

Mechanism of the Ossicles of the Ear.—^liQ ossicles of the middle ear, in connection
with the muscles, have a twofold function : First, by the action of the muscles, the
membrana tympani may be brought to different degrees of tension. Second, the chain
of bones serves to conduct sonorous vibrations to the labyrinth. It must be remembered
that the handle of the malleus is closely attached to the membrana tympani, especially
near its lower end. Near the short process, the attachment is looser and there is even
an incomplete joint-space at this point. The long process is attached closely to the
Glasserian fissure of the temporal bone.

The malleus is articulated with the incus by a very peculiar joint, which has been
accurately described by Helmholtz. This joint is so arranged, presenting a sort of cog,
that the handle of the malleus can rotate only outward ; and, when a force is applied
which would have a tendency to produce a rotation inward, the malleus must carry the
incus with it. This mechanism has been aptly compared by Helmholtz to that of a
watch-key with cogs which are fitted together and allow the whole key to turn in one
direction, but are separated so that only the upper portion of the key turns when the force
is applied in the opposite direction. In the articulation between the malleus and the
incus, the only difference is that there is but one cog ; but this is sufficient to prevent an
independent rotation of the malleus inward. This enables us to understand the action
of the tensor tympani muscle. By the contraction of this muscle, " all the bands which
give firmness to the position of the ossicles are rendered tense. This muscle, in the first
place, draws the handle of the hammer inward, and with it the membrana tympani. At
the same time it pulls upon the axis-band of the hammer, drawing it inward and putting
it upon the stretch. Another effect, as we have shown, is to draw the head of the ham-
mer away from the tympano-incudal joint, to tighten all the ligaments of the anvil, those
toward the hammer as well as those at the end of its short process, and to lift the latter
up from its bony bed. In this way the anvil is brought into the position where the cogs
of the malleo-incudal joint fit into one another the tightest. Finally, the long process
of the anvil is compelled to form a rotation inward in company with the handle of the
hammer ; in so doing, as we shall see further on, it presses upon the stirrup and drives
it into the oval window against the fluid of the labyrinth.

"In this respect the construction of the ear is very remarkable. By the contraction
of the single mass of elastic fibres constituting the tensor tympani (whose tension, besides,
is variable and may be adapted to the wants of the ear) all the inelastic tendinous liga-
ments of the ossicles are simultaneously put upon the stretch." (Helmholtz.)

The body of the incus is attached to the posterior bony wall of the tympanic cavity.
Its articulation with the malleus has just been indicated. By the extremity of its long
process, it is also articulated with the stapes, which completes the chain. In situ, the
stapes forms nearly a right angle with the long process of the incus.

The stapes is articulated with the incus, as indicated above, and its oval base is applied
to the fenestra ovalis. Surrounding the base of the stapes, is a ring of elastic fibro-carti-
lage, which is closely united to the bony wall of the labyrinth, by nn e\un>ion of the
periosteum over the base of the stapes.

"The relation of the stirrup to the anvil is such that, if the handle of the haiimuT be
drawn inward, the long process of the anvil presses firmly airainst the knob of the stirrup;
the same takes places if the capsular ligament between both be cut thnmdi." (IMm-
holtz.)

The articulations between the malleus and the incus and between the innn and the
stapes are so arranged that, when the membrana tympani is forced out\\ -ar.I. u it may
be by inflation of the tympanic cavity, there is no danger of tearing the Btapea from ii
attachment to the fenestra ovalis ; for, when the handle of the malleus is dra\\ n outward,
the cog-joint between the malleus and the incus is loosened and no great traction c;,;
exerted upon the stapes.

Although experiments have demonstrated pretty conclusively the mechanism of the

842 SPECIAL SENSES.

ossicles and the action of the tensor tympani muscle, both as regards the chain of bones
and the membrana tympani, direct observations are wanting to show the exact relations
of these different conditions of the ossicles and of the membrane to the physiology of
audition. One very important physical point, however, which has been the subject of
much discussion, is settled. The chain of bones acts as a single solid body in conducting
vibrations to the labyrinth. It is a matter of physical demonstration that vibrations of
the bones themselves would be infinitely rapid as compared with the highest tones which
can be appreciated by the ear, if it were possible to induce in these bones regular vibra-
tions. Practically, then, the ossicles have no independent vibrations that we can appre-
ciate. This being the fact, the ossicles simply conduct to the labyrinth the vibrations
induced in the membrana tympani by sound-waves ; and their arrangement is such that
these vibrations lose very little in intensity. While it has been shown experimentally
that the amplitude of vibration in the membrana tympani and the ossicles diminishes
with the tension of the membrane, it would seem that, when the tensor tympani con-
tracts, it must render the conduction of sound-waves to the labyrinth more delicate than
when the auditory apparatus is in a relaxed condition, which we may compare with the
"indolent" condition of the apparatus of accommodation of the eye. When the mem-
brana tympani is relaxed and the cog-like articulation between the malleus and the incus
is loosened, the vibrations of the membrane and of the malleus may have a greater ampli-
tude ; but, when the malleo-incudal joint is tightened and the stapes is pressed against
the fenestra ovalis, the loss of intensity of vibration in conduction through the bones to
the labyrinth must be reduced to the minimum. With this view, the tensor tympani
muscle, while it contracts to secure for the membrana tympani the degree of tension
most favorable for vibration under the influence of certain tones, puts the chain of bones
in the condition best adapted to the conduction of the vibrations of the membrane to the
labyrinth, with the smallest possible loss of intensity.

Physiological Anatomy of the Internal Ear.

The internal ear consists of the labyrinth, which is divided into the vestibule, semi-
circular canals, and cochlea. The general arrangement of these parts has already been
described ; and it remains for us only to study the structures contained within the bony
labyrinth, in so far as their anatomy bears upon the physiology of audition. The most
delicate and complicated points, by far, in the anatomy of the auditory apparatus are
connected with the histology of the internal ear, which, since the researches of Corti, has
been studied very closely, particularly in Germany. We shall avoid, however, the dis-
cussion of histological questions of purely anatomical interest and confine ourselves to
those points which have a direct bearing upon physiology.

Passing inward from the tympanum, the first division of the internal ear is the ves-
tibule. This cavity communicates with the tympanum by the fenestra ovalis, which is
closed in the natural state by the base of the stapes. It communicates, also, with the
semicircular canals and with the cochlea.

General Arrangement of the Membranous Labyrinth. — The bony labyrinth is lined
by a moderately thick periosteum, consisting of connective tissue, a few delicate elastic
fibres, numerous nuclei, and blood-vessels, with spots of calcareous concretions. This
membrane adheres closely to the bone and extends over the fenestra ovalis and the fenes-
tra rotunda. Its inner surface is smooth and covered with a single layer of cells of pave-
ment-epithelium, which in some parts is segmented and in others forms a continuous
nucleated sheet. In certain portions of the vestibule and semicircular canals, the perios-
teum is united to the membranous labyrinth, more or less closely, by fibrous bands,
which have been called ligaments of the labyrinth. The fenestra rotunda, which lies
between the cavity of the tympanum and the cochlea, is closed by a membrane formed

PHYSIOLOGICAL ANATOMY OF THE INTERNAL EAR. 843

by an extension of the periosteum lining the cochlea, on the one side, and the mucous
membrane lining the tympanic cavity, on the other.

In the bony vestibule, occupying about two-thirds of its cavity, are two distinct sacs ;
a large, ovoid sac, the utricle, situated in the upper and posterior portion of the cavity,
and a smaller, rounded sac, the saccule, situated in its lower and anterior portion. The

FIG. 264.— Diagram of the labyrinth, vestibule, and semicircular canals. From a photograph, and somewhat

reduced. (Rudinger.)

Upper figure: 1, utricle; 2, saccule; 8, 5, membranous cochlea; 4, canalis reunions ; 6, semicircular canals.
Lower figure: 1, utricle ; 2, saccule; 8, 4. (>. !unpull:t> ; 5. 7, 8, 9. semicircular oanuls : 1". an litory norve (partly dia-
grammatic) ; 11, 12, 13, 14, 15, distribution of the branches of the nerve to the vestibule and the semicircular canals ;
16, ganglioforin enlargement.

utricle communicates with the semicircular canals; and the saccule opens into the mem-
branous canal of the cochlea by the canalis reuniens. At a point in the utricle corre-
sponding to the entrance of a branch of the auditory nerve, is a round, whitish spot, called
the acoustic spot (macula acustica), containing otoliths, or otoconia, which are attached
to the inner surface of the membrane. A similar spot, containing otoliths, exists in the
saccule at the point of entrance of its nerve. Otoliths are also found in the ampulla? of the
semicircular canals. These calcareous masses are composed of crystals of carbonate of lime,
which are hexagonal and pointed at their extremities. Nothing drtinite is known of the
function of these calcareous bodies, which exist in man. mammals, birds, and reptiles.

The membranous semicircular canals occupy about one-third of the cavity of the bony
canals. They present little ovoid dilatations, called ampulla?, corresponding to the ampul-
lary enlargements of the bony canals.

The membrane of the cochlea, including the lining periosteum, occupies the spiral
canal of the cochlea, which it fills completely. Viewed externally, it appears as a single

844 SPECIAL SENSES.

tube, following the turns of the bony cochlea, beginning below, at the first turn, by a
blind extremity, and terminating in a blind extremity at the summit of the cochlea. If
we make a section of the cochlea in a direction vertical to its coils, it will be seen that
this canal is divided, partly by bone and partly by membrane, into an inferior portion, a
superior portion, and a triangular canal, lying between the two, which is external. The
bony septum is in the form of a spiral plate, extending from the central column (the
modiolus) into the cavity of the cochlea, about half-way to its external wall, and termi-
nating above in a hook-shaped extremity, called the harnulus. The free edge of this
bony lamina is thin and dense. Near the central column, it divides into two plates,
with an intermediate spongy structure in which are lodged vessels and nerves. The
surface of the bony lamina looking toward the base of the cochlea is marked by numer-
ous regular, transverse ridges, or striaa.

Fro. 265. — Otolifhsfrom various animals. (Kudinger.)

1, from the goat ; 2, from the herrin,' ; 3, from the devil-fish ; 4, from the mackerel; 5, from the flying-fish ; 6, from
the pike ; 7, from the carp ; 8, from the ray ; 9, from the shark ; 10, from the grouse.

Attached to the free margin of the bony lamina, is a membrane (the membrana basi-
laris) which extends to the outer wall of the cochlea. In this way, the canal of the cochlea
is divided into two portions, one above and the other below the septum. The portion
below begins at the fenestra rotunda and is called the scala tympani. The portion
above, exclusive of the triangular canal of the cochlea, communicates with the vestibule
and is called the scala vestibuli.

Above the membrana basilaris, is a membrane (the limbus laminae spiralis) the external
continuation of which is called the membrana tectoria, or the membrane of Corti. Be-
tween the membrana tectoria and the membrana basilaris, is the organ of Corti. The
membrane of Reissner extends from the inner portion of the limbus upward and outward
to the outer wall of the cochlea. This divides the portion of the cochlea situated above
the scala tympani into two portions ; an internal portion, the scala vestibuli, and an
external, triangular canal, called the canalis cochleae, or the membranous cochlea.

In the anatomical description of the contents of the bony cochlea, the membranous
parts may be designated as follows :

1. The portion below the bony and membranous septum, called the scala tympani.
This is formed by the periosteum lining the corresponding portion of the cochlea and the
under surface of the bony lamina, and the membrana basilaris.

PHYSIOLOGICAL ANATOMY OF THE INTERNAL EAR. 845

2. The scala vestibuli. This is formed by the periosteum lining the corresponding
portion of the bony cochlea and the upper surface of the bony septum and is bounded
externally by the membrane of Reissner.

3. The true membranous cochlea. This is the spiral triangular canal, bounded ex-
ternally by the periosteum of the corresponding portion of the wall of the cochlea,

Fio. 266.— Sectionof the first tivm of the spiral canal of a cat newly-born.— Section of the cochlea of a human
fmtw at the fourth month. From a photograph, and somewhat reduced. (Rfidinger.)

Upper figure : 1, 2, 6, lamina spiralis ; 2, lower plate ; 8, 4, 6, 5, nervus cochlearis ; 7, membrane <>t mem-

brana tectoria; 9, epithelium ; 10, 11, pillars of Corti; 12, inner hair-cells; 13, outer hair-cells ; 14. Hi. mombrana
basilaris; 15, epithelium in the sulcus spiralis; 17, 18, 19, ligainentum spirale; 20, spiral canal below the niembrana
basilaris.

Lower figure: S T, S T, 5, 5, 7, 7, 8, 8, scala tympani ; 8 V, 8 V, 9, 9, scala vestibuli; 1, base of the cochloa ; 2, apex ;
8, 4, central column; 10, 10, 10, 10, ductus cochlearis; 11, branches of the nervns cochlearis: ]•_'. l-J. I-.1, sj.ir.il
ganglion; 13, 14, limbus laminse spiralis; 15, membrane of Reissner; 16, epithelium : 17. outer h:iir-o-lls; H,
epithelium of the membrana basilaris; 10, nervous filaments; 20, union of the nicml.rann basilaris with th«>
ligamentum spirale ; 21, epithelium of the peripheral wall of the ductus cochlearis; 22, 23, membrana tectoria ;
24, spiral canal below the membrana basilaris.

internally, by the membrane of Reissner, and, on the other side, by the membrana basi-
laris.1 What we thus call the membranous cochlea is divided by the limbus liiminro spi-
ralis and the membrana tectoria into two portions ; a triangular canal above, which is the

i Some anatomists include this canal in the scala vestibuli. For the sake of clearness, we describe it by itself, as a
distinct canal.

846 SPECIAL SEXSES.

larger, and a quadrilateral canal below, between the limbus and menibrana tectoria and
the raembrana basilaris. The quadrilateral canal contains the organ of Corti and various
structures of a very complicated character. The relations of these divisions of the cochlea,
a knowledge of which is essential to the comprehension of the physiological anatomy of
this portion of the auditory apparatus, are shown in Fig. 266.

The membranous cochlea, as described above, follows the spiral course of the cochlea,
terminates superiorly in a blind, pointed extremity at the cupola, beyond the hamulus,
and is connected below with the saccule of the vestibule by the canalis reuniens. The
relations of the different portions of the membranous cochlea to each other and to the
scalae of the cochlea are shown in Fig. 266.

We shall now describe, as possessing the most physiological interest, the liquids of the
labyrinth, the distribution and connections of the nerves in the labyrinth, and the organ
of Corti.

Liquids of the Labyrinth. — The labyrinth contains a certain quantity of a clear,
watery liquid, called the humor of Cotugno, or of Valsalva. A portion of this liquid
surrounds the membranous sacs of the vestibule, the semicircular canals, and the mem-
branous cochlea, and this is known as the perilymph of Breschet. Another portion of
the liquid fills the membranous labyrinth. This is sometimes called the humor of Scarpa,
but it is known more generally as the endolymph of Breschet. The perilymph occupies
about one-third of the cavity of the vestibule, of the semicircular canals, and of both scalar
of the cochlea. Both this liquid and the endolymph are clear and. watery, becoming
somewhat opalescent on the addition of alcohol. The perilymph seems to be secreted
by the periosteum lining the osseous labyrinth. As far as we know, the uses of the
liquid of the internal ear are to sustain the delicate structures contained in this portion
of the auditory apparatus and to conduct sonorous vibrations to the terminal filaments
of the auditory nerves and the parts with which they are connected.

Distribution of the Nerves in the Labyrinth. — As the auditory nerves enter the inter-
nal auditory meatus, they divide into an anterior, or cochlear, and a posterior, or vestib-
ular branch. The vestibular branch divides into three smaller branches, a superior and
anterior, a middle, and a posterior branch. The superior and anterior branch, the largest
of the three, is distributed to the utricle, the superior semicircular canal, and the external
semicircular canal. The middle branch is distributed to the saccule. The posterior
branch passes to the posterior semicircular canal. The nerves distributed to the utricle
and saccule penetrate at the points occupied by the otoliths, and the nerves going to the
semicircular canals pass to the ampulla, which also contain otoliths. (See Fig. 264.) In
each ampulla, at the point where the nerve enters, is a transverse fold, projecting into
the canal and occupying about one-third of its circumference, called the septum trans-
versum.

The nerves terminate in essentially the same way in the sacs of the vestibule and the
ampulla) of the semicircular canals. At the points where the nerves enter, in addition
to the otoliths, are cells of cylindrical epithelium, of various forms, which pass gradually
into the general pavement-epithelium of the cavities. In addition to these cells, are fusi-
form, nucleated bodies, the free ends of which are provided with hair-like processes,
called fila acustica. These are about ¥^ of an inch in length and are distributed in
quite a regular manner around the otoliths. The nerves form an anastomosing plexus
beneath the epithelium, and they probably terminate in the fusiform bodies just described
as presenting the fila acustica at their free extremities. In the sacs of the vestibule
and in the semicircular canals, nerves exist only in the macula acustica and the
ampullae.

The cochlear division of the auditory nerve breaks up into numerous small branches,
which pass through foramina at the base of the cochlea, in what is called the tractus

PHYSIOLOGICAL ANATOMY OF THE INTERNAL EAR. 847

srriralis foraminulentus. These follow the axis of the cochlea and pass in their course
toward the apex, between the plates of the bony spiral lamina. Between these plates of
bone, the dark-bordered nerve-
fibres pass each one through a r -T-'-T--^
bipolar cell, these cells together
forming a spiral ganglion, known
as the ganglion of Corti. Beyond
this ganglion, the nerves form an
anastomosing plexus and finally
enter the quadrilateral canal, or
the canal of Corti. As they pass
into this canal, they suddenly be-
come pale and exceedingly fine,
and probably they are connected
finally with the organ of Corti,
although their exact mode of ter-
mination has not yet been deter-
mined. The course of the nerve-

to fhpir dUrribntinn in tliA FrG- 2G~-— Distribution of the cochlear nerce in tlie npiral lamina
distribution in tlie ^ the cochlea (the coch(ea isfrom the right Sid« and is seen

COchlea is shown in Fig. 267. from its antero-inferwr part). (Sappey.)

1, trunk of the cochlear nerve ; 2, 2, 2, membranous zone of the spiral
lamina ; 8, 8, 8, terminal expansion of the cochlear nerve exposed in

Organ of CoTti. Of all the ^8 w^°le extent by the removal of the superior plate of the lamina

spiralis ; 4, orifice of communication of the scala tympani with the

parts contained within the bony ecala vestibuii.
labyrinth, the organ of Corti pos-
sesses the greatest physiological interest; for it is this organ which is supposed to receive
the sonorous vibrations and communicate them directly to the terminal filaments of the
auditory nerves. Although this view has not received the support of actual demonstra-
tion, it affords an explanation, more or less plausible, of the mechanism of audition, car-
ried to the point of the actual reception of impressions by the nerves. In view of this,
it is important to have a clear comprehension of the arrangement of those parts which
are supposed to receive the sonorous vibrations ; and we shall, for the sake of simplicity,
eliminate from our description certain accessory structures, the functions of which are
obscure.

In the quadrilateral canal, bathed in the endolymph, throughout its entire spiral
course, is an arrangement of pillars, or rods, regular, like the strings of a harp in minia-
ture, which are supposed to repeat the varied vibrations of sound. These are the pillars
of Corti.

The structures contained in the quadrilateral canal are so delicate that their investi-
gation presents great difficulty ; but the arrangement of the pillars, or rods of Corti is
pretty well understood. These pillars are external and internal, with their bases attached
to the basilar membrane, and their summits articulated above, so as to form a regular,
spiral arcade, enclosing a triangular space, which is bounded below by the basilar mem-
brane. The number of the elements of the organ of Corti is estimated at about 3,500, for
the outer, and 5,200, for the inner rods, the proportion of inner rods to the outer beim:
about three to two. The relations of these structures to the membranous labyrinth are
seen in Fig. 206. The external pillar is longer, more delicate and rounded, and is also
attached to the basilar membrane. The form of the pillars is more exactly >ln>wn in
Figs. 268 and 269, the latter figure, however, exhibiting other structures wl.ieh enter
into the constitution of the organ of Corti. It will be remarked that a small nucleated
body is attached to the base of each pillar. At the summit, where the internal and the
external pillars are joined together, is a delicate prolongation, directed outward, which
is attached to the covering of the quadrilateral canal.

The above description comprises about all that is definitely known of the arrangement

848

SPECIAL SENSES.

of the pillars, or rods of Corti. They are nearly homogeneous, except when treated with
reagents, and are said to be of about the consistence of cartilage. They are closely set
together, with very narrow spaces between them, and it is difficult to see how they can
be stretched to any considerable degree of tension. The arch is longer at the summit

Fio. 26S.— The two pillars of the organ of Corti. (Sappey.)

A, external pillar of the organ of Corti : 1, body, or middle portion ; 2, posterior extremity, or base ; 8, cell on its in-

ternal side ; 4, anterior extremity ; 5, convex surface by which it is joined to the internal pillar ; 6, prolongation
of this extremity.

B, internal pillar of the organ of Corti : 1, body, or middle portion ; 2, posterior extremity ; 8, cell on its external side;

4, anterior extremity; 5, concave surface by which it is joined to the external pillar; 6, prolongation, lying above
the corresponding prolongation of the external pillar.

C, the two pillars of the organ of Corti, united by their anterior extremity, and forming an arcade, the concavity of

which presents outward : 1, 1, body, or middle portion of the pillars ; 2, 2, posterior extremities ; 3, 3, cells at-
tached to the posterior extremities; 4, 4, anterior extremities joined together; 5, terminal prolongation of this
extremity.

than at the base of the cochlea, the longest rods, at the summit, measuring about -yfa of
an inch, and the shortest, at the base, about -^-^ of an inch. As we before remarked, the
relations between the pillars and the terminal filaments of the auditory nerves are not
definitely settled.

In addition to the pillars just described, various cellular elements enter into the struct-
ure of the organ of Corti. The most important of these are the inner and the outer hair-

FIG. 269.— Vertical section of the organ of Corti of the dog; magnified 800 diameters. (Waldeyer.)
o^&, homogeneous layer of the basilar membrane ; u, tympanic layer, with nuclei, granular cell-protoplasm, and con-
nective tissue: «!, tympanic lip of the crista spiralis; c, thickened portion of the basilar membrane ; d, spiral
vessel ; e, blood-vessel ; f\ h, bundle of nerves ; Q, epithelium ; i, inner hair-cell, with its basilar process, Jc ; I, head-
plate of the inner pillar; m, union of the two pillars; n, base of the inner pillar; o. base of the outer pillar; p, q,
r, outer hair-cells, with traces of the cilia; t, bases of two other hair-cells; z, Hensen's prop-cell; Wx, lamina
reticularis ; w, nerve-fibre passing to the first hair-cell, p.

cells. The inner hair-cells are arranged in a single row, and the outer hair-cells, in three
rows. Nothing definite is known of the function of these cells. The relations of these
parts are shown in Fig. 269, which is rather complex, but, on careful study, gives a good

FUNCTIONS OF DIFFERENT PARTS OF THE INTERNAL EAR. 849

idea of the arrangement of all of the structures which compose the organ of Corti. It is
supposed by some anatomists that the filaments of the auditory nerves terminate in the
cells above described ; but this point is not definitively settled.

Functions of Different Parts of the Internal Ear.

The precise function of the different parts which are found in the internal ear is
obscure, notwithstanding the careful researches that have been made into the anatomy
and the physiology of the labyrinth. There are several points, however, bearing upon
the physiology of this portion of the auditory apparatus, concerning which there can be
no doubt :

First, it is certain that impressions of sound are received by the terminal filaments of
the auditory nerves and by these nerves are conveyed to the brain.

Second, the functions of the parts composing the external and the middle ear are
simply accessory. The sonorous waves are collected by the pavilion and are conveyed
by the external meatus to the middle ear ; the membrana tympani vibrates under their
influence ; and they are thus collected, repeated, and transmitted to the internal ear,
under the most favorable conditions for producing a proper impression upon the auditory
nerves.

In view of these facts, we must look to the functions of semicircular canals and the
cochlea, for an elucidation of the problem of the mechanism of the final process of audi-
tion ; and, in doing this, we come at once to the question of the relative importance of
different divisions of the internal ear.

Functions of the Semicircular Canals. — In a memoir presented to the French Acad-
emy of Sciences, in 1824, Floureiis detailed a number of experiments upon pigeons and rab-
bits, in which he destroyed different portions of the internal ear. In these experiments,
the results of which were very definite, it was shown that destruction of the semicircular
canals had apparently no effect upon the sense of hearing, while destruction of the coch-
lea upon both sides produced complete deafness. In addition, it was observed that
destruction of the semicircular canals on both sides was followed by remarkable dis-
turbances in equilibration. The animals could maintain the standing position, but, as
soon as they made any movements, " the head commenced to be agitated ; and this
agitation increasing with the movements of the body, walking and all regular move-
ments finally became impossible, in nearly the same way as when equilibrium and stabil-
ity of movements are lost after turning several times or violently shaking the head."
These observations of Flourens, at least as far as regards the influence of the semicircular
canals upon equilibration, have been confirmed by Goltz and are sustained by observa-
tions upon the human subject in the condition known as Meniere's disease. In some more
recent experiments, however, Boettcher assumes to have demonstrated that the semi-
circular canals have nothing to do with equilibration ; but all of his observations were
made upon frogs, in which deficiency of equilibration and of hearing would be very diffi-
cult to determine. As far as we can judge from experimental data, it does not seem
probable that the nerves directly concerned in audition are distributed to any con-i<l-
erable extent in the semicircular canals. Indeed, the function of these parts is ex<
ingly obscure; for we can hardly admit, upon purely anatomical ground*, that they un-
concerned in the discrimination of the direction of sonorous vibrations, an idea which
has been advanced by some physiologists.

Functions of the Parts contained in the Cochlea.— -There can be no doubt with r
to the capital point in the physiology of the cochlea; namely, that those branches of the
auditory nerve which are essential to the sense of hearing and which receive the hn;
eions of sound are distributed mainly in the cochlea. When we come to analyze sonorous
impressions, we find that they possess various attributes, such as intensity, quality, and
54

850 SPECIAL SENSES.

pitch, which have been discussed rather fully under the head of the physics of sound.
As far as the terminal filaments of the auditory nerve are concerned, it is evident that
the intensity of sound is appreciated in proportion to the power of the impression made
upon these nerves, and this point does not demand elaborate discussion. With regard to
quality of sound, we have seen that this is due to the form of sonorous vibrations, and
that most musical tones are compound, their quality depending largely upon the relative
power of the harmonics, partial tones, etc. We have also seen that consonating bodies
repeat by influence, not only the actual pitch of tones, but their quality. If there be in
the cochlea an anatomical arrangement of rods or fibres by which the sonorous vibra-
tions, conveyed to the ear by the atmosphere, are repeated, there is reason to believe
that the quality, as well as the pitch, is reproduced. Narrowing down the question,
then, to its most interesting and important point, viz., the appreciation of differences in
the pitch of musical tones, we inquire whether there be in the cochlea any arrangement
by which the pitch can be repeated. This inquiry can only be answered by a study of
the anatomical arrangement of the structures connected with the terminal filaments of
the nerves, and by the application of physical laws.

The arrangement of the rods which enter into the structure of the organ of Corti has
afforded a theoretical explanation of the final mechanism of the appreciation of pitch.
Until we come to the internal ear, the action of different portions of the auditory appa-
ratus is simply to conduct and repeat sonorous vibrations ; and the sole function of these
accessory parts, aside from the protection of the organs, is to convey the vibrations to
the terminal nervous filaments. Whatever be the functions of the membrana tympani in
repeating sounds by influence, it is certain that this membrane possesses no true auditory
nerves, and that the auditory nerves only are capable of receiving impressions of sound.
Thus, hearing, and even the appreciation of pitch, is not necessarily lost after destruction
of the membrana tympani; and, if sonorous vibrations reach the auditory nerves, they
will be appreciated and appreciated correctly. With this point clearly understood, we
are prepared to study the probable functions of the organ of Corti.

When we consider the organ of Corti, with its eight thousand or more rods of differ-
ent lengths arranged with a certain degree of regularity, a number more than sufficient
to represent all the tones of the musical scale, we are not surprised that eminent physi-
ologists regard them as capable of repeating all the shades of tone heard in music.
Helmholtz formularizes this idea in the theory that tones conveyed to the cochlea throw
into vibration those elements of the organ of Corti which are tuned, so to speak, in unison
with them. According to this hypothesis, the rods of Corti constitute a harp of several
thousand strings, played upon, as it were, by the sonorous vibrations.

It would be difficult to imagine any tiling more satisfactory and simple than such an
hypothesis as we have just quoted. Attention and education enable persons endowed
with what is called a musical ear to discriminate between different tones with great
accuracy. Experiments have shown that the situation of the actual appreciation of
tones may be restricted to the cochlea ; and, in the cochlea, the only anatomical arrange-
ment, as far as we know, which points toward an appreciation of the pitch of different
tones is that of the rods of Corti. Still, it must be remembered that the cochlea is so
situated as to be removed from the possibility of experimental investigation to prove the
theory; and we must carefully study the anatomical arrangement of the parts and the
possible application of physical laws to the supposed vibration of the rods.

Viewing the question from its anatomical aspect, it is by no means certain that the
rods of Corti are so attached and stretched that they are capable of separate and indi-
vidual vibrations. It has not been demonstrated that certain of these rods vibrate under
the influence of certain tones or that they are tuned in accord with certain tones. Hensen,
who has written elaborately upon the very question under consideration, denies the accu-
racy of the theory of Helmholtz, basing his opinion upon the anatomical arrangement of
the rods of Corti, and he assumes that it is a physical impossibility for the different rods

SUMMARY OF THE MECHANISM OF AUDITION. 351

to vibrate individually, and that it is not certain that they are tuned in accord with dbiV-r-
ent tones. Hensen makes, upon this point, the following statement :

" It is now my conviction, that by the hypothesis * more and more corroborated ' that
the fibres of Corti constitute the organ of the labyrinth tuned to the appreciation of
tones, our comprehension and the investigation of the internal ear have taken a false
direction.

" I assert, next, that the rods of Corti cannot play the important part in the appreci-
tion of tones, which has been attributed to them in the hypothesis of Helmholtz."

It is pretty evident that, although the theory of Helmholtz is undoubtedly the only
one affording any reasonable explanation of the appreciation of tones, it lacks positive
anatomical confirmation. And, farthermore, we do not even know the anatomical con-
nections between the rods of Corti and the filaments of the auditory nerves.

In view of the considerations just given, we have simply recited the theory of Du
Verney, Le Cat, and Helmholtz, as one which may or may not be sustained hereafter by
more exact researches ; but at present it must be acknowledged that there is no more
satisfactory explanation of the mechanism of the final appreciation of musical tones.

Summary of the Mechanism of Audition.

The waves of sound are simply collected by the pavilion of the ear and are conveyed,
through the external meatus, to the membrana tympani. The membrana tympani, a
delicate, rounded, concave membrane, receives these waves and is thrown into vibration.

The arrangement of the bones and muscles of the middle ear admits of variations in
the tension of the membrana tympani. By increasing the tension of this membrane, the
ear may be rendered insensible to grave sounds, while high-pitched sounds become more
intense ; and, in cases of voluntary tension, the limit of perception of high tones may be
greatly extended. The membrana tympani obeys the laws of consonance and vibrates
strongly under the influence of sounds in unison or in harmony with its fundamental
tone, returning, in this way, not only the pitch, but the quality of tones and combina-
tions of tones in harmony. Destruction of the membrane does not necessarily of itself
destroy hearing, or even the appreciation of tones, for the impressions may be conduct-
ed to the cochlea by the chain of ossicles.

The arrangement of the ossicles and muscles of the middle ear is such that contrac-
tion of the tensor tympani renders the articulations firm, tightens the little ligaments,
and presses the stapes against the liquid of the labyrinth, so that the chain resembles, in
its action, a solid and continuous bony rod. By this arrangement, the sonorous vibra-
tions are conducted to the labyrinth with very little loss of intensity.

The cavity of the tympanum is filled with air, communicates with the mastoid cells,
and with the pharynx by means of the Eustachian tube; and, by this means, the press-
ure of air in its interior is regulated. The labyrinth, consisting of the vestibule, semi-
circular canals, and cochlea, is filled with liquid, and the different cavities communicate
with each other. The vibrations, repeated by the membrana tympani, are conveyed by
the chain of bones to the liquid of the labyrinth, and by it to the terminal filaments of
the auditory nerves.

The vestibule and semicircular canals seem to possess much less importance in the
appreciation of sound than the cochlea. In the cochlea, throughout the entire extent of
the spiral canal, is the organ of Corti, presenting, among other structures, about 8,700
rods, varying in length, called the rods of Corti. But little is known of the anatomical
relations between the auditory nerves and the organ of Corti; still, it is thought, as a
matter of pure theory, that the rods of Corti are tuned in unison with dim-rent tones,
that they repeat the tones conveyed to the cochlea, and that we are thus enabled to dis-
tinguish the different tones in music.

We have no very definite knowledge of the functions of the cells of the organ of Cor-

852 GENERATION.

ti, of the otoliths, and of various . other structures in the auditory apparatus. Sounds
may be conducted to the auditory nerves through the bones of the head and the Eus-
tachian tube, as is shown by the simple and familiar experiment of placing a tuning-fork
in vibration in contact with the head or between the teeth.

CHAPTER XXVI.

ORGANS AND ELEMENTS OF GENERATION.

General considerations— Sexual generation— Spontaneous generation (so called)— Female organs of generation— Gen-
eral arrangement of the female organs — External and internal organs — The ovaries — Development of the Graa-
fian follicles — The parovarium — The uterus — The Fallopian tubes — Structure of the ovum— Vitelline membrane —
Yitellus— Germinal vesicle and germinal spot — Discharge of the ovum — Puberty and menstruation — Descrip-
tion of a menstrual period — Characters of the menstrual flow — Changes in the uterine mucous membrane during
menstruation — Changes in the Graaflan follicle after its rupture (corpus luteum) — The testicles — Tunica vagi-
nalis — Tunica albuginea— Tunica vasculosa — Seminiferous tubes — Epididymis— Vas deferens — Vesiculse seminales

— Prostate— Glands of the urethra— Semen — Secretions mixed with the products of the testicles— Spermatozoids

Development of the spermatozoids — Seminal fluid in advanced age.

A EEVIEW of the physiological processes which we have thus far studied shows that
the functions of the perfected organism are divided into two great classes:

The first class of functions may be grouped under the general head of nutrition,
taken in its widest sense. Nutrition is common to animal and vegetable life, and this is
sometimes called a vegetative process.

The study of nutrition involves the following considerations : First, the blood, which
is the great nutritive fluid, contained in the innumerable vessels which penetrate nearly
all of the tissues and organs of the body and are connected with the system of lymphatic
and lacteal vessels. Second, the process by which the blood is circulated, sent by the
heart to all parts in the capillary system, used by the tissues for their nutrition, then los-
ing oxygen, gaining carbonic acid, and being returned by the veins. Third, respiration,
the blood being freed from carbonic acid and getting a new supply of oxygen in the
lungs, by which it is rendered capable of again circulating through the general system.
Fourth, as the blood, in its passage through the capillary vessels, not only loses oxygen,
but is more or less impoverished by the assimilation of its nutritive constituents by the
tissues, it is necessary to keep it up to the proper nutritive standard ; and this is effected
by alimentation, digestion, and absorption. Fifth, we have certain secretions, necessary
to the above-mentioned processes ; and the products of physiological waste or decay of
the tissues are removed by excretion. Sixth, the processes of vegetative life involve the
production of heat and are regulated and coordinated by the nervous system.

The second class of functions relates to animal life, and these are called the functions
of relation. In this class, are included movements, voice and speech, the functions of
the cerebro-spinal nervous system, and the operation of the special senses.

In studying the processes of nutrition of the general system, we observe that certain
constituents of the organism, which contain nitrogen and are exclusively of organic ori-
gin, have the property, in the living body, of self-regeneration ; i. e., when these parts
are brought in contact with nutritive matter in proper form, as it exists in the blood,
this matter is appropriated and transformed into the substance of each tissue and organ.
It is in this way that, during adult life, the different parts of the organism are maintained
in a tolerably uniform condition. In the absence of an exact knowledge of the cause
and nature of these assimilative processes, we call them vital ; which term is applied to
a constant property of living, organized parts. Physiologists have ascertained that each
tissue and organ of the body possesses one or more characteristic organic nitrogenized
constituents which are possessed of this so-called vital property. But, at the same time,

GENERAL CONSIDERATIONS. 853

it is always observed that the organic nitrogenized constituents of the organism are
combined most intimately with a tolerably definite quantity of inorganic matter, which
latter regulates, to a certain extent, nutritive processes, and constitutes, also, an impor-
tant component part of the tissues. It is observed, in addition, that, during early life,
when the system is proceeding toward its perfect development by growth, the proportion
of inorganic matter is less than in the adult, and that the process of nutrition is then at
its maximum of activity, the regeneration being superior to the waste. During the adult
period, repair and physiological decay are nearly balanced ; but, in the decline of life,
there seems to be a gradual accumulation of inorganic matter, and this continues until
the so-called vital properties of some important organ become so feeble that its func-
tions cease, and we have physiological death. This regeneration of the tissues is a neces-
sary consequence of the constant waste or decay of every part of the organism, resulting
in a change of constituents into effete matters, which are discharged ; there being, during
life, a constant waste and repair. If no new matter be introduced as food, the system
wastes to a point which is incompatible with life, and death results from inanition.

With some very insignificant exceptions, we cannot conceive that living tissues exist
in an absolutely stationary condition. The organized parts of the body are undergoing
constant molecular destruction and repair. Again, the so-called vital properties of the
tissues, which involve self-regeneration, seem to have certain limits. We cannot intro-
duce nutritive matter in sufficient quantity to produce growth beyond a certain point,
although we may limit development and growth by deficient supply. When we ask why
the organs develop with fixed regularity, why, when an occasional excess of nutritive
matter is presented, this excess is not used, we must confess our ignorance or say that
the parts are endowed with vital properties. We also find, to come to the most impor-
tant point of this discussion, that, however carefully we may supply nutritive matter to
the system, we cannot arrest the gradual enfeeblement of the assimilative powers of the
tissues, which occurs in old age. In short, as we cannot conceive of a living tissue
without decay and regeneration of its substance, so it is impossible for the organism to
last for an indefinite period. A necessary, invariable, and inevitable consequence of
individual life is death. The constant molecular death — if we can apply this term to the
transformation of living into effete matter — of every tissue of the body is always, in the
end, superior to the power of repair. There seerns, indeed, to be an antagonism of pro-
cesses during life ; a view which was so fully adopted by Bichat, that it led to his cele-
brated definition of life ; " the ensemble of functions which resist death.1' Although death
is thus inevitable, and, in the circulation of material in Nature, the organic parts of the
body become changed in the arrangement of their ultimate elements and appropriated by
the vegetable kingdom, during adult life, certain anatomical elements, male and female, are
formed in the human subject, which, when they come together under proper conditions,
develop into new beings, which pass through the same course of existence as the parents.
By the concourse of two beings, new organisms come into life, which perpetuate exist-
ence and preserve species. The function by which this is accomplished is called genera-
tion, or reproduction.

In our study of generation, we shall confine ourselves as closely as possible to the
process as it takes place in the human subject. There are many considerations of g
interest connected with the generation of the lowest orders of animal or-rnni/ution,
among the most prominent of which is the question of so-called spontaneous -reneration.
While this may have a certain bearing upon the genesis of anatomical elements, it has
little or nothing to do with the development of the fecundated human ovum, and will,
therefore, receive little more than an incidental consideration. For similar reasons, wo
shall not engage in a discussion of the development-theory applied to the origin of spe-
cies, which is exciting so much controversy at the present day, nor shall we treat of gen-
eration in the lower animals, except to illustrate the history of development in man.

854 GENERATION.

The study of human generation will naturally assume the following course : First,
the female organs of generation and the formation of the female element, the ovum ;
second, the discharge of the ovum and the phenomena which attend this process ; third,
the male organs and the development and discharge of the male elements, the spermato-
zoids ; fourth, the union of the two elements of generation, or fecundation ; fifth, the
development of the fecundated ovum into the foetus at term ; sixth, the development
of the body after birth and at different ages, or stages of existence ; finally, the natural
cessation of the so-called vital functions, or physiological death.

Sexual Generation.

Before we describe the actual phenomena of sexual generation, as they are observed
in man and the mammalia, it will be interesting to note some of the salient points in the
history of our knowledge of this process in the inferior animals. This we can do, with-
out exceeding the limits we have laid down in our general remarks.

In the history of sexual generation, there seems to have been a limiting line between
the production of animals from preexisting organisms and of those produced in some
unknown manner, or, as it has been said, spontaneously. This line of distinction has
always receded toward organisms lower and lower in the scale of being, with our advance
in positive knowledge. The ancients understood that the higher animals required for
their production a concourse of the sexes ; but they thought that many fishes, reptiles,
insects, worms, etc., were produced spontaneously. Indeed, with the limited knowledge
of natural history possessed by Aristotle and those who succeeded him for many hun-
dred years, the classes of animals said to be produced spontaneously represented simply
those, the generation of which was not understood. But, as the habits of many animals
became better understood, more and more of them were observed to lay eggs, which
were found to undergo development.

Dating from Aristotle, who lived between three and four hundred years B. c., it was
nearly two thousand years before any thing was known of the generation of insects ;
the difficulty here being that the young are first in a larval state and bear no resem-
blance to the parents. Anterior to the experiments of Eedi, it was thought that certain
organic matters in course of putrefaction developed living organisms, as maggots in meat
and the larvae in cheese.

We refer to the experiments of Eedi, made about the year 1668, for the reason that
these mark an era in our knowledge of the process of generation. This observer, noting
that flies frequently lighted upon meat when it was exposed, simply protected it by
gauze and found that no maggots were developed, while other pieces of meat, placed
under the same conditions, except that the flies had free access to them, developed mag-
gots in great numbers. By this simple experiment, Redi showed that the maggots in
putrefying meat were produced by insects and not by the meat ; but it remained for
Swammerdam and Vallisneri to study the metamorphoses of insects, and to show how
the eggs were developed, first into sexless larvse, and finally into perfect beings resembling
the parents. It is curious to note the condition of science anterior to Redi and Vallis-
neri and compare it with the ideas that are current at the present day. When maggots
appeared in putrefying meat, they were thought to be produced by a spontaneous aggre-
gation of organic particles, simply because observers knew of no other way in which
these beings could come into existence. Now, the advocates of spontaneous generation
have the same ideas as those advanced anterior to 1668 ; but, in the place of meat, they
have organic infusions, and for maggots, they substitute infusorial animalcules. It is
possible that the discussion of the question then was as energetic as it is now ; but the
positive advances in a knowledge of the generation of insects has swept away the memory
of such discussions, if they existed, as future advances may possibly cause many of the
controversial writings of the present day to pass into oblivion.

SEXUAL GENERATION". 355

For a time after the researches to which we have just alluded had taken their place
in the history of science, there was little written about spontaneous generation. IU-di
had satisfactorily described the mode of generation of many of the entozoa, the origin
of which had been obscure ; Harvey had enunciated, in substance, his famous axiom,
" omne animal ex ovo ; " Regnerus de Graaf had described, in the ovaries, the vesicles
which have since borne his name ; and the knowledge of ovulation and development
began to make definite progress, the important fact having been ascertained, that vivipa-
rous, as well as oviparous animals, are produced from ova.

With the discovery, by Leeuwenhoek, of living beings in water, called by him ani-
malcules, but since known as infusoria, a new problem was presented to students of
natural history. Here were animal organisms, so small as to be invisible to the naked
eye, existing in great variety and in infinite numbers, the mode of generation of which
was not understood. As these organisms were studied more closely, their multiplication
by segmentation and by budding became known, and these have since been described as
processes of generation peculiar to some of the lower orders of beings; but, at the same
time, some writers revived the theory of spontaneous generation, to account for the
original appearance of animalcules in water, and this idea has its advocates at the pres-
ent day. If, however, we follow out the history of the spontaneous-generation theory,
we find that the different epochs have repeated themselves ; that the theory took its
origin from an ignorance of the mode of generation of organisms quite high in the scale
of being ; that the progress of exact knowledge gradually restricted the theory to lower and
lower organisms, until, by this rigid process, it became extinct, simply from want of ma-
terial ; that its application to entozoa was eliminated in the same way ; that it was revived
by the discovery of infusoria ; and that now its limits have been restricted by positive
advances in knowledge, it being demonstrated, by Balbiani and others, that many varie-
ties of infusoria present the phenomena of sexual generation.

Of the advocates of spontaneous generation within a comparatively recent period,
perhaps the most prominent has been Pouchet ; but modern researches have shown
pretty clearly that the infusoria produced in organic infusions are due, in all probability,
to the introduction of ova or spores floating in the air, which are developed when they
meet with proper conditions of heat and moisture. In numerous experiments by differ-
ent observers, which it is not necessary to cite in detail, it appeared that, when organic
infusions had been exposed to a degree of heat sufficient to destroy germs, and the intro-
duction of new germs from the air was prevented, no infusoria were developed ; and tins
was the case when air was admitted to the infusions, care being taken to pass the air
through heated tubes or sulphuric acid, so as to destroy all organic matter. The present
aspect of the question of spontaneous generation is the following :

First, it is reduced to the very lowest orders of infusoria, such as vibriones and bac-
teria, which simply present movement, have no distinguishable internal structure, and
are exceedingly minute.

Second, the question is discussed as to what degree of temperature and length of
exposure to heat are necessary in order to destroy preexisting germs in organic intu-
sions; for the idea that living organisms ever result from an aggregation pf ino^gank
particles has been generally abandoned, and the so-called spontaneous prod iu-t ion «>1
animals has been reduced to a coming together of organic molecules.

It is at once apparent to the rigidly scientific mind that tin- Moond divi-ion "f the
question presents great difficulties in the way of its positive solution. ^ It is -ranted, f.
example, that vibriones and bacteria are living, animal organisms. It N proposed by tin-
advocates of the theory of spontaneous generation, that these beings arise without pro
existing germs, by an aggregation of organic particles. The opponents of this view aw
that, when the air admitted to organic infusions is freed from germs or organic pai
and when the organic infusions are subjected to a hijrh temperature for a time suffi<
to destroy all possible preexisting germs, no generation of infusoria can take place

856 GENERATION.

Now, what degree of temperature is required, what is the duration of exposure to heat
necessary to destroy germs, and how are the limits of these conditions to be ascertained?
The only answer to this question lies in the experimental test. When infusoria make
their appearance in solutions that have been exposed to heat and protected from the
entrance of germs, it is said that the heat has not been sufficiently high or the exposure
has been of too short duration. When infusoria do not appear, the conditions are
assumed to have been fulfilled. This mode of reasoning assumes the fact, from the begin-
ning, that there is no such thing as spontaneous generation. Suppose, now, we start
with the contrary assumption, that there may be spontaneous generation in an organic
infusion. We admit to such an infusion, air, carefully purified from germs, which is
logically an essential experimental condition ; we have previously exposed the infusion
to a high temperature for a certain period. Under these conditions, no infusoria appear.
It may then be assumed that the heat has destroyed the properties of the organic mole-
cules, so that they cannot come together and generate new beings.

Under these circumstances, all that we can do is to argue logically from such facts as
have been positively established, and to take the most reasonable view of other points,
that are not as yet capable of satisfactory and definite explanation.

We shall assume that it has been demonstrated, beyond a reasonable doubt, that, in
organic infusions, subjected to a temperature somewhat above that of boiling water, and
supplied with air that has been effectually deprived of organic matter, ova, spores, or
whatever it may be, no living organisms make their appearance so long as these experi-
mental conditions are maintained. We also assume that simple boiling, at 212° Fahr.,
does not necessarily destroy all germs, which excludes experiments made in this way.
This reduces the question to a single, simple point : In infusions in which the organic
matter has not been destroyed by heat, do the living organisms come from a spontaneous
aggregation of organic molecules, or are they the result of the development of ova?

In the case of the very lowest organisms making their appearance under these con-
ditions, they are themselves so small, that it would be reasonable to suppose that we
might be unable to see the ova, assuming that they exist. The organic particles that are
supposed to come together spontaneously are also invisible, even under the highest mag-
nifying powers at our command. If we come to an exact definition of the term spon-
taneous, we may say that it means an action " arising or existing from natural inclination,
disposition, or tendency, or without external cause " (Worcester). With this definition,
the statement that a living organism is generated spontaneously can only mean that there
is no cause that can be assigned for its production. In point of fact, we simply acknowl-
edge that the mode and cause of generation of certain infusoria are unknown, and the
history of our knowledge of generation shows that the term spontaneous generation has
always been applied to the production of beings in a manner that is incapable of satis-
factory explanation. What we actually know of the mode of generation of animal organ-
isms teaches us that all beings are produced and multiplied by ova, or by processes of
segmentation or budding of preexisting organisms ; and our knowledge of these processes
now extends to all except the most minute infusoria, which have no apparent structure.
We know, also, that such organisms may develop in pure water from particles floating in
the atmosphere ; and that particles in the air, singly invisible, may be developed into
infusoria that are quite highly organized. If we reason that the products of so-called
spontaneous generation are formed by the fortuitous aggregation of organic molecules,
we assume a fact of which we have no other example in Nature; and we assume, also,
that such an aggregation of particles produces beings of a definite and uniform character.
For such a supposition, we have no basis in analogy. If, on the other hand, we regard
these low orders of beings as produced by the development of invisible germs, which
have found favorable conditions of heat and moisture, we rest upon a basis of reasonable
analogy, and we merely confess that this is a form of generation, the processes of which
are not as yet capable of demonstration.

FEMALE ORGANS OF GENERATION. 857

As the only true philosophic view to take of the question, we shall assume, in common
with nearly all modern writers upon physiology, that there is no such thing in Nature
as spontaneous generation ; admitting that the exact mode of production of some of the
infusoria, lowest in the scale of being, is not understood.

Female Organs of Generation.

An accurate knowledge of certain points in the anatomy of the female organs of gen-
eration is essential to the comprehension of the most important of the processes of repro-
duction. Following a fruitful intercourse of the sexes, the function, as regards the male,
ceases with the comparatively simple process of penetration of the male element through
the protective covering of the ovum and its fusion with the female element. The fecun-
dated ovum then passes through certain changes, which are the first processes of its
development, forms its attachments to the body of the mother, continues its develop-
ment, materials being derived from the mother, is nourished and grows, until the foetus
at term is brought into the world. An exact knowledge of the mechanism of these com-
plicated processes can only be obtained after a careful study of the anatomy of the female
organs. We must know precisely how the ovum is developed in the ovary and how it
is discharged ; how, after its discharge, it is received by the oviduct and carried to the
uterus ; if fecundation do not take place, there is nothing more to study, as the ovum is
lost ; but, as the fecundated ovum must form certain attachments within the uterus, we
must be acquainted with the anatomy of this organ, before we can comprehend its devel-
opment. Again, we have to study the phenomena which attend the discharge of ova,
and the changes which take place in the ovaries, anterior to, during, and subsequent to
ovulation. It will not be essential for us to study very closely the anatomy of the exter-
nal parts, as these are only concerned in sexual intercourse and in parturition ; which
latter, though a purely physiological process, forms the greatest part of the science of
obstetrics, is considered elaborately in treatises on this subject, and is not usually treated
of, to any great extent, in works upon physiology.

The female organs of generation are divided anatomically into internal and external.
The external organs are the vulva, the adjacent parts, and the vagina ; the internal
organs are the uterus, Fallopian tubes, and ovaries. When we come to study the func-
tions of the internal parts, we shall see that the ovaries are the true female organs, in
which, and in which alone, the female element can be produced. The Fallopian tubes
and the uterus are accessory in their functions, the female element (the ovum) passing
through the Fallopian tubes to the uterus, where it forms the attachments to the body
of the mother which are essential to its nourishment and full development after fecun-
dation.

Before we proceed to study the structure of any of the female organs, it is important
to have a clear idea of the general arrangement and the relations of these parts ; for,
without this, we shall be constantly in the dark as to the bearing of certain important
anatomical points that have been brought forward within the last few years.

The vagina has a direction, slightly curved anteriorly, which is nearly coincident with
the axis of the outlet, or the inferior strait of the pelvis. Projecting into the vagina, at
its upper extremity, is the lower part of the neck of the uterus. The uterus extends in -m
the vagina nearly to the brim of the pelvis. It is situated between the bladder and the
rectum, and has an antero-posterior inclination, when the bladder is moderately distended,
which brings its axis nearly coincident with that of the superior strait of the pelvk1
Supposing the body to be erect, the angle of the uterus with the perpendicular would
be about forty-five degrees. These details with regard to the position of the uterus

1 The statements given above, with mrnrd to the position of the utiTiis. are very ireneral. The uterus i-
ingly movable nntero-posteriorly, and the direction of its axis is lankly dependent upon the condition <.f the other
pelvic organs. When the bladder is distended, the fundus is moved upward ; and, when tho bladder is empty, tho
axis of the uterus may be inclined forward so as to become nearly horizontal.

858 GENERATION.

are essential to a comprehension of the situation and relations of the ovaries and Fallo-
pian tubes.

The uterus is held in place by ligaments, certain of which are formed of folds of the
peritoneum. The anterior ligament is reflected from the anterior surface to the bladder ;
the posterior ligament extends from the posterior surface to the rectum ; the round liga-
ments extend from the upper angle of the uterus, on either side, between the folds of the
broad ligament and through the inguinal canal, to the symphysis pubis ; the broad liga-
ments, which extend from the sides of the uterus to the walls of the pelvis, are the most
interesting of all, as they lodge the ovaries and the Fallopian tubes.

If we imagine the uterus, occupying, as it does, the upper part of the pelvis, and
remember its angle of inclination, it is evident that it, with the broad ligaments, must
partially divide the pelvis into two portions ; and these ligaments, which are formed of
a double fold of peritoneum, present a superior, or posterior surface, and an inferior, or
anterior surface. The superior, or anterior border of this fold is occupied by the Fallopian
tubes, the peritoneum constituting their outer coat. Laterally, at the free extremities of
the tubes, the peritoneum ceases, and there is an actual opening of each Fallopian tube
into the peritoneal cavity. Attached to the broad ligament and projecting upon its pos-
terior surface, is the ovary. This little, almond-shaped body is connected with the fibrous
tissue between the two layers of the ligament, and has no proper peritoneal investment ;
so that it is actually within the peritoneal cavity. If we look at the ovary from the
front, we simply see the rounded prominence which marks the point of its attachment to
the broad ligament ; but, if we look from behind, the projecting surface is seen, and we

FIG. 270.— Uterus, Fallopian tubes, and ovaries ; posterior view. (Sappey.)

1, ovaries; 2,2, Fallopian tubes ; 3, 3, ftmbriated extremity of the left Fallopian tube seen from its concavity; 4,
opening of the left tube ; 5, fimbriated extremity of the right tube, posterior view ; 6, 6, fimbriae which attach
the extremity of each tube to the ovary ; 7, 7, ligaments of the ovary ; 8, 8, 9, 9, broad ligaments ; 10, uterus ; 11,
cervix uteri ; 12, os uteri ; 13, 13, 14, vagina.

have a distinct ring of demarcation at the base, which indicates where the tessellated,
serous epithelium ceases, and where the proper columnar epithelium of the ovary begins.
If a vesicle should rupture upon the surface of the ovary, its contents might thus be
taken up by the Fallopian tube and be carried to the uterus. Each ovary is attached to
the uterus by a ligament, lying just beneath the peritoneum, called the ligament of the
ovary. This ligament is composed of non-striated muscular fibres. Between the folds
of the broad ligament, are the following structures: the round ligament of the uterus,
blood-vessels, nerves, and a thin layer of non-striated muscular fibres, continuous with
the superficial muscular fibres of the uterus.

FEMALE ORGANS OF GENERATION. 859

We are now prepared to study Fig. 270, which shows the general arrangement of
these parts, viewed from behind. A portion of the figure which, in the original, shows
the external parts, is cut off, to avoid complicating our description. A careful examina-
tion of Fig. 270 will give a general idea of the relations of the different parts and enable
us to study intelligently their minute anatomy.

The Ovaries. — The situation of these bodies has already been indicated. Attached
as they are, to the broad ligament, and projecting from its posterior surface, they lie
nearly horizontally in the pelvic cavity, on either side of the uterus. They are of a
whitish color, and their form is ovoid and flattened, with the anterior border, sometimes
called the base, attached to the broad ligament. If we closely examine their mode of
connection with the broad ligament, it is seen that, at the margin of the attached surface
of the ovary, the posterior layer of the ligament ceases, and that the fibrous stroma of
the medullary portion of the ovary is continuous with the fibrous tissue lying between
the two layers. It is at this portion of the ovary, called the hilum, that the vessels pene-
trate, to be distributed in its substance.

Each ovary is about an inch and a half in length, half an inch in thickness, and three-
quarters of an inch in width at its broadest portion. The outer extremity is somewhat
rounded and is attached to one of the fimbriae of the Fallopian tube. The inner extremi-
ty is more pointed and is attached to the side of the uterus by means of the ligament of
the ovary. This ligament is shown in Fig. 270 (7, 7). It is a rounded cord, composed
of non-striated muscular fibres spread out upon the attached extremity of the ovary and
the posterior surface of the uterus, and is covered by peritoneum. The weight of each
ovary is from sixty to one hundred grains, and these organs are largest in the adult virgin.
Its attached border is called the hilum ; and, at this portion, the vessels and nerves pene-
trate. The surface is marked by rounded, translucent elevations, produced by distended
Graafian follicles ; and we frequently see here little cicatrices, indicating the situation of
ruptured follicles. We may also see, between the distended follicles, corpora lutea in
various stages of atrophy.

Within the last few years, anatomical researches have shown that the surface of the
ovaries does not present the appearance of a continuation of the peritoneum. At the
base, is a distinct line, surrounding the hilum, which indicates where the peritoneum
ceases and where the proper epithelial covering of the ovary begins; and there is a well-
marked and abrupt distinction between the tessellated epithelium of the serous surface
and the layer of cylindrical cells covering the ovary itself. This peculiarity has led
to the idea that the ovary is really covered by a mucous membrane. Indeed, there
seems to be little difference between the cells covering the ovaries and those lining the
Fallopian tubes, except that the latter are provided with cilia.

Most anatomists describe a proper fibrous membrane investing the ovaries wliirh
they call the tunica albuginea, and which is compared to the fibrous covering of the
testes. This, however, is not a proper term. Sappey denies the existence of a tunica
albuginea; and, indeed, in the sense in which it was formerly described, such a membrane
cannot be demonstrated. On making a section of the ovary, it is readily seen by tin-
naked eye that the organ is composed of two distinct structures ; a cortical substance.
formerly called the tunica albuginea, which is about ^ of an inch in thickness, and a
medullary substance, containing a large number of blood-vessels. The cortical substance
alone contains the Graafian follicles. The external layer of this may be a little deii-er
than the deeper portion, but there is no distinct fibrous membrane.

The structure of the cortical substance of the ovary is very simple. It counts of con-
nective tissue in several layers, the fibres of which are continuous with the looser tibn-x
of the medullary portion. In the substance of this layer, are embedded the ova. end
in the sacs called Graafian follicles. This layer contains a few blood-vessels, coming
from the medullary portion, which surround the follicles.

860 GENERATION.

The medullary portion of the ovary is exceedingly vascular and is composed of numer-
ous small bands, or trabeculse of connective tissue, with smooth muscular fibres. The
blood-vessels, which penetrate at the hilum, are large and convoluted, especially at the
hilum itself, where there is a mass of convoluted veins, forming a sort of vascular bulb,
which has been described particularly by Rouget. In the medullary portion of the ovary,
which is sometimes called the vascular zone, the muscular fibres follow the vessels, in the
form of muscular sheaths. According to Rouget, the mass of vessels at the hilmn con-
stitutes a true erectile organ.

In addition to the blood-vessels, the ovary receives nerves from the spermatic plexus
of the sympathetic, the exact mode of termination of which has not been ascertained.
Lymphatics have also been demonstrated at the hilum.

Graafian Follicles. — These vesicles, or follicles, were described and figured by De
Graaf and are known by his name. They contain the ova. undergo a series of interest-
ing changes, enlarge, approach the surface of the ovary, and finally are ruptured, dis-
charging their contents into the fimbriated extremity of the Fallopian tube.

It was formerly supposed that the smallest Graafian follicles were situated deeply in
the medullary portion of the ovaries, approaching the surface gradually, as they became
larger ; but it is now known that they are developed exclusively in the cortical substance.
If, indeed, we examine the ovary at any period of life, we find no follicles properly in the
medullary substance; but a few of the larger may project downward, so as to encroach
somewhat upon it, being actually of a diameter greater than the thickness of the cortex.

The earlier anatomists supposed that the Graafian follicles were few in number, fifteen
or twenty, but they counted those only that were readily seen with the naked eye. "When,
however, it was calculated that ova might be discharged every month during a period of
about forty years, it became evident that the follicles must either be quite numerous or
become successively and constantly developed. This led some anatomists, who believed
that, at the age of puberty, the ovaries contained, either partially or fully developed, all
the follicles that ever existed in these organs, to increase their estimates of the number
of follicles. Sappey, from a series of careful observations on this point, puts the number
of follicles at from 600,000 to TOO, 000. We cannot but regard this estimate as very much
exaggerated. According to the table of measurements given by Waldeyer, the primor-
dial follicles in the human embryo, at the seventh month, measure from -^ to ^-^ of an
inch, and the primordial ova, from y^-g- to y^Vo °f an inch. From what has been written
on this point, it seems difficult, if not impossible, to give an approximation, even, of the
number of follicles in the ovaries, but there certainly must be several thousands, many
of which may never become fully developed.

Within the last few years, very important advances have been made in our knowledge
of the mode of development of the ova and ovaries, which will be more fully considered
hereafter; but we must here refer to these points briefly, in order to give a clear idea of
the relations of the Graafian follicles, in the different forms which they present under
varied conditions of development.

The ovary appears, particularly from observations upon the development of the chick,
very early in embryonic life, in the form of a cellular outgrowth from the Wolifian body.
Most of its cells are small, but, as early as the fourth or fifth day, some of them are to be
distinguished by their large size, their rounded form, and the presence of a large nucleus.
These cells are supposed to be primordial ova. In the process of development of the
ovary, some of the peripheral cells penetrate in the form of tubes (the so-called ova-
rian tubes) and, at the same time, delicate processes, formed of connective tissue and
blood-vessels, extend from the fibrous stroma underlying the epithelium and enclose col-
lections of cells. It is probable that we have these two modes of formation of follicles ;
one, by the penetration of epithelial tubes from the surface, which become constricted
and divided off into closed cavities, and the other, by the extension of fibrous processes

FEMALE OKGANS OF GENERATION.

861

from below, which enclose little collections of cells. By both of these processes, little
cavities are formed, which contain a number of cells. In each of these cavities, we
observe a single, large, rounded cell, with a large nucleus, this cell being a primordial
ovum ; and, in addition, we have in the same cavity, other cells, which are the cells of
the Graafian follicle. The exact nature of the processes we have just described has been
studied in the fowl, but it is probable that the same kind of development occurs in mam-
malia and in the human female.

From birth until just before the age of puberty, the cortical substance of the ovary
contains thousands of what are termed primordial follicles, enclosing the primordial ova;
and it is probable that, after the ovaries are fully developed at birth, no additional ova
or Graafian follicles make their appearance. The prevailing idea is, indeed, that the
great majority of these never arrive at maturity, and that they undergo atrophy at vari-

FIG. 2T1 —Portion of a sagittal section of the ovary of an old litch (Waldcyer.1

a, ovarian epithelium; 6,6, ovarian tubes; c, c, younger follicles; «f, older folliH.- : * ..jisrus orolip ™, ^th th<
' ovum ; /; epithelium of a second ovum in the same follicle ; ff, fibrous mat -t thr MAde: *. pr

follicle ; i, epithelium of the follicle (mombrana -r.-mulosa) ; *. <•<.lh.ps.-l. atrop n«-<l f. ,f tV,< o v in'-m r -

cell-tubes of the parovanum. divided longitudinally and transvps-ly ; y. tubular « ,• >»™™rttl^ ^ *' ^
theh'uin in the tissue of the ovary ; z, beginning of the ovarian epithelium close to tin- k

ous stages of their development. According to the table of meMorementa given l.y AVS,1-
deyer, the primordial follicles of the human embryo, at the seventh month, ai
about T&S to jfaf of an inch in diameter, and the primordial ova, from -nVv to ^ ol
inch. In the adult, the smallest follicles measure from about ^ to ^ of an nch, ai

862 GENERATION.

the smallest ova, a little more than -j-oV? °f an inch. The primordial ova have the form
of rounded cells, each with a large, clear nucleus, and a nucleolus. Other structures are
developed in and surrounding these cells, as they arrive at their full development.

The most interesting stage in the development of the ova and Graafian follicles is
observed at about the period of puberty. At this time, a number of follicles (twelve,
twenty, thirty, or even more) enlarge, so that we have all sizes, between the smallest
primordial follicles, -g-J-g- of an inch, and the largest, nearly $ an inch in diameter. In
follicles that have attained any considerable size, we have the fully-developed ova, one in
each follicle, except in very rare instances, when there are two, and these ova have a
pretty uniform diameter of about T^ of an inch. In the process which culminates in
the discharge of the ovum into the fimbriated extremity of the Fallopian tube, the Graa-
fian follicle gradually enlarges, becomes distended with liquid, and finally breaks through
and ruptures upon the surface of the ovary. It becomes necessary, then, to study the
structure of these large follicles and their relations to the ova ; but, before we do this,
we can review, with advantage, the relations of the different portions of the ovary and
the follicles and ova of various sizes, by an examination of Fig. 271.

Fig. 271 shows the follicles and ova of various sizes. It is observed that the larger
follicles contain fully-formed ova and have a proper fibrous coat. The ova here present
an epithelial covering and are embedded in a mass of the epithelial lining of the follicle
(membrana granulosa), this mass being called the-discus or cumulus proligerus.

According to the measurements given by "Waldeyer, the smallest Graafian follicles are
from ^i^ to ^^-5- of an inch in diameter, while the largest measure from f to \ an inch.
At or near the period of their maturity, the follicles present several coats and are filled
with an albuminous liquid. The mature follicles project just beneath the surface and
form little, rounded, translucent elevations. The smallest follicles are near the surface,
and, as they enlarge, at first become deeper, as is seen in Fig. 271, becoming superficial
only as they approach the period of fullest distention.

FIG. WL.—Graafian follicle, ; magnified 80 diameter*. (Lusclika.)

1, 1, stroma of the ovary; 2, 2. convoluted, cork-screw blood-vessels ; 3, fibrous wall of the follicle ; 4, membrana
granulosa; 5, cumulus proligerus ; 6, zona pellucida of the ovum; 7, vitellus of the ovum ; 8, germinal vesicle
with the germinal spot.

Taking one of the largest follicles as an example, two fibrous layers can be distin-
guished ; an outer layer, of ordinary connective tissue, and an inner layer, the "tunica
propria, formed of the same kind of tissue, with the difference that, as the follicle en-

FEMALE ORGANS OF GENERATION.

863

larges, the inner layer becomes vascular. The vascular tunica propria is lined by cells
of epithelium, forming the so-called membrana granulosa. At a certain point in this
membrane, is a mass of cells, called the discus or cumulus proligerus, in which the ovum
is embedded. The situation of the discus proligerus and the ovum has been a subject of
discussion. Some anatomists describe it in the most superficial portion, and others, in
the deepest part of the follicle. Waldeyer states that he has observed it in both situa-
tions ; and it is probable that its position is not invariable.

The liquid of the Graafian follicle is alkaline, slightly yellowish, not viscid, and it con-
tains a small quantity of albuminoid matter coagulable by heat, alcohol, and acids. This
liquid is supposed to be secreted by the cells lining the inner membrane of the follicle.

It is important to remember that the ovum is not a product of secretion, nor can the
ovary be properly considered as a glandular organ. The ovum is an anatomical ele-
ment ; and the ovary is the only organ in which this anatomical element can be devel-
oped. The only process of secretion which takes place in the ovary is the production,
probably by the cells of the membrana granulosa, of the liquid of the Graafian follicles.

The Parovarium. — The parovarium, or organ of Rosenmuller, is simply the remains
of the Wolffian body, lying in the folds of the broad ligament, between the ovary and
the Fallopian tube. It consists of from twelve to fifteen tubes of fibrous tissue, lined by
ciliated epithelium, and it has no physiological importance. The Wolffian bodies will be
fully described in connection with the development of the genito-urinary system.

The Uterus. — The form, situation, and relations of the uterus and Fallopian tubes
have already been indicated and are shown in Fig. 270.

The uterus is a pear-shaped body, somewhat flattened antero-posteriorly, presenting
a fundus, a body, and a neck. At its lower extremity, is an opening into the vagina,

B

FIG. 273.— Virgin -utern*. A.— anterior view. B.— meflinn Action. ('.— fr,in*rf*e *-

A. 1, body ; 2, 2, angles ; 3, cervix ; 4, site of the os internum ; 5, vaginal portion of the cervix : «. external os ; 7. 7.

vagina.

B. 1, 1, profile of the anterior surface: 2, vesico-uterine ciil-rlt-*nc; 8. 8. profile of the posterior •»«

5, neek; «, isthmus; 7. envirv of the body; 8, cavity of the cervix; 9, os internum; 10, anterior Up of the
os externum ; 11. posterior lip; 12. 12. vagina.

C. 1, cavity of the body: 2. lateral wall : 8. superior w-,11 : 4, 4, cornua ; 5, os internum ; 6, cavity of the 0

7, arbor vite of the cervix ; 8, os externum ; 9, 9, vagina.

called fhe os externum. At the upper portion of the neck, is a constriction, which indicates
the situation of the os internum. The form of the uterus ia shown in Fig. 273 (A). It \3

864

GENERATION.

usually about three inches in length, two in breadth, at its widest portion, and one inch in
thickuess. Its weight is from one and a half to two and a half ounces. It is somewhat
loosely held in place by the broad and round ligaments and by the folds of the peritoneum
in front and behind. The delicate layer of peritoneum which forms its external covering
extends behind as far down as the vagina, where it is reflected back upon the rectum, and
anteriorly, a little below the upper extremity of the neck (os internum), where it is re-
flected upon the urinary bladder. At the sides of the uterus, the peritoneal covering, a lit-
tle below the entrance of the Fallopian tubes, becomes loosely attached and leaves a line
for the penetration of the vessels and nerves. Fig. 273 (0), giving a view of the interior

FIG. 274.— Muscular fibres of the uterus. (Sappey.)
A, fibres of the uterus of the foetus at term ; B, of a woman twenty years of age ; C, of a woman just delivered.

of the uterus, shows a triangular cavity, with two cornua, corresponding to the openings
of the Fallopian tubes, and exceedingly thick walls, the greatest part of which is com-
posed of layers and bands of non-striated muscular fibres.

The muscular walls of the uterus are composed of fibres of the involuntary variety,
arranged in several layers. These fibres are spindle-shaped, always nucleated, the nu-
cleus presenting one or two large granules, which have been taken for nucleoli. They
are closely bound together, so that they are isolated with great difficulty. In addition to
an amorphous adhesive substance between the muscular fibres, we find numerous round-
ed and spindle-shaped cells of connective tissue of the variety called embryonic, and a
few elastic fibres. The muscular tissue of the uterus is remarkable from the fact that
the fibres enlarge immensely during gestation, becoming, at that time, ten or fifteen
times as long and five or six times as broad as they are in the unimpregnated state. They
are united into bundles, or fasciculi, which, in certain of the layers, interlace with each
other in every direction.

It is quite difficult to follow out the course of the fasciculi of the muscular tissue of
the uterus, and the layers of fibres are described somewhat differently by different
writers. All agree, however, that there is a superficial layer, tolerably distinct, very
thin, resembling the platysma myoides, which is sometimes called the platysma of the
uterus. In addition to this layer, we shall describe two, making, in all, three layers, an
external, middle, and internal, although this division is somewhat arbitrary.

FEMALE ORGANS OF GENERATION. 865

The external muscular layer, which is very thin but distinct, is closely attached to the
peritoneum. When the uterus is somewhat enlarged after impregnation, we observe
oblique and transverse superficial fibres passing over the fundus and the anterior and pos-
terior surfaces to the sides. Here they are prolonged upon the Fallopian tubes, the round
ligament, and the ligament of the ovary, and also extend between the layers of the broad
ligament. This external layer is so thin that it cannot be very efficient in the expulsive
contractions of the uterus; but, from its connections with the Fallopian tubes and the
ligaments, it is useful in holding the uterus in place. It does not extend entirely over
the sides of the uterus. Rouget, who has given a very elaborate description of the ex-
ternal layer in the human subject and in various classes of animals, has found it prolonged

Fio. 275.— Superficial muscular fibres of the anterior surface of the uterus. (Llegeois.)
a, a, round ligaments ; 6, 6, Fallopian tubes ; c, c, e, 0, transverse fibres ; d, /, longitudinal fibres.

into the ligaments and extending to the ovaries and Fallopian tubes. lie regards the
uterus and its so-called appendages as lying between two thin, muscular sheets, and con-
siders the action of the muscular fibres as very efficient in producing an engorgement of
the erectile tissue of the internal organs, by constriction of the veins. Erection, accord-
ing to this observer, occurs at the period of menstruation, determines the application of
the fimbriated extremity of the Fallopian tubes to the surface of the ovary, and assists
in the expulsion of the ovum. These points will be more fully considered under the head
of ovulation.

The middle muscular layer is the one most efficient in the parturient contractions of
the uterus. It is composed of a thick and complicated net-work of fasrieuli interlacing
with each other in every direction.

The inner muscular layer is arranged in the form of broad rinirs, which surround the
Fallopian tubes, become larger as they extend over the body of the uterus and meet at
the centre of the organ near the neck.

The mucous membrane of the uterus is of a pale, reddish color; and that portion
lining the body is smooth, and so closely attached to the subja.vnt structures that it
cannot be separated to any great extent by dissection. There is, however, no proper
55

866

GENERATION.

submucous areolar tissue, the membrane being applied directly to the uterine walls. It is
covered by a single layer of cylindrical epithelial cells with delicate cilia, the movements
of which are from without inward, toward the openings of the Fallopian tubes. Ex-
amination of the surface of the membrane
with a low magnifying power shows the
openings of numerous tubular glands.
These glands are usually simple, some-
times branched, dividing, about midway
between the opening and the lower ex-
tremity, into two and, very rarely, into
three secondary tubules. Their course is
generally tortuous, so that their length
frequently exceeds the thickness of the
mucous membrane. The openings of these
tubes are about F|^ of an inch in diameter.
The uterine tubes are of considerable
physiological interest and have been the
subject of much discussion. Their secre-
tion, which forms a thin layer of mucus
on the surface of the membrane in health,
is grayish, viscid, and feebly alkaline. The
tubes themselves have exceedingly thin,
structureless walls, and are lined with
cylindrical ciliated epithelial cells.

The changes which the mucous mem-
brane of the body of the uterus undergoes
during menstruation are remarkable. Un-
der ordinary conditions, its thickness is
but it measures, during the menstrual period, from £ to £ of

276. — Inner layer of muscular fibres of the uterus.

(Liegeois.)

a, a, rin^s around the openings of the Fallopian tubes ; b, &,
circular fibres of the cervix.

of an inch

from 3*5- to
an inch.

In the cervix, the mucous membrane is paler, firmer, and thicker than the mem-
brane of the body of the uterus, and between these two surfaces, there is a distinct
line of demarkation. It is here more loosely attached to the subjacent tissue in the
cervix, and the anterior and posterior surfaces of the neck present an appearance of
folds radiating from the median line, forming what has been called the arbor vita3 uteri,
or plicaa palmatse. These so-called folds are supposed by some anatomists to be formed
by rows of large, papillary elevations of the membrane. Throughout the entire cervical
membrane, are numerous mucous glands, and, in addition, in the lower portion, are a
few rounded, semitransparent, closed follicles, called the ovules of Naboth, which are
probably cystic enlargements of obstructed follicles. The upper half of the cervical
membrane is smooth, but the lower half presents numerous villi. The epithelium of
the cervix presents great variations in its character in different individuals. Before the
time of puberty, the entire membrane of the cervix is covered with ciliated epithelium.
After puberty, however, the epithelium of the lower portion changes its character, and
we have cylindrical cells above, with squamous cells in the inferior portion. The latter
extend upward in the neck to a variable distance.

The blood-vessels of the uterus are very large and present certain important peculi-
arities in their arrangement. The uterine arteries pass between the layers of the broad
ligament to the neck, and then ascend by the sides of the uterus, presenting an exceed-
ingly rich plexus of convoluted vessels, anastomosing above with branches from the
ovarian arteries, sending branches over the body of the uterus, and Bnally penetrating
the organ, to be distributed mainly in the middle layer of muscular fibres. In their
course, these vessels present the convoluted arrangement characteristic of erectile tissue

FEMALE ORGANS OF GENERATION.

867

and form a sort of mould of the body of the uterus. Rouget calls this the erectile tissue
of the internal generative organs. By placing the pelvis in a bath of warm water and
injecting what he calls the spongy bodies of the ovaries and uterus by the ovarian veins,
he produced a distention of the vessels and a true erection, the uterus executing a move-
ment analogous to that of the penis during venereal excitement.

FIG. 277. — Blood-vessels of the uterus and ovaries ; posterior rieic. (Rouget.)

T, T, Fallopian tubes; O, O, ovaries; U, uterus; V, vagina; P, pubis; L, anterior round ligament; 1, 2, muscular
fibres of the vagina; 3, 4, ligament of the ovary; 5, superior round ligament; 6, ovarian artery; 7, ovarian vein;
8, uterine artery; 9, uterine vein; 10, 11, uterine plexus; 12, vaginal plexus.

In addition to the erectile action above described, Wernich has lately noted a true
erection of the lower portion of the uterus, particularly the neck, which he believes to
be very efficient in aiding the penetration of spermatozoids. In several observations, he
noticed, during a vaginal examination by the touch, that the neck of the uterus, which
at first was soft and flaccid, became elongated, hardened, and apparently in a condition
of erection, giving an impression to the finger comparable to the hardened glans penis.
As an anatomical explanation of the phenomena observed, Wernich quotes from Henle
an account of the arrangement of the blood-vessels of the cervix and his physiological
deductions from the presence, in this portion of the uterus, of a true erectile tissue.
This question will be considered more fully under the head of the mechanism of fecun-
dation.

In the muscular structure of the uterus, are numerous large veins, the walls of which
are closely adherent to the uterine tissue. During gestation, these vessels become en-
larged, forming the so-called uterine sinuses.

Lymphatics are not very numerous in the unimpregnated uterus, but they become
largely developed during gestation. They exist in a superficial and a deep layer, the
deeper vessels coming from the muscular substance and probably also from the mucous
membrane.

The uterine nerves are derived from the inferior hypogastric and the spermatic plex-
uses, and the third and fourth sacral. In the substance of the uterus, they present in
their course small collections of ganglionic cells and it is said that the nerves pass finally
to the nucleoli of the muscular fibres.

868 GENERATION-,

The Fallopian Tubes. — The Fallopian tubes, or oviducts, lead from the ovaries to the
uterus. They are shown in Fig. 270. These tubes are from three to four inches long,
but their length is not always equal upon the two sides. They lie between the folds of
the broad ligament at its upper border. Opening into the uterus upon either side at the
cornua, they present a small orifice, about -fa of an inch in diameter. From the cornua,
they take a somewhat undulatory course outward, gradually increasing in size, so that
they are rather trumpet-shaped. Near the ovary, they turn downward and backward.
The extremity next the ovary is marked by from ten to fifteen fimbrise, or fringes, which
has given this the name of the fimbriated extremity, or morsus diaboli. All of these

Fid. 278.— Fallopian tube. (Liegeois.)

fringe-like processes are free, except one ; and this one, which is longer than the others,
is attached to the outer angle of the ovary and presents a little gutter, or furrow, ex-
tending from the ovary to the opening of the tube. At this extremity, is the abdominal
opening of the tube, which is two or three times as large as the uterine opening. Pass-
ing from the uterus, the caliber of the tube gradually increases as the tube itself en-
larges, and there is an abrupt constriction at the abdominal opening.

Beneath the peritoneal coat, which is formed by the layers of the broad ligament, in
a layer of connective tissue, containing a rich plexus of blood-vessels. This constitutes
the proper fibrous coat of the Fallopian tubes.

The muscular layer is composed mainly of circular fibres of the non-striated variety,
with a few longitudinal fibres prolonged over the tube from the external muscular layer
of the uterus. This coat is quite thick and sends bands between the layers of the broad
ligament to the ovary, which are supposed to act in adapting the fimbriated extremity of
the tube to the surface of the ovary.

The mucous membrane of the tube is thrown into folds, which are longitudinal and
transverse near the uterus, and are more complicated at the dilated portion. In this
portion, next the ovary, embracing about the outer two-thirds, the folds project far into
the caliber of the tube. These are sometimes simple, but more frequently they present
secondary folds, often meeting as they project from opposite sides. This arrangement
gives an arborescent appearance to the membrane on transverse section of the tube.
The mucous membrane is covered by cylindrical ciliated epithelium, the movement of
the cilia being from the ovary toward the uterus. At the margins of the fimbrise, the
ciliated epithelium is continuous with the epithelium of the peritoneum, presenting the
exceptional example of an opening of a mucous-lined tube into the cavity of the perito-
neum. The membrane of the tubes has no mucous glands.

It is not necessary to enter into a minute description of the external organs of the
female. Opening by the vulva, externally, and terminating at the neck of the uterus, is
a membranous tube, the vagina. This lies between the bladder and the rectum. It has

STRUCTURE OF THE OVUM. 869

& curved direction, being about four inches long in front, and five or six inches long pos-
teriorly. There is a constricted portion at the outer opening, where we have a muscle,
called the sphincter vaginas, and the tube is somewhat narrowed at its upper end, where
it embraces the cervix uteri. The inner surface presents a mucous membrane, marked by
transverse rugae, with papillae and mucous glands. Its surface is covered with flattened
epithelium. The vagina is quite extensible, as it must be during parturition, to allow

Fm. 279.— External erectile organs of the female. (Lie<*eois.)

A, pubis; B, B, ischinm ; C, clitoris ; O, gland of the clitoris ; E. bulb ; F. constrictor muscle of the vulva; G-, left
pillar of the clitoris ; H, dorsal vein of the clitoris ; I, intermediary plexus ; J, vein of communication with the
obturator vein ; K, obturator vein ; M, labia minora.

the passage of the child. It presents a proper coat of dense fibrous tissue, with longi-
tudinal and circular muscular fibres of the non-striated variety. We have, also, sur-
rounding it, a rather loose erectile tissue, which is most prominent at its lower portion.

The parts composing the external organs are abundantly supplied with vessels and
nerves. In the clitoris, which corresponds to the penis of the male, and on either side
of the vestibule, we find a true erectile tissue.

Structure of the Ovum.

The ripe ovum lies in the Graafian follicle, embedded in the mass of cells which con-
stitutes the discus proligerus. Within the discus, surrounding the ovum, there seem to
be two kinds of cells ; first, cells evidently belonging to the Graafian follicle and similar
to the cells in other parts of the membrana granulosa ; second, a single layer of columnar
cells belonging to the ovum and probably concerned in the production of the proper
membrane of the ovum, the vitelline membrane. Regarding the vitelline membrane as
the external covering, we can see, in the ovum, a clear, transparent membrane, a granu-
lar mass (the vitellus) filling this membrane completely, a large, clear nucleus, called the
germinal vesicle, and a nucleolus, called the germinal spot.

The size of the ripe ovum, in the human subject and in mammals, is about TJy of an
inch, and its form is globular.

The external membrane of the ovum is clear, apparently structureless, quite strong
and resisting, and it measures about FTVff °f an mcn m thickness. As it forms a trans-
parent ring in the mass of cells in which the ovum is embedded, this is sometimes called
the zona pellucida. According to recent researches, it seems that the primordial ovum
has at first no special investing membrane ; as it develops, it presents, surrounding the

870 GENERATION.

vitellus, a single layer of columnar cells ; at the deepest portion of these cells, a homo-
geneous basement-membrane is gradually formed ; and the cells undergo a sort of cuticu-
lar transformation, becoming finally the vitelline membrane.

An important point, in this connection, is the question of the existence of pores, or per-
forations in the vitelline membrane. As we shall see farther on, there can be no doubt
with regard to the actual penetration of the spermatozoids through this membrane, so
that they come in contact with the vitellus ; and it is in this way that the ovum is fecun-
dated. In the osseous fishes and in mollusks, there seems to be no question with regard
to the existence of numerous pores in the vitelline membrane ; but these are not so easily
demonstrated in the ova of mammals. Admitting the existence of a micropyle and pores
in the vitelline membrane in fishes and mollusks, it is certain that openings are very
much more indistinct, if they can be seen at all, in the ova of mammals; still, the fact
of the actual penetration of spermatozoids almost of necessity presupposes the presence
of orifices. We have often thought, in studying this subject, that it must be difficult,
examining a perfectly transparent and homogeneous membrane in water, which would
fill up all pores, to distinguish any openings, and we have been disposed to admit their
presence, mainly because the spermatozoids are known to pass through. The idea of
their existence in mammals certainly receives support from analogy with the lower
orders of animals.

The vitellus, called the principal yolk or the formative yolk, contains the elements
which are to undergo development into the embryon. It is composed of a semifluid
mass, containing, in addition to the germinal vesicle, numerous granules. Some of these
granules are large, strongly-refracting, globular bodies, which are so bright and so numer-
ous, that they obscure the other parts of the vitellus. Between these, are numerous albu-
minoid granules, which are much smaller and not so distinct.

The germinal vesicle, sometimes called the vesicle of Purkinje, is the enlarged nucleus
of the primordial ovum. It is a clear, globular vesicle, about 7^ of an inch in diameter,
embedded in the vitellus, its position varying in different ova. It presents in its interior
a number of fine granules, and a large, dark spot, called the germinal spot, or the spot
of Wagner, which measures about -^Vo of an inch in diameter. This spot corresponds
to the nucleolus of the primordial ovum. In mammals, the mature ovum contains but
one germinal vesicle and one germinal spot. The various points we have described are
illustrated in Fig. 280.

Discharge of the Ovum.

A ripe Graafian follicle measures from f to \ of an inch in diameter and presents a
rounded elevation, containing a plexus of blood-vessels, upon the surface of the ovary.
At its most prominent portion, is an ovoid spot, in which the membranes are entirely free
from blood-vessels. At this spot, which is called the macula folliculi, the coverings finally
give way, and the contents of the follicle are discharged. For a short time anterior to
the rupture of the follicle, important changes have been going on in its structure. In
the first place, the non-vascular portion, situated at the very surface of the ovary, under-
goes fatty degeneration, by which this part of the wall becomes gradually weakened. At
the same time, at the other portions of the follicle, there is a growth of cells, which pro-
ject into the interior, and an extension, into the interior, of blood-vessels in the form of
loops. These changes, with an increase in the pressure of liquid and the fatty degen-
eration of the macula, cause the follicle to burst ; and, with the liquid, the discus prolige-
rus and the ovum are expelled. The formation of a cell-growth in the interior of the
follicle is really the beginning of the corpus luteum ; and this occurs some time before
the discharge of the ovum takes place. It is a disputed question whether or not a
haemorrhage occurs into the follicle at the time of its rupture. This may, and undoubtedly
does sometimes occur, but it cannot be regarded as constant and has been denied by
many observers.

DISCHARGE OF THE OVUM. 871

The time at which the follicle ruptures, particularly with reference to the menstrual
period, is probably not definite; but it is certain that, while sexual excitement mav
hasten the discharge of an ovum by producing a greater or less tendency to congestion
of the internal organs- ovulation takes place independently of the action of coition. The
opportunities for determining this fact in the human female are not frequent ; but it has
been fully demonstrated by observations upon the inferior animals, and there is now no
doubt with regard to the identity of the phenomena of rut and of menstruation. It is
useless, at the present day, to enter into an elaborate discussion of this point, which
occupied so much the attention of the earlier writers. From the earliest times, it was
recognized, not only that women became fruitful only after the appearance of the menses,
but that sexual intercourse was most likely to be followed by conception when it
occurred near the periods ; a point which we shall discuss more fully under the head of
fecundation. When it was recognized that rupture of Graafian follicles was followed by
the formation of corpora lutea, it became easy to verify the supposition that the ova
were discharged at regular intervals, by an examination of the ovaries in women who
had died suddenly; and such observations, showing corpora lutea in virgins, demon-
strated that ovulation was not necessarily dependent upon coitus.

FIG. 280— Ovum of the rabbit, from a Graafian follicle fa of an inch in diameter. (Waliltyor.t
o, epithelium of the ovum ; 6, zona peUucida, with radiating striations (viteliine membrane) ; c, germinal vesicle ;

<Z, germinal spot ; e, vitellus.

Observations upon the lower animals have shown, notwithstanding the fact of dis-
charge of ova without copulation or even the sight of the male, that sexual excitement
has a certain influence upon ovulation. The experiments of Coste upon this point are
very interesting. This observer noted that, in rabbits killed from ten to fifteen hours
after copulation, there was evidence of the recent discharge of ova. In two experiments,
however, he took female rabbits in heat and manifesting the greatest ardor for the male,
presented them to the male, in order to show that they were really in heat, but care-
fully prevented copulation. This was done for three days in succession, there lu-ing. <>n
each occasion, a manifest desire for the approach of the male. One rabbit was killed on
the third day, while still in heat ; and six distended Graafian follicles were found in one

872 GENERATION.

ovary and two in the other ; but there was no trace of ruptured follicles. The other
rabbit ceased to be in heat on the fourth day and was killed on the fifth. This animal
presented seven distended follicles on one side, and one on the other, but no ruptured
follicles. From these and other experiments upon the lower animals, there seems to be
no doubt that copulation hastens the rupture of ripe Graafian follicles; but, on the other
hand, it is equally true that follicles rupture independently of the sexual act.

To return to the phenomena which attend ovulation in the human subject, there is
every reason to suppose, at least from analogy, that the excitement of the genital organs
during sexual intercourse may determine the rupture of a ripe Graafian follicle. At
stated periods, marked by the phenomena of menstruation, one, and sometimes more
Graafian follicles become distended and usually rupture and discharge their contents into
the Fallopian tubes. This discharge of an ovum or ova may occur at the beginning, at
the end, or at any time during the continuance of the menstrual flow. Upon this
point, the observations of Coste, which were made many years ago, seem entirely con-
clusive. In a woman who died on the first day of menstruation, he found a recently-
ruptured follicle ; in other instances, at a more advanced period and toward the decline
of the menstrual flow, he found evidences that the rupture had occurred later ; in the
case of a female who drowned herself four or five days after the cessation of the menses,
a follicle was found in the right ovary, so distended that it was ruptured by very slight
pressure ; and other instances were observed in which follicles were not ruptured during
the menstrual period. The most striking case of this kind was of a young girl, nineteen
years of age, who committed suicide fifteen days after the menstrual period. The ovaries
were examined with the greatest care. "By the side of the Graafian vesicles largely
developed, were found traces of ruptured vesicles ; but the corpora lutea were evidently
too old to be reasonably referred to the last menstruation ; the Graafian vesicle, conse-
quently, had not matured, or at least had been arrested in its development."

In conclusion, remembering that coitus may hasten the rupture of ripe follicles, we
quote from Coste the following as representing what we know of the relations between
ovulation and menstruation:

" As a summary, then, of all the facts that I have observed, I believe it to be con-
clusive, that, in the human female, there is always, at each menstrual period, as during
the condition of rut in animals, a vesicle of the ovary which has a marked preponder-
ance over the others; that it spontaneously arrives at maturity, and, most generally, is
ruptured at some time during this period to give issue to the ovum which it contains;
but there are cases, also, in which, in the absence of sufficiently favorable conditions,
this distended vesicle cannot accomplish this end, and, as in mammals again, may remain
stationary or be entirely reabsorbed."

Passage of Ova into the Fallopian Tubes.

The fact that the ova, in the great majority of instances, pass into the Fallopian
tubes, is sufficiently evident. The fact, also, that ova may fall into the cavity of the
peritoneum is shown by the occasional occurrence of extra-uterine pregnancy, a rare
accident, which shows that, in all probability, the failure of unimpregnated ova to enter
the tubes is exceptional. When we come, however, to the mechanism of the passage
of the ova into the tubes, the explanation is difficult. At the present time there are two
theories with regard to this process ; one, in which it is supposed that the fimbriated
extremities of the Fallopian tubes, at the time of rupture of the Graafian follicles, be-
come adapted to the surface of the ovaries; and the other, that the ova are carried to
the- openings of the tubes by ciliary currents. Neither of these theories is capable of
actual demonstration ; and we can only judge of their probable correctness from ana-
tomical facts. Rouget, an earnest advocate of the first-mentioned theory, has given an
exact description of the muscular structures connected with the tubes and ovaries. We

PASSAGE OF OYA INTO THE FALLOPIAN TUBES.

873

haro already seen that one of the fimbria) of the tube is longer than the others and is
attached to the outer angle of the ovary. The other fimbrifle arc unattached and are
distant from about half an inch to an inch from the ovarian surface. Accordinir to this
observer, there is a double layer of muscular fibres, passing from the lumbar region of
the uterus and embracing the whole of the dilated portion of the tube ; and the action of
these fibres must draw the extremity of the tube toward the ovary and apply it to its sur-
face. That the muscular fibres described by Rouget exist, there can be scarcely a doubt;
but that their action is essential to the passage of ova into the Fallopian tubes, is a ques-
tion for discussion. If we could assume with certainty that the ova are discharged only
during sexual intercourse, or that follicles are usually ruptured as a consequence of
pressure exerted by the muscular action described by Rouget, this theory would be ren-
dered exceedingly probable, to say the least ; but the facts do not admit of this exclusive
view. However, observations upon the lower animals, particularly rabbits, have shown
that copulation actually hastens the discharge of ova from ripe Graafian follicles ; but it
must be a question of theory simply, whether the act be attended with the muscular
contraction indicated by Rouget, or whether there be a determination of blood to the
ovary, which produces an additional tendency to rupture at this time. We can hardly
adopt unreservedly the theory of Rouget, unless it be evident that there is no other way
in which the ova can enter the tubes. The fact is that, in the human female, an ovum
may be discharged at the beginning of menstruation, at any time during the flow, or
even after the flow has ceased ; and it is more than probable that pressure within the
follicle alone may cause its rupture, and that this may occur independently of sexual
excitement. In view of these facts, while we cannot deny that the fiinbriated extrem-
ities of the tubes may, by muscular action, be drawn toward the surface of the ovary,
we cannot admit that such an action is constant, or that it is necessary to the passage
of ova into the tubes, though the theory of Rouget has been adopted, entirely or in
part, by some writers of authority.

If we take into account the situation of the ovaries and the relations of the Fallopian
tubes, we can understand how an ovum may pass into the tube, without invoking the aid
of muscular action. Let us suppose, for example, that a Graafian follicle be ruptured
when the fimbriated extremity of the tube is not applied to the surface of the ovary. One
of the fimbrisB, longer than the others, is attached to the outer angle of the ovary and
presents a little furrow, or gutter, leading to the opening of the tube. This furrow is
lined by ciliated epithelium, as indeed, is the mucous membrane of all of the fimbriffl, the
movements of which produce a current in the direction of the opening, which we might
suppose would be sufficient to carry a little globule, only y^- of an inch in diameter, into
the tube. At the same time, there is probably, as has been suggested by Becker, a con-
stant flow of liquid over the ovarian surface, directed by the ciliary current toward the
tube; and when the liquid of the ruptured follicle is discharged, this, with the ovum,
takes the same course.

In all probability, what we have just described is the mechanism of the passage of the
ova into the Fallopian tubes; and it is possible that the timbriafcd extremity may be
drawn toward the ovarian surface, though we can hardly understand how it can ho closely
applied to the ovary and exert any considerable pressure upon the distended follicle. It
is proper to note, also, thnt the conditions dependent upon the currents of liquid din
by the movements of cilia are constant and could influence the passage of an ovum at
whatever time it might be discharged, while a muscular action would be more or
intermittent.

It is somewhat difficult to understand the exact mechanism t.f the pasture of MM ovu
discharged from an ovary into the Fallopian tube upon the opposite side, although it oafl
be doubted that this sometimes occurs. Schroeder has collected, from various authors, the
reports of several cases, in which an ovum has been discharged, has found iN way into
the uterus, and has undergone development, one tube being closed and the corpus luteum

874 GENERATION.

existing upon the side on which the tube was impervious. In some instances in which
the corpus luteum has been found on the side on which the tube was closed, tubal preg-
nancy has occurred upon the opposite side. In these cases, the ovum must have passed
across the uterus. It is possible that, the subject lying upon one side, a current of liquid
may have taken a direction from the ovary to the opposite tube, but this can be only a
matter of conjecture.

Puberty and Menstruation.

At a certain period of life, usually between the age of thirteen and of fifteen years,
the human female undergoes a remarkable change and arrives at what is termed the age
of puberty. At this time, there is a marked increase in the general development of the
body ; the limbs become fuller and more rounded ; a growth of hair makes its appearance
upon the mons veneris ; the mammary glands increase in size and take on a new stage of
development ; Graafian follicles enlarge, and one or more approach the condition favor-
able to rupture and the discharge of ova. At this time, also, certain changes are observed
in the moral as well as in the physical attributes of the female. There is then a sort of
indefinite consciousness of a capacity for new functions, with an indescribable change in
feeling for the opposite sex, due to the first development of sexual instincts. The female
becomes capable of impregnation, and continues so, in the absence of pathological condi-
tions, until the cessation of the menses.

It is a commonly-recognized fact that the age of puberty is earlier in warm than in
cold climates; and numerous instances are on record, in which the menses have appeared
exceptionally, much before the usual period. Generally, at the age of forty or forty-five,
the menstrual flow becomes irregular, occasionally losing its sanguineous character, and
it usually ceases at about the age of fifty years. Sometimes it is said that the menses
return, with a second period of fecundity, though this is rare. According to most writers,
while climate has a certain influence over the time of cessation as well as the first appear-
ance of the menses, this is not very marked. When the menses appear early in life, they
usually cease at a correspondingly early period ; but this is by no means constant. There
are, also, numerous exceptions to the ordinary limits to the period of fecundity. Haller
observed a case of a young girl, nine years of age, who had menstruated for several years,
and others, who had become pregnant at nine, ten, and twelve years. He also quotes
cases of women who have been fruitful at from fifty-four to seventy years of age. Other
instances of this kind are on record, which it is unnecessary to quote. The occurrence
of pregnancy after the age of fifty or fifty-five is certainly doubtful.

Menstruation.

It is unnecessary to discuss farther the correspondence between menstruation in the
human female and the condition of heat in the lower animals, as we have already seen,
under the head of ovulation, that these two conditions are essentially identical. In the
lower animals, the female will admit the male only at the period of heat ; and, in some
animals in the savage state, it is only at this time that the male is capable of copulation.
The variations in sexual temperament in the human female are so considerable, and the
sentiments toward the opposite sex are so subordinate to artificial conditions of society
and civilization, that it is difficult to establish a parallel, in this regard, between her and
the lower animals. Some females rarely or never experience sexual excitement and have
no orgasm during intercourse; while others seem to be capable of sexual ardor at any time.
Women who are in the habit of promiscuous relations with the other sex frequently lose
the sexual feeling and simulate excitement during coitus. It is very difficult, indeed, to
say positively how far the facts observed in the lower animals are applicable to the human
subject, as we must depend largely upon statements which, of themselves, are entitled to
but little consideration. It is nevertheless true that, in some women, sexual desire is

MENSTRUATION. 375

decidedly marked just after the cessation of the menses, and in many, it really exists at
no other time. Still, mercenary or other considerations may induce women to admit
intercourse at any time, and the sexual orgasm, and even fecundation, may at any tinu-
occur. As a rule, the female yields to advances made by the male and is reputed to
experience a less degree of sexual desire and ardor, although this has marked exceptions.
It is probably true that, eliminating, as far as we can, all considerations except those
of a purely sexual character, there is less of a promiscuous feeling for the opposite sex in
females than in males, and that sexual desire, aside from feelings of fatigue or satiety, is
sometimes markedly periodical in women. If we may take certain individual cases as
representing physiological conditions, it appears that, in some women, there is a period
of comparative indifference to the opposite sex ; as the menses approach, there is more
or less irritability of temper and disinclination for society, which disappear as the flow is
established ; and, at or following the cessation of the menses, sexual desire is manifested
to an unusual degree, this continuing for only a few days.

Although there is a periodical condition of heat in the lower animals, connected with
ovulation, a sanguineous discharge from the genital organs is not often observed. It is
only in monkeys that we have a counterpart of what occurs in the human female ; and
observations upon these animals have shown that they are subject to a monthly discharge
of blood, at this time giving evidence of unusual salacity.

In the human female, near the time of puberty, there is sometimes a periodical sero-
mucous discharge from the genital organs, preceding, for a few months, the regular estab-
lishment of the menstrual flow. Sometimes, also, after the first discharge of blood, the
female passes several months without another period, when the second flow takes place,
and the menses then become regular. In a condition of health, the periods recur every
month, until they cease, at what is termed the change of life. In the majority of cases,
the flow recurs on the twenty-seventh or the twenty-eighth day; but sometimes the
interval is thirty days. As a rule, also, utero-gestation, lactation, and most severe dis-
eases, acute and chronic, suspend the periods ; but this has exceptions, as some females
menstruate regularly during pregnancy, and it is not very uncommon for the menses to
appear during lactation.

As we should naturally expect, from the connection between menstruation and ovu-
lation, removal of the ovaries, especially when this occurs before the age of puberty, is
usually followed by arrest of the menses. It is a well-known fact that animals do not
present the phenomena of heat after extirpation of the ovaries. Raciborski has quoted
cases of this operation in the human subject, in which the menses were arrested ; but
this rule does not appear to be absolute, as Dr. H. R. Storer reports at least one case, in
which menstruation continued with regularity for more than a year after removal of both
ovaries. Dr. T. G. Thomas, of New York, in three cases of removal of both ovaries
from menstruating women, which he followed for from five and a half months to two
years and eleven months after the operation, noted no return of menstruation. In one
case, nearly six months after the operation, the patient had " a bloody discharge from
the vagina and all the symptoms accompanying the menstrual function." When a cow
brings forth twins, one a male and the other apparently a female, the latter is called a
free-martin and generally has no ovaries. Hunter, in his paper on the tree-martin,
gives a full description of this anomalous animal and states that it dors not Lived or
show any inclination for the bull. In 1868, we had an opportunity of examining th.»
generative organs of a free-martin raised and killed by Prof. James R. Wood,
this animal, the uterus was rudimentary and there were no ovari.-.

A menstrual period usually presents three stages : first, invasion ; second, a wngtrim
ous discharge ; third, cessation.

The stage of invasion is variable in different females. There is usually, anterior to
the establishment of the flow, more or less of a feeling of general w -e «>f ful-

ness and weight in the pelvic organs, accompanied with a greater or less increase in tho

876 GENERATION.

quantity of vaginal mucus, which becomes brownish or rusty in color. It is probable
that, at this time, the discharge has a peculiar odor, though this point is somewhat diffi-
cult to determine. In the lower animals, at least, there is certainly a characteristic odor
during the rutting period, which attracts the male. At this time, also, the breasts be-
come slightly enlarged in the human female, showing the connection between these
organs and the organs of generation. This stage may continue for one or two days,
although, in many instances, the first evidence of the access of a period is a discharge
of blood.

When the general symptoms above indicated occur, the sense of uneasiness is usually
relieved by the discharge of blood. During this, the second stage, blood flows from the
vagina in variable quantity, and the discharge continues for from three to five days.
With regard to the duration of the flow, there are great variations in different individu-
als. Some women present a flow of blood for only one or two days ; while, in others,
the flow continues for from five to eight days, within the limits of health. A fair aver-
age, perhaps, is four days.1 It is also difficult to arrive at an approximation, even, of the
total quantity of the menstrual flow. Burdach estimated it at from five to six ounces.
According to Longet, this estimate is rather low, the quantity ordinarily ranging from
ten to twelve ounces, occasionally amounting to seventeen ounces, or even more. It is
well known that the quantity is exceedingly variable, as is the duration of the flow,
and the difficulties in the way of collecting and estimating the total discharge are
evident.

The characters of the menstrual flow are sufficiently simple. Supposing the discharge
to continue for four days, on the first day, the quantity is comparatively small ; on the
second and third, the flow is at its height ; and the quantity is diminished on the fourth
day. During this, the second stage, the fluid has the appearance of pure arterial blood,
not coagulated, and mixed, as has been shown by microscopical examination, with pave-
ment-epithelium from the vagina, cylindrical cells from the uterus, leucocytes, and a
certain amount of sero-mucous secretion. Chemical examination of the fluid does not
show any marked peculiarities, except that the quantity of fibrin is either not estimated
or is given as much less than in ordinary blood.

The mechanism of the haemorrhage, which will be considered more fully when we
come to study the changes in the uterine mucous membrane during menstruation,
is probably the same as in epistaxis. There is a rupture of small blood-vessels, prob-
ably capillaries, and blood is thus exuded from the entire surface of the membrane
lining the uterus, and sometimes from the membrane of the Fallopian tubes. The
blood is then discharged into the vagina and is kept fluid by the vaginal mucus.
The mucus of the body of the uterus is viscid and alkaline ; the mucus secreted at
the neck is gelatinous, viscid, tenacious, and also alkaline ; the vaginal mucus is decid-
edly acid, creamy, and not viscid, containing numerous cells of scaly epithelium, and
leucocytes.

The third stage, that of cessation of the menses, is very simple. During the latter
part of the second stage, the flow of blood gradually diminishes ; the discharge becomes
rusty, then lighter in color ; and, in the course of about twenty-four hours, it assumes
the characters observed in the intermenstrual period.

When the menstrual flow has become fully established, there is no very marked gen-
eral disturbance, except a sense" of lassitude, which may become exaggerated if the dis-
charge be unusually abundant. It has been noted, however, by Rabuteau, that, during
the menstrual period, the production of urea is diminished more than twenty per cent.,
that the pulse becomes slower, and that the temperature falls at least one degree (hal/'
a degree, centigrade).

1 Burdach makes the following statement with regard to certain conditions capable of modifying the menstrua?
flow : " The flow is more abundant in the indolent than in women accustomed to labor ; in those of feeble con
stitution than in those who enjoy robust health ; in inhabitants of cities than in inhabitants of villages."

MENSTRUATION.

877

Changes in the Uterine Mucous Membrane during Menstruation.— -If the mucous mem-
brane of the uterus be examined during the menstrual flow, it is found smeared with
blood, which sometimes extends into the Fallopian tubes. It is then much thicker and
softer than during the intermenstrual period. Instead of measuring about T^ of an inch
in thickness, as it does under ordinary conditions, its thickness is from | to i of an inch.
It becomes more loosely attached to the subjacent parts, is somewhat rugous, and the
glands are very much enlarged. At the same time, there are developed, in the substance
of the membrane, numerous spherical and fusiform cells. According to the recent and
very striking researches of Kundrat and Engelmann, this condition probably precedes the
discharge of blood by several days, during which time, the membrane is gradually pre-
paring for the reception of the ovum. One of the most important points in these re-
searches is that there is a fatty degeneration of the different elements entering into the
structure of the mucous membrane, including the blood-vessels, this change being most
marked at the surface; and it is on account of the weakened condition of the vascular
walls that the haemorrhage takes place. A short time after the flow has ceased, the
mucous membrane returns to its ordinary condition.

We have already noted that there is a considerable desquamation of epithelium from,
the uterus with the flow of blood, during the menstrual period. Sometimes, in normal
menstruation, the epithelium is in the form of patches ; and, in certain cases of dysmen-
orrhea, there is a membranous exfoliation, which has led to the idea that the mucous
membrane is actually thrown off. In normal menstruation, there is no true exfoliation
of the membrane, and, even in what is called membranous dysmenorrhea, the so-called
membrane is usually nothing more than a membraniform
exudation, secreted by the mucous surface.

Changes in the Graafian Follicles after their Rupture
(Corpus Luteum}. — After the discharge of an ovum, its d~
Graafian follicle undergoes certain retrograde changes, in-
volving the formation of what is called the corpus luteum.
Even when the discharged ovum has not been fecundated,
the corpus luteum persists for several weeks, so that, ovu-
lation occurring every month, several of these bodies, in
various stages of retrogression, may sometimes be seen in the ^
ovaries.

For a certain time anterior to the discharge of the ovum,
there is a cell-growth from the proper coat of the Graafian fol-
licle, and probably from the raembrana granulosa, with a pro-
jection of looped blood-vessels into the interior of the follicle,
which is the first formation of the corpus luteum. At the
time of rupture of the follicle, the ovum, with a great part
of the membrana granulosa, is discharged. Sometimes, at the
time of rupture of the follicle, there is a discharge of blond
into its interior ; but this is not constant, though we usually 2
have a gelatinous exudation, more or less colored with blood.
At the same time, the follicular wall undergoes hypertrophy,
and it becomes convoluted, or folded, and highly vascular.
This convoluted wall, formed by the proper coat of the fol-
licle, is surrounded by the fibrous tunic, and its thickening is most
est portion of the follicle. At the end of about three weeks, tin- body- wind
called the corpus luteum, on account of its yellowish or reddfch-yellow n,W- ha* o
at the height of its development and measures about half an inch ill depth b
three-quarters of an inch in length, its form being ovoid. The confuted wall then
contains a layer of large, pale, finely granular cells, which are internal and are

FIG. 9Sl.—&rtffm* of tiro cor-
pora lutea; natural tiM.

(Kolliker.)

1, corpus luteum eiirht days after
ciineeptiiin : ''. external coat
of the ovary : />. stroinii of the
ovarv: <'. convoluted wall of
Croatian follicle ; </, clot of

blood.

lid..; e. (1 >lori/ed H"t : .t\

lil.roll* envelope of tl.
luieuin.

878 GENERATION".

posed to be the remains of the epithelium of the follicle. The great mass of this wall,
however, is composed of large nucleated cells, containing fatty globules and granules
of reddish or yellowish pigmentary matter. The thickness of the wall is about one-
eighth of an inch, at its deepest portion.

After about the third week, the corpus luteum begins to retract ; its central portion
and the convoluted wall become paler, and, at the end of seven or eight weeks, a small
cicatrix marks the point of rupture of the follicle.

The above are the changes which occur in the Graafian follicles after their rupture
and the discharge of ova, when the ova have not been fecundated ; and the bodies thus
produced are called false corpora lutea, as distinguished from corpora lutea found after
conception, which are called true corpora lutea.

Corpus" Luteum of Pregnancy. — Before the process of spontaneous ovulation and its
connection with menstruation were understood, anatomists were unable to make a defi-
nite distinction between the corpus luteum following the discharge of an ovum without
fecundation, called the corpus luteum of menstruation, and the corpus luteum of preg-
nancy. Coste exactly described the various points of distinction between them ; and
his account of the differences in the development of these bodies, dependent upon the
non-fecundation or the fecundation of the ovum, is still regarded as entirely accurate and
answers the requirements of science at the present day, even in its medico-legal aspects,
as well as in 1849, when his observations were published.

"When a discharged ovum has been fecundated, the corpus luteum passes through its
various stages of development and retrogression much more slowly than the ordinary
corpus luteum of menstruation. It is then called, to distinguish it from the latter, the
true corpus luteum. We cannot do better than to quote, in the words of Coste, the
description of the changes which this body undergoes in pregnancy :

" I have followed, with the greatest care, in the pregnant female, all the phases of
this retrogression. This commences to be really appreciable toward the end of the third
month. During the fourth month, the corpus luteum diminishes by nearly a third, and
toward the end of the fifth, it is ordinarily reduced one-half. It still forms, however,
during the first days after parturition, and in the greatest number of cases, a tubercle
which has a diameter of not less than from f to £ of an inch. The tubercle afterward
diminishes quite rapidly ; but it is nearly a month before it is reduced to the condition
of a little, hardened nucleus, which persists more or less as the last vestige of a process
so slow in arriving at its final term. Nevertheless, there is nothing absolute in the retro-
grade progress of this phenomenon. I have seen women, dead at the sixth and even the
eighth month of pregnancy, present corpora lutea as voluminous as others at the fourth
month.

" Although, in general, it is only after parturition that the corpora lutea disappear,
it is nevertheless not without examples that they disappear much more promptly. I
have had the opportunity of examining the body of a woman, dead in the course of the
eighth month of pregnancy, in whom the absorption was already complete. Facts
of this kind are doubtless very rare, as only one has occurred in my observations,
notwithstanding the numerous researches to which I have devoted myself for a long
time. . . .

" There exists a notable difference between the corpora lutea which are formed as
the sequence of conception, and those which occur aside from the conditions developed
by impregnation. The duration of the former is much longer than that of the latter,
and the volume becomes, also, much more considerable, although their nature is, in truth,
identical. I have too often had occasion to remark this, in the ovaries of suicides, to
retain the slightest doubt in this regard."

The following table, quoted from Coste, shows the different stages of the corpus
luteum of pregnancy. It will be remembered that the corpus luteum of menstruation is
at its maximum of development at the end of about three weeks, when it measures half

MALE ORGANS AND ELEMENTS OF GENERATION. 879

an inch in depth by three-quarters of an inch in length, that it then begins to retract
and becomes a small cicatrix at the end of seven or eight weeks.1

Dimensions of the Corpus Luteum at different Stages.

Corpor
Long diameter.

a lutea.
Short diameter.

Observations.

I After parturition. Stages of pregnancy.

f25 to 30 days

f inch.

1 "
1 «
1 "
§ "

i '
i 4

i!

JL (

f "
1 ."

1 "

£ "
JL a

1 "

f "
f U

\ inch.

* "
£ "
t "
£ "

£ "
I "
£ "

1"

i «

1 "

t"
t"

1 "

I "

It is rare that a corpus lu-
teum assumes a spherical form,
and that, whatever be the sec-
tion, its diameters are equal, or
nearly so. It generally under-
goes, in its development, a sort
of compression in the same
way as does the ovary. Here,
only the long and the short
diameters, taken from a section
of the copora lutea, have been
measured, the ovary being di-
vided longitudinally, and, as
it is, generally figured in the
plates of the atlas.

• Double gestation.
• Double gestation.

About 40 days

2 months ...

3 months

In the 4th month

Idem

Idem. .

In the 5th month

5 months. ...

In the 6th month

7 months. . . .

In the 9th month

20 hours after .

3 days after -J

Idem •]

7 days after

Male Organs and Elements of Generation.

There is not the same physiological interest attached to the anatomical study of the
male genital ia, particularly the external organs, as there is to the corresponding parts
in the female, for the reason that the function of the spermatozoids is accomplished
within the female organs, where they unite with the ovum and where the processes of
development take place. The anatomy of the penis and urethra has a more exclusively
surgical interest. As physiologists, we have to study the testicles (organs which cor-
respond to the ovaries, and in which the male generative element is developed), the
various glandular structures which secrete fluids forming a part of the ejaculated semen,
the mechanism of erection, by which penetration of the male organ into the vagina is
rendered possible, the composition of the seminal fluid and the mechanism of its ejac-
ulation, and the course of the semen in the generative passages of the female until it is
brought in contact with and fecundates the ovum. As regards the penis, it will be suffi-
cient to describe, as we shall under the head of coitus, the mechanism of erection and
of the ejaculation of semen. It will be necessary, however, to study the structure of
the testicles and of the various glandular organs connected with the urethra, in order
to understand the development of the spermatozoids aud the composition of the seminal
fluid.

The Testicles.— The testicles are two symmetrical organs, situated, during a rvrtain
portion of intra-uterine life, in the abdominal cavity, but finally descending into the
scrotum. Within the scrotum, which is a pouch-like process of integument, are the

1 In 1851, Dr. J. C. Dalton published an essay on the " Corpus Luteum of Menstruation and Pregnancy." ir. which
he pointed out very accurately the different points of distinction between what had boon known as the false and t he-
true corpora lutea. These observations it is unnecessary to quote in detail, as the results wore almost idontical with
those obtained by Coste ; but they are peculiarly interesting, not only from the accuracy of the descriptions, but a*
they were made independently, and without any knowledge of the publication by Coste two years before.

880 GENERATION.

two testicles, with their coverings, vessels, nerves, etc. The skin of the scrotum encloses
both testicles, but is marked by a median raphe. Immediately beneath the skin, is a
loose, reddish, contractile tissue, called the dartos, which forms two distinct sacs, one
enveloping each testicle, the inner portion of these sacs fusing in the median line, to form
the septum. Within these two sacs, the coverings of each testicle are distinct. These
organs are, as it were, suspended in the scrotum by the spermatic cords, the left usually
hanging a little lower than the right. The coverings for each testicle, in addition to
those just mentioned, are the intercolumnar fascia, the cremaster muscle, the infundi-
buliform fascia, the tunica vaginalis, and the proper fibrous coat.

The tunica vaginalis is a shut sac of serous membrane, covering the testicle and epi-
didymis, and reflected from the posterior border of the testicle to the wall of the scrotum,
lining the cavity occupied by the testicle on either side, and also extending over the
spermatic cord. This tunic is really a process of peritoneum, which has become shut off
from the general lining of the abdominal cavity. The spermatic cord is composed of
the vas deferens, blood-vessels, lymphatics, and nerves, with the various coverings already
described, which expand and surround the testicle.

Beneath the tunica vaginalis, are the testicles, with their proper fibrous coat. These
organs are ovoid, and flattened laterally and posteriorly. " They are from an inch and
a half to two inches long, about an inch and a quarter from the anterior to the posterior
border, and nearly an inch from side to side. The weight of each varies from three-
quarters of an ounce to an ounce, and the left is often a little the larger of the two."
(Quain.) The proper fibrous coat is everywhere covered by the closely adherent tunica
vaginalis, except at the posterior border, where the vessels enter and the duct passes
out. At the outer edge of this border, is the epididymis, formed of convoluted tubes, pre-
senting a superior enlargement, called the globus major, a long mass running the length
of the testicle, called the body, and a smaller enlargement inferiorly, called the globus
minor. This, too, is covered with the tunica vaginalis. Between the membrane cover-
ing the testicle and epididymis and the layer lining the scrotal cavity, is a small quan-
tity of serum, just enough to moisten the serous surfaces. At the superior portion
of the testicle, we usually find one or more small, ovoid bodies, each attached to the
testicle by short, constricted processes, which are called the hydatids of Morgagni.
These have no physiological importance and are supposed to be the remains of foetal
structures.

The proper fibrous coat of the testicle is called the tunica albuginea. It is white,
dense, inelastic, measures about -fa of an inch in thickness, and is simply for the protec-
tion of the contained structures. Sections of the testicle, made in various directions,
show an imcomplete vertical process of the tunica albuginea, called the corpus Highmo-
rianum, or the mediastinum testis. This is wedge-shaped, about | of an inch wide at
its superior and thickest portion, is pierced by numerous openings, and lodges blood-
vessels and seminiferous tubes. From the mediastinum, numerous delicate, radiating
processes of connective tissue pass to the inner surface of the tunica albuginea, dividing
the substance of the testicle into imperfect lobules, which lodge the seminiferous tubes.
The number of these lobules has been estimated at from one hundred and fifty to two
hundred. Their shape is pyramidal, the larger extremities presenting toward the sur-
face, and the pointed extremities situated at the mediastinum.

Lining the tunica albuginea and following the mediastinum and the processes which
penetrate the testicle, is a tunic, composed of blood-vessels and delicate connective tissue,
called the tunica vasculosa, or pia mater testis.

Lodged in the cavities formed by the trabeculse of connective tissue, are the semi-
niferous tubes, in which the male elements of generation are developed. These tubes
exist to the number of about eight hundred and forty in each testicle and constitute
almost the entire substance of the lobules. The larger lobules contain five or six tubes,
the lobules of medium size, three or four, and the smallest frequently enclose but a single

MALE ORGANS AND ELEMENTS OF GENERATION.

881

tube. Each tube presents a convoluted mass, which can frequently be disentangled under
water, particularly if the testicle be macerated for several months in water with a little
nitric acid. The entire length of the tube, when thus unravelled, is about thirty in.-
and its diameter is from -gfa to Ti^ of an inch. It begins by from two to seven short,
blind extremities and sometimes by anastomosing loops. The csecal diverticula are found
usually in the external half of the tube, and their length is from -fa to £ of an inch. Tin-
anastomoses are sometimes between the tubes of different lobules, sometimes between
tubes in the same lobule, and sometimes between different points in the same tube. As
the tubes pass toward the posterior portion of the testicle, they unite into about twenty
straight canals, called the vasa recta, about TV of an inch in diameter, which penetrate
the mediastinum testis. In the mediastinum, the tubes form a close net-work, called the
rete testis; and, at the upper portion of the posterior border, they pass out of the
testicle, by from twelve to fifteen openings, and are here called the vasa efferentia.

Having passed out of the testicle, the
vasa efferentia form a series of small, con-
ical masses, which together constitute the
globus major, or head of the epididymis.
Each of these tubes, when unravelled, is
from six to eight inches long, gradually
increasing in diameter, until they all unite
into a single, convoluted tube, which forms
the body and the globus minor of the epi-
didymis. This single tube of the epididy-
mis, when unravelled, is about twenty feet
in length.

The walls of the seminiferous tubes in
the testicle itself are composed of connec-
tive tissue, a basement-membrane, and a
lining of granular, nucleated cells. In the
rete testis, it is uncertain whether the tubes
have a special fibrous coat or are simple
channels in the fibrous structure. They
are here lined with pavement-epithelium.
In the vasa efferentia and the epididymis,
we have a fibrous membrane, with longi-
tudinal and circular fibres of involuntary

FIG. 282.— Testicle and epididymi* of Vie human tub-
(Arnold.)

muscular tissue and a lining of ciliated

epithelium. The movement of the cilia is a testide . 6 & & jjobuies of the testicle; c, c, yasa rec-
to ward the vas deferens. In the lower ' ta; d,Vre'te testis ; «,«, vasa, .ff.-n-ntia ;/,//, cone,

of the globus major of the epidnlymis; ff, ff, epi-
didymis ; h, //, *M ih-fi-n-ns ; /. vas aberrans : »i. HI.
branches of the spermatic art.-ry t.. th- testicle an.l
I'nididvinis : ;,. n. n. nuninVati.m of th«- Vterj upon
th- testicle; <-. d.-f.-n-ntial artrry: j: anastomosis of
the deferential with the spermatic artery.

portion of the epididymis, the cilia are ab-
sent. The tubular structures of the testicle,
the epididymis, and the commencement of
the vas deferens are shown in Fig. 282.

At the lower portion of the epididymis, communicating with the canal, there i
usually found a small mass, formed of a convoluted tube of variable K-n-t
vas aberrans of Ilaller. (i, Fig. 282.) This is sometimes wanting, and i
which cannot be very important, is unknown.

Vas Deferens.— The excretory duct of the testicle extends from the epididymis to t
prostatic portion of the urethra' and is a continuation of the sin-le ti.K- win
body and globus minor of the epididymis. It is somewhat tortuous lu-ar
becomes larger at the base of the bladder, just before it is joined by the <
nal vesicle. Near its point of junction with this duct, it becomes narro
length is nearly two feet.
56

otire

882

GENERATION.

The course of the vas deferens is in the spermatic cord to the external abdominal
ring, through the inguinal canal to the internal ring, where it leaves the blood-vessels,
passes beneath the peritoneum to the side of the bladder, then along the base of the
bladder by the inner side of the seminal vesicle, finally joining the duct of the seminal
vesicle, the common tube forming the ejaculatory duct, which opens into the prostatic
portion of the urethra.

The walls of the vas deferens are thick, abundantly supplied with vessels and nerves,
and provided with an external fibrous, a middle muscular, and an internal mucous coat.
The greater part of that portion of the tube which is connected with the bladder is dilated
and sacculated. The fibrous coat is composed of strong connective tissue. The muscular
coat presents three layers ; an external, rather thick layer of longitudinal fibres, a thin,
middle layer of circular fibres, and a thin, internal layer of longitudinal fibres, all of the
non-striated variety. By the action of these fibres, the vessel may be made to undergo
energetic peristaltic movements, and this has followed galvanization of that portion of
the spinal cord corresponding to the fourth lumbar vertebra, which is described by Budge
as the genito-spinal centre.

The mucous membrane of the vas deferens is pale, thrown into longitudinal folds in
the greatest part of the canal, and presents numerous additional rug& in the sacculated
portion, these rug& enclosing little, irregular, polygonal spaces. The membrane is cov-
ered with columnar epithelium, which is not ciliated. In the sacculated portion, are
numerous mucous glands.

Attached to the vas deferens, near the head of the epididymis, is a little mass of con-
voluted and sacculated tubes, called the organ of Giraldes, or the corpus innominatum.

This body is from £ to % of an inch long and
-^z of an inch broad. Its tubes are lined with
cells of pavement-epithelium, which are often
filled with fatty granules. Generally, the tubes
present only blind extremities, but some of
them occasionally communicate with the tubes
of the epididymis. This organ has no physio-
logical importance. It is regarded by Giraldes
as a remnant of the Wolffian body, analogous
to the parovarium.

Vesiculm Seminales. — Attached to the base
of the bladder and situated externally to the
vasa deferentia, are the two vesicul® semi-
nales. These bodies are each composed of a
coiled and sacculated tube, from four to six
inches in length when unravelled, and some-
what convoluted, in the natural state, into an
ovoid mass which is firmly bound to the vesical
wall. The structure of the seminal vesicles is
not very unlike that of the sacculated portion
of the vasa deferentia. They have an external
fibrous coat, a middle coat of muscular fibres,
and a mucous lining. Muscular fibres pass
over these vesicles from the bladder, both in a longitudinal and in a circular direction,
and serve as compressors, by the action of which their contents may be discharged. The
mucous coat is pale, finely-reticulated, and is covered with cells of polygonal epithelium,
nucleated and containing brownish granules. No mucous glands have been found in its
substance.

The vesiculas seminales undoubtedly serve, in part at least, as receptacles for the

FicK 283. — Vas deferens, vesicular serninales, and

qjaculaiory ducts. (Lie«,reois.)
a, vas deferens ; 6, seminal vesicle ; c, ejaculatory

duct ; c7, termination of the ejaculatory duct ;

«, opening of the prostatic utricle ; /, g, varu

montanum ; A, I, prostate.

MALE ELEMENTS OF GENERATION. 883

seminal fluid, as their contents often present a greater or less number of sperm atozoids.
Although the mucous membrane of the vesicles seems to produce an independent s.
tion, the presence of glands has not been demonstrated. The fact that the fluid capable
of fecundating the ovum is produced only by the testicles, that the spermatozoids are
the true fecundating elements of the male, and that these are developed in the testicles,
shows that the spermatozoids found in the seminal vesicles pass into their cavity from the
vasa deferentia.

The ejaculatory ducts are formed by the union of the vasa deferentia with the ducts
of the vesicula3 seminales on either side and open into the prostatic portion of the urethra.
Except that their coats are much thinner, they have essentially the same structure as the
vasa deferentia.

Prostate.— Surrounding the vesical extremity of the urethra, including what is known
as its prostatic portion, is the prostate gland, or body. This organ, except as it secretes
a fluid which forms a part of the ejaculated semen, has chiefly a surgical interest, so that
it is unnecessary to describe minutely its form and relations. It is enveloped in an
exceedingly dense, fibrous coat, contains many glandular structures opening into the
urethra, and presents a great number of n on -striated, with a few striated muscular fibres
some just beneath the fibrous coat and others penetrating its substance and surrounding
the glands.

The glands of the prostate are most distinct at that portion which lies behind the
urethra. In the posterior portion of this canal, are found about twenty openings, which
lead to tubes ramifying in the glandular substance. These tubes are formed of a struct-
ureless membrane, branching as it penetrates the gland. They present hemispherical
diverticula in their course, and terminate in dilated extremities, which are looped and
coiled. In the deeper portions of the tubes, the epithelium is columnar or cubical, becom-
ing tesselated near their openings, and sometimes laminated.

The prostatic fluid is probably secreted only at the moment of ejaculation. Its char-
acters will be considered under the head of the seminal fluid ; but we may here note
that it has been thought by Kraus, that the prostatic fluid has the important function of
maintaining the vitality of the spermatozoids. " The spermatozoa, in the absence of the
prostatic fluid, cannot live in the mucous membrane of the uterus of mammalia ; but
with its aid they may live for a long time in the uterine mucus, often more than thirty-
six hours."

Glands of the Urethra. — In front of the prostate, opening into the bulbous portion of
the urethra, are two small racemose glands, called the glands of M6ry or of Cowper.
These have each a single excretory duct, are lined throughout with cylindrical epithe-
lium, and secrete a viscid, mucus-like fluid, which forms a part of the ejaculated scinon.
Sometimes there exists only a single gland, and occasionally, though rarely, both are
absent. Their function is probably not very important.

The glands of Littre, found throughout the entire urethra and most abundant on its
anterior surface, are simple racemose glands, extending beneath the mucous nuinbrane
into the muscular structure, presenting here four or five acini. As these acini are
surrounded by muscular fibres, we can readily understand how their secretion \\\^\
pressed out during erection of the penis. They are lined throughout with cc.lmnnar
or conoidal epithelium, and secrete a clear and somewhat viscid mucus, which is mixed
with the ejaculated semen.

Male Elements of Generation.

The ejaculated seminal fluid contains the male elements of generation; hut it
be remembered that the complex fluid known as the semen is composed of anat<
elements developed in the testicle itself, mixed with the secretion of the r*M d, :, ; vntia,

884 GENERATION.

of the vesiculse seminales, of the glands of the prostate, and of the glands of the urethra,
As we shall see when we come to discuss the mechanism of fecundation of the ovum, the
spermatozoids are the essential male elements, and these are produced in the substance
of the testicle, by a process analogous to that of the development of other true anatomi-
cal elements, and not by the mechanism with which we are familiar in secreting glands.
The testicles cannot be regarded strictly as glandular organs. They are analogous to the
ovaries, and they are the only organs in which spermatozoids can be developed, as the
ovaries are the only organs in which the ovum can be formed. If the testicles be absent,
the power of fecundation is lost, none of the fluids secreted by the accessory organs of
generation being able to perform the functions of the true fecundating elements.

In the healthy male, at the climax of a normal venereal orgasm, from half a drachm
to a drachm of seminal fluid is ejaculated with considerable force from the urethra, by an
involuntary muscular spasm. This fluid is slightly mucilaginous, grayish or whitish,
streaked with lines more or less opaque, and it evidently contains various kinds of mucus.
It has a faint and peculiar odor, sui generis, which is observed only in the ejaculated
fluid and not in any of its constituents examined separately. It is a little heavier than
water and does not mix with it or dissolve. After ejaculation, it becomes jelly-like and
dries into a peculiar, hard mass, which may be softened by the application of appropriate
liquids. The liquid is not coagulated by heat and does not contain albumen. Its reac-
tion is faintly alkaline. It contains, in the human subject, from 100 to 120 parts of solid
matter per 1,000.

The chemical constitution of the semen has not been very thoroughly investigated
and does not present the same physiological interest as its anatomical characters. Aside
from the anatomical elements derived from the testicles and the genital passages, it pre-
sents an organic principle (spermatine) which has nearly the same chemical characters as
ordinary mucosine. It also contains a considerable quantity of phosphates, particularly
the phosphate of magnesia. During desiccation, the characteristic crystals of this salt
usually make their appearance ; and, in the decomposed fluid, we frequently find crystals
of the triple phosphates.

The composite character oi the seminal fluid will be better understood if we examine
briefly the properties of the different mucous secretions which enter into its composition.

In the dilated portion of the vasa deferentia, the mucous glands secrete a fluid which is
the first that is added to the spermatozoids as they come from the testicles. This fluid is
brownish or grayish. 'It contains epithelium, and small, rounded granulations, which are
dark and strongly refractive. The liquid itself is very slightly viscid. In the vesiculee semi-
nales, there is a more abundant secretion of a grayish fluid, with epithelium, little color-
less concretions of nitrogenized matter, called by Robin, sympexions, and a few leucocytes.
The glandular structures of the prostate produce a creamy secretion, which contains nu-
merous fine granulations. It is chiefly to the admixture of this fluid that the semen owes
its whitish appearance. Finally, as the semen is ejaculated, it receives the exceedingly
viscid secretion of the glands of Cowper, a certain amount of stringy mucus from the
follicles of the urethra, with, perhaps, a little of the urethral epithelium.

Anatomically considered, the seminal fluid contains no important elements except the
spermatozoids, the various secretions we have mentioned serving simply as a vehicle for
the introduction of these bodies into the generative passages of the female. We shall
therefore consider only the structure of the spermatozoids, their movements, and the pro-
cess of their development.

Spermatozoids. — In August, 1677, a German student, named Yon Hammen, discov-
ered the spermatozoids in the human semen, and exhibited them to Leeuwenhoek, who
studied them as closely as was possible with the instruments at his command. For along
time, they were regarded as living animalcules; though now they are considered simply
as peculiar anatomical elements, endov/cd with movements, like ciliated epithelium.

MALE ELEMENTS OF GENERATION. 885

These elements are developed within the seminiferous tubes; and they differ, not so much
in their mode of development, as in their form, in different animals. AVe shall describe,
however, only the spermatozoids of the human subject.

If we examine a specimen of the fluid taken from the vesicular seminales of an adult
who has died suddenly, or the ejaculated semen, we find that it contains, in addition to
the various accidental or unimportant anatomical elements which we have mentioned,
innumerable bodies, resembling animalcules, which present a flattened, conoidalhead and
a long) tapering, filamentous tail. The caudate appendage is in active motion, and the
spermatozoids move about the field of view with considerable rapidity and force, pushing
aside little corpuscles or granules with which they come in contact. This is supposed to
be an indication of the vitality of the spermatozoids, which are not thought to be capable
of fecundating the ovum after their movements
have ceased. Under favorable conditions, par-
ticularly in the generative passages of the fe-
male, the movements continue for days ; and
this fact is important, as we shall see here-
after, in its bearing upon the limits of the time
of fecundation.

Microscopical examination does not reveal
any very distinct structure in the substance
of the spermatozoids. The head is about
WTO of an inch long, ^Vs of an incn broad,
and Yvfans °f an mcn m thickness. The tail
is about ^i¥ of an inch in length. La Vallette
St. George has found, in man and many of the
inferior animals, the "intermediate segment"
described first by Schweigger-Seidel, though

•L-. M.t a v • 0-11 .4.1 * FIG. 284 — Human spermatotolds ; magnified 800

he does not agree with Schweigger-Seidel that diameters. (Luschka.)

this portion is motionless. The length of the

intermediate segment is about ^Vs of an inch. It is usually described as the beginning

of the tail ; and the only difference between this and other portions is that it is a little

thicker.

Water speedily arrests the movements of the spermatozoids, which may be restored
by the addition of dense saline and other solutions. All of the alkaline animal fluids of
moderate viscidity favor the movements, while the action of acid or of very dilute solu-
tions is unfavorable. The movements are suspended by extreme cold, but they return
when the ordinary temperature is restored.

Before the age of puberty, the seminiferous tubes are much smaller than in the adult,
and they contain small, transparent cells, which, in their form and arrangement, resemble
epithelium. As puberty approaches, however, the tubes become larger, and the evil-con-
tents increase in size. At this time, there seem to be two kinds of cells; an epithelium,
in the form of irregularly-shaped cells, lining the tubes, and rounded cells containing one
or more nuclei, some of the cells appearing to be in process of iegmentRtioiL Many o
the cells lining the tubes present a rounded portion, with a lanre, clear nucleus appIU
the tube-wall, each with a caudate prolongation projecting into the tube,
the projections from the different cells anastomose with each other, forming a k;
work. In the central portions of the tubes of the adult, are rounded v,
rf, of an inch in diameter, each containing from two to twenty transparent nnc
uring from ^ to ^ of an inch. In these, which are called the iemind C
boid movemlnte havSbTen observed. The large vesicles with multiple nuclei are th, „
of development of the spermatozoids. The nuclei of the veriota appeal-
formed into the heads of the spermatozoids, and the filamentous appendages, winch ar,
seen in the vesicles in various stages of formation, are developed gradually.

886

GENERATION.

occurs that, when from ten to twenty spermatozoids are developed in a single vesicle, the
heads and tails are arranged regularly, side by side ; but, when only two or three are ob-
served, their arrangement is irregular. The vesicular envelopes finally disappear and the
spermatozoids are liberated ; but this occurs only in the rete testis and in the epididymis.
In the epididymis and the vasa deferentia, the spermatozoids are motionless, though they
are not enclosed in vesicles, apparently from the density of the substance in which they
are embedded ; for movements are sometimes presented when the contents of the vasa
deferentia are examined with the addition of water or saline solutions. Once in the
vesiculse seininales, or after ejaculation, the spermatozoids are invariably in active motion.

Fie. 285.— Development of the spermatozoids in the rabMt. (Liegeois.)

a, a, spermatozoids ; ft, spermatic cell containing thirteen nuclei, two of which contain each a head of a spermatozoid
developed; c, spermatic cell containing two secondary cells, each one provided with a nucleus from which two
epermatozoids are to be developed ; ef,/, spermatic cells, each with one nucleus; «, spermatic cell containing a
secondary cell with a nucleus ; A, bundle of spermatozoids.

The semen, thus developed and mixed with the various secretions before mentioned, is
found during adult life and even at an advanced age ; and, under physiological condi-
tions, it contains innumerable spermatozoids in active movement. But if sexual inter-
course be frequently repeated at short intervals, the ejaculated fluid becomes more and
more transparent, homogeneous, and scanty, and it may consist of a small amount of secre-
tion from the vesiculse seminales and the glands opening into the urethra, without sper-
matozoids, and consequently deprived of fecundating properties.

In old men, the seminal vesicles may not contain spermatozoids ; but this is not always
the case, even in very advanced life. Instances are constantly occurring of men who
have children in their old age, in which the paternity of the offspring can hardly be
doubted. Duplay, in 1852, examined the semen of a number of old men, and found, in
about half the number, spermatozoids, normal in appearance and quantity, though, in
some, the vesiculse seminales contained either none or very few. Some of the individu-
als in whom the spermatozoids were normal were between seventy-three and eighty-two
years of age. More recently, M. A. Dieu has investigated the same question. In his
conclusions, adding to his own observations the fifty-one cases noted by Duplay, he gives
the following results, in one hundred and fifty-six old men :

" 25 sexagenarians gave a proportion, still presenting spermatozoids, of 68'5 per 100.

COITUS. g§7

" 76 septuagenarians gave a proportion, still presenting spermatozoids of 59-5 per
100.

"51 octogenarians gave a proportion, still presenting spermatozoids, of 48 per 100.

" 4, having passed the age of ninety years, gave entirely negative results."

The oldest man, in the cases reported by Duplay, was eighty-two, and, in those
noted by Dieu, eighty-six years, which latter Dieu fixes as the limit, not having observed
spermatozoids after that age. The observations were made by examining the contents of
the generative passages twenty -four hours after death. Some of the subjects died of
acute, and others, of chronic diseases ; but the mode of death did not present any differ-
ences in the cases classed with reference to the presence of spermatozoids. As a result
of his own and other investigations, Dieu comes to the conclusion that the power of
fecundation in the male often persists for a considerable time after copulation has become
impossible simply from incapacity for erection of the penis.

CHAPTER XXVII.

FECUNDATION AND DEVELOPMENT OF TUE OVUM.

Coitus — Action of the male — Action of the female — Entrance of spermatozoids Into the uterus— Course of the sper-
matozoids through the female generative passages — Mechanism of fecundation — Determination of the sex of
offspring— Hereditary transmission— Superfecundation— Influence of the maternal mind on offspring— Union of
the male with the female element of generation— Passage of the spermatozoids through the vitelline membrane
— Deformation and gyration of the vitellus — Polar globule — Vitelline nucleus — Segmentation of the vitellus—
Primitive trace of the embryon— Blastodermic layers— Formation of the membranes— Amniotic fluid— Umbili-
cal vesicle— Formation of the allantois and the permanent chorion- Umbilical cord— Membranse decidme—
Development and structure of the placenta — General view of the development of the embryon— Development
of the cavities and layers of the trunk in the chick — External blastodermic membrane— Intermediate mem-
brane, in two layers— Internal blastodermic membrane— Neural canal— Chorda dorsalis— Primitive aortse— Ver-
tebrae—Origin of the Wolffian bodies— Pleuro-peritoneal cavity— Development of the skeleton— Development of
the muscles — Development of the skin — Development of the nervous system — Development of the encephalon
— Development of the organs of special sense— Development of the alimentary system— Formation of the me-
sentery—Formation of the stomach— Development of the large intestine— Formation of the pharynx and oesopha-
gus— Development of the anus — The liver, pancreas, and spleen — Development of the respiratory system— De-
velopment of the face — Development of the teeth — Development of the genito-urinary system — Development
of the Wolffian bodies— Ducts of the Wolffian bodies and ducts of Muller-Development of the testicles and
ovaries — Development of the urinary apparatus — External organs of generation — Hormaphroditism— Develop-
ment of the circulatory system— First, or vitelline circulation— Second, or placental circulation— Branchial arches
and development of the arterial and the venous system— Development of the heart— Description of the foetal
circulation— Third, or adult circulation.

Coitus.

As far as the male is concerned, coitus is rendered possible by erection of the penis.
This may occur before puberty, but, at this time, intercourse cannot be fruitful. As we
have seen in a previous chapter, coitus may be impossible in old age, from absence of the
power of erection ; but spermatozoids may still exist in the vesicular seminaU-s, and
fecundation might occur, if the seminal fluid could be discharged into the generative pas-
sages of the female. Coitus may take place in the female before the age of puberty or
after the final cessation of the menses, but intercourse cannot then be fruitful. T
are sufficiently numerous examples of conception following what woul.l be called imper-
fect intercourse, as in cases of unruptured hymen, deformities of the male or-
to show that the actual penetration of the male organ is not essential, and that ferimd.i-
tion may occur, provided the seminal fluid find its way into even the lower part of the
vagina. Conception has also followed intercourse, when the female haa been Insensible
or entirely passive ; but we shall consider only the physiology of complete and nor:
intercourse, when both the male and female participate, more or less, in the sexual act.

888 GENERATION.

Action of the Male. — The act of sexual intercourse is preceded, in the male, by a
longer or shorter period of excitement, the most important manifestation of which is
erection and rigidity of the penis. This is largely controlled by the nervous system. It
may be due to distention of the vesiculae seminales, and, perhaps, of the tubes of the
testicle and epididymis after prolonged continence, to the imagination, or to the presence
or thought of a female exciting desire. The excitement may, also, be arrested by a sud-
den feeling of disgust, modesty, or fear ; and it sometimes happens that the erethism
is so intense that the male organ becomes flaccid without ejaculation. An occurrence of
this kind frequently occasions such an amount of mortification and apprehension for the
future, that, from the mere dread of a similar accident, there is frequently an incapacity
for intercourse when, in all other respects, the conditions are absolutely normal. Physi-
cians have frequent occasion to observe this, especially in the newly-married, who are
often afflicted with the fear of permanent sexual incapacity and seek professional advice.
This illustrates the influence of the nervous system upon the sexual organs, in the ab-
sence of diseased conditions.

Unlike certain of the lower animals, the human subject presents no distinct perio-
dicity in the development of the spermatozoids ; but, in reiterated connection, excite-
ment and an orgasm may occur when the ejaculated fluid has no fecundating properties.
Such frequently-repeated sexual acts are abnormal ; but, from a purely physiological
point of view, prolonged continence is equally unnatural and may react unfavorably on
the nervous system. No absolute or even approximative rule can be laid down with re-
gard to the frequency with which intercourse may take place within physiological limits.
We may assume that these conditions are fulfilled, first, when intercourse is confined
within the limits of legitimacy, after the unusual excitement of novelty has passed ;
second, when both the male and female are in perfect health, and no undue degree of
lassitude follows coitus, after a proper period of repose ; third, when there is no marked
diminution of sexual desire, except that which may be accounted for by age ; fourth,
when pregnancy occurs at proper intervals, progresses normally, and is followed by the
normal period of lactation ; fifth, when menstruation is regular, and when there is a
period, usually after the cessation of the flow, during which there is unusual sexual ex-
citement, responded to by the male, and disappearing after the sexual desires have been
satisfied. It may be somewhat rare to find these conditions fulfilled in all respects, as so
few men and women in civilized life are absolutely normal during adult age, and as the
sources of unnatural sexual excitement are so numerous ; but they approximative^ rep-
resent the physiological performance of the generative functions in both sexes. It is true
that the female can frequently endure sexual excesses better than the male, because she
is more passive, and may often not participate in the venereal excitement ; but, if we
assume that intercourse is physiologically confined within the limits fixed by social laws,
the same rules as regards frequency of the sexual act should apply to both. It is certain
that intercourse is not normal in the female during menstruation or during the greater
part of the period of utero-gestation ; and, at these times, it is physiological that the male
should be continent. Taking our view chiefly from what appear to be the sexual require-
ments of the female, intercourse most properly takes place at the time following the men-
strual flow, when there is usually a certain amount of sexual excitement, and this should
not be immediately repeated, though it may be physiological after a few days. As sexual
excitement is gratified and diminishes, intercourse, as far as the desires of the female are
concerned, is suspended, and it does not take place to any great extent during pregnancy.
This seems to correspond with the normal progress of the generative functions, as we
have traced it in the female. It is evident that this is a subject of great delicacy and
one that is with difficulty brought to the requirements of rigid scientific inquiry; still
it can hardly be avoided in a full account of the physiology of generation, and it is a
question often presented to the practical physician.

Although we have not yet considered fully the mechanism of erection, but little re-

COITUS. 889

mains to be said upon this subject after our discussion, in connection with the circulatory
system, of the general structure of erectile tissues. The cavernous and spou.
of the penis are usually taken as the type of erectile organs. In these parts, the art
are large, contorted, provided with unusually thick muscular coats, and connected with
the veins by vessels considerably larger than the true capillaries. They are supported
by a strong fibrous net-work of trabeculse which contains non-striated muscular fibres ;
so that, when the blood-vessels are completely filled, the organ becomes enlarged and
hardened and can penetrate the vagina. Researches upon the nerves of erection show con-
clusively that the vessels of erectile tissues are distended by an enlargement of the
arterioles of supply, and that there is not simply a stasis of blood produced by constric-
tion of the veins, except, perhaps, for a short time, during the period of most intense
venereal excitement. In experiments upon dogs, Eckhard discovered a nerve derived
from the sacral plexus, stimulation of which produced an increase in the flow of blood
through the penis, attended with all the phenomena of erection. This nerve arises by
two roots at the sacral plexus, from the first to the third sacral nerves. In the experi-
ments referred to, by a comparison of the quantity of venous blood coining from the
penis before and during the stimulation of the nerve, Eckhard found a great increase
during erection. It is probable that, in addition to the arterial dilatation, when the penis
attains its maximum of rigidity, there is a certain amount of obstruction to the outflow
of blood, by compression of the veins, and that the rigidity is increased by contraction
of the trabecular muscular fibres of the corpora cavernosa.

During erection, the penis becomes exquisitely sensitive, especially at the glans ; and the
introduction of the organ into the vagina, pressure by the constrictor muscle, and friction,
increase this sensibility, until the venereal orgasm occurs. At this time, there is a pecul-
iar and indefinable sensation, almost immediately followed by spasmodic contractions of
the vesiculge seminales and the ejaculatory muscles, and, at the climax of the orgasm, the
semen is forcibly discharged from the urethra. This is followed by a feeling of lassitude,
a general sense of fatigue of the generative organs, flaccidity of the penis, and it is some
time before the venereal appetite can be again excited. Although this is the physiolo-
gical mechanism of a seminal discharge, friction of the- parts is not absolutely necessary,
as is shown by the occurrence of orgasm during sleep, which is liable to take place in
healthy men after prolonged continence.

After the seminal fluid has been ejaculated during intercourse, the generative act, as
far as the male is concerned, is accomplished. It now remains for us to study the action
of the female and the process by which the spermatozoids are brought in contact with
the ovum.

Action of the Female.— If we can credit the statements made to physicians in their
professional intercourse — and we have few other reliable sources of information — there
are some females, in whom the generative function is performed, even to the extent <>t'
bearing children, who have no actual knowledge of a true venereal orpism: but there
are others who experience an orgasm fully as intense as that which accompanies ejacula-
tion in the male. There is, therefore, the important difference in the sexes, that prelimi-
nary excitement and an orgasm are necessary to the performance of the <,-vn.-rati\ .
in the male, but are not essential in the female. Still, there can bo <canvly a «b.ubt but
that venereal excitement in the female facilitates conception, other conditions I .
favorable.

The first intercourse in the female is usually more or loss painful, on nemiint of
ture of the hymen, and the external organs are unduly sensitive until tho parts are
healed. After this, if there bo a preliminary excitement there i> a certain u
erection of the clitoris (which corresponds to the penis) and of tho erectile bulb;
at the vaginal orifice. There is also an increase in the secretions about these parts ai
there may be an ejaculation from two glands opening near the labia mm..:-

890 GENERATION.

glands of Bartholinus, which correspond to the glands of Cowper in the male. How far the
internal erectile parts participate at this time, it is difficult to determine. By the friction
against the clitoris — which, at its maximum of erection, is directed toward the axis of the
vagina — against the vaginal walls, and probably, also, by the contact of the glans penis
with the neck of the uterus, the excitement of the female increases, the vessels of the
vagina become turgid, the secretion of mucus by the external organs becomes abundant,
and this finally culminates in an orgasm, similar to that experienced by the male, with a
farther increase in the secretion of the glands at the vaginal orifice. As we have stated
in our account of the discharge of the ovum from the Graafian follicle, this congestion
and excitement may hasten the rupture of a ripe follicle in the human female, as it un-
doubtedly does in many of the lower animals ; but follicles certainly rupture indepen-
dently of coitus. There is a certain degree of lassitude in the female following sexual
intercourse, but this is usually not so marked or so prolonged as in the male.

The most important physiological point in this connection is with regard to the prob-
able action of the internal organs of the female during sexual excitement. We have al-
ready studied what has been described as the erectile tissue of the uterus and ovaries.
Whether this be or be not a true erectile tissue, seems to be rather a question of defini-
tion. The blood-vessels certainly have an erectile arrangement; still, they are not
enclosed by those distinct, fibrous trabeculse which are observed in the penis. In the
body of the uterus and in the ovaries, the idea of erection during sexual excitement
rests simply upon anatomical descriptions and artificial distention of the vessels after
death, and the parts cannot be investigated during life ; but it is different with the neck
of the uterus, as we shall see farther on ; and, upon this point, we may refer to a very
remarkable paper, by Dr. Joseph R. Beck (8t. Louis Medical and Surgical Journal, 1872J,
which is interesting from the fact that a somewhat similar observation was made by
Litzmann, in 1846. We do not vouch for the accuracy of the observations by Dr. Beck,
but, when we consider that it has been positively demonstrated that spermatozoids find
their way to the surface of the ovaries, we can appreciate the importance of observations
with regard to the action of the internal organs during coitus.

August 11, 1872, Dr. Beck was called to see a lady, thirty-two years of age, of ner-
vous temperament, blonde, married eight years, with one child, a son, living and seven
years old. She had an abortion six years before, and has suffered from symptoms indi-
cating uterine disease ever since. She commenced to menstruate at the age of fourteen.
Examination with the finger showed that the os uteri was just inside the vulva, and
Mclntosh's stem-pessary was introduced. The rest of the history, as the observation is
so remarkable, we quote in full :

" Calling at the residence of the patient next day, for the purpose of adjusting the
uterine supporter, I made an examination by the touch, and upon introducing my finger
between the pubic arch and the anterior lip of the prolapsed cervix, I was requested by
her to be very careful in manipulating those parts, as she was very prone, by reason of
her passionate nature, to have the sexual orgasm produced by a very slight contact of the
finger. Indeed, she stated that this had more than once occurred to her, when making
digital investigation of herself. Here then was an opportunity never before offered any
one to my knowledge, and one not to be lost on any consideration. Carefully separating
the vulvaa with my left hand, so that the os uteri was brought clearly into view in a
strong light, I swept the right forefinger across the cervix twice or three times, when
almost immediately the orgasm occurred, and the following is what was presented to my
view:

"The os and cervix uteri had been firm, hard, and generally in a normal condition,
with the os closed so as not to admit the uterine probe without difficulty ; but immedi-
ately the os opened to the extent of fully an inch, made five or six successive gasps, draw-
ing the external os into the cervix each time powerfully, and at the same time becoming
quite soft to the touch. All these phenomena occurred within the space of twelve sec-

COITUS. 891

onds time certainly, and in an instant all was as before ; the os had closed, the cervix
hardened, and the relation of the parts had become as before the orgasm.

"Now I carefully questioned my patient as to the nature of the sensations experienced
by her at the period of excitement, and she was positive that they were the same in quali-
ty as they ever were during coition, even before the occurrence of the prolapse ; but ad-
mits that they were not exactly the same in quantity, believing that during coition the
orgasm had lasted longer, although not at all or in any respect different as to sensation.
I had almost forgotten to make mention of the intense congestion of the parts during the
'crisis,' and introduce the statement here."

Certainly, the description we have just quoted is sufficiently graphic, and the mechan-
ism of the penetration of spermatozoids into the uterus, if this be the action of the cervix
during an orgasm, seems simple enough; but it cannot explain fecundation, when it
occurs, as it undoubtedly may, without orgasm. In physiological literature, we find a
number of allusions to a suction force exerted by the uterus during coitus, but this is moat
frequently stated as of possible or probable occurrence, without being sustained by any
positive observations. Still, as early as 1846, we find a direct observation, recorded by
Litzmann, as follows :

" I myself lately had the opportunity, in an internal exploration of a young and very
erethistic female, of observing that suddenly the uterus assumed a more perpendicular
position, was drawn more deeply into the pelvis, the lips of the os uteri immediately
became separated, the os became rounded, softer and accessible to the finger, and imme'
diately the highest sexual excitement was betrayed by the respiration and voice."

In considering the mechanism of the penetration of spermatozoids into the uterus, it
is also necessary to take into account the secretions, particularly of the mucous glands at
the neck. Most writers of the present day admit that, during the height of the orgasm,
there is an ejaculation from the uterus of a small amount of alkaline mucus. That an
erection of the cervix, followed by sudden relaxation and opening of the os, may occur,
cannot be doubted, and there is no evidence of a muscular action in the uterus sufficient
to project this fluid forcibly, as the semen is discharged by the male. Assuming that the
views just stated be correct, we can readily understand how the neck may be erected and
hardened during the orgasm, extruding an alkaline mucus, that the semen is ejaculated
forcibly toward the uterus and becomes mixed with the mucus, and that the sudden
relaxation of the cervix and opening of the os may exert a force of aspiration and thus
draw in the fecundating elements. Certain it is that spermatozoids may be found in the
mucus of the cervix a very short time after coitus. It is possible, also, that a sexual con-
nection may be occasionally even more intimate, and that a portion of the glans penis
may be actually embraced by the dilated cervix, though this must be unusual. This
latter idea of the establishment of a "continuous canal" during intercourse is one that
was advanced by many of the older writers.

Quite a strong argument in favor of the view that the spermatozoids are imprisoned,
as it were, in the cervical mucus soon after ejaculation, is the fact that vaginal injections
immediately after intercourse, which are frequently resorted to to prevent conception,
often fail to produce the desired result, even when they are so thorough :;s t<> wash out
the vagina completely.

While we must accept as probable the view that the uterus may draw into tl,
an alkaline mucus previously ejaculated, and with it a certain amount of seminal tl
the fact that conception may take place without orgasm on the part of the female, ninl
even without complete penetration of the male organ, shows that the action i
described is not absolutely essential, and that the semen may find it- way into the i
in some other way, which it is certainly very difficult to explain.

Course of tlte Spermatozoids tlirougli the Female Genemtire ftttoptt.— Th<
tozoids, once within the cervix uteri, and in contact with the alkaline mucus, w

892 GENERATION.

Increases the activity of their movements, may pass through the uterus, into the Fallo-
pian tubes, and even to the surface of the ovaries. Precisely how their passage is
effected, it is impossible to say. We can attribute it only to the movements of the sper-
matozoids themselves, to capillary action, and to a possible peristaltic action of the mus-
cular structures, and must acknowledge that these points have as yet been incapable of
positive demonstration.

In a very interesting memoir by Lott, which contains numerous observations bearing
upon the mechanism of conception, the experiments upon the behavior of the spermatozoids
under the microscope, in the presence of currents observed in the liquid between the two
plates of glass, develop some very curious points. It was shown, in these experiments,
that motionless spermatozoids followed the currents freely ; that, when the current in any
part of the field was strong, the moving spermatozoids were carried along with it ; but that,
when the current was comparatively feeble, spermatozoids endowed with active movements
made their way, as it were, against it. In reflecting upon these observations, it has
seemed to us that they offered an explanation, to a certain extent, of the passage of sper-
matozoids in the Fallopian tubes toward the ovaries. It is undoubtedly true that the
ciliary motion in the Fallopian tubes, in which the direction is from the ovaries toward
the uterus, would produce a feeble current. This current would naturally direct the
heads of the spermatozoids toward the interior, provided it were not too powerful, and
the movements of progression would therefore be from without inward. A little reflec-
tion makes it evident that, with a feeble current in the Fallopian tubes from within out-
ward, the spermatozoids, if the current were not strong enough to carry them with it,
could only progress in the opposite direction; but this cannot explain the passage of the
spermatozoids through the uterus itself, where, according to the best authorities, the
ciliary current is from without inward.

As regards the human female, we cannot give a definite idea of the time required for
the passage of the spermatozoids to the ovaries or for the descent of the ovum into the
uterus; and it is readily understood how these questions are almost incapable of experi-
mental investigation. We know, however, that spermatozoids reach the ovaries, and
they have been seen in motion on their surface seven or eight days after connection.

There are many elements of uncertainty in all investigations as to the usual or the
normal situation of fecundation. As the spermatozoids are found in movement in all
parts of the generative passages, the question resolves itself into that of the duration of
vitality of the ovum after its discharge ; and here we must rely exclusively upon obser-
vations made on the inferior animals. Coste, who demonstrated beyond a doubt that
fecundation occurs in fowls at or very near the ovary, recognized fully the difficulties
attending similar experiments upon mammals. He succeeded, however, in two observa-
tions upon rabbits, in which copulation took place after the period of heat and some time
after the discharge of ova. In both of these, he found ova at the superior extremity of
the cornua of the uterus, a position which he had found that the ova reached toward the
end of the third day. These ova, which were apparently advanced in decomposition,
presented no evidence of fecundation and were enveloped in a dense zone of albumen
which they had received from the Fallopian tubes. They were surrounded by sperma-
tozoids in active movement, but none had penetrated the adventitious albuminous cov-
ering. From these observations, the conclusion is deduced that fecundation can only
take place at the ovary or in the most dilated portion of the Fallopian tubes. When
we come to apply these observations to the human subject, we have, in confirmation of
them, only the abnormal phenomenon of abdominal pregnancy, which cannot occur
unless the ovum have been fecundated at the ovary, afterward falling into the abdominal
cavity instead of passing to the uterus. Still, the fact that conception may follow a
single intercourse occurring at any time with reference to the menstrual period throws
a doubt upon the theory that fecundation takes place only at or near the ovary ; and
another element of uncertainty is in the fact that we do not know positively that ovula-

MECHANISM OF FECUNDATION. 893

tion takes place at any definite time before, during, or after the menstrual period, nor
do we know precisely how long the spermatozoids may retain their vitality in the female
generative passages.

The question of the duration of vitality of the spermatozoids after their passage into the
uterus has an important bearing upon the time when conception is most liable to follow
sexual intercourse. The alkaline mucus of the internal organs actually favors their move-
ments ; the movements are not arrested by contact with menstrual blood ; and, indeed,
when the spermatozoids are mixed with the uterine mucus, they simply change their
medium, and there is no reason to believe that they may not retain their vitality as well
as in the mucus of the vesiculse seminales. We cannot, therefore, fix any limit to the
vitality of these anatomical elements under physiological conditions ; and we cannot say
positively that spermatozoids may not remain in the Fallopian tubes and around the
ovary, when intercourse has taken place immediately after a menstrual period, until the
ovulation following. There is an idea, based upon rather general and indefinite obser-
vation, that conception is most liable to follow an intercourse which occurs soon after a
monthly period ; but it is certain that it may occur at any time. It is extremely probable
that, during the unusual sexual excitement which the female generally experiences after
a period, the action of the internal organs attending and following coitus presents the
most favorable conditions for the penetration of the fecundating elements, and this may
explain the more frequent occurrence of conception as a consequence of intercourse at
this time.

'Mechanism, of Fecundation.— -In considering the intimate mechanism of fecundation,
we may begin with the proposition that this is accomplished by an actual union with the
substance of the ovum of a greater or less number of spermatozoids. This fact, which
has long since been positively demonstrated by experiments, affords a material explana-
tion of hereditary transmission, not only of maternal, but of paternal physical and mental
qualities.

There are many questions connected with hereditary transmission, which, if they
were susceptible of any thing approaching a positive scientific explanation, would be of
great interest and might appropriately be discussed in a work upon physiology; hut.
although the facts of hereditary influence, as regards the inheritance both of physiologi-
cal and morbid attributes and tendencies, the influence of the maternal mind upon the
development of the foetus, the effects of previous pregnancies, etc., cannot be doubted,
their consideration would involve little more than a mere enumeration of remarkable
phenomena.

The first question which naturally arises, and which has engaged the attention of
ancient as well as modern authors, relates to the conditions which determine the sex of
the offspring. The older writers, whose exact physiological knowledge was compara-
tively limited, were able to present explanations of some of the phenomena of generation,
which were more or less satisfactory in their day ; but many of these have been contra-
dicted by more recent facts, which have only rendered the causes of the phenomena more
obscure. Iconoclasm in physiology is almost a necessary consequence of the requisition
of definite knowledge ; and too often the exact student must fail to substitute anything
to supply the places of the broken images of antiquity. This is illustrated in the ./
tion of the determination of the sex of offspring. Statistics show clearly enough the
proportions between male and female births; but nothing has ever been done in the
of procreating male or female children at will. According to Longet. the proportion of
male to female births is about 104 to 105, these figures presenting certain nioditiea'
under varying conditions of climate, season, nutrition, etc. It has been shown, by \
extensive observations upon certain of the inferior animals, that the preponder.-u.
in births bears a certain degree of relation to the vigor and age of the parent*: and that
old and feeble females fecundated by young and vigorous males bring forth a gre.

894 GENEKATIOST.

number of males, and vice versa; but no exact laws of this kind have been found applica-
ble to the human subject. The idea that one testicle produces males and the other,
females, or that the two ovaries have distinct functions in this regard, has no foundation
in fact ; for men with one testicle, or females with a single ovary, produce offspring of
both sexes.

Two ideas with regard to the determination of sex in the foetus have obtained at dif-
ferent times. One of these is that the sex is dependent upon nutritive or other con-
ditions subsequent to fecundation, and the other, that the sex is determined at the time
of union of the male with the female element. Of these two opinions, the weight of
evidence appears to be in favor of the latter. Aside from facts in comparative physiol-
ogy, it is pretty certain that several spermatozoids are necessary for the fecundation of
a single ovum. It may be that, when just enough of the male element unites with the
ovum to secure fecundation, or when it might be said that the female element predomi-
nates, the faatus is a female, and when a greater number of spermatozoids unite with the
vitellus, the male sex is determined. Such an idea, however, is purely theoretical ; and
the question of the determination of sex presents thus far hardly the shadow of a satis-
factory explanation.

No definite rule can be laid down with regard to the transmission of mental or physi-
cal peculiarities to offspring. Sometimes the progeny assumes more the character of the
male than of the female parent, and sometimes the reverse is the case, without any refer-
ence to the sex of the child ; sometimes there appears to be no such relation ; and
occasionally we note peculiarities derived apparently from grandparents. This is true
with regard to pathological as well as physiological peculiarities, as in inherited tenden-
cies to certain diseases, malformations, etc.

A peculiar, and it seems to be, an inexplicable fact is that previous pregnancies have
an influence upon offspring. This is well known to breeders of animals. If pure-blooded
mares or bitches have been once covered by an interior male, in subsequent fecun-
dations the young are likely to partake of the character of the first male, even if they be
afterward bred with males of unimpeachable pedigree. What the mechanism of the
influence of the first conception is, we can form no definite idea; but the fact is incon-
testable. The same influence is observed in the human subject. A woman may have,
by a second husband, children who resemble a former husband, and this is particularly
well marked in certain instances by the color of the hair and eyes. A white woman who
has had children by a negro may subsequently bear children to a white man, these chil-
dren presenting some of the unmistakable peculiarities of the negro race.

Superfecundation of course does not come in the category of influences such as we
have just mentioned. It is not infrequent to observe twins, when two males have had
access to the female, which are entirely distinct from each other in their physical char-
acter ; a fact which is readily explained by the assumption that two ova have been
separately fecundated. This view is entirely sustained by observation and experiment.
Cases illustrating this point are numerous, but we cite one, simply to add to the number
of positive observations.

The following very interesting communication was received in January, 1869, from
Dr. John H. Janeway, Assistant Surgeon U. S. A., and it illustrates Superfecundation in
the human subject ; or, at least, that was the view taken by the negro father:

" Frances Hunt, a freedwoman, aged thirty-five years, gave birth to twins, February
4, 1867, in New Kent County, Virginia. One of these twins was black, the other was
white. Frances is a mulatto. The black child is much darker than she is. Previous to
the parturition, she had given birth to seven children, all single births. She was living
at the time of her impregnation in the family of a white man as house-servant, sleeping
with a black man at night. She insists, however, that she never had carnal intercourse
with a white man. She probably does this because the black man turned her out of his
house when he saw that one of the children was white."

MECHANISM OF FECUNDATION. 895

This history was accompanied by an excellent photograph of the mother an,] the tw,
biHren, a copy of which ,s given in Fig. 286. One of the children has tl,, ,,,],,'
characteristics of the negro, and the other looks like a white child. '< T he mother „
eh, dren were mmate. of Howard Grove Hospital near this city (Richmo ll, ,e
p,cture was taken and I saw them frequently. Both children are now dead Tie block

was killed br a tobacco-plaster applied to its

FIG. 2S6.— Mulatto mother with ticins, one white and the other black. From a photograph.

" The only negro feature in the white child was its nose. There, its resemblance to
its mother was perfect. Its hair was long, light, and silky. Complexion hrilli.

We have already referred to the curious fact that, when a cow gives birth to twins,
one male and the other female, the female, which is called the free-martin, is sterile and
presents an imperfect development of the internal organs of generation. This has !<.•<! to
the idea that possibly the same law may apply to the human subject, in .
one male and the other female ; but numerous observations are recorded in «r\ :
cal works, showing the incorrectness of this view, to which we may add tin- t'ollou
The author of the report on Rinderpest to the New York State Atrriniltnra'
1867, stated that his father was one of twins, male and female, and that his father's twin
sister had borne several children.

It has long been a question whether impressions made upon the nervous system <
mother can exert an influence upon the foetus in utero. While many jmthors admit that
violent emotions experienced by the mother may affect the nutrition and the gt-m ral
development of the foetus, some writers of high authority deny that the imagination can
have any influence in producing deformities. It mu>t be admitted that many of the

896 GENERATION.

remarkable cases recorded in works upon physiology as instances of deformity due to the
influence of the maternal mind are not reliable. It is often the case that, when a child
is born with a deformity, the mother imagines she can explain it by some impression
received during pregnancy, which she only recalls after she knows that the child is
deformed. Still, there are cases which cannot be doubted, but which, in the present
state of our knowledge of development and the connection between the mother and the
fostus, we cannot attempt to explain.

Union of the Male with the Female Element of Generation. — The first important step
in our positive knowledge of the mechanism of fecundation was the discovery of the
spermatozoids, in 1677, to which we have already referred ; the second was the demon-
stration, by Spallanzani, in his experiments upon artificial fecundation, that, when the
seminal fluid is carefully filtered, the liquid which passes through has no fecundating
properties, the male element remaining on the filter ; and the third was the demonstra-
tion of the presence of spermatozoids within the vitelline membrane, showing that fecun-
dation consists in a direct union of the male with the female element.

As to the mechanism of the penetration of spermatozoids to the vitellus, we can only
refer to the micropyle discovered in the ova of fishes and mollusks, which we have
already described. In the ova of the Nephclis, a small species of leech, Robin has seen
spermatozoids, to the number of several hundreds, penetrate the vitelline membrane,
always at one point, continuing their movements upon the surface of the vitellus.
" Almost always, when the penetration has ceased, a bundle of spermatozoids are
arrested in the micropyle." We had an opportunity of witnessing a demonstration of

these phenomena by Prof. Robin, in 1861, in the ova
of the Limnfeus stagnalis, and actually saw a sper-
matozoid half-way through the vitelline membrane.
According to numerous direct observations, the sper-
matozoids move actively around the ovum, collect
toward a certain point, and there penetrate the vitel-
line membrane. Coste, and many other observers
whom it is unnecessary to quote, have seen the sper-
matozoids within the vitelline membrane, in the ovum
of the rabbit ; and, more recently, "Weil has seen sper-
matozoids wedged in the substance of the zona pellu-
cida, has added blood to the specimen under observa-
tion, and has restored the movements of the sperma-
FIG. 287.— Penetration of spermatozoids tozoids while in this position. He has also seen, in

through the, vitelline membrane. • /> ,-, n -i , • i • ,-1

(Haeckei.) some instances, pertectly-formed spermatozoids m the

very substance of the vitellus.

All direct observations upon the lower orders of animals have shown that several sper-
matozoids are necessary for the fecundation of a single ovum ; but we have no definite
idea of the number required in mammals, much less in the human subject. Nor do we
know what becomes of the spermatozoids after they have come in contact with the vitel-
lus. All that we can say upon this point is, that there is probably a molecular union
between the two generative elements, soon to be followed by the remarkable series of
changes involved in the first processes of development.

Segmentation of the Vitellus.

As we have already stated, it is probable that the ovum is fecundated, either just as
it enters the Fallopian tube or in the dilated portion near the ovary. As it passes down
the tube, whether it be or be not fecundated, it becomes covered with an albuminous
layer. This layer probably serves to protect the fecundated ovum, and, when the sper-
matozoids do not penetrate the vitelline membrane near the ovary, it presents an obstacle

SEGMENTATION OF THE VITELLUS.

897

to their passage. Shortly after fecundation, the germinal vesicle disappears ; but this
occurs in ova that have not been fecundated. Soon after ovulation, also, the vitellus
gradually withdraws itself from certain portions of the vitelline membrane, or
deformed, and then often rotates upon itself; a phenomenon which has long been obs^ :
in the ova of some of the lowest orders of animals and of rabbits. The deformation
and gyration of the vitellus, however, have been observed in ova before fecundation ;m<l
have nothing to do with the process of development. They are of the class of move-
ments called amoeboid.

After the penetration of spermatozoids and their union with the vitellus, at lea-t in
many of the lowest orders of animals, the appearance of the vitellus undergoes a remark-
able change, by which ova that are about to pass through the first processes of develop-
ment may be readily distinguished from those which have not been fecundated. This
change consists in an enlargement of the granules and their more complete separation
from the clear substance of the vitellus. The granules then refract light more strongly
than before, so that the fecundated ova are distinctly brighter than the others. This is
the first appearance that is distinctive of fecundation.

Polar Globule. — The next process observed in the ovum is the separation from the
vitellus of a comparatively clear, rounded mass, called by Robin the polar globule. This
body has been observed before by various anatomists and described under different
names. The exact mode of its formation has been studied by Robin in some of the lower

FIG. 288.— Formation of thepolar globules in the ova of the Xephelis octocuhtta. (

orders of animals. We shall describe briefly this process as it was demonstrated to us by
Robin, in 1861, the description being taken from notes made at that turn- :

Five hours after the entrance of the spermatozoids, we see a li
point in the vitellus. This is the beginning of the polar globule. It iDcreai
gradually, and becomes constricted at its base, until it is attached to the viU-11.

57

898

GENERATION.

little pedicle. There is then, usually, a second globule
formed just behind the first, in the same manner ; and
sometimes a third makes its appearance. As soon as
the globules are perfectly formed, they all become de-
tached from the vitellus, but remain adherent to each
other, gradually fusing to form a single, rounded, very
faintly granular mass ; and it is opposite this globule
that the first furrow of segmentation of the vitellus is
observed. The complete formation of the polar globules
and their fusion into one occupy three hours. It is prob-
able that the polar globule is formed in the mammalia in
the manner above indicated. Sometimes the polar glob-
ule is formed in ova that have not been fecundated.

HHHl

Vitelline Nucleus. — A short time after the complete
formation of the polar globule, the germinal vesicle hav-
ing disappeared, the deformed vitellus resumes its original
rounded appearance and fills again the cavity of the vi-
telline membrane. At this time, the extreme periphery
of the vitellus becomes clearer, the granules collect in a
large zone around the centre, and, in the centre itself, a
clear, rounded body makes its appearance, which is called
the nucleus of the vitellus. This mass is viscid, amorphous,
without granules, and is entirely different from the germi-
nal vesicle, having no nucleus at first, a nucleolus, how-
ever, appearing in each of the numerous nuclei which re-
sult from its segmentation. The formation of the nucleus
of the vitellus is a positive evidence of fecundation.
It appears from fifteen to thirty hours after fecundation.

FIG. %&.— Segmentation of the vitel-
lus. (Liegeois.)

a, a. a, a, a, spermatozoids. The four
upper figures represent the progres-
sive segmentation of the vitellus.
The lowest figure shows the cells of
the blastoderm.

Segmentation of the Vitellus. — Almost immediately
following the phenomena we have just described, the
vitellus begins to undergo the remarkable process of
segmentation, by which it is divided into numerous
small cells. This process may take place to a- limited
extent in non-fecundated ova ; but in this case the
cells soon disappear, as the disintegration of the ovum
advances. The true segmentation of the vitellus, how-
ever, results in the formation of what are called the
blastodermic cells. As segmentation has been studied
in the inferior animals, there appears first a furrow in
the vitellus, at the site of the polar globule, and there
is then a furrow on the opposite side, both deepening
until the entire vitellus is divided into two globes. These
are at first spherical ; but they soon become flattened
upon each other into two hemispheres. There follows
then a similar division into four, another into eight, and
so on, until the entire vitellus is divided into numerous
cells, each with a clear nucleus resulting from the seg-
mentation of the original nucleus of the vitellus. It is
probable that, at first, the cells of the vitellus have no
membrane ; but a membrane is soon formed, a nucleus
appears, and the cells are perfect.

PRIMITIVE TRACE OF THE EMBRYON. 399

Most of the phenomena of segmentation have been observed in the lower orders of
animals ; but there can be no doubt that analogous processes take place in the human
ovum. In the rabbit, Weil observed, forty-five and a half hours after copulation, an
ovum, with sixteen segmentations, situated in the lower third of the Fallopian tube.
Ninety-four hours after copulation, he observed an ovum, with a delicate mosaic appear-
ance, presenting a small, rounded eminence on its surface.

It is impossible to say how long the process of segmentation continues in the human
ovum. It is stated that it is completed in rabbits in a few days, and, in dogs, that it occu-
pies more than eight days. When the cells of the blastoderm are completely formed,
they present a polygonal appearance as they are pressed against the vitelline membrane,
their inner surface being rounded. The ovum then contains, within the external layer
of cells, a small quantity of liquid. It is probably in this condition that the ovum passes
from the Fallopian tube into the uterus, at about the eighth day after fecundation.

Primitive Trace of the Embryon. — The cells formed by the segmentation of the vitel-
lus, after this process is completed, are arranged in the form of a membrane (the blasto-
dermic membrane) which is farther subdivided, as development advances, into layers,
which will be fully described hereafter. The albuminous covering which the ovum IK.S
received in the upper part of the Fallopian tube gradually liquefies and penetrates the
vitelline membrane, furnishing, it is thought, matter for the nourishment and develop-

FIG. 290.— Prim itive trace of the embryon. (Liegeois.)

a, primitive trace ; 5, urea pellucida; c, area obscura ; d, blastodermic cells; «, villl beginning to appear on the vitel-
line membrane.

ment of the vitellus. In the Fallopian tube, indeed, the adventitious albuminous cover-
ing of the ovum presents an analogy to the albuminous coverings which the eggs of
oviparous animals receive in the oviducts; with the difference that this albunii
matter is almost the sole source of nourishment in the latter, and exist* in lar-o quantity,
while, in viviparous animals, the quantity is small, is generally consumed as the
passes into the uterus, and, in the uterus, the ovum forms attachments to and draws i
nourishment from the vascular system of the mother.

At the period when the fecundated ovum enters the uterus, it has increased in ita
about five times. It is then composed of an external covering (the vitelline membrane)
with a cellular membrane internal to this (the blastodermic membrane) and a certain
amount of liquid in its interior.

Soon after the formation of the single blastodermic membrane, at a certain point c

900 GENERATION.

its surface, there appears a rounded elevation or heap of smaller cells, forming a distinct
spot, called the embryonic spot. As development advances, this spot becomes elongated
and oval. It is then surrounded by a clear, oval area, called the area pellucida, and the
area pellucida is itself surrounded by a zone of cells, more granular and darker than the
rest of the blastoderm. The elongated line thus formed and surrounded by the area
pellucida is called the primitive trace. It has been shown, however, that this primitive
trace, or primitive groove, is a temporary structure and has nothing to do with the
development of the neural canal. After the groove is formed, there appears fti front of,
but not continuous with it, a new fold and a groove leading from it. This is the " head-
fold," and the groove is the true medullary groove, which is subsequently developed into
the neural canal. If we adopt this view — and the difference is not very important — we
simply substitute the new trace, which is the seat of the development of the neural canal,
for the original primitive trace, which is temporary. It is probable that embryologists
have heretofore noted the so-called primitive trace and studied subsequently the develop-
ment of the true medullary groove, supposing that they were identical structures in dif-
ferent stages of formation, and not observing that the first trace disappears.

Blastodermic Layers. — Shortly after the appearance of the primitive trace, the blasto-
dermic cells, which are at first arranged so as to form a single membrane, separate into
layers. These layers have been differently described by various observers, and there is
some uncertainty with regard to the application of direct researches made upon the chick,
in which most of these early processes of development have been studied, to the mam-
malia and the human subject. We shall endeavor to describe the different layers in as
simple a manner as is consistent with our positive knowledge, omitting all points that are
unsettled or which seem to be of minor importance.

The blastodermic cells, resulting originally from the segmentation of the vitellus, are
first apparently split into two layers, which may be termed the external and the internal
blastodermic membranes. According to the most recent observations, the main portion
of the external layer, sometimes called the serous layer, simply forms a temporary invest-
ment for the rest of the vitellus and is not developed into any part of the embryon. The
internal layer, called the mucous layer, is developed into nothing but the epithelial lining
of the alimentary canal. There is a thickening of both of these layers at the line of devel-
opment of the cerebro-spinal system, with a furrow, which is finally enclosed by an ele-
vation of the ridges and their union posteriorly, forming the canal for the spinal cord.

As the spinal canal is thus developed, a new layer is formed, by a genesis of cells from
the internal surface of the original external layer and the opposite surface of the internal,
or mucous layer. This layer of new cells may be termed the intermediate layer ; and it
is from this that nearly all the parts of the embryon are developed.

To summarize the development of the layers just mentioned, we may state that the
external layer is a temporary structure ; the internal layer is very thin and is for the
development of the epithelial lining of the alimentary canal ; the most important structure
is a thick layer of cells, developed from the opposite surfaces of the external and the
internal layer and situated between them, called the intermediate layer; and it is from
these cells that the greatest part of the embryon is formed.

Formation of the Membranes.

The brief description we have just given of the formation of the blastodermic layers
seemed necessary as an introduction to the study of the membranes ; and we shall defer,
for the present, the description of their development into the different parts of the
embryon.

In the mammalia, a portion of the blastoderm is developed into membranes, by which
a communication and union are established between the ovum and the mucous membrane
of the uterus. From the ovum, two memhranes are developed; one non-vascular, the

FORMATION OF THE MEMBRANES. 901

amnion, and another vascular, the allantois. From the raucous membrane of the uterus,
are developed the two layers of the decidua. At a certain part of the uterus, a vascular
connection is established between the mucous membrane and the allantois, and the union
of these two structures forms the placenta. The fcetal portion of the placenta is con-
nected with the foetus by the vessels of the umbilical cord ; and the maternal portion is
connected with the great uterine sinuses. Development takes place from material sup-
plied to the foetus by the blood of the mother.

The external covering of the ovum, during the first stage of its development, is the
vitelline membrane. As the ovum is received into the uterus, the vitelline membrane
develops upon its surface little villosities, which are non- vascular and are formed of amor-
phous matter with granules. These are the first villosities of the ovum, and they assist
in fixing the egg in the uterine cavity. They are not permanent, they do not become
developed into the vascular villosities of the chorion, and they disappear as the true
membranes of the embryon are developed from the blastodermic layers. It is probable
that the vitelline membrane disappears about the fourth or fifth day, when it is replaced
by the amnion.

Formation of the Amnion. — As the ovum advances in its development, it is observed
that a portion of the blastoderm becomes thickened, to form the first trace of the embryon.
At this portion, where the body of the embryon subsequently makes its appearance, as
we have already seen, we have the external layer, the internal layer, and a thick, inter-
mediate layer of cells, which are developed from the opposite surfaces of the external and
the internal layer, called the middle layer. At nearly the time when this thickening begins,
a fold of the external layer makes its appearance, surrounding the thickened portion, and
most prominent at the cephalic and the caudal extremity of the furrow for the neural canal.
This fold increases in extent as development advances, passes over the dorsal surface of
the embryon, and finally meets so as to enclose the embryon completely. We can readily
figure to ourselves this process and understand how, at a certain period of the develop-
ment of the amnion, this membrane consists of an external layer, formed of the external
layer of the fold, and an internal layer ; the point of union of the two layers, or the point
of meeting of the fold, being marked by a membranous septum.

The two amniotic layers are formed in the way that we have just described, and a
complete separation finally takes place, by a disappearance of the septum formed by the
meeting of the folds over the back of the embryon. This process occupies four or five
days in the human ovum. The point where the folds meet is called the amniotic umbili-
cus. When the amnion is thus completely formed, the vitelline membrane has been
encroached upon by the external amniotic layer and disappears, leaving this layer of the
amnion as the external covering of the ovum. At this time, there is a growth of villosi-
ties upon the surface of the external amniotic layer, which, like the villosities of the vitel-
line membrane, are not vascular.

Soon after the development of the amnion, the allantois is formed. This membrane
is vascular, encroaches upon and takes the place of the external amniotic membrane,
becomes villous, and its villosities take the place of those of the amnion. Over a certain
portion of the membrane, the villosities are permanent. The mode of development of the
amnion, as we have described it, is illustrated by the diagrammatic Fig. -'.'1. This \\.
illustrates the formation of the amnion, the umbilical vesicle, and the allantois. Thela-t two
structures are not derived from the external blastodermic layer, and they will be de-rribed
farther on, after we have studied the full development of the amnion and it* rett

When the allantois has become the chorion, or the external membrane of the ovum,
having taken the place of the external layer of the amnion, tin- structures of the ovum
are the following: 1. The chorion, formed of the two layers of the allantois. .lerive.l from
the internal blastodermic membrane, and penetrated by Mood-v, -
cord, which connects the embryofl with the placental portion of the chorion, and the urn-

902

GENERATION.

bilical vesicle, formed from the same layers as the allantois. 3. The amnion, which is the
internal layer of the amniotic fold, persisting throughout the whole of fcetal life. 4. The
enibryon itself.

During the early stages of development of the umbilical vesicle and the allantois, the

FIG. 291.— Five diagrammatic representations of the formation of the membranes in the mammalia. (Kolliker.)

FIG. 1 : «, a', external layer of the blastoderm; d, vitelline membrane; a', villi on the vitelline membrane; *, inter-
nal layer of the blastoderm ; m, m', middle layer.

FIG. 2: a', external layer of the amnion; d, d'. vitelline membrane; 0, embryon; rf .<*, umbilical vesicle; vl, ks. «*,
foldfi of the amnion ; dd, m', st, internal layer of the blastoderm ; d d, connection of the embryon with the um-
bilical vesicle.

Fro. 3: d, d', vitelline membrane; vl, internal amniotic layer; e, embryon ; ah. amniotic cavity; sh, $7i, external
amniotic layer; am, space between the two layers of the amnior ; dd, internal layer of the blastoderm ; (?,/, st, i,
walls of the umbilical vesicle ; d g, omphalo-mesenteric canal ; d «, cavity of the umbilical vesicle ; a I, first ap-
pearance ol the allantois.

FIG. 4: sh, external layer of the amnion; ss, villi of the external layer of the amnion, which has now become the
chorion, the vitelline membrane having disappeared; hh, am., internal layer of the amnion; e, embryon; ah.
amniotic cavity: dg, omphalo-mesenteric canal; ds, cavity of the umbilical vesicle ; a I, allantois; r, space be-
tween the two layers of the amnion.

FTG. 5: ch;sh, ch, a I, allantois (which has now become the chorion, the external amniotic layer having disap-
peared), with its villi ; am, amnion ; as, amniotic covering of the umbilical cord ; r, space between the amnioc
and the allantois; ah, amniotic cavity; ds, umbilical vesicle; dg, omphalo-mesenteric canal.

AMXIOTIC FLUID. 903

internal amniotic layer, or the true amniotic membrane, is closely applied to the su>
of the embryon and is continuous with the epidermis at the umbilicus. It is tlu-n sepa-
rated from the allantois by a layer of gelatinous matter; and in this layer, between the
amnion and the allantois, is embedded the umbilical vesicle. At this time, the uml.ilical
cord is short and not twisted. As development advances, however, the inter-meml.ra-
nous gelatinous matter gradually disappears; the cavity of the amnion is enlarged by the
production of a liquid between its internal surface and the embryon; and, at about the
end of the fourth month, the amnion comes in contact with the internal surface of the
chorion. At this time, the embryon floats, as it were, in the amniotic cavity, surrounded
by the amniotic fluid. The amnion forms a lining membrane for the chorion ; by its
gradual enlargement it has formed a covering for the umbilical cord ; and, between it and
the cord, is the atrophied umbilical vesicle. The amnion then resembles a serous mem-
brane, except that it is non-vascular. It is lined by a single layer of pale, delicate cells
of pavement-epithelium, which contain a few fine, fatty granulations. At term, the am-
nion adheres to the chorion, though it may be separated, with a little care, as a distinct
membrane, and may be stripped from the cord. From its arrangement and from the
absence of blood-vessels, it is evident that this membrane is simply for the protection of
the foetus and is not directly concerned in its nutrition and development. (See Plate
III., Fig. 2, facing page 922.) The gelatinous mass referred to above, situated, during
the early periods of intra-uterine life, between the amnion and the chorion, presents a
semifluid consistence, and it is marked by the presence of numerous very delicate, inter-
lacing fibres of young connective tissue and fine grayish granulations scattered through its
substance. These fibres gradually develop as the quantity of gelatinous matter diminishes
and the amnion approaches the chorion, until, finally, it forms a rather soft, reticulated
layer, which is sometimes called the membrana media.

Amniotic Fluid. — The process of enlargement of the amnion shows that the amniotic
fluid gradually increases in quantity as the development of the foetus progresses. At
term, the entire quantity is variable, being rarely more than two pints or less than one
pint. In the early periods of utero-gestation, it is clear, slightly yellowish or greenish.
and perfectly liquid. Toward the sixth month, its color is more pronounced, and it be-
comes slightly mucilaginous. Its reaction is usually neutral or faintly alkaline, though
sometimes it is feebly acid in the latest periods. It sometimes contains a small quantity
of albumen, as determined by heat and nitric acid ; and there is generally a gelatinous
precipitate on the addition of acetic acid. The following table, compiled by Robin, ji
its chemical composition :

Composition of the Amniotic
\vater _ ...................................... o'.n-oi) tn 971

Albumen and mucosine .......................................... °'82

Urea ......................................................... 2>0° " 3'50

Creatine and creatinine (Scherer, Robin and Verdeil) ................. not estimated

Lactate of soda (Vogt, Regnauld) ..................................

Fatty matters (Rees, Mack) .......................................

Glucose (Cl. Bernard) ............................................ o»ot

Chloride of sodium and chloride of potassium .......................

Chloride of calcium .............. ...............................

Carbonate of soda ..............................................

Sulphate of soda ...............................................

Sulphate of potassa (Rees) .......................................

Calcareous and magnesiun phosphates and sulphates ..................

The presence of certain of the urinary constituents in the amniotic fluid ha> led I
view that the urine of the foetus is discharged, in greater or less quantity, into the am-

904 GENERATION.

niotic cavity. Bernard, who is cited in the above table as having determined the pres-
ence of sugar in the amniotic fluid, has shown that, in animals with a multiple placenta,
the amnion has a glycogenic function during the early part of intra-uterine existence.

"With regard to the origin of the amniotic fluid, it is impossible to say how much of it
is derived from the general surface of the foetus, how much from the urine, and how
much from the amnion itself, by transudation from the vascular structures beneath this
membrane. The quantity is apparently too great, especially in the early months, to be
derived entirely from the urine of the foetus, and there is probably an exudation from the
general surface of the foetus and from the membranes. After the third month, the seba-
ceous secretion from the skin of the foetus prevents the absorption of any of the liquid.

An important property of the amniotic fluid is that of resisting putrefaction and of
preserving dead tissues. It is statetd by Eobin to be the best fluid for the preservation
of the embryonic tissues, when it is desired to keep them for examination.

Formation of the Umbilical Vesicle. — As the visceral plates, which will be described
hereafter, close over the front of the embryon, that portion of the blastoderm from which
the intestinal canal is developed presents a vesicle, which is cut off, as it were, from the
abdominal cavity, but which still communicates freely with the intestine. This is the um-
bilical vesicle. On its surface, is a rich plexus of blood-vessels ; and this is a very important
organ in birds and in many of the lower orders of animals. In the human subject and in
mammals, however, the umbilical vesicle is not so important, as nutrition is effected by
means of vascular connections between the chorion and the uterus. The vesicle becomes
gradually removed farther and farther from the embryon, as development advances, by
the elongation of its pedicle, and it is compressed between the amnion and the chorion as
the former membrane becomes distended.

When the umbilical vesicle is formed, in the way which we have indicated, it receives
two arteries from the two aortae, and the blood is returned to the embryon by two veins,
which open into the vestibule of the heart. These are called the omphalo-mesenteric
vessels. At about the fortieth day, one artery and one vein disappear, and, soon after,
all vascular connection with the embryon is abolished. At first there is a canal of com-
munication with the intestine, called the omphalo-mesenteric canal. This is gradually
obliterated, and it closes at the thirtieth or the thirty-fifth day. The point of communica-
tion of the vesicle with the intestine is called the intestinal umbilicus ; and, early in the
process of development, there is here a true hernia of a loop of intestine. The umbilical
vesicle remains as a tolerably prominent structure as late as the fourth or fifth month,
but it may often be discovered at the end of pregnancy.

The umbilical vesicle presents three coats; an external, smooth membrane, formed
of connective tissue, a middle layer of transparent, polyhedric cells, and an internal layer
of spheroidal cells. The membrane, composed of these layers, encloses a pulpy mass,
composed of a liquid containing cells and yellowish granulations.

Formation of the Allantois and the Permanent Chorion.— During the early stages 01
development of the umbilical vesicle, and while it is being shut off from the intestine,
there appears an elevation at the posterior portion of the intestine, which rapidly in-
creases in extent, until it forms a membrane of two layers, which is situated between
the internal and the external layer of the amnion. This membrane becomes vascular
early in the progress of its development, increases in size quite rapidly, and finally com-
pletely encloses the internal layer of the amnion and the embryon, the gelatinous mass
already described being situated between it and the internal amniotic layer, before this
membrane becomes enlarged. While the formation of the two layers of the allantois is
quite distinct in certain of the lower orders of animals, in the human subject and in mam-
mals, it is not so easily observed ; still there can be no doubt as to the mechanism of its
formation, even in the human ovum. Here, however, the allantois soon becomes a single

FORMATION OF THE ALLANTOIS AND PERMANENT CHORION. 905

membrane, the two original layers of which cannot be separated from each other. The
process of the development of the allantois is shown in the diagrammatic Figure 291
(3, 4, 5).

It is the vascularity of the allantois which causes the rapid development by which it
invades and finally supersedes the external layer of the amnion, becoming the permanent
chorion, or external membrane of the ovum. At first there are two arteries extending
into this membrane from the lower portion of the aorta, and two veins. The two arte-
ries persist and form the two arteries of the umbilical cord, coming from the internal
iliac arteries of the foetus ; and the two veins are reduced to one, the umbilical vein,
which returns the blood from the placenta to the foetus. These vessels are connected
with the permanent vascular tufts of the chorion.

The development of the allantois cannot be well observed in human ova before the
fifteenth or the twenty-fifth day. We have already noted the formation of villosities,

first upon the vitelline membrane, and
next upon the external amniotic mem-
brane, and we have seen that both of
these membranes are temporary struct-
ures. As the vascular allantois en-
croaches upon the external amniotic
layer, the villosities become vascular;
and, when the allantois becomes the per-
manent chorion, it is marked by a mul-
titude of compound villi over its entire
surface, which give the ovum a shaggy
appearance. It is difficult to say whether
new villi appear upon the allantois, or
whether the villi of the amnion are pene-
trated by the vessels of the allantois ;
but it is certain that the true or perma-
nent .chorion presents upon its surface
vascular villi. As the ovum enlarges,
over a certain area surrounding the point
of attachment of the pedicle winch con-
nects it with the embryon, the villi are
developed more rapidly than over the rest of the surface. Indeed, as the egg becomes
larger and larger, the villi of the surface outside of this area become more and more
scanty, lose their vascularity, and finally disappear. That portion upon which the villi
persist and increase in length and in the number of their branches is destined to form
connections with the mucous membrane of the uterus, and it constitutes the foetal portion
of the placenta. This change begins at about the end of the second month, and the pla-
centa becomes distinctly limited at about the end of the third month.

It must be remembered that, as the changes progress which result in the formation of
the permanent chorion and the limitation of the foetal portion of the placenta, the forma-
tion of the umbilical vesicle and the enlargement of the amnion are also going on. The
amnion is gradually becoming distended by the increase in the quantity of amniotic
fluid. It reaches the internal surface of the chorion at about the end of the fourth month,
extends over the umbilical cord to form its external covering, including the cord of the
umbilical vesicle, and the umbilical vesicle itself lies in the gelatinous matter between
the two membranes.

At about the beginning of the fifth month, then, the ovum is constituted as follows :
The foetus floats freely in the amniotic fluid, attached to the placenta by the umbili-
cal cord ; the chorion presents a highly-vascular, thickened, and villous portion, the fcetnl
portion of the placenta ; the rest of the chorion is a simple membrane, without villi and

906 GENERATION.

without blood-vessels; the amnion lines the internal surface of the chorion and also
forms the external covering of the umbilical cord ; the umbilical vesicle has become
atrophied and has lost its vascularity ; the hernia at the point of connection of the um-
bilical vesicle with the intestine of the fcetus has closed ; and, finally, the foetus has under-
gone a considerable degree of development.

It now remains for us to study the structure of the umbilical cord, the membranes
formed from the mucous membrane of the uterus, or the membransQ decidua), and the
mode of development and the structure of the placenta.

Umbilical Cord. — From the description we have given of the mode of development
of the chorion and the amnion, it is evident that the umbilical cord is nothing more than
the pedicle which connects the embryon with that portion of the chorion which enters
into the structure of the placenta. It is, indeed, a process of the allantois, in which the
vessels eventually become the most important structures. The cord is distinct at about
the end of the first month ; and, as development advances, the vessels consist of two
arteries coming from the body of the fcetus, which are usually twisted from left to right
around the single umbilical vein. In addition to the spiral turns of the arteries around
the veins, the entire cord may be more or less twisted, probably from the movements of
the fcetus.

The fully-developed cord extends from the umbilicus of the fcetus to the central por-
tion of the placenta, in which its insertion is usually oblique ; though it may be inserted
at other points, and even outside of the border of the placenta, its vessels penetrating
this organ from the side. Its usual length, which varies very considerably, is about
twenty inches. It has been observed as long as sixty, and as short as seven inches.
When the cord is very long, it sometimes presents knots, or it may be wound around the
neck, the body, or any of the members of the fcetus ; and this can only be accounted for
by the movements of the fcetus in utero.

The external covering of the cord is a process of the amnion, which, as it extends
over the vessels, includes a gelatinous substance (the gelatine of Wharton) which sur-
rounds the vessels and protects them from compression. This gelatinous substance is
identical with the so-called membrana intermedia, or the substance included between the
amnion and the chorion. The entire cord, covered with the gelatine of Wharton and
the amnion, is usually about the size of the little finger. According to Eobin, the nor-
mal cord will sustain a weight of from ten pounds and ten ounces to twelve pounds and
twelve ounces avoirdupois. As the amniotic fluid accumulates and distends the amniotic
membrane, it becomes more and more closely applied to the cord. This pressure extends
from the placental attachment of the cord toward the fcetus and gradually forces into
the abdomen of the foetus the loop of intestine, which, in the early periods of intra-
uterine life, forms an umbilical hernia.

It is generally stated by writers upon embryology that the vessels of the cord present
no valves ; but recent observations have demonstrated the presence of semilunar folds,
both in the vein and in the arteries. These are simple inversions of the walls of the ves-
sels ; and they do not exist in pairs, nor do they seem to influence the current of blood.
In the arteries, these folds are situated at intervals of from half an inch to two inches,
and they are more abundant where the vessels are very contorted. In the vein, the folds
are most abundant near the placenta ; they are very irregularly placed, and, in a length of
four inches, fifteen folds were found. It is not apparent that these folds have any physio-
logical importance.

As the allantois is developed, it presents, in the early stages of its formation, three
portions ; an external portion, which becomes the chorion, an internal portion, enclosed
in the body of the embryon, and an intermediate portion. The intermediate portion, as
we have seen, becomes the umbilical cord. As the umbilicus of the foetus closes around
the cord, it shuts off a portion of the allantois contained in the abdominal cavity, which

MEMBRANE DECIDtLE. 907

becomes the urinary bladder; but there is a temporary communication between the inter-
nal portion and the lower portion of the cord, which is called the urachus. This is gen-
erally obliterated before birth and is reduced to the condition of an impervious cord ;
but it may persist during the whole of intra-uterine life, in the form of a narrow canal,
extending from the bladder to the umbilicus, which is closed soon after birth.

Membran® Deciduce. — In addition to the two membranes connected with the foetus,
there are two membranes formed from the mucous membrane of the uterus, which are
derived from the mother and which serve still farther to protect the ovum. The cho-
rion, as we have just seen, is for the protection of the fetus ; but a portion of this
membrane, about one-third of its surface, becomes closely united with a corresponding
portion of the uterine mucous membrane, to form the placenta. This organ, which
serves for the nutrition of the foatus, will be described by itself; but, before we can
thoroughly comprehend its structure and the process of its development, we must study
carefully the formation of the membranoo deciduas.

As the fecundated ovum descends into the uterus, it is usually invested with a shaggy
covering, which is either the permanent chorion or one of the membranes which invests
the ovum previous to the complete development of the allantois. At this time, the
mucous membrane of the uterus has undergone certain changes by which it is prepared
for the reception of the ovum. The changes which this membrane undergoes in men-
struation have already been studied. It has been seen that, during an ordinary men-
strual period, the membrane has been increased three or four times in thickness and has
become more or less rugous. Without being able to state from positive observation the
character of the first changes in the uterine mucous membrane preceding the descent of
the fecundated ovum — for the opportunities for direct inspection of these parts after
fecundation and before the arrival of the ovum are not frequent — it is almost certain
that this hypertrophy occurs and progresses. One of the most favorable occasions for
observing these early changes in the human subject lately presented itself, and the ap-
pearances were minutely described by Reichert. In this case, the ovum was lenticular,
measuring nearly one-fourth of an inch in its long and about one-sixth of an inch in
its short diameter. It was covered with simple, empty, cylindrical villi, and was esti-
mated to be at from the twelfth to the thirteenth day of its development, dating from
fecundation. It was enclosed in the decidua reflexa, and it was thought that this
had been accomplished from twenty-four to forty-eight hours before the death of the
mother.

According to Reichert, the thickening of the mucous membrane of the uterus which
occurs at each menstrual period, in case the ovum be not fecundated, is relieved by a flow
of blood and disappears ; but, if fecundation take place, the membrane continues to hyper-
trophy and to prepare itself to enclose the ovum. In this process, when an ovum has
been fecundated, there are formed, upon the surface of the mucous membrane, little ele-
vations, or islands, provided with primary and secondary papillae everywhere except at
their borders, where the membrane is smooth and presents the enlarged orifices of the
uterine follicles. The ovum observed by Reichert was found embedded in the parenchyma
of one of these islands ; and, as it was detached, several villi were drawn immediately out
from the uterine tubules.

It is now well known that the mucous membrane lining the gravid uterus forms what
has been called the decidua vera, and that a portion is reflected over the ovum, to form
the decidua reflexa. Reichert is of the opinion that the view entertained by most ob-
servers, that the fecundated ovum lodges itself in one of the furrows of the hypertrophied
membrane and is finally enclosed by an elevation of the walls of the furrow, cannot be
sustained. He thinks that the ovum first becomes attached to one of the " islands; " at
the point of attachment, the island does not increase in size as rapidly as at other por-
tions, so that the ovum rests in a cup-shaped depression ; and, finally, a growth takes place

908 GENERATION.

from the margin of this depression, which extends around and encloses the ovum, pre-
senting a spot where the final closure takes place, called the decidual umbilicus.

We have given the recent views of Reichert thus fully, for the reason that they are
based upon the study of a remarkably young ovum and appear to be more exact and
definite than any observation hitherto recorded ; and we shall adopt this description as
representing the early stages of the formation of the membranee deciduse.

According to Reichert, the ovum is completely enclosed at the twelfth or the thir-
teenth day. The mucous membrane lining the uterus becomes the decidua vera, and the
border from which the new growth is formed which covers the ovum is the boundary
between this and the decidua reflexa. The new growth, springing from this border, en-
velops the ovum completely and is called the decidua reflexa; and, in this membrane,
there is no trace of the uterine tubules.

As development advances, a portion of the decidua vera — the description of which we
reserve for the present — undergoes development into the maternal portion of the placenta.
The rest of the decidua vera becomes extended, loses its vessels and glands, and is reduced
to the condition of a simple membrane. The cylindrical epithelial cells of the mucous
membrane of the body of the uterus, soon after fecundation, become gradually exfoliated,
and their place is supplied by flattened epithelial scales, of the pavement-variety. This
change is effected at from the sixth to the eighth week, and the pavement-cells are then
found covering both the decidua vera and the reflexa. The epithelium of the cervix
retains its cylindrical character, but most of the cells lose their cilia.

During the first periods of utero-gestation, the two layers of decidua are separated by
a small amount of an albuminous and sometimes a sanguinolent fluid ; but this disappears
at about the end of the fourth month, and the membranes then come in contact with each
other. They soon become so closely adherent as to form a single membrane, which is in
contact with the chorion. Sometimes, at full term, the membranes of the foetus can be
separated from the decidua; but frequently all of the different layers are closely adherent
to each other.

The changes we have just described are not participated in by the mucous membrane
of the neck of the uterus. The glands in this situation secrete a semisolid, transparent,
viscid mucus, which closes the os and is sometimes called the uterine plug.

Toward the fourth month, a very delicate, soft, homogeneous layer appears over the
muscular fibres of the uterus, beneath the decidua vera, which is the beginning of a new
mucous membrane. This is developed very gradually, and the membrane is completely
restored about two months after parturition.

Development and Structure of the Placenta. — In describing the formation of the mem-
branas decidusB and of the chorion, we have necessarily hinted at the mode of development
of the placenta. Although there is considerable difference of opinion among anatomists
with regard to the exact relations between the vessels of the mother and of the foetus in
utero, it is admitted by all that the foetus derives its nourishment from the maternal blood,
and that the placenta is, in addition, a respiratory organ. Reasoning from what we
should consider to be the requirements of the foetus, it would be natural to suppose that
the foetal vessels are bathed in maternal blood ; and it is certain that the two sets of
vessels have no direct communication with each other. It is also well known that the
foetus has an independent circulation, its heart beating about twice as fast as the heart of
the mother. In our description of the placenta, we shall first give the views which we
conceive to be correct, and then advance the facts and arguments by which these views
are apparently supported.

Beginning with the first development of the placenta, the observation which we have
quoted from Reichert, in which, it will be remembered, the tufts of the foetal chorion
were actually drawn out of the tubules of the uterine mucous membrane, seems to de-
monstrate beyond question the fact of penetration of the villi of the chorion into the

DEVELOPMENT AND STRUCTURE OF THE PLACENTA. 909

maternal tubes. This is a capital point in our view of the mode of development of the
placenta; and this cannot be questioned, if we admit the accuracy of Reichert's descrip-
tion. It is certain that the portion of the chorion which eventually becomes attached to
the uterus undergoes a much greater degree of development than the rest of the mem-
brane. The villi in this situation become branched and arborescent; they are filled with
blood-vessels, while the vascularity in other parts of the chorion disappears ; the mucous
membrane corresponding to this portion of the chorion also becomes thickened ; the tubes
in which the villi have penetrated are correspondingly enlarged and branched, and the
vessels which surround them are increased in size ; and, finally, the union between the villi
and the tubes becomes so close that they cannot be separated from each other. It is
evident that, if this be the mode of development of the placenta, the maternal portion is
formed from a restricted and an hypertrophied part of the mucous membrane bf the uterus,
and the foetal portion is simply an exceedingly vascular and villous part of the chorion.

As development advances, the vessels of the maternal portion of the placenta coalesce
into great lakes, which communicate freely with the uterine sinuses. In these great
cavities, we find the vascular foetal tufts ; and it is easy to understand how transudation
of nutritive material and gases can take place from the blood of the mother to the vascular
system of the foetus.

If the above description be correct, we should be able to pass an injection from the
uterine sinuses into the maternal portion of the placenta, even as far as its foetal surface ;
but this is a point concerning which there has been a great deal of discussion.

In injected specimens of the placenta, when an attempt has been made to fill the
maternal as well as the foetal vessels, the material injected into the uterine vessels has
sometimes passed through the entire thickness of the placenta and appeared just beneath
the transparent chorion at the foetal surface of the organ. This appearance, however,
has been thought by some writers to be due to extravasation ; and many physiologists
are of the opinion that the placenta has no maternal portion, that it is entirely a fcetal
organ, and that the maternal vessels do not pass beyond the surface by which it is
attached to the walls of the uterus. This opinion, however, we believe to be erroneous.

The important point in the determination of the connection of what may be termed
the placental maternal sinuses with the vessels of the uterus can be settled by injection
of the uterine vessels in cases in which the observation can be made while the placenta
is still attached to the uterine walls. Dalton, since 1853, has examined the parts in situ
in four cases of women who died undelivered at or near the full term of pregnancy, and
he adopted the ingenious expedient of filling the uterine vessels with air, by which the
course of the injection could be directly observed. This operation is performed in the
following manner : The uterus, with its contents, is removed from the body, is carefully
opened, and the foetus is taken out, after dividing the umbilical cord. The parts are
then placed under water, the end of a blow-pipe is introduced into one of the divided
vessels of the uterine walls, and air is forced in by gentle insufflation. By this process,
the venous sinuses of the uterus itself are first filled, next, the deeper portions of the
placenta, and finally, " the bubbles of air insinuate themselves everywhere between the
foetal tufts, and appear in the most superficial portions of the placenta, immediately
underneath the transparent chorion. If the chorion be now divided at any point by an
incision, passing merely through its own thickness, the air, which was confined beneath
it in the placental sinuses, will escape, and rise in bubbles to the surface of the water.
Such an experiment shows conclusively that the placental sinuses communicate freely
with the uterine vessels, occupy the entire thickness of the placenta, and are equally
extensive with the tufts of the foetal chorion." Dalton farther states that the uterine
vessels, as they penetrate the placenta, have an exceedingly oblique direction, and that
their orifices may be easily overlooked, but can be seen by careful inspection.

We have no doubt with regard to the accuracy of the observations of Dalton, and we
conceive that they have settled the question of the existence of a true maternal portion

910

GENERATION.

of the placenta. In corroboration of this, in 1864, we examined the uterus, with the
placenta attached, of a woman who died in the latter months of pregnancy, in the pres-
ence of the late Prof. G. T. Elliot and Prof. J. P. White, and forced air from the uterine
sinuses throughout the entire thickness of the placenta, between the foetal tufts. In
view of these facts, concerning which there can be no doubt, it seems unnecessary to
discuss the more or less theoretical views of writers who have not made injections of the
uterus with the placenta attached. The observations of Dalton have since been con-
firmed by numerous anatomists, so that we must consider the fact of an intra-placental
circulation of maternal blood as definitively established.

Structure of the Fully -developed Placenta. — The placenta of the human subject pre-
sents certain differences in its structure at various periods of utero-gestation, most of
which have been indicated in treating of its development. At about the end of the third
month, the limits of the placenta become distinct, and the organ rapidly assumes the ana-
tomical characters observed after it may be said to be fully developed. It then occupies

FIG. 293.— Diagrammatic figure, showing the placenta and deciduce. (Li6geois.)

c, embryon ; i, intestine ; p, pedicle of the umbilical vesicle ; o, umbilical vesicle ; m, m, m, amnion ; a', chorion ;
a, lower end of the umbilical cord ; g, 5, vascular tufts of the chorion, constituting the foetal portion of the pla-
centa ; M', w, maternal portion of the placenta ; ?i, n, decidua vera ; «, decidua reflexa.

about one-third of the uterine mucous membrane, and it is generally rounded or ovoid in
form, with a distinct border connected with the decidua and the chorion. It is from
seven to nine inches in diameter, a little more than an inch in thickness at the point of
penetration of the umbilical cord, slightly attenuated toward the border, and weighs
from fifteen to thirty ounces. Its foetal surface is covered with the smooth amniotic
membrane, and its uterine surface, when detached, is rough, and divided into numerous
irregular lobes or cotyledons, from half an inch to an inch and a half in diameter. Be-
tween these lobes, are membranes, called dissepiments, which penetrate into the sub-
stance of the organ, frequently as far as the foetal surface.

DEVELOPMENT OF THE EMBRYON. • 9H

Upon the uterine surface of the placenta, is a thin, soft membrane, sometimes called
the decidua serotina. This is merely a portion of the mucous membrane of the uterus
situated next the muscular walls, the greater part of it not being thrown off with the pla-
centa. It is composed of amorphous matter, numerous granulations, and colossal cells with
enlarged and multiple nuclei. If we scrape the uterine surface of a fresh placenta, these
cells appear, upon microscopical observation, very much like the so-called cancer-cells.
There has been and is now considerable difference of opinion with regard to the formation
of the decidua serotina. Some writers, who do not admit that the placenta has any true
maternal portion, regard it as the portion of decidua imprisoned between the chorion
and the muscular walls of the uterus ; but, if we adopt the view that the placenta is
formed in part of the uterine mucous -membrane, we must regard the serotina, so called,
as simply the deeper portion of this membrane.

Blood-vessels of the Placenta. — The two arteries of the umbilical cord branch upon
the foetal surface of the placenta beneath the amnion and finally penetrate the substance
of the organ. The branches of the veins, which are about sixteen in number, converge
toward the cord and unite to form the umbilical vein. Upon the uterine surface of the
placenta, are numerous oblique openings of the veins which return the maternal blood to
the uterine sinuses. There are also numerous small spiral arteries, which pass into the
substance of the organ to supply blood to the maternal portion. These are the " curling
arteries," described by John Hunter.

If we inject the umbilical arteries, the fluid is returned by the umbilical vein, having
passed through the vascular tufts of the foetal portion of the placenta. According to
Farre, the small arteries and the veins of the villi at first communicate through a true
capillary plexus ; but, toward the end of pregnancy, the capillaries disappear, leaving
loops of vessels, " simple, compound, wavy, or much contorted, and in parts varicose."

According to the recent researches of Winkler, there are three kinds of foetal villi :
1. Those which terminate just beneath the chorion, without penetrating the vascular
lacunae. 2. Longer villi, which hang free in the lacuna?. 3. Long, branching villi, which
penetrate more deeply into the placenta, some extending as far as its uterine surface.

The formation of the great vascular lakes of the maternal portion of the placenta has
already been described. These, according to Winkler, present numerous trabeculse,
which extend from the uterine to the foetal surface ; and, between these trabecuta, are
numerous exceedingly delicate transverse and oblique secondary trabecular processes.
The chorionic villi contain blood-vessels, which we have already described, surrounded
by a gelatinous, connective-tissue structure (Schleimgewebe), and are generally covered
with a layer of nucleated cells of pavement-epithelium.

In parturition, the curling arteries and the veins on the uterine surface of the pla-
centa are torn off, and the placenta then consists of the parts we have just described ;
the torn ends of these vessels attached to the uterus are closed by the contractions of the
surrounding muscular fibres ; and the blood which is discharged is mainly derived from
the placenta itself. Thus the very contractions which expel the contents of the uterus
close the vessels and prevent loss of blood by the mother.

Development of the Embryon.

The product of generation retains the name of ovum until the form of the body begins
to be apparent, when it is called the embryon. At the fourth month, about the time of
quickening, it is called the foetus, a name which it retains during the rest of intra-uterine
life. The membranes which we have described are appendages developed for the pur-
poses of protection and nutrition ; and the embryon itself, in the mammalia, is developed
from a restricted portion of the layers of cells resulting from the segmentation of the
vitellns.

We have already described the formation of the blastodermic cells and the appearance

912 GENERATION.

of the groove which is subsequently developed into the neural canal. At this portion of
the ovuin, there is a thickening of the blastoderm, which then presents three layers, the
middle layer, the thickest and most important, being developed from the opposite sur-
faces of the external and the internal layer. We have to study, then, the changes which
take place in three layers of cells, which we shall call the external, the intermediate,
and the internal blastodermic membranes. The earliest stages of development have been
studied almost exclusively in the chick, and the processes here observed cannot be as-
sumed to represent exactly the mode of development of the human subject. For this
reason, we feel justified in adopting the simplest division of layers, which is into three,
and shall not attempt to follow the excessively minute descriptions of the early arrange-
ment of cells, given by some recent observers.

A general idea of the development of certain of the important parts of the embryon will
aid us in comprehending the more minute processes and the formation of special organs ;
and this we can give without reference to the various divisions of the blastodermic layers
adopted by different writers. It makes very little difference, indeed, as regards our actual
knowledge of development, whether we restrict the external blastodermic membrane to
the development of the epidermis, or whether we assume that a portion of it forms the
walls of the neural canal. In the latter case, we simply make a thicker external layer
at the expense of a portion of the intermediate layer. It is the discussion of such minor
points as this, which depend mainly upon observations made upon the chick, that we
propose to avoid, in our endeavor to make the description of the first processes of devel-
opment as simple as possible.

We may assume that the furrow for the spinal canal and its dilated superior portion,
the head, have been closed over by the union of the dorsal, or medullary plates behind.
At a later period, there has been a growth of the abdominal, or visceral plates, which
finally close over the front of the embryon. Now, to adopt, with slight modifications, a
simile given by Hermann, we may imagine a young mammal, with a short, straight ali-
mentary canal, taking no account, for the present, of its glandular appendages. We take
the entire body as a tube, the caliber of which is the alimentary canal, with walls formed
of concentric layers. Counting these layers from within outward, we have first, the
mucous membrane ; next, the muscular coat of the intestine ; then, the visceral serous
membrane, the parietal serous membrane, the muscles of the trunk, with the bones ; and
finally, the integument. All of these layers are developed, to a greater or less degree,
simultaneously, from different layers of the blastodermic cells. With the view that we
shall adopt, the external blastodermic membrane becomes the epidermis, and the internal
blastodermic membrane, the epithelium of the alimentary canal. The intermediate mem-
brane splits into two layers; the outer layer becoming attached to the external blasto-
dermic membrane and forming the muscular layer of the trunk, while the inner layer is
connected with the internal blastodermic membrane and contributes to the formation of
the viscera. At a later period, the extremities are developed, as solid processes con-
nected with the outer layer of the intermediate membrane and covered by a prolonga-
tion of the external blastodermic membrane.

Development of the Cavities and Layers of the Trunk in the Chicle. — As an intro-
duction to a description of the development of special organs in the human subject and
in mammals, it will be found very useful to study the first stages of development in the
chick, by which we can get an idea of the arrangement of the different blastodermic
layers, and the way in which they are developed into the different parts of the trunk,
with the mode of formation of the great cavities. In doing this, we shall endeavor to
describe the figures given by Briicke, which were photographed on wood from large dia-
grams, made from actual preparations, by Seboth. In this description, we shall take no
account of the formation of the membranes.

Fig. 294 illustrates one of the earliest stages of development in the chick. In this

DEVELOPMENT OF THE EMBRYON.

913

figure, the superior layer of dark cells (5, &) represents the external blastodermic mem-
brane. The inferior layer of dark cells (d, d) represents the internal blastodermic mem-
brane. The middle layer of lighter cells is the intermediate membrane, which, toward

FIG. 294.

the periphery, is split into two layers. This figure represents a transverse section. At
a, is a transverse section of the groove which is subsequently developed into the canal
for the spinal cord. Beneath this groove, is a section of a rounded cord (V), the chorda
dorsalis. The openings (</, g) represent the situation of the two aorta}. The other cavities
are as yet indistinct in this figure.

FIG. 295.

Fig. 295 shows the same structures at a more advanced stage of development. The
dorsal, or vertebral plates, which bound the furrow (a) in Fig. 294, are closed above,
and include (a) the neural canal. The chorda dorsalis (e) is separated from the cells sur-
rounding it in Fig. 294. We have still the external blastodermic membrane (5, 5) and the
internal blastodermic membrane (d, d), presenting various curves which follow the arrange-
ment of the cells of the intermediate layer. By
the sides of the boundaries of the neural canal,
are two distinct masses of cells (c, c), which are
developed into the vertebra). Outside of these
masses of cells, are two smaller collections of
cells, afterward developed into the Wolffian
bodies, which will be described farther on.
Beneath those two masses, are two large cavi-
ties (0r, g\ the largest cavities shown in Fig.
295, presenting an irregular form, which are
sections of the two primitive aorta3. The two
openings (A, 7i) become afterward the pleuro-
peritoneal cavity.

In Fig. 296, the parts are still farther de-
veloped. The neural canal is represented (a)
nearly the same as in Fig. 295, with the chorda
dorsalis (e) just beneath it. A groove, or gutter
(d) has been formed in front, which is the groove of the intestinal canal. This remains
open at this time and is lined by the internal blastodermic membrane. Just above d, is
58

FIG. 296.

914 GENERATION".

a single opening (g\ which is formed by the union of the two openings (g, g) in Figs.
294 and 295, and this is the abdominal aorta, which has here become single. The two
openings (h, h) represent a section of the pleuro-peritoneal cavity. The outer wall of
this cavity is the outer visceral plate, which is developed into the muscular walls of the
abdomen. The lower and inner wall is the inner visceral plate, which forms the main
portion of the intestinal wall. The outer wall is the outer layer of the intermediate
membrane, and the inner wall is the inner layer of the same membrane. The two round
orifices (i, i) are sections of the Wolffian ducts. The space (&, 5) is the amniotic cavity.

The figures we have just described, it must be borne in mind, represent transverse sec-
tions of the body of the chick, made through the middle portion of the abdomen. In our
explanations of these figures, we have not adhered absolutely to the text of Briicke, but
have made use of the very elegant semi-diagrammatic illustrations by Waldeyer, whose
explanations are remarkably clear and satisfactory. Our explanations, however, particu-
larly those of Fig. 296, are sufficiently extended to enable us to study the development
of special organs. The posterior parts, it is seen, are developed first, the situation of the
vertebral column being marked soon after the enclosure of the neural canal by the verte-
bral plates ; and, at about the same time, the two aortse make their appearance, with the
first traces of the pleuro-peritoneal cavity. The next organs in the order of development,
after the vascular system, are the Wolffian bodies, which are so large and important in
the early life of the embryon. The intestinal canal is then a simple groove, and the em-
bryon is entirely open in front. Were we now to follow the process of development far-
ther, we should see that the visceral plates advance and close over the abdominal cavity,
as the medullary plates have closed over the neural canal. Thus there would be formed a
closed tube, the intestine, lined by the thin, internal blastodermic membrane, the walls of
the intestine being formed of the inner layer of the intermediate membrane. This would
bring the external layer of the intermediate membrane around the intestine to form the
muscular walls of the abdomen, the cavity (Fig. 296, A, Ji) being the peritoneal cavity, and
the external covering being the external blastodermic membrane. At this time, the great
Wolffian bodies lie next the spinal column, between the intestine and the abdominal
walls, with the single abdominal aorta situated behind the intestine.

Development of the Skeleton, Muscular System, and Skin.

Chorda Dorsalis. — One of the earliest structures observed in the developing embryon
is the chorda dorsalis. This is situated beneath the neural canal and extends the entire
length of the body. It is formed of a cord of simple cells, and marks the situation of the
vertebral column, though itself it is not developed into the vertebrae, which grow around
it and encroach upon its substance, until it finally disappears. This structure has been
very minutely described by Robin, under the name of the notocorde. In many mam-
mals, the notocorde presents a slight enlargement at the cephalic extremity, which ex-
tends to the auditory vesicles and it is somewhat diminished in size at the caudal extrem-
ity. By the sides of this cord, are the masses of cells which are eventually developed
into the vertebrae. The vertebrae, as they are developed, are formed of temporary car-
tilaginous structure, gradually extending around the chorda dorsalis, which then occupies
the axis of the spinal column. Between the bodies of the vertebras, the chorda dorsalis
presents regular enlargements, surrounded by a delicate membrane. As ossification of
the spinal column advances, that portion of the chorda dorsalis which is surrounded by
the bodies of the vertebrae disappears, leaving the enlargements between the vertebrae
distinct. These enlargements, which are not permanent, are gradually invaded by fibrous
tissue, their gelatinous contents disappear, and the intervertebral disks, composed of fibro-
cartilaginous structure, remain. These disks are permanent between the cervical, the
dorsal, and the lumber vertebraB ; but they eventually disappear from between the dif-
ferent parts of the sacrum and coccyx, as these are consolidated, this occurring, in the

DEVELOPMENT OF THE SKELETON, MUSCULAR SYSTEM, AND SKIN. 915

human subject, at from the ninth to the twelfth year,
just described are represented in Fig. 297.

The processes of development

Vertebral Column, etc. — In Figs. 295 and 296 (c, c), are seen the two masses of cells,
situated by the sides of the neural canal, which are destined to be developed into the
vertebrae. These cells extend around and encroach upon the chorda dorsalis and form

the bodies of the vertebrae. They also ex-
tend over the neural canal, closing above,
and these processes are called the medul-
lary, or dorsal plates. Sometimes the dorsal
plates fail to close at a certain point in the
spinal column, and this constitutes the mal-
formation known as spina bifida. From the
sides of the bodies of the vertebrae, the va-
rious processes of these bones are formed.
As the spinal column is developed, its lower
portion presents a projection beyond the
pelvis, which constitutes a temporary caudal
appendage, curved toward the abdomen ; but
this no longer projects after the bones of the
pelvis are fully developed. At the same time,
the entire vertebral column is curved toward
the abdomen, and it is twisted upon its axis
from left to right, so that the anterior face
of the pelvis presents a right angle to the

FIG. 297.— The first six cervical vertebrae of the embryon
of a rabbit one inch in length. (Robin.)

rt, b, cephalic portion of the notocorde exposed by the re-
moval of the cartilage ; b, portion of the chorda dor-
salis slightly enlarged, which, in this embryon, was
situated between the atlas and the occipital bone ; c,
odontoid process ; d, base of the odontoid process ; e,
inferior, or second part of the body of the axis; /, fc,
enlargements of the chorda dorsalis between the ver-
tebrae ; a, cartilage of the lateral portion of the atlas ;
h, lateral portion of the axis ; i, i, transverse apophy-
ses of vertebrae.

FIG. 298. — Human embryo, about one month old, show-
in^ the large sine of the head and upper parts of fie
body, the twisted form of the spinal column, the
rudimentary condition of the upper and lou-er
extremities, and the rudimentary tail at the end
of the spinal column. (Dalton.)

upper part of the body ; but, as the inferior extremities and the pelvis become developed,
the spine becomes straight. The vertebrae make their appearance first in the middle of
the dorsal region, from which point, they rapidly extend upward and downward, until
the spinal column is complete.

At the base of the skull, on either side of the superior prolongation of the chorda dor-
salis, are two cartilaginous processes, which are developed into the so-called cranial ver-
tebra. In this cartilaginous mass, three ossific points appear, one behind the other.
The posterior point of ossification is for the basilar portion of the occipital bone, which
is developed in the same way as one of the vertebrae ; the middle point is for the poste-
rior portion of the sphenoid ; and the anterior point is for the anterior portion of the
sphenoid. The frontal bone, the parietal bone, the temporal bone, and a portion of the
occipital bone are developed from the connective tissue, without the intervention of pre-

916 GENERATION.

existing cartilaginous structure. The development of the face will be described separately.
At the time when the vertebree are being developed, with their lamina? and their spinous
and transverse processes, the ribs extend over the thorax, and the clavicle, scapula, and
sternum make their appearance.

At about the beginning of the second month, four papillary prominences, which are
the first traces of the arms and legs, appear on the body of the embryon. These progres-
sively increase in length, the arms appearing near the middle of the embryon, and the
legs, at the lower portion. Each extremity is divided into three portions, the arm, fore-
arm, and hand, for the upper extremities, and the thigh, leg, and foot, for the lower ex-
tremities. At the end of each extremity, there are, finally, divisions into the fingers and
toes, with the various cartilages and bones of all of these parts, and their articulations.
(See Plates I. and II., Figs. I) and II, facing page 920.)

Very early in intra-uterine life, the skeleton, which is at first entirely cartilaginous,
begins to ossify, from little bony points which appear in the cartilaginous structure. The
first points appear at nearly the same time (about the beginning of the second month) in
the clavicle and the upper and the lower jaw. Similar ossific points, which gradually
extend, are also seen in other parts, the head, ribs, pelvis, scapula, metacarpus, and meta-
tarsus, and the phalanges of the fingers and toes. At birth, the carpus is entirely cartila-
ginous, and it does not begin to ossify until the second year. The same is true of the
tarsus, except the calcaneum and astragalus, which ossify just before birth. The pisiform
bone of the carpus is the last to take on osseous transformation, this occurring at from
the twelfth to the fifteenth year. As ossification progresses, the deposits in the various
ossific points gradually extend until they reach the joints, which remain incrusted with
the permanent articular cartilage.

While the skeleton is being thus developed, the muscles are formed from the outer
layer of the intermediate blastodermic membrane, and the visceral plates close over the
thorax and abdomen in front, leaving an opening for the umbilical cord. The various
tissues of the external parts, particularly the muscles, begin to be distinct at the end of
the second month. The deep layers of the dorsal muscles are the first to be distin-
guished ; then, successively, the long muscles of the neck, the anterior straight muscles
of the head, the straight and transverse muscles of the abdomen, the muscles of the ex-
tremities, the superficial muscles of the back, the oblique muscles of the abdomen, and
the muscles of the face.

The skin appears at about the beginning of the second month, when it is very delicate
and transparent. At the end of the second month, the epidermis may be distinguished.
The sebaceous follicles are developed at the third month ; and, at about the fifth month,
the surface is covered with their secretion mixed with desquamated epithelium. This
cheesy substance constitutes the vernix caseosa. At the third month, the nails make
their appearance, and the hairs begin to grow at about the fifth month. The sudoripa-
rous glands first appear at about the fifth month, by the formation of flask-like processes
of the true skin, which are gradually elongated and convoluted, until they are fully
developed only a short time before birth.

Development of the Nervous System.

We have seen, in studying the development of the spinal column, how the dorsal, or
medullary plates close over the groove for the neural canal. In the interior of this
canal, the cerebro-spinal axis is developed, by cells, which gradually encroach upon its
caliber, until we have remaining only the small central canal of the spinal cord, commu-
nicating with the ventricles of the brain. As the nervous tissue is developed in the inte-
rior of the neural canal, there is a separation of the histological elements at the surface,
to form the membranes. The dura mater and the pia mater are formed first, appearing
at about the end of the second month, while the arachnoid is not distinct until the fifth

DEVELOPMENT OF THE NERVOUS SYSTEM. 917

month. The nerves are not produced as prolongations from the cord into the various
tissues, nor do they extend from the tissues to the cord ; but they are developed, in each
tissue, by a separation of histological elements from the cells of which the parts are
originally constituted, which at first appear to be identical in their morphological char-
acters. The nerves of the sympathetic system are developed in the same way.

The mode of development of the spinal cord is thus sufficiently simple ; but, with the
growth of the embryon, we observe dilatations at the superior and at the inferior extrem-
ities of the neural canal. The cord is uniform in size in the dorsal region, marked only
by the regular enlargements at the sites of origin of the spinal nerves ; but we soon
observe an ovoid dilatation below, which forms the lumbar enlargement, from which the
nerves are given off to the inferior extremities, and the brachial enlargement above, where
the nerves of the superior extremities take their origin. At the same time, there is a
more marked dilatation of the canal at its cephalic extremity. Here, a single enlargement
appears, which is soon divided into three vesicles, called the anterior, middle, and poste-
rior cerebral vesicles. These become more and more distinct as development advances.
The formation of these parts is illustrated in Fig. 299, taken from "Wagner, and mado
more distinct by Longet, as they are drawn upon a black ground. This figure, in C,
shows the projections, on either side, of the vesicles which are eventually developed
into the nervous portions of the organ of vision.

FIG. 299. — Development of the nervous system of the chick (Longet )

A, the two primitive halves of the nervous system, twenty-four hours after incubation ; B, the same, thirty-six hours
after ; C. the same, at a more advanced stage, c, the two primitive halves of the vertebrae ; d, anterior dilata-
tion of the neural canal; A, posterior dilatation (the lumbar enlargement) ; 1, 2, 8, anterior, middle, and inferior
cerebral vesicles ; a, slight flattening of the anterior cerebral vesicle ; o, formation of the ocular vesicles.

The three cerebral vesicles now undergo farther changes. The superior, which we
may call the first primitive vesicle, enumerating them from above downward, is soon
divided into two secondary vesicles, the anterior of which becomes the cerebral hemi-
spheres, and the posterior, the optic thalami, which are eventually covered, by the great-
er relative development of the hemispheres. The middle, or second primitive vesicle,
does not undergo division and is developed into the tubercula quadrigemina, or centres
of vision. The posterior, or third primitive vesicle, is divided into two secondary vesi-
cles, the anterior of which becomes the cerebellum, and the posterior, which is covered
by the anterior, the medulla oblongata and the pons Varolii. While this division of the
primitive cerebral vesicles is going on, the entire chain of encephalic ganglia becomes
curved from behind forward, forming three prominent angles. The first of these angles
or prominences («, Fig. 300, A, B, C), counting from before backward, is formed by a
projection of the tubercula quadrigemina, which, at this time, constitute the most pro-
jecting portion of the encephalic mass ; the second prominence (>, Fig. 300), situated
behind the tubercula quadrigemina, is formed by the projection of the cerebellum ; the

918 GENERATION.

third (<#, Fig. 300, A, B, C), is the bend of the superior portion of the spinal cord.
These projections and the early formation of certain parts of the encephalon in the
human subject are illustrated in Fig. 300.

The cerebrum, as we have just seen, is developed from the anterior division of the
first primitive cerebral vesicle. The development of this part is more rapid in its lateral
portions than in the median line, which divides the cerebrum imperfectly into two lateral
halves, forming, in this way, the great longitudinal fissure. At the same time, by the
rapid development of the posterior portion, it extends over the optic thalami, the cor-
pora quadrigemina, and the cerebellum. Up to the end of the fourth month, the hemi-
spheres are smooth on their surface ; but they then begin to present large depressions,
following folds of the pia mater, which are the first convolutions, these increasing rap-

FIG. 300.— Development of the spinal cord and brain of the human subject. (Longet.)

A, brain and spinal cord of an embryon of seven weeks ; lateral view.

B, the same, from an embryon farther advanced in development; ft, spinal cord; d. enlargement of the spinal cord

with its anterior curvature ; c, cerebellum ; e, tubercula quadrigemina ; /, optic thalamus ; gr, cerebral hemi-
spheres.

C, brain and spinal cord of an embryon of eleven weeks ; b. spinal cord ; d, enlargement of the spinal cord, with

its anterior curvature ; c, cerebellum ; e, tubercula quadrigemina ; g, cerebral hemispheres ; o, optic nerve of
the left side.

C', the same parts in a vertical section in the median line from before backward ; ft, membrane of the spinal cord
turned backward ; d, second curvature of the upper portion of the spinal cord, which has become thickened and
constitutes the peduncles of the cerebrum ; e, tubercula quadrigemina ; /; optic thalami covered by the hemi-
spheres.

idly in number and complexity, especially after the seventh month. The septum lucidum
is then formed by an elevation of nervous matter from the base, which divides the lower
portion of the space left between the hemispheres as they ascend, and forms the two
lateral ventricles. At the base of these, are developed the corpora striata. The septum
lucidum is formed of two laminae, with a small space between them, which is the cavity
of the fifth ventricle. The posterior division of this first primitive vesicle forms the
optic thalami. These become separated in front into two lateral halves, but they remain
connected together at their posterior portion, which becomes the posterior commissure.
The central canal of the cord is prolonged upward between the optic thalami, and forms
the third ventricle, which is covered by the hemispheres.

The second, or middle cerebral vesicle becomes filled with medullary substance, ex-
tends upward, and forms the peduncles of the cerebrum, the upper portion being divided
to form the tubercula quadrigemina.

The anterior portion of the third primitive vesicle is developed into the cerebellum,
the convolutions of which appear at about the fifth month. Its posterior portion forms
the medulla oblongata, in the substance of which is the fourth ventricle, communicating
with the third ventricle by a little canal, the aqueduct of Sylvius, which is left in the
development of the middle vesicle. At about the fourth month, there is a deposition of
nervous matter in front and above, forming the pons Varolii.

In Fig. 299 ((7, 0), it is seen that the vesicles for the organs of vision appear very early,
as lateral offshoots of the anterior cerebral vesicle. These gradually increase in size and
advance anteriorly, as development of the other parts progresses. We shall see, when
we come to study the development of the face, that the eyes are situated at first at the
sides of the head, gradually approaching the anterior portion. At the extremity of each
of these lateral prolongations, a rounded mass appears, which becomes the globe of the

DEVELOPMENT OF THE ALIMENTARY SYSTEM. 919

eye. The superficial portions of the globe are developed into the sclerotic and the cornea,
which seem to be formed of a process from the dura mater. The pedicle attached to the
globe becomes the optic nerve. The iris is developed at about the seventh week, and is
at first a simple membrane, without any central opening. As the pupil appears, it is
closed by a vascular membrane — which probably belongs to the capsule of the crystal-
line lens — called the pupillary membrane. This membrane gradually disappears by an
atrophy extending from the centre to the periphery. It attains its maximum of develop-
ment at the sixth month and disappears at the seventh month. The vitreous humor is
formed of the fluid contents of the optic vesicle. The crystalline lens is regarded as a
product of the tegumentary layer. At the tenth week, we observe the beginning of the
formation of the eyelids. These meet at about the fourth month and adhere together by
their edges. In many mammals, the eyelids remain closed for a few days after birth ; but
they become separated in the human subject in the later periods of foetal life.

It is probable that the vesicle which becomes developed into the internal ear is formed
independently ; at least, cases have been observed in which there was congenital absence
of the auditory nerves, the parts of the internal ear being perfect. Soon after the forma-
tion of the auditory vesicle, however, it communicates with the third primitive cerebral
vesicle, the filament of communication being developed into the auditory nerve.

The auditory vesicle, which appears subsequently to the organ of vision, is eventually
developed into the vestibule. The next formations are the arches, or diverticula, which
constitute the semicircular canals. The membranous labyrinth appears long before the
osseous labyrinth ; anl it has been found perfectly developed at three months. The bones
of the middle ear, which have no connection, in their development, with the nervous
system, but which it is convenient to mention here, are remarkable for their early appear-
ance. They appear at the beginning of the third month and are as large in the foetus at
term as in the adult. A remarkable anatomical point with relation to these structures is
the existence of a cartilage, attached to the malleus on each side and extending from this
bone along the inner surface of the lower jaw, the two cartilages meeting and uniting in
the median line to form a single cord. " This cartilage now ossifies, although, in the
commencement, it forms most of the mass of the bone ; it disappears at the eighth month."
(Meckel.) This curious structure is known as the cartilage of Meckel.

There are no special points for description in the development of the olfactory lobes,
which is very simple. These are offshoots from the first cerebral vesicle, appearing at the
inferior and anterior part of the cerebral hemispheres, a little later than the parts con-
nected with vision and audition. The vesicles themselves become filled with ganglionic
matter, and constitute the olfactory bulbs, their pedicles being the so-called olfactory
nerves, or commissures. The development of some of the parts of the central nervous
system is illustrated in Plates I. and II., facing page 920.

As far as the functions of the nervous system of the foetus are concerned, it is probable
that they are restricted mainly to reflex phenomena depending upon the action of the
spinal cord, and that perception and volition hardly exist. It is probable that many reflex
movements take place in utero. When a foetus is removed from the uterus of an animal,
even during the early periods of pregnancy, movements of respiration occur, a fact which
we have often demonstrated to medical classes; and it is well known that efforts of respi-
ration sometimes occur within the uterus. This we believe to be due to the want of
oxygen-carrying blood in the medulla oblongata when the pincental circulation is inter-
rupted. We have already discussed these phenomena under the head of respiration.

Development of the Alimentary System.

The intestinal canal is the first formation of the alimentary system. As we have
already seen, this is at first open in the greatest part of its extent, presenting, at either
extremity of the longitudinal gutter, in front of the spinal column, a rounded, blind ex-

920 GENERATION.

tremity, which is closed over in front for a short distance. The closure of the abdominal
plates then extends laterally and from the two extremities of the intestine, until we have
only the opening remaining for the passage of the umbilical cord and the pedicle of the
umbilical vesicle. There is at first an open communication between the lower part of the
intestinal tube and the allantois, which forms the canal known as the urachus ; but that
portion of this communication which remains enclosed in the abdominal cavity becomes
separated from the urachus, is dilated, and eventually forms the urinary bladder. When
the bladder is first shut off, it communicates with the lower portion of the intestine, which
is called the cloaca ; but it finally loses this connection and presents a special opening)
the urethra.

As development advances, the intestine grows rapidly in length and becomes convo-
luted. It is held loosely to the spinal column by the mesentery, a fold of the peritoneum,

this membrane being reflected along the walls of the ab-
dominal cavity. In the early stages of development, a por-
tion of the intestine protrudes at the umbilicus, where the
first intestinal convolution appears; and sometimes there
is a congenital hernia of this kind at birth, which usually
disappears under the influence of gentle and continued
pressure. An illustration of this is given in Fig. 301. This
protrusion, in the normal process of development, is grad-
ually returned into the abdomen, as the cavity of the pedi-
cle of the umbilical vesicle is obliterated, at about the tenth
week.

At the upper part of the abdominal cavity, the aliment-
.— Fatal piff,8hou>inff a loop &TJ canal presents two lateral projections, or pouches.

The one on the left side' as Jt increases in size> becomes the
the possession of Prof. Daiton. greater pouch of the stomach, and the one on the right

side> the lesser pouch.

umbilical vesicle, which is here At a short distance below the attachment of the pedicle

flattened into a leaf-like form. f .. , .,. , . , ,, . , ,. ,,

of the umbilical vesicle to the intestine, there appears a

rounded diverticulum, which is eventually developed into the caecum, or the commence-
ment of the larger intestine. The caecum gradually recedes from the neighborhood of the
umbilicus, which is its original situation, and finally becomes fixed, by a shortening of the
mesentery, in the right iliac region. As the csecum, or caput coli, is developed, it presents
a conical appendage, which is at first fully as large as the small intestine and is relatively
longer than in the adult. During the fourth week, this appendage becomes relatively smaller
and more or less twisted, forming the appendix vermiformis. At the second month, the
caecum, or caput coli, as we have seen, is at the umbilicus, and the large intestine extends
in a straight line toward the anus ; at the third month, it is situated at about the middle
of the abdomen ; and it gradually descends, until it reaches the right iliac region at about
the seventh month. Thus, at the second month, there is only a descending colon ; the
transverse colon is formed at the third month ; and the ascending colon, at the fifth
month. The ileo-caecal valve appears at the third month ; the rectum, at the fourth
month ; and the sigmoid flexure of the colon, at the fifth month. During this time, the
large intestine increases more rapidly in diameter than the small intestine, while the latter
develops more rapidly in its length.

In the early stages of development, the surface of the intestines is smooth ; but villi
appear upon its mucous membrane during the latter half of intra-uterine existence.
These are found at first both in the large and the small intestine. At the fourth month,
they become shorter and less numerous in the large intestine, and they are lost at about
the eighth month, when the projections which bound the sacculi of this portion of the
intestinal canal make their appearance. The valvulae conniventes appear, in the form of
slightly-elevated, transverse folds, in the upper portion of the small intestine. The villi
of the small intestine are permanent.

Gerins or Embryos

Fios. A, B, E, F.-v, anterior cerebral hemispheres ; 2, optic thalami, m, tubercula quadii-
gemina ; h, cerebellum ; w, pons Varolii ; r, spinal cord ; w, spine ; *, tail ; a, eyes ;
na, nose ; o, ear; *t, k^ A;3, visceral arches ; bv, anterior extremity ; M, posterior ex-
tremity. (Haeckel.)

of four Vertebrates.

PI. IT.

FIGS. (7, 2), #, H.— v, anterior cerebral hemispheres ; z, optic thalami ; m, tubercula quadri-
gemina ; A, cerebellum ; w, pons Varolii ; r, spinal cord ; w, epine ; «, tail ; a, eyes
no, nose ; 0, ear; *n A;,, *s, visceral arches ; Jr, anterior extremity ; bh, posterior ex-
tremity. (Haeckel.)

DEVELOPMENT OF THE ALIMENTAKY SYSTEM. 921

The mesentery is first formed of two perpendicular folds, attached to the sides of the
spinal column. As the intestine undergoes development, a portion of the peritoneal
membrane extends in a quadruple fold from the stomach to the colon, to form the great
omentum, which covers the small intestine in front.

As the head undergoes development, a large cavity appears, whieh is eventually
bounded by the arches that are destined to form the different parts of the face. This is
the pharynx. It is entirely independent, in its formation, of the intestinal canal, the
latter terminating in a blind extremity at the stomach ; and, between the pharynx and
the stomach, there is at first no channel of communication. The anterior portion of the
pharynx presents, during the sixth week, a large opening, which is afterward partially
closed in the formation of the face. The rest of this cavity remains closed until a com-
munication is effected with the oesophagus. The oesophagus appears in the form of a
tube, which finally opens into the pharynx above and into the stomach below. At this
time, there is really no thoracic cavity, the upper part of the stomach is very near the
pharynx, the resophagus is short, the rudimentary lungs appear by its sides, and the heart
lies just in front. As the thorax is developed, however, the O3sophagus becomes longer,
the lungs increase in size, and finally the diaphragm shuts off its cavity from the cavity
of the abdomen. The growth of the diaphragm is from its periphery to the central por-
tion, which latter gives passage to the vessels and the oesophagus. Sometimes, when this
closure is incomplete, we have the malformation known as congenital diaphragmatic
hernia.

The development of the anus is sufficiently simple. At first, as we have seen, the
intestine terminates below in a blind extremity ; but, at about the seventh week, a lon-
gitudinal slit appears below the external organs of generation, by which the rectum
opens. This is the anus. It is not very unusual to observe an arrest in the development
of this opening, the intestine terminating in a blind extremity, a short distance beneath
the integument. This constitutes the malformation known as imperforate anus, a de-
formity which can usually be relieved; without much difficulty, by a surgical operation, if
the distance between the rectum and the skin be not too great. The opening of the anus
appears about a week after the opening of the mouth, at or about the seventh week.

The rudiments of the liver appear very early, and, indeed, at the end of the first
month, this organ has attained an enormous size. Two projections, or buds, appear on
either side of the intestine, which form the two principal lobes of the liver. This organ
is at first symmetrical, the two lobes being of nearly the same size, with a median fis-
sure. One of these prolongations from the intestine becomes perforated and forms the
excretory duct, of which the gall-bladder, with its duct, is an appendage. During the
early part of foetal life, the liver occupies the greatest part of the abdominal cavity.
According to Burdach, its weight, in proportion to the weight of the body at different
ages, is as follows : At the end of the first month, 1 to 3 ; at term, 1 to 18 ; in the
adult, 1 to 36. Its structure is very soft during the first months, and it is only at about
the fourth or fifth month that it assumes one of its most important functions, viz., the
production of sugar. As development advances, and as the relative size of the liver
gradually diminishes, its tissue becomes more solid.

The pancreas appears at the left side of the duodenum, by the formation of two ducts
leading from the intestine, which branch and develop glandular structure at their ex-
tremities. The spleen is developed, about the same time, at the greater curvature of the
stomach. This organ is abundantly supplied with blood-vessels, but it has no excretory
duct. The spleen becomes distinct during the second month.

There is no reason to believe that any of the digestive fluids are secreted during
infra-uterine life. The stomach, at least, never contains, at this time, an acid secretion.
At birth, the intestine contains a peculiar substance, called meconium, which will be
described farther on. Cholesterine, an important constituent of the bile, is found in the
meconiura in large quantity, but its function is connected exclusively with excretion.

923 GENERATION.

Development of the Respiratory System.

On the anterior surface of the membranous tube which becomes the oesophagus, an
elevation appears, which soon presents an opening into the oesophagus, the projection
forming, at this time, a single, hollow cul-de-sac. This opening becomes the rima glotti-
dis, and the single tube with which it is connected is developed into the trachea. At the

lower extremity of this tube, a bifurca-
tion appears, terminating first in one,
and afterward, in several culs-de-sac.
The bifurcated tube constitutes, after
the lungs are developed, the primitive
bronchi, at the extremities of which are
the branches of the bronchial tree. As
the bronchi branch and subdivide, they
extend downward into what becomes
eventually the cavity of the thorax.

.— Formation of the bronchial ramifications and „.,

e pulmonary cells.— A, B, development of the hm(js, The pulmonary vesicles, according to

S% &&*&!&• "e°el0llmeni °fi"e Bnrdaoh, are developed before the tra-

chea. The lungs contain no air at any

period of intra-uterine life, and receive but a small quantity of blood ; but, at birth,
they become distended with air, are increased thereby in volume, and receive all the
blood from the right ventricle. This process of development is illustrated in Fig. 302.
The lungs appear, in the human embryon, during the sixth week. The two portions into
which the original bud is bifurcated constitute the true pulmonary structure, and the
formation of the trachea and bronchial tubes occurs afterward and is secondary. We
have indicated the pulmonary structure as branching processes from the bronchial tubes,
merely for convenience of description.

Development of the Face.

The development of the face in the embryon of mammals is somewhat complex, but
it is peculiarly interesting, as its study enables us to comprehend the manner in which
various very common malformations of the face and palate are produced. The anterior
portion of the embryon, as we have seen in studying the development of the trunk, re-
mains open in front long after the medullary plates have met at the back and enclosed
the neural canal. The common cavity of the thorax and abdomen is closed by the
growth of the visceral plates, which meet in front. These are projecting plates of the
intermediate blastodermic layer, which gradually extend forward from the vertebral col-
umn. At the same time that the visceral plates are thus closing over the thorax and
abdomen, four distinct, tongue-like projections appear, one above the other, by the sides
of the neck. These are called the visceral arches, and the slits between them are called
the visceral clefts.1 The first three arches, enumerating them from above downward, cor-
respond, in their origin, to the three primitive cerebral vesicles. The fourth arch, which
is not enumerated by some authors, who recognize but three arches, corresponds to the
superior cervical vertebrsD. Of these four arches, the first is the most important, as its
development, in connection with that of the frontal process, forms the face and the mal-
leus and incus of the middle ear. The second arch forms the lesser cornua of the hyoid
bone, the stapes, and the styloid ligament. The third arch forms the body and the greater
cornua of the hyoid. The fourth arch forms the larynx. The first cleft, situated be-
tween the first and the second arch, becomes obliterated in front by a deposition of
plastic matter, but an opening remains by the side, which forms, externally, the external

1 These arches correspond to the branchial vascular arches, which will be fully described in connection with the
development of the circulatory system.

Fil.l.

m

Fig. 2

1. Human embryo, at the ninth week, removed from the membranes ; three times the natural

size. (Erdl.)

2. Human embryo, at the twelfth week, inclosed in the amnion ; natural size. (Erdl.)

DEVELOPMENT OF THE FACE. 923

auditory meatus, and internally, the tympanic cavity and the Eustachian tube. The
other clefts become obliterated as the arches advance in their development.

From the above sketch, it is seen that the face and the neck are formed by the
advance and closure in front of projections from behind, in the same way as the cavities
of the thorax and abdomen are closed ; but the closure of the first visceral arch is
complicated by the projection, from above downward, of the frontal, or intermaxillary
process, and by the formation of several secondary projections, which leave certain per-
manent openings, forming the mouth, nose, etc. These processes of development, we
shall now attempt to follow.

In the very first stages of development of the head, there is no appearance of the
face. The cephalic extremity consists simply of the cerebral vesicles, the surface of this
enlarged portion of the embryon being covered, in front as well as behind, by the exter-
nal blastodermic membrane. During the sixth week, after the cavity of the pharynx
has appeared, the membrane gives way in front, forming a large opening, which may be
called the first opening of the mouth. At this time, however, the face is entirely open
in front as far back as the ears. The first, or the superior visceral arch, now appears
as a projection of the middle blastodermic layer, extending forward. This is soon marked
by two secondary projections, the upper projection forming the superior maxillary por-
tion of the face, and the lower, the interior maxilla. The two projections which form
the lower jaw soon meet in the median line, and their superior margin is the lower lip.
At the same time there is a projection from above, extending between the two superior
projections, which is called the frontal, or intermaxillary process. This extends from
the forehead (that portion which covers the front of the cerebrum) downward. The
superior maxillary projections then advance forward, gradually passing to meet the
frontal process, but leaving two small openings on either side of the median line, which
are the openings of the nostrils. The upper portion of the frontal process thus forms
the nose ; but below, is the lower end of this process, which is at first split in the median
line, projects below the nose, and forms the incisor process, at the lower border of which
are finally developed the incisor teeth. As the superior maxillary processes advance
forward, the eyes are moved, as it were, from the sides of the head and present anteriorly,
until finally their axes become parallel. These processes advance from the two sides,
come to the sides of the incisor process beneath the nose, unite with the incisor process
on either side, and their lower margin, with the lower margin of the incisor process,
forms the upper lip ; but, before this, the two lateral halves of the incisor process have
united in the median line. At the bottom of the cavity of the mouth, a small papilla
makes its appearance, which gradually elongates and forms the tongue.

While this process of development of the anterior portion of the first visceral arch
is going on, at its posterior portion, we have developing, the malleus and incus, the
former being at first connected with the cartilage of Meckel, which extends along the
inner surface of the inferior maxilla, the cartilages from either side meeting at the chin.
The cleft between the first and the second visceral arch has closed, except at its posterior
portion, where an opening is left for the external auditory meatus, the cavity of the
tympanum, and the Eustachian tube.

At the same time, the second visceral arch advances and forms the stapes, the styloid
ligament, and the lesser cornua of the hyoid bone. The third arch advances in the same
way ; and the arches from the two sides meet, become united in the median line, and
form the body and the greater cornua of the hyoid. The clefts between the second and
the third and between the third and fourth arches become obliterated by the deposition
of plastic matter.

The fourth arch forms the sides of the neck and the larynx, the arytenoid cartilages
being developed first. In front of the larynx and just behind the tongue, is a little ele-
vation, which is developed into the epiglottis. The openings of the nostrils appear during
the second half of the second month. A little elevation, the nose, appears between these

924

GENERATION.

openings, and the nasal cavity begins to be separated from the mouth. The lips are
distinct during the third month, and the tongue first appears in the course of the
seventh week.

The above sketch of the mode of develop-
ment of the face enables us to understand the
origin of certain of the more common malfor-
mations of this part. When, by an arrest of
development, the superior maxilla on one side
fails to unite with the side of the incisor
process, we have the very common deformity
known as single hare-lip. If this union fail on
both sides, we have double hare-lip, when the
incisor process is usually more or less project-
ing. As a very rare deformity, it is sometimes
observed that the two sides of the incisor pro-
cess have failed to unite with each other, leav-
ing a fissure in the median line.

It is somewhat difficult to comprehend the
exact mode of development of the face by ver-
bal description alone; but it will be readily
understood, after the account we have just
given, by studying Figs. 303, 304, and 305,
copied from the great atlas of Coste, and plates
I. and II., Figs. A, B, C, and D, facing page
920.

The palatine arch is developed by two pro-
cesses, which arise on either side from the in-
cisor process, pass backward and upward, and
finally meet and unite in the median line. The
union of these forms the plane of separation
between the mouth and the nares ; and want
of fusion of these processes, from arrest of de-
velopment, produces the malformation known as cleft palate, in which the fissure is
always in the median line. At the same time, a vertical process forms in the median
line, between the palatine arch and the roof of the nasal cavity, which separates the
two nares.

Development of the Teeth. — Recent embryological researches have shown that the old
idea of the development of the dental papillae in the bottom of a gutter formed at the
border of either jaw is erroneous. According to the most recent observers, the first
appearance of the organs for the development of the teeth is marked by the formation
of a cellular projection extending the entire length of the rounded border of each jaw,
which forms a rounded band above and dips down somewhat into the subjacent struct-
ure. This band is readily separated by maceration, and the removal of the portion that
dips into the maxilla leaves a groove, which is thought to be the explanation of the
description of a groove by the earlier writers. This band extends the entire length of
the jaws without interruption. Its superior surface is rounded, and that portion which
dips into the subjacent mucous structure is wedge-shaped, so that its section has the
form of a V.

As soon as this primitive band is formed, which occurs at the sixth or seventh week,
a flat band projects from its internal surface, near the mucous structure, which is called
the epithelial band. This also extends over the entire length of the jaws. It is thin,
flattened, with its free edge curved inward and toward the jaw, and is composed, at
first, of a central layer of polygonal cells, covered by a layer of columnar epithelium.

FIG. 303. — Mouth of a human embryon of from
twenty-Jive to twenty-eight days ; magnified 15
diameters. (Ooste.)

1, median or frontal process, the inferior portion of
which is considerably enlarged; 2, right nostril;
3, left nostril; 4, 4, inferior maxillary processes,
already united in the median line ; 5, 5, superior
maxillary processes, which have become quite

process ; 6, mouth ; 7, first vis-
ceral arch ; 8. second visceral arch ; 9, third visceral
arch ; 10, eye ; 11, ear.

DEVELOPMENT OF THE FACE.

925

At certain points — these points corresponding to the situation of the true dental
bulbs — there appear rounded enlargements at the free margin of the epithelial band-
just described. Each one of these is developed into one of the structures of the perfect
tooth. The mechanism of the formation of this, which is called the enamel-organ, and
of the dental bulb is as follows :

Fro. 304.— Mouth of a human embryon of thirty -five
days. (Coste.)

1, frontal process widely sloped at its inferior portion ;
2, 2, incisor processes produced by this sloping; 3, 3,
nostrils; 4, lower lip and maxilla, formed by the
union of the inferior maxillary processes; 5, 5, supe-
rior maxillary processes contiguous to the incisor
process; 6, mouth, still confounded with the nasal
fossae; 7, first appearance of the closure of the nasal
fossae ; 8, 8, first appearance of the two halves of
the palatine arch; y, tongue ; 10, 10, eyes; 11,12,
13, visceral arches.

FIG. 305. — Mouth of an embryon of forty days. (Coste.)
1, first appearance of the nose; 2, 2, first appearance of
the alee of the nose ; 3, appearance of the closure be-
neath the nose ; 4, middle, or median portion of the up-
per lip, formed by the approach and union of the two
incisor processes, a little notch in the median line still
indicating the primitive separation of the two processes ;
5, 5, superior maxillary processes, forming the lateral
portions of the upper lip ; 6. 0. groove for the develop-
ment of the lachrymal sac and the nasal canal ; 7, lower
lip; 8, mouth; 9, 9, the two lateral halves of the pala-
tine arch, already nearly approximated to each other
in front, but still widely separated behind.

A rounded enlargement appears at the margin of the epithelial band. This soon be-
comes directed downward (adapting our description to the lower jaw) and dips into the
mucous structure, being at first connected with the epithelial band by a narrow pedicle,
which soon disappears, leaving the enlargement enclosed completely in a follicle. This
is the dental follicle, and it has no connection with the wedge-shaped band which we de-
soribed first. While this process is going on, a conical bulb appears at the bottom of the
follicle. The enamel-organ, formed from the epithelial band, becomes excavated or cup-
shaped at its under surface and fits over the dental bulb, becoming united to it.

The tooth, at this time, consists of the dental bulb, with the enamel-organ closely
fitted to its projecting surface. The enamel-organ is developed into the enamel ; the
dental bulb, which is provided with vessels and nerves, becomes the tooth-pulp ; and,
upon the surface of the dental bulb, the dentine, or ivory, is developed in successive
layers. The cement is developed by successive layers upon that portion of the dentine
which forms the root of the tooth. As these processes go on, the tooth projects more
and more, the upper part of the wall of the follicle gives way, and the tooth finally
appears at the surface.

1 The periods of development indicated for these diagrams are somewhat earlier than those which we have
noted in the text ; but it Is impossible to fix these with absolute accuracy, and all the estimates given by authors are
understood to be merely approximative.

926

GENERATION.

The permanent teeth are developed beneath the follicles of the temporary, or milk-
teeth. The first appearance is a prolongation or diverticulum from the enamel-organ of
the temporary tooth, which dips more deeply into the mucous structure. This becomes
the enamel-organ of the permanent tooth ; and the successive stages of development of
the dental follicles and the dental pulp progress in the same way as in the temporary
teeth. As the permanent teeth increase in size, they gradually encroach upon the roots
of the temporary teeth. The roots of the latter are absorbed, the permanent teeth ad-

FIG. 306.— Temporary and permanent teeth. (Sappey.)

1, 1, temporary central incisors ; 2, 2, temporary lateral incisors ; 8, 8, temporary canines : 4. 4, temporary anterior
molars; 5, 5, temporary posterior molars; 6,6, permanent central incisors; 7, 7, permanent lateral incisors;
8, 8, permanent canines ; 9, 9, permanent first bicuspids ; 10, 10, permanent second bicuspids; 11, 11, first molars.

1, 1, tern]

vance more and more toward the surface, and the crown of each temporary tooth is
finally pushed out. The number of the temporary teeth is twenty, while there are
thirty-two permanent teeth. Thus there are three permanent teeth on either side of
both jaws, which are developed de now and are not preceded by temporary structures.

The first dental follicles usually appear in regular succession. The follicles for the
internal incisors of the lower jaw appear first, this occurring at about the ninth week.
All of the follicles for the temporary teeth are completely formed at about the eleventh
or the twelfth week.

The temporary teeth appear successively, the corresponding teeth appearing a little
earlier in the lower jaw. The usual order, subject to certain exceptional variations,
according to Sappey, is as follows :

The four central incisors appear from six to eight months after birth.

The four lateral incisors appear from seven to twelve months after birth.

The four anterior molars appear from twelve to eighteen months after birth.

The four canines appear from sixteen to twenty-four months after birth.

The four posterior molars appear from twenty-four to thirty-six months after birth.

DEVELOPMENT OF THE GENITO-URINAKY SYSTEM. 927

The order of eruption of the permanent teeth is as follows :

The two central incisors of the lower jaw appear from the sixth to the eighth year.

The two central incisors of the upper jaw appear from the seventh to the eighth year.

The four lateral incisors appear from the eighth to the ninth year.

The four first bicuspids appear from the ninth to the tenth year.

The four canines appear from the tenth to the eleventh year.

The four second bicuspids appear from the twelfth to the thirteenth year.

The above are the permanent teeth which replace the temporary teeth, The per-
manent teeth which are developed de novo appear as follows :

The first molars appear from the sixth to the seventh year.

The second molars appear from the twelfth to the thirteenth year.

The third molars appear from the seventeenth to the twenty-first year.

Development of the Genito - Urinary System.

The genital and the urinary organs are developed together and are both preceded by
the appearance of two large, symmetrical structures, known as the Wolffian bodies, or
the bodies of Oken. These are sometimes called the false or the primordial kidneys.
They appear at about the thirtieth day, develop very rapidly on either side of the spinal
column, and are so large as to almost fill the cavity of the abdomen. Fig. 307, rep-
resenting a specimen in the possession of Prof. Dalton, shows how large these bodies
are in the early life of the embryon, at which time their function is undoubtedly very
important.

Very soon after the Wolffian bodies have made their appearance, we can distinguish,
at their inner borders, two ovoid bodies, which are finally developed into the testicles,
for the male, or the ovaries, for the female. At their external borders, are two ducts,
on either side, one of which, the internal, is called the duct of the Wolffian body. This
finally disappears, in the female, but it is developed into the vas
deferens, in the male. The other duct, which is external to
the duct of the Wolffian body, disappears, in the male, but it
becomes the Fallopian tube, in the female. This is known as
the duct of Muller. Behind the Wolffian bodies, are devel-
oped the kidneys and the suprarenal capsules.

As the development of the Wolffian bodies attains its maxi-
mum, their structure becomes somewhat complex. From their
proper ducts, which are applied directly to their outer bor-
ders, tubes make their appearance at right angles to the
ducts, which extend into the substance of the bodies and be-
come somewhat convoluted at their extremities. These tubes
communicate directly with the ducts, and the ducts them- ., *on-

1, heart; 2, anterior extremity,'

selves open into the lower part of the intestinal canal, oppo- 8, posterior extremity; 4,
site to the point of its communication with the allantois. The S S8 ttbe^cufaw^
tubes of the Wolffian bodies are simple, terminating in single, S thfwlVtn bodie's POSiti6°
somewhat dilated, blind extremities, are lined with epithe-
lium, and are penetrated, at their extremities, by blood-vessels, which form coils or con-
volutions in their interior. These are undoubtedly organs of depuration for the embryon
and take on the function to be subsequently assumed by the kidneys; but, in the female,
they are temporary structures, disappearing as development advances, and having noth-
ing to do with the development of the true urinary organs.

The testicles or ovaries are developed at the internal and anterior surface of the Wolf-
fian bodies, first appearing in the form of small, ovoid masses. Beginning just above
and passing along the external borders of the Wolffian bodies, are the tubes called the
ducts of Muller. These at first open into the intestine, near the point of entrance of the

928 GENERATION.

Wolffian ducts. In the female, their upper extremities remain free, except the single
fimbriu which is connected with the ovary. Their inferior extremities unite with each
other, and, at their point of union, they form the uterus. "When this union is incomplete,
we have the malformation known as double uterus, which may be associated with a
double vagina. The Wolffian bodies and their ducts disappear, in the female, at about
the fiftieth day. A portion of their structure, however, persists, in the form of a col-
lection of closed tubes, constituting the parovarium, or organ of Rosenmiiller.

In the female, the ovaries pass down no farther than the pelvic cavity ; but the testi-
cles, which are at first in the abdomen of the male, finally descend into the scrotum.
As the testicles descend, they carry with them the Wolffian duct, that portion of the
Wolffian body which is permanent constituting the head of the epididymis. At the
same time, a cord appears, attached to the lower extremity of the testicle and extending
to the symphysis pubis. This is called the gubernaculum testis. It is at first muscular,
but the muscular fibres disappear during the later periods of utero-gestation. It is not
known that its muscular structure takes any part, by contractile action, in the descent
of the testicle in the human subject. The epididymis and the vas deferens are formed
from the Wolffian body and the Wolffian duct.

At about the end of the seventh month, the testicle has reached the internal abdom-
inal ring ; and, at this time, a double tubular process of peritoneum, covered with a few
fibres from the lower portion of the internal oblique muscle of the abdomen, gradually
extends into the scrotum. The testicle descends, following this process of peritoneum,
which latter becomes eventually the visceral and parietal portion of the tunica vaginalis.
The canal of communication between the abdominal cavity and the cavity of the scrotum
is finally closed, and the tunica vaginalis is separated from the peritoneum. The fibres
derived from the internal oblique constitute the cremaster muscle.

At the eighth or the ninth month, the testicles have reached the external abdominal
ring and then soon descend into the scrotum. The vas deferens, as we have seen, passes
from the testicle, along the base of the bladder, to open into the prostatic portion of
the urethra ; and, as development advances, two sacculated diverticula from these tubes
make their appearance, which are attached to the bladder and constitute the vesicula3
seminal es.

As the ovaries descend to their permanent situation in the pelvic cavity, there appears,
attached to the inner extremity of each, a rounded cord, analogous to the gubernaculum
testis. A portion of this, connecting the ovary with the uterus, constitutes the ligament
of the ovary ; and the inferior portion forms the round ligament of the uterus, which
passes through the inguinal canal and is attached to the symphysis pubis.

The development of the external organs of generation will be studied after we have
described the development of the urinary apparatus.

Development of the Urinary Apparatus. — Behind the Wolffian bodies, and developed
entirely independently of them, the kidneys, suprarenal capsules, and ureters make their
appearance. The kidneys are developed in the form of little, rounded bodies, composed
of short, blind tubes, all converging toward a single point, which is the hilum. These tubes
increase in length, branch, become convoluted in a certain portion of their extent, and
finally assume the structure and arrangement of the renal tubules, with their Malpighian
bodies, blood-vessels, etc. They all open into the hilum. At the same time that the kid-
neys are undergoing development, the suprarenal capsules are formed at their superior
extremities. These bodies, the function of which is unknown, are relatively so much
larger in the foetus than in the adult, that they have been supposed to be peculiarly
important in intra-uterine life, though nothing definite is known upon this point. The
kidneys are relatively very large in the fcetus. Their proportion to the weight of the
body, in the foetus, is 1 to 80, and, in the adult, 1 to 240. The ureters are undoubtedly
developed as tubular processes from the kidneys, which finally extend to open into the

DEVELOPMENT OF THE GENITO-URINARY SYSTEM.

929

bladder. This fact is shown by certain cases of malformation, in which the ureters have
not reached the bladder, but terminate in blind extremities. The development of the

FIG. 808. — Diagrammatic representation of the genito-urinary system, (Ilenle.)
A, embryonic condition, in which there is no distinction of sex ; B, female form; C, male form. The dotted lines in

J3 and 0 represent the situations which the male and female genital organs assume after the descent of the ovaries

and testicles. The small letters in B and C correspond to the capital letters in A.
Fig. 308 A.— A, kidney ; B, ureter ; C, bladder ; D, urachus, developed into the median ligament of the bladder ; E,

constriction which becomes the urethra ; F', Wolffian body ; G, Wolffian duct, with its opening below, G' ; II,

duct of Muller, united below, from the two sides, into a single tube, J, which presents a single opening, J'.

between the openings of the Wolffian ducts ; K, ovary or testicle ; L, gubernaculum testis or round ligament of

the uterus ; M, genito-urinary sinus ; N, O, external genitalia.
Fig. 308, B (female).— a, kidney ; b, ureter; c. bladder; d, urachus; e, urethra; f remains of the Wolffian body (paro-

varium) ; g, remnant of the Wolffian duct; h, Fallopian tube ; i, uterus ; i', vagina ; k. ovary; 1. round ligament

of the uterus; m, extremity of the urethra; n, clitoris; n' corpus cavernosum of the clitoris; n", bulb of the

vestibule ; o. external genital opening ; p. excretory duct of the gland of Bartholinus.
Fig. 308, C (male).— a, kidney ; b, ureter ; c, bladder ; d, urachus ; e, m. urethra ; f. epididymis ; g, vas deferens ; g',

seminal vesicle ; g", ejaculatory duct ; h, i. remains of the duct of Muller ; k, testicle ; 1, gubernaculum testis ; n,

n', n". urethra and penis; o, scrotum ; p, gland of Cowpcr; q, prostate.

59

930 GENERATION.

genito-urinary system can be readily understood, after the description we have just
given, by a study of Fig. 308.

External Organs of Generation. — The external organs of generation begin to be
developed at about the fifth week. At the inferior extremity of the body of the embryon,
a small, ovoid eminence appears in the median line, at the lower portion of which there
is a longitudinal slit, which forms the common opening of the anus and the genital and
urinary passages. This is the cloaca. There is soon developed, internally, a septum,
which separates the rectum from the vagina, the urethra of the female opening above.
In the male, this septum is developed between the rectum and the urethra, the gener-
ative and the urinary passages opening together. From this median prominence, two
lateral, rounded bodies make their appearance. These are developed, with the median
elevation, into the glans penis and corpora cavernosa of the male, or into the clitoris and
the labia minora of the female. In the male, these two lateral prominences unite in the
median line and enclose the spongy portion of the urethra. When there is a want of
union in the cavernous bodies in the male, we have the malformation known as hypospa-
dias. In the female, there is no union in the median line, and an opening remains
between the two labia minora. The scrotum in the male is analogous to the labia
majora of the female; the distinction being that the two sides of the scrotum unite
in the median line, while the labia majora remain permanently separated. This anal-
ogy is farther illustrated by the anatomy of inguinal hernia, in which the intestine
descends into the labia, in the female, and into the scrotum, in the male. It sometimes
occurs, also, that the ovaries descend, very much as the testicles pass down in the male,
and pass through the external abdominal ring.

From the above description, it is easy to imagine how malformation and malposition
of the genital organs may occur, so that it is difficult to determine the sex of the indi-
vidual. We may have, in a male, absence of beard and a certain degree of development
of the mammary glands, with a pelvic conformation approximating, more or less, that of
the female ; and, on the other hand, a female may have a beard, slight mammary devel-
opment, and a general conformation of the body resembling that of a male. This may
be associated with corresponding malformations of the genital organs. We may, for
example, have a large development of the clitoris, descent of the ovaries, more or less
complete occlusion of the vagina, and union of the labia majora, so that it is difficult to
determine the sex from an external examination ; and opposite vices of formation may
occur in the male, the testicles remaining in the pelvic cavity. It is not surprising,
therefore, that beings have existed of undetermined sex, and many cases of this kind are
on record. Two cases have been reported in which, apparently, the two sexes were
combined. The first case was presented to the Medical Society of Vienna, by Roki-
tansky, in 1869. This case presented, on post-mortem examination, two ovaries with
their Fallopian tubes, a rudimentary uterus, a testicle, and a vas deferens containing
spermatozoids. This individual menstruated, had an imperfect penis, and a bifid scro-
tum. The sexual indifference was absolute. The second case was published by Hepp-
ner, in 1872. This was a child, six weeks old, which had been preserved in alcohol for
several years. It presented ovaries, Fallopian tubes, a uterus, and a vagina opening into
the urethra. There were also two bodies which were shown, upon microscopical examina-
tion, to be testicles, a penis with hypospadia, and a prostate ; but there were neither
vesiculaa seminales nor vasa deferentia.

Development of the Circulatory System.

The blood and the blood-vessels are developed very early in the life of the ovum and
make their appearance nearly as soon as the primitive trace. The mode of development
of the first vessels differs from that of vessels formed later, as they appear de *iovo in the
blastodermic layers, while afterward, vessels are formed as prolongations of preexisting

DEVELOPMENT OF THE CIRCULATORY SYSTEM. 931

tubes. Soon after the external and the internal blastodermic membranes have become
separated from each other, and the intermediate membrane has been formed at the
thickened portion of the ovum which is destined to be developed into the embryon, cer-
tain of the blastodermic cells undergo a transformation into blood-corpuscles. These are
larger than the blood-corpuscles of the adult and are generally nucleated. At about the
same time (it may be before or after the appearance of the corpuscles, for this point is
undetermined) certain of the blastodermic cells fuse with each other and arrange them-
selves so as to form vessels. Leucocytes are probably developed in the same way as the
red corpuscles. The vessels thus formed constitute the area vasculosa, which is the
beginning of what is known as the first circulation.

It is evident that the relations of the embryon at different stages of development must
require certain variations in the arrangement of the circulatory system, i'ne ovum nas,
of course, no vascular connection with the mother before the lorrnation of the allantois.
It has undergone, however, a certain degree of development, and presents a circulator^
system, which extends over the umbilical vesicie. This stage of development of the vas-
cular system constitutes what is known as the first circulation. As the allantois is devel-
oped, the circulation over tne umbilical vesicle becomes unimportant, and its vessels disap-
pear. Vessels then extend into the allantois, are finally developed into the foetal portion
of the placenta, and what is known as the second circulation is established. This circu-
lation continues throughout intra-uterine life, and, as we know, the embryon and foetus
depend entirely upon the placenta for materials for respiration, nutrition, and growth.
At birth, the requirements are again changed. The placental circulation is then abol-
ished, and the arrangement of vessels peculiar to it disappears. Now, for the first
time, the pulmonary circulation becomes important. All the blood passes through the
lungs before it is sent to the general system, the two sides of the heart become com-
pletely separated from each other, and the third, the pulmonary, or adult circulation, is
established.

The First, or Vitelline Circulation. — In the development of oviparous animals, the
first, or vitelline circulation is very important ; for, by these vessels, the contents of the
nutritive yolk are taken up and carried to the embryon, constituting the only source of
material for its nutrition and growth. In mammals, however, nutritive matter is ab-
sorbed almost exclusively from the mother, by simple endosmosis, before the placental
circulation is established, and by the placental vessels, at a later period. The vitelline
circulation is therefore not important, and the vessels disappear with the atrophy of the
umbilical vesicle.

The area vasculosa, in mammals, consists of vessels coming from the body of the
embryon, forming a nearly circular plexus in the substance of the vitellus, around the
embryon. The vessels of this plexus open into a sinus at the border of the area, called
the sinus terminalis. It is probable that these vessels are developed de now in the inter-
mediate blastodermic layer and are not preceded by a distinct membrane ; but such a
membrane has been described under the name of the vascular blastodermic layer.

If we examine the ovum when the area vasculosa is first formed, we see the embryon
lying in the direction of the diameter of the nearly circular plexus of blood-vessels. The
plexus surrounds the embryon, except at the cephalic extremity, where the terminal
sinuses of the two sides curve downward toward the head, to empty into the omphalo-
mesenteric veins. As the umbilical vesicle is separated from the body of the embryon,
it carries the plexus of vessels of the area vasculosa with it, the vessels of communication
with the embryon being the omphalo-mesenteric arteries and veins. As these processes
are going on, the great central vessel of the embryon becomes enlarged and twisted upon
itself, at a point just below the cephalic enlargement of the embryon, between the inferior
extremity of the pharynx and the superior cul-de-sac of the intestinal canal. The exca-
vation which receives this vessel is called the fovea cardiaca. The different stages of

932

GENERATION.

development of the heart, which is formed of the twisted portion of the central vessel,
will be described farther on. Simple, undulatory movements take place in the heart of
the chick at about the middle of the second day ; but there is not, at that time, any
regular circulation. At the end of the second day or the beginning of the third, the cur-
rents of the circulation are established. The tune of the first appearance of the circula-
tion in the human embryon has not been accurately determined.

FIG. 309.— Area vasculosa. (Bischoff.)
a, a, Z>, sinus terminals ; c, omphalo-mesenteric vein ; d, heart ; «,/,/, posterior vertebral arteries.

In the arrangement of the vessels for the first circulation of the embryon, the heart is
situated exactly in the median line and gives off two arches which' curve to either side
and unite into a single central trunk at the spinal column below. These are the two aorta3,
and the single trunk formed by their union becomes the abdominal aorta. The two aortic
arches, one of which only is permanent, are sometimes called the inferior vertebral arteries.
These vessels give off numerous branches, which pass into the area vasculosa. Two of
these branches, however, are larger than the others, pass to the umbilical vesicle, and are
called the omphalo-mesenteric arteries. In the embryon of mammals, there are, at first,
four omphalo-mesenteric veins, two superior, which are the larger, and two inferior ;
but, as development advances, the two inferior veins are closed, and we then have two
omphalo-mesenteric arteries and two omphalo-mesenteric veins. At about the fortieth
day, one artery and one vein disappear, and we have then but one omphalo-mesenteric
artery and one vein. Soon after, as the circulation becomes established in the allantois,
the vessels of the umbilical vesicle and the omphalo-mesenteric vessels are obliterated,
and the first circulation is superseded by the second.

As the septum between the two ventricles makes its appearance, that division of the
right aortic arch which constitutes the vascular portion of one of the branchial arches dis-
appears and loses its connection with the abdominal aorta ; a branch, however, persists
during the whole of intra-uterine life and constitutes the ductus ai'teriosus, and another
branch is permanent, forming the pulmonary artery.

DEVELOPMENT OF THE CIRCULATORY SYSTEM.

933

The Second, or Placental Circulation. — As the omphalo-mesenteric vessels disappear,
and as the allantois is developed to form the chorion, two vessels (the hypogastric arte-
ries) are given off, first from the abdominal aorta ; but afterward, as the vessels going to
the lower extremities are developed, the branching of the abdominal aorta is such that
the vessels become connected with the internal iliac arteries. The hypogastric arteries
pass to the chorion through the umbilical cord and constitute the two umbilical arteries.
At first, there are two umbilical veins; but one of them afterward disappears, and there
is finally but one vein in the umbilical cord. It is in this way — the umbilical arteries car-
rying the blood to the tufts of the foetal placenta, which is returned by the umbilical
vein — that the placental circulation is established.

Corresponding to the four visceral arches, which we have described in connection with
the development of the face, are four vascular arches. One of these disappears, and the
remaining three undergo certain changes, by which they are converted into the vessels
going to the head and the superior extremities. The anterior arches on the two sides
are converted into the carotids and subclavians ; the second, on the left side, is converted
into the permanent aorta, and the right is obliterated ; the third, on either side, is con-
verted into the right and left pulmonary arteries. In the early stages of the develop-
ment of the vascular system of mammals, the conditions have been compared to the per-
manent arrangement of the circulatory system in fishes. The heart of fishes remains
single ; and the heart of mammals is at first single, but afterward it becomes divided by the
development of the intra-ventricular septum. The branchial arches in fishes are perma-
nent, they receive all the blood from the aortic bulb, and the blood
from these arches then passes into the dorsal aorta. This is very
nearly the condition of the vascular system when the branchial
arches first appear in the embryon of mammals.

The changes of the branchial arches which we have described
are illustrated in the diagrammatic Fig. 310. In this figure, the
three branchial arches that remain and participate in the devel-
opment of the upper portion of the vascular system are 1, 2, 3,
on either side. The two anterior (3, 3) become the carotids (c, c)
and the subclavians (s, «). The second (2, 2) is obliterated on the
right side, and becomes the arch of the aorta on the left side.
The third (1, 1), counting from above downward, is converted
into the pulmonary arteries of the two sides. Upon the left side,
there is a large anastomosing vessel (ca), between the pulmonary
artery of that side and the arch of the aorta, which is the ductus
arteriosus. The anastomosing vessel (cd) between the right pul-
monary artery and the aorta, is obliterated.

The mode of development of the veins is very simple. Two
venous trunks make their appearance by the sides of the spinal
column, which are called the cardinal veins, and run parallel with
the superior vertebral arteries, or the two aortae, emptying finally
into the auricular portion of the heart by two canals, which are
called the canals of Cuvier. These veins change their relations
and connections as the first circulation is replaced by the second.
The omphalo-mesenteric vein opens into the heart between the
two canals of Cuvier. As development advances, the liver is
formed in the course of this vessel, a short distance below the
heart, and the vein ramifies in its substance ; so that the blood of
the omphalo-mesenteric vein passes through the liver before it
gets to the heart. We have seen that the omphalo-mesenteric vein is obliterated as the
umbilical vein makes its appearance. The blood from the umbilical vein is at first
emptied directly into the heart ; but this vessel soon establishes the same relations

FIG. 810. — Transformation
of the system of aortic
arches into permanent
arterial trunks, in the
mammalia. (Von Baer.)

B, aortic bulb : 1, 2. 3, 4, 5, on
either side, the five pairs of
aortic arches ; 5, 5, the earli-
est in their appearance; 1. 1,
the most recent; c, c, the
two carotids, still united,
which are separated at a
later period; «, «, the two
subclavians, the ri^rlit aris-
ing' from the arteria innonii-
nata ; a. </. the aorta; p, p,
the pulmonary arteries; ca,
the ductus arteirosus ; c<7,
the left artieral canal, which
is finally obliterated.

934 GENERATION".

with the liver as the omphalo-mesenteric vein, and its blood passes through the liver
before it reaches the central organ of the circulation. As the omphalo-mesenteric vein
atrophies, the mesenteric vein, bringing the blood from the intestinal canal, is developed,
and this penetrates the liver, becoming, finally, the portal vein.

As the lower extremities are developed, the inferior vena cava makes its appearance
between the two inferior cardinal veins. This vessel receives an anastomosing branch
from the umbilical vein, before it penetrates the liver, and this branch is the ductus
venosus. As the inferior vena cava increases in size, it communicates below with the
two inferior cardinal veins; and that portion of the two inferior cardinal veins which
remains constitutes the two iliac veins. The inferior cardinal veins, between that "portion
which forms the iliac veins and the heart, finally become the right and the left azygos
veins.

The right canal of Cuvier, as the upper extremities are developed, enlarges and be-
comes the vena cava descendens, receiving, finally, ail the blood from the head and the
superior extremities. The left canal of Cuvier undergoes atrophy and finally disappears.
The upper portion of the superior cardinal veins is developed into the jugulars and sub-
clavians on the two sides. As the lower portion of the left cardinal vein and the left
canal of Cuvier atrophy, a venous trunk appears, connecting the left subclavian with the
right canal of Cuvier. This increases in size and becomes the left vena innominata, which
connects the left subclavian and internal jugular with the vena cava descendens.

Development of the Heart. — The central enlargement of the vascular system in the
first circulation, which becomes the heart, is twisted upon itself by a single turn. The
portion connected with the cephalic extremity of the embryon gives origin to the
arterial system, and the portion connected with the caudal extremity receives the blood
from the venous system. The walls of the arterial portion of the heart soon become
thickened, while the walls of the venous portion remain comparatively thin. There then
appears a constriction, which partly separates the auricular from the ventricular portion.
At a certain period of development, the heart presents a single auricle and a single ven-
tricle.

The division of the heart into two ventricles appears before the two auricles are sepa-
rated. This is effected by a septum, which gradually extends from the apex of the heart
upward toward the auricular portion. At the seventh week, there is a large opening be-
tween the two ventricles. This gradually closes from below upward, the heart becomes
more pointed, and the separation of the two ventricles is complete at about the end of the
second month.

At about the end of the second month, a septum begins to be formed between the
auricles. This extends from the base of the heart toward the ventricles, but it leaves an
opening between the two sides (the foramen ovale, or the foramen of Botal) which per-
sists during the whole of foetal life. At the anterior edge of the opening of the vena
cava ascendens into the right auricle, there is a membranous fold, which projects into
the auricle. This is the valve of Eustachius, and it divides the right auricle incompletely
into two portions.

During the sixth week, the heart is vertical and situated in the median line, with the
aorta arising from the centre of its base. At the end of the second month, it is raised
up by the development of the liver, and its point presents forward. During the fourth
month, it is twisted slightly upon its axis, and the point presents to the left. At this
time, the auricular portion is larger than the ventricles ; but the auricles diminish in their
relative capacity during the latter half of intra-uterine life. The pericardium makes its
appearance during the ninth week.

Early in intra-uterine life, the relative size of the heart is very great. At the second
month, its weight, in proportion to the weight of the body, is 1 to 50. This proportion,
however, gradually diminishes until, at birth, the ratio is 1 to 120. The proportionate

DEVELOPMENT OF THE CIRCULATORY SYSTEM. 935

weight in the adult is about 1 to 160. During about the first half of intra-uterine life,
the thickness of the two ventricles is nearly the same ; but, after that time, the relative
thickness of the left ventricle gradually increases.

Peculiarities of the Foetal Circulation. — In studying the complete course of the blood
in the foetus, which constitutes the second, or the placental circulation, we note peculiari-
ties in two portions of the circulatory system. In the one, a peculiar arrangement is
necessitated by the passage of blood to and from the placenta ; and in the other, the char-
acter of the blood coming from the placenta necessitates a peculiar arrangement of the
heart and the great vessels.

The branches from the internal iliac arteries, which pass to the foetal tufts of the pla-
centa, do not exist in the adult. The ductus venosus, which conveys a portion of the
blood of the umbilical vein to the vena cava ascendens, and the umbilical vein itself do
not exist in the adult.

The Eustachian valve, situated at the inner margin of the vena cava ascendens as it
opens into the right auricle, does not exist in the adult. The foramen ovale, or the open-
ing between the right and the left auricle, through which the blood from the vena cava
ascendens is directed into the left auricle, does not exist in the adult. The ductus arte-
riosus, which conveys the blood from the left pulmonary artery to the arch of the aorta,
does not exist in the adult. In the adult, the pulmonary arteries receive all the blood
from the right ventricle. In the foetus, the pulmonary arteries receive a small quantity
of blood, as compared with that which passes to the aorta through the ductus arteriosus.
Keeping in view these peculiarities of the circulatory apparatus, the entire course of the
blood, during foetal life, is as follows :

Beginning with the abdominal aorta, we follow the course of blood into the two
primitive iliacs, and thence into the internal iliacs. From the two internal iliacs, the two
hypogastric arteries arise, which ascend along the sides of the bladder to its fundus, thence
pass to the umbilicus and go to the placenta, forming the' two umbilical arteries. In this
way, the blood of the foetus goes to the placenta.

The umbilical vein enters the body of the foetus at the umbilicus ; it passes along the
margin of the suspensory ligament to the under surface of the liver ; it gives off one
branch of large size, and one or two smaller branches to the left lobe ; it sends a branch
each to the lobus quadratus and the lobus Spigelii ; and the vessel reaches the transverse
fissure. At the transverse fissure, it divides into two branches, the larger of which joins
the portal vein and enters the liver; and the smaller, which is the ductus venosus,
passes to the vena cava ascendens, at the point where it receives the left hepatic vein.
Thus, the greater part of the blood returned to the foetus from the placenta passes
through the liver, a relatively small quantity being emptied into the vena cava by the
ductus venosus.

The vena cava ascendens, containing the placental blood which has passed through
the liver, the blood conveyed directly from the umbilical vein by the ductus venosus, and
the blood from the lower extremities, passes to the right auricle. As the blood enters
the right auricle, it is directed by the Eustachian valve, passing behind the valve, through
the foramen ovale, into the left auricle. At the same time, the blood from the head and
the superior extremities passes down, by the vena cava descendens, in front of the Eusta-
chian valve, through the right auricle, into the right ventricle. The arrangement of the
Eustachian valve is such, that the right auricle simply affords a passage for the two cur-
rents of blood ; the one, from the vena cava ascendens, through the foramen ovale, passes
into the left auricle and the left ventricle ; and the other, from the vena cava descendens,
passes through the right auriculo-ventricular opening, into the right ventricle. It is
probable, indeed, that there is very little admixture of these two currents of blood in the
natural course of the foetal circulation. Reid injected the vena cava ascendens with red,
dhd the vena cava descendens with yellow, in a foetus of seven months, and he found very

936 GENERATION.

little mixture of the two colors in the passage of the injected material through the right
auricle.

The blood poured into the left auricle from the vena cava ascendens through the fora-
men ovale passes from the left auricle into the left ventricle. The left auricle and the
left ventricle also receive a small quantity of blood from the lungs, by the pulmonary
veins. Thus the left ventricle is filled. At the same time, the right ventricle is filled
with blood which has passed through the right auricle, in front of the Eustachian valve.
The two ventricles, thus distended, then contract simultaneously. The blood from the
right ventricle passes in small quantity to the lungs, the greater part passing through the
ductus arteriosus into the descending portion of the arch of the aorta. This duct is short
(half an inch in length) and about the size of a goose-quill. The blood from the left ven-
tricle passes into the aorta and goes to the system. The vessels of the head and superior
extremities being given off from the aorta before it receives the blood from the ductus
arteriosus, these parts receive almost exclusively the pure blood from the vena cava
ascendens, the only mixture with the placental blood being the blood from the lower
extremities, the blood from the portal system, and the small amount of blood received
from the lungs. After the aorta has received the blood from the ductus arteriosus, how-
ever, it is mixed blood; and it is this which supplies the trunk and lower extremities.
This is one of the reasons assigned by physiologists for the greater relative development
of the upper parts of the foetus.

In Fig. 311, which is partly diagrammatic, the foetal circulation is illustrated. In
endeavoring, in this figure, to give a clear idea of the second circulation, we have not
attempted to preserve the exact relations or the relative size of the organs. We have
endeavored to represent, by dotted lines, the Eustachian valve, the foramen ovale, and
the two auriculo-ventricular orifices. The liver, which is smaller in the diagram than it
really is, and the bladder, are represented by dotted lines.

There can be no doubt that the foetus derives materials for its nutrition and growth
from the placenta, and that this also serves as a respiratory organ. In another chapter,
under the head of respiration before birth, we have stated that " Legallois frequently
observed a bright-red color in the blood of the umbilical vein ; and, on alternately com-
pressing and releasing the vessel, he saw the blood change in color successively from red
to dark and from dark to red." This difference in color between the blood of the umbili-
cal arteries and of the umbilical vein has, however, been denied by some authors, who
state that all of the foetal blood, while it is of nearly a uniform color, is lighter than the
venous blood of the adult ; but Dalton, in a direct observation upon a cat, " nearly arrived
at the term of pregnancy," noted that " the difference in color between the umbilical
arteries and veins was very distinct. They were both dark, but the color of the veins
was very decidedly more ruddy than that of the arteries." By means of the spectroscope,
Zweifel has demonstrated the presence of oxyhsemaglobine in the blood of the umbilical
vessels, showing that it contains oxygen, which must be derived from the maternal blood
circulating in the placental sinuses.

There are numerous observations showing that the foetus in utero makes respiratory
efforts when the umbilical vessels are compressed. We believe that these, as well as the
first respiration after birth, are due to a want of oxygenated blood in the medulla oblon-
gata, and we think that we have demonstrated this fact by experiments. This point has
already been elaborately discussed in another chapter. If our experiments and the deduc-
tions drawn from them be correct, there can be no doubt with regard to the respiratory
function of the placenta, although, as far as we know, there has never been an accurate
comparison of the gases contained in the blood of the umbilical arteries and the umbili-
cal vein.

The Third, or Adult Circulation. — When the child is born, the placental circulation
is suddenly arrested. After a short time, the sense of want of air becomes sufficiently

DEVELOPMENT OF THE CIRCULATORY SYSTEM.

937

intense to give rise to an inspiratory effort, and the first inspiration is made. The pul-
monary organs are then, for the first time, distended with air, the pulmonary arteries

Pulmonary Art,

Foramen Ovale. /

Eustachian Valve.-— (-
Right Auric. -Vent. Opening.

•y Art.

Left Auricle.
—Left Auric. - Vent.

Hepatic Vcin.^

Branches of the /"'•--.. Liver.

Umbilical

to the Liver.

Bladder.

\/

Internal Iliac Arteries.
FIG. 311. — Diagram of the fo&tal circulation.

carry the greatest part of the blood from the right ventricle to the lungs, and a new cir-
culation is established. During the later periods of fetal life, the heart is gradually pre-
pared for the new currents of blood. The foramen ovale, which is largest at the sixth

938 GENERATION.

month, after that time, is partly occluded by the gradual growth of a valve, which extends
from below upward and from behind forward, upon the side of the left auricle. The
Eustachian valve, which is also largest at the sixth month, gradually atrophies after this
time, and, at full term, it has nearly disappeared. At birth, then, the Eustachian valve is
practically absent; and, after pulmonary respiration becomes established, the foramen
ovale has nearly closed. The arrangement of the valve of the foramen ovale is such, that,
at birth, a small quantity of blood may pass from the right to the left auricle, but none
can pass in the opposite direction. The situation of the Eustachian valve, on the right
side of the inter-auricular septum, is marked by an oval depression, called the fossa ovalis.

As a congenital malformation, the foramen ovale may remain open, producing the
condition known as cyanosis neonatorum. This may continue into adult life, and it is then
attended with more or less disturbance of respiration and difficulty in maintaining the
normal heat of the body. Usually, the foramen ovale is completely closed at about the
tenth day after birth. The ductus arteriosus begins to contract at birth, and it is occluded,
being reduced to the condition of an impervious cord, at from the third to the tenth day.

When the placental circulation is arrested at birth, the hypogastric arteries, the um-
bilical vein, and the ductus venosus contract, and they become impervious at from the
second to the fourth day. The hypogastric arteries remain pervious at their lower por-
tion and constitute the superior vesical arteries. A rounded cord, which is the remnant
of the umbilical vein, forms the round ligament of the liver. A slender cord, the rem-
nant of the ductus venosus, is lodged in a fissure of the liver, called the fissure of the
ductus venosus.

A history of the development of the various tissues of the body belongs really to gen-
eral anatomy and is usually given in works specially devoted to that subject. We have
only treated of it incidentally, in our account of the development of the various organs
and systems.

CHAPTER XXVIII.

FCETAL LIFE— DEVELOPMENT AFTER BIRTH— DEATH.

Enlargement of the uterus in pregnancy — Duration of pregnancy — Size, weight, and position of the foetus — The foetus
at different stages of intra-uterine life— Multiple pregnancy— Cause of the first contractions of the uterus in nor-
mal parturition— Involution of the uterus— Meconium— Dextral preeminence— Development after birth— Ages-
Death— Cadaveric rigidity— Putrefaction.

As the development of the ovum advances, the uterus is enlarged and its walls are
thickened. The form of the organ, also, gradually changes, as well as its position. Im-
mediately after birth, its weight is about a pound and a half, while the virgin uterus
weighs less than two ounces. It is a remarkable fact, demonstrated upon the living sub-
ject, by Prof. I. E. Taylor, of New York, that the neck of the uterus, while it becomes
softer and more patulous during pregnancy, does not change its length, even in the very
latest stages of utero-gestation. This fact is in opposition to the statements of most
obstetricians, who believe that the os internum dilates, and that the neck is gradually
absorbed, as it were, by the body of the uterus, during the later months of pregnancy.

We have already studied the remarkable changes which take place in the mucous
membrane of the uterus during pregnancy and the mode of formation of the decidua,
and we have seen that the mucous membrane of the neck does not participate in these
changes and is not thrown off in parturition. The only change, indeed, which we note
in the neck, aside from the softening of its texture, is the secretion of the plug of mucus
which closes the os.

DURATION OF PREGNANCY. 939

The changes in the walls of the uterus during pregnancy are very important. The
blood-vessels become much enlarged, and the muscular fibres increase immensely in size,
so that their contractions are very powerful when the foetus is expelled.

It is evident that, on account of the progressive increase in the size of the uterus dur-
ing pregnancy, it cannot remain in the cavity of the pelvis at the later months. During
the first three months, however, when it is not too large for the pelvis, it sinks back into
the hollow of the sacrum, the fundus being directed somewhat backward, with the neck
presenting downward, forward, and a little to the left. After this time, however, the
increased size of the organ causes it to extend into the abdominal cavity, so that its
fundus eventually reaches the epigastric region. Its axis then has the general direction
of the axis of the superior strait of the pelvis.

The enlargement of the uterus and the necessity of carrying on a greatly-increased
circulation in its walls during pregnancy are attended with a temporary hypertrophy of
the heart. According to Robin, it is mainly the left ventricle which is thickened during
utero-gestation, and the increase in the weight of the heart at full term amounts to more
than one-fifth. After delivery, the weight of the heart soon returns to nearly the nor-
mal standard.

Duration of Pregnancy. — The duration of pregnancy, dating from a fruitful inter-
course, must be considered as variable, within certain limits. The method of calculation
most in use by obstetricians is, to date from the end of the last menstrual period. Dr.
Matthews Duncan, who has made quite a number of observations upon this point, states
that the 278th day after the end of the last menses is the average day of delivery ; but
he admits that his method of calculation is rough, though he cannot find any that is more
reliable. The observations upon which this opinion is based are the following : The day
was predicted in 153 cases; in 10 cases, confinement occurred on the exact day; in 80
cases, the confinement occurred sooner, presenting an average of 7 days for each case ;
and, in 63 cases, the confinement occurred later, presenting an average of 8 days for each
case. The great difficulty in predicting the exact time of confinement, which is very
important in practice, is mainly due to the comparatively small number of reliable obser-
vations in which the pregnancy can be dated from a single intercourse or from intercourse
occurring within two or three days. We have received from Prof. Fordyce Barker the
following very interesting account of a case in which this observation was made in his
own practice : A lady, concerning whose statements there could be no suspicion of inac-
curacy, residing in New York, received a visit from her husband, after along interval of
absence. He arrived in this city from New Orleans, remained thirty-six hours, and then
went to Europe, where he remained for four months. Exactly 298 days from the date of
the first visit of the husband, the lady was confined and delivered by Prof. Barker. This
occurred in 1852. Taking into account the various cases which are quoted by authors,
in which conception has been supposed to follow a single coitus, there appears to be a
range of variation in the duration of pregnancy of no less than 40 days, the extremes
being 260 and 300 days.

In the very interesting observations of Kundrat and Engelmann, upon the changes of
the uterine mucous membrane during menstruation, published in 1873, the idea is ad-
vanced that pregnancy dates really from a menstrual period which is prevented, as far as
a discharge of blood is concerned, by fecundation of an ovum, and not from the period
immediately preceding, in which the flow takes place. This theory was proposed by
Loewenhardt, in 1872. If we adopt this view, the changes in the mucous membrane of
the uterus ordinarily terminate in a fatty degeneration of the vascular walls, which re-
sults in a capillary hemorrhage ; if, however, an ovum be fecundated, these changes do
not pass into fatty degeneration, but advance to an hypertrophy, which is the first stage
in the formation of the decidua. The arguments in opposition to this method of calcu-
lating the duration of pregnancy are the following: The time, with relation to the men-

940 GENERATION.

strual flow, at which an ovum is discharged has not yet been accurately determined ; and
it is subject, undoubtedly, to very considerable variations. It is certain, also, that ovu-
lation frequently does not take place until after the flow of blood has been established.
It is probable that intercourse is most liable to be followed by fecundation, when it
occurs just after the cessation of a menstrual period, and when the female often presents
unusual sexual excitement. If we admit, with Loewenhardt and Kundrat, that fecunda-
tion dates more nearly from a menstrual period prevented than from the last appear-
ance of the flow, it would be necessary to assume that ovulation usually takes place
before the flow, and fecundation would be most liable to follow intercourse occurring at
that time ; for we could hardly suppose that an ovum, fecundated at the cessation of a
menstrual period, could remain in the generative passage of the female for two or three
weeks before the mucous membrane of the uterus is prepared for its reception. In
a later memoir by Engelmann, published in 1875, he dissents from the view advanced
in the article published in connection with Kundrat, in 18T3, and states that he con-
siders the theory with regard to the temporal relations between menstruation and ovu-
lation to be " erroneous and wholly untenable."

As regards the practical applications of calculations of the probable duration of preg-
nancy in individual cases, we must recognize the fact that the period is variable. Dat-
ing from the end of the last menstrual flow, we may adopt the average of 278 days, or a
little more than nine calendar months.

Size, Weight, and Position of the Foetus. — The estimates of writers with regard to the
size and weight of the embryon and foetus at different stages of intra-uterine life present
very wide variations ; still, it is important to have an approximate idea, at least, upon
these points, and we shall adopt the figures given by Scanzoni, as presenting fair aver-
ages. As the measurements and weights are simply approximative, the slight differ-
ences between the German and the English standards are not important. It will be
useful, also, to give, as is done by Scanzoni, a review of the general development of the
organs at different stages.

At the third week, the embryon is from two to three lines in length. This is about
the earliest period at which measurements have been taken in the normal state.

At the seventh week, the embryon measures about nine lines. Points of ossification
have appeared in the clavicle and the lower jaw ; the Wolffian bodies are large ; the
pedicle of the umbilical vesicle is very much reduced in size ; the internal organs of gen-
eration have just appeared; the liver is of large size ; the lungs present several lobules.

At the eighth week, the embryon is from ten to fifteen lines in length. The lungs
begin to receive a small quantity of blood from the pulmonary arteries; the external
organs of generation have appeared, but it is difficult to determine the sex ; the abdomi-
nal walls have closed over in front.

At the third month, the embryon is from two to two and a half inches long and
weighs about one ounce. The amniotic fluid is then more abundant, in proportion to th<?
size of the embryon, than at any other period. The umbilical cord begins to be twisted ;
the various glandular organs of the abdomen appear ; the pupillary membrane is formed ;
the limitation of the placenta has become distinct. At this time, the upper part of the
embryon is relatively much larger than the lower portion.

At the end of the fourth month, the embryon becomes the foetus. It is then from
four to five inches long and weighs about five ounces. The muscles begin to manifest
contractility ; the eyes, mouth, and nose are closed ; the gall-bladder is just developed ;
the fontanelles and sutures are wide.

At the fifth month, the foetus is from nine to twelve inches long and weighs from
five to nine ounces. The hairs begin to appear on the head ; the liver begins to secrete
bile, and the meconium appears in the intestinal canal ; the amnion is in contact with
the chorion.

MULTIPLE PREGNANCY. 941

At the sixth month, the foetus is from eleven to fourteen inches long and weighs
from one and a half to two pounds. If the foetus be delivered at this time, life may con-
tinue for a few moments ; the bones of the head are ossified, but the fontanelles and
sutures are still wide ; the prepuce has appeared ; the testicles have not descended.

At the seventh month, the foetus is from fourteen to fifteen inches long and weighs
from two to three pounds. The hairs are longer and darker ; the pupillary membrane
disappears, undergoing atrophy from the centre to the periphery ; the relative quantity
of the amniotic fluid is diminished, and the foetus is not so free in the cavity of the
uterus ; the foetus is now viable.

At the eighth month, the foetus is from fifteen to sixteen inches long and weighs from
three to four pounds. The eyelids are opened and the cornea is transparent ; the pupil-
lary membrane has disappeared; the left testicle has descended; the umbilicus is at
about the middle of the body, the relative size of the lower extremities having increased.

At the ninth month, the foetus is about seventeen inches long and weighs from five to
six pounds. Both testicles have usually descended, but the tunica vaginalis still commu-
nicates with the peritoneal cavity.

At birth, the infant weighs a little more than seven pounds, the usual range being
from four to ten pounds, though these limits are sometimes exceeded.

The position of the foetus, in the great majority of cases, excluding abnormal presenta-
tions, is with the head downward ; and why this is the usual and the normal position, is a
question which has been the subject of much discussion. As we have just seen, in the
early stages of pregnancy, the foetus floats quite freely in the amniotic fluid. Upon this
point, Dr. Matthews Duncan has made the following interesting experiments : Securing
the limbs of the foetus in the natural position which it assumes in utero, by means of
threads, and immersing it in a solution of salt of nearly its own specific gravity, he found
that it naturally gravitated to nearly the normal position, with the head downward. It
is probable, judging from these observations, that the natural gravitation of the head and
of the upper part of the foetus is the determining cause of the ordinary position in utero.

The shape of the uterus at full term is ovoid, the lower portion being the narrower.
The foetus has the head slightly flexed upon the sternum, the arms flexed upon the chest
and crossed, the spinal column curved forward, the thighs flexed upon the abdomen, the
legs slightly flexed and usually crossed in front, and the feet flexed upon the legs, with
their inner margin drawn toward the tibia. This is the position in which the foetus is
best adapted to the size of the uterine cavity, and in which the expulsive force of the
uterus can be most favorably exerted, both as regards the foetus and the generative pas-
sages of the mother.

Multiple Pregnancy. — It is not very rare to observe two children at a birth, and cases
are on record where there have been four and even five, though in these latter instances
the children generally survive but a short time, or, as is more common, abortion takes
place during the first months. Three at a birth, though rare, has been often observed ;
and we have in mind at this moment a case of three females, triplets, all of whom lived
past middle age.

In cases of twins, it is an interesting question to determine whether the development
always takes place from two ova, or whether a single ovum may be developed into two
beings. In the majority of cases, twins are of the same sex, though sometimes they are
male and female. In some cases, there are two full sets of membranes, each foetus hav-
ing its distinct decidua, placenta, and chorion ; in others, there is a single chorion and a
double amnion ; but, in some, both foetuses are enclosed in the same amnion. As a rule,
the two placentae are distinct ; but sometimes there is a vascular communication between
them, or what appears to be a single placenta may give origin to two umbilical cords.
If there be but a single chorion and amnion and a single placenta, it has been thought
that the two beings are developed from a single ovum ; otherwise, it would be necessary

942 GENERATION".

to assume that there were originally two sets of membranes, which had become fused
into one. The instances on record, one of which we have given, of twins, one white and
the other black, show conclusively that two ova may be developed in the uterus at the
same time. While there can be no doubt upon this point, the question of the possibility
of the development of two beings from a single ovum remains unsettled. It is thought
to be more difficult to understand how two conjoined monsters, like the celebrated
Siamese twins, who died in 1874 at the age of sixty-three years, could be developed

ENG. CHANG.

FIG. 312.— The Siamese twins.

V V, vena cava ; V P, V P, portal vein ; a, upper hepatic pouch of Chang ; &, peritoneal, or umbilical pouch of Eng ; <•,
lower peritoneal, or umbilical pouch of Chang ; D, D, connecting liver-band ; e, lower border of the band ; /, upper
border of the band.

from two ova which became fused, than to imagine the development of two beings from
a single ovum. This question, however, belongs to teratology and could be settled only
by observations of conjoined monsters very early in their development, which do not
exist in literature.

As pathological conditions, we have extra-uterine pregnancies, in which the fecun-
dated ovum, forming its attachments in the Fallopian tube (Fallopian pregnancy) or within
the abdominal cavity (abdominal pregnancy), undergoes a certain degree of development.
The uterus usually enlarges, in these instances, and forms an imperfect decidua.

Cause of the First Contractions of the Uterus in Normal Parturition. — The cause
of the first contraction of the uterus in normal parturition is undoubtedly referable to
some change in the attachment of its contents, which causes the foetus and its membranes
to act as a foreign body. When, for any reason, it is advisable to cause the uterus to
expel its contents before the full term of pregnancy, the most physiological method of
bringing on the contractions of this organ is to cautiously separate a portion of the mem-
branes, as is often done by introducing an elastic catheter between the ovum and the
uterine wall. A certain time after this operation, the uterus contracts to expel the ovum,
which then acts as a foreign body.

In the normal state, toward the end of pregnancy, the cells of the decidua vera and
of that portion of the placenta which is attached to the uterus undergo fatty degenera-
tion, and, in this way, there is a gradual separation of the outer membrane, so that the

INVOLUTION OF THE UTEKUS— MECONIUM. 943

contents of the uterus gradually lose their anatomical connection with the mother. When
this change has progressed to a certain extent, the uterus hegins to contract ; each con-
traction then separates the membranes more and more, the most dependent part pressing
upon the os internum ; and the subsequent contractions are probably due to reflex action.
The first " pain " is induced by the presence of the foetus and its membranes as a foreign
body, a mechanism similar to that which obtains when premature labor has been brought
on by separation of the membranes.

We shall not describe the mechanism of parturition, although this is entirely a physi-
ological process, for the reason that it is necessarily considered elaborately in works upon
obstetrics. The first contractions of the uterus, by pressing the bag of waters against
the os internum, gradually dilate the cervix ; the membranes usually rupture when the os
is pretty fully dilated, and the amniotic fluid is discharged ; the head then presses upon the
outlet; and, the uterine contractions becoming more and more vigorous and efficient, the
child is brought into the world, this being followed by the expulsion of the membranes and
placenta. There then follows a tonic contraction of the muscular walls of the uterus,
which becomes a hard, globular mass, easily felt through the flaccid abdominal walls.
The very contractions of the muscular fibres of the uterus which expel the foetus close
the vessels ruptured by the separation of the placenta and arrest the haemorrhage from
the mother. The changes which then take place in the respiration and the circulation
of the infant have been fully considered in connection with the development of the circu-
latory system.

Involution of the Uterus. — At from four to six days, and seldom later than eight days
after parturition, the uterus has sensibly advanced in the process of involution ; and it is
then gradually reduced to the size and structure which it presents during the non-preg-
nant condition, though it never becomes quite as small as in the virgin state. The new
mucous membrane, which has been developing during the latest periods of pregnancy,
becomes perfect at about the end of the second month after delivery. It has then united,
at the os internum, with the mucous membrane of the neck, which does not participate
in the formation of the decidua. The muscular fibres, after parturition, present granules
and globules of fat in their substance, and are gradually reduced in size, as the uterus
becomes smaller. Their involution is complete at about the end of the second month.
During the first month, and particularly within the first two weeks after delivery, there
is a sero-sanguinolent discharge from the uterus, which is due to disintegration of the
blood and of the remains of the membranes in its cavity, this debris being mixed with a
certain amount of sero-mucous secretion. This discharge constitutes the lochia, which
are at first red, but become paler as they are reduced in quantity and disappear.

During lactation, the processes of ovulation and menstruation are usully arrested,
though this is not always the case. In treating of secretion, we have given a full descrip-
tion of the vernix caseosa, and we have also stated what is known with regard to the
properties and composition of the urine of the foetus.

Meconium. — At about the fifth month, there appears a certain amount of secretion in
the intestinal canal, which becomes more abundant, particularly in the large intestine, as
development advances. This is rather light-colored or grayish in the upper portion of
the small intestine, becoming yellowish in the lower portion, and is of a dark-greenish
color in the colon. The dark, pasty, adhesive matter, which is discharged from the rec-
tum soon after birth, is called the meconium.

The meconium appears to consist of a thick, mucous secretion, with numerous grayish
granules, a few fatty granules, intestinal epithelium, and, frequently, crystals of choleste-
rine. The color seems to be due to granulations of the coloring matter of the bile, but
the biliary salts cannot be detected in the meconium by Pettenkofer's test. The con-
stituent of the meconium which, in our own observations, we have found to possess the

944

GENERATION.

FIG. 813. — Cholesterine extracted from meconium
inch olyective.

greatest physiological importance, is cholesterine. Although but few crystals of cho-

lesterine are found upon microscopical examination, the simplest processes for its ex-
traction will reveal the presence of this
principle in large quantity. In a specimen
of meconium in which we made a quantita-
tive examination, the proportion of choles-
terine was 6'245 parts per 1,000. It is a
significant fact, that the meconium contains
cholesterine and no stercorine, the sterco-
rine, in the adult, resulting from a trans-
formation of cholesterine by the digestive
fluids, which are probably not secreted dur-
ing intra-uterine life.

None of the secretions concerned in di-
gestion appear to be produced in utero, and
it is also probable that the true biliary salts
are not formed at that time ; but we know
that the processes of disassimilation and
excretion are then active, and the choles-
terine of the meconium is the product of the
excretory action of the liver. The relations

of cholesterine as an excrementitious principle have already been very fully discussed, in

connection with the bile and with excretion.

Dextral Preeminence. — The curious fact, that most persons by preference use the
right arm, leg, eye, etc., instead of the left, while, as exceptions, some use the left in
preference to the right, has excited a great deal of discussion, even among the earlier
writers. There can be no doubt with regard to the fact of a natural dextral pre-
eminence ; and, also, that left-handedness is congenital, difficult, if not impossible, to
correct entirely, and not due simply to habit. It would appear that there must be some
condition of organization, which produces dextral preeminence in the great majority of
persons, and left-handedness, as an exception ; but what this condition is, it is very diffi-
cult to determine. An explanation, very often offered by anatomists, is, that the right
subclavian artery arises nearer the heart than the left, that the right arm is therefore
better supplied with arterial blood, develops more fully, and is, consequently, generally
used in preference to the left; but we cannot explain the exceptional predominance of
the left hand by an inversion of this arrangement of vessels.

The most important anatomical and pathological facts bearing upon the question
under consideration are the following: Dr. Boyd has shown that the left side of the brain
almost invariably exceeds the right in weight, by about one-eighth of an ounce. In
aphasia, the lesion is almost always on the left side of the brain. These facts point to a
predominance of the left side of the brain, which presides over the movements of the
right side of the body. Again, a few cases of aphasia with left hemiplegia, the lesion
being on the right side of the brain, have been reported as occurring in left-handed per-
sons. These points we have noted in treating of the nervous system.

Dr. Ogle, in a recent paper on right-handedness, gives several instances of aphasia in
left-handed persons, in which the brain-lesion was on the right side. In two left-handed
individuals, the brain was examined and compared with the brain of right-handed per-
sons. It was found that the brain was more complex on the left side in the right-
handed, and on the right side in the left-handed. In the discussion which followed the
presentation of this paper, Dr. Oharlton Bastian stated that he had found the gray mat-
ter of the brain to be generally heavier on the left than on the right side. With regard
to the cause of the superior development of the left side of the brain, the only explana-

DEVELOPMENT AFTER BIRTH, AGES, AND DEATH. 945

tion offered was the fact that the arteries going to the left side are usually larger than
those on the right. There were no observations with regard to the comparative size of
the arteries upon the two sides in left-handed persons.

Reasoning from the facts just stated, Dr. Ogle conceives that dextral preeminence
depends upon a natural predominance of the left side of the brain, the reverse obtaining
in the left-handed. This view seems to afford the most rational explanation of dextral
preeminence. It is generally true that the members on the right side are stronger than
the left, particularly the arm ; but this is not always the case, even in the right-handed.
A not inconsiderable practical experience in athletic exercises has led us to observe that
the right hand is more conveniently and easily used than the left, from which fact we
derive the term dexterity ; but that the left arm is often stronger than the right. In
many feats of strength, the left arm appears less powerful than the right, because we
have less command over the muscles. As a single illustration of this, we may mention
the feat of drawing the body up with one arm, which requires unusual strength, but very
little dexterity. In a number of right-handed persons, we find many who perform this
feat more easily with the left arm, and not a few who can accomplish it with the left
arm and not with the right. When we come to the cause of the superior development
of the left side of the brain, we must confess that the anatomical explanation is not
entirely satisfactory. We can only say that the two sides of the brain are generally not
exactly equal in their development, the left side being usually superior to the right, and
that we ordinarily use the muscles of the right side of the body in preference to those
of the left side.

Development after Birth, Ages, and Death.

When the child is born, the organs of special sense and the intelligence are dull ;
there is then very little muscular power ; and the new being, for several weeks, does lit-
tle more than eat and sleep. The natural food at this time is the milk of the mother, and
the digestive fluids do not, for some time, possess the varied solvent properties that we
find in the adult, though observations upon the secretions of the infant are few and
rather unsatisfactory. The full activity of pulmonary respiration is gradually and slowly
established. Young animals appropriate a comparatively small quantity of oxygen, and,
just after birth, they present a much greater power of resistance to asphyxia than the adult.
The power of maintaining the animal temperature is also much less in the newly-born.
The process of ossification, development of the teeth, etc., have already been considered.
The hairs are shed and replaced by a new growth a short time after birth. The fonta-
nelles gradually diminish in size after birth, and they are completely closed at the age of
about four years.

The period of life which dates from birth to the age of two years is called infancy
At the age of two years, the transition takes place from infancy to childhood. The
child is now able to walk without assistance, the food is more varied, and the digestive
operations are more complex. The special senses and the intelligence become more
acute, and the being begins to learn how to express ideas in language. The child gradu-
ally develops, and the milk-teeth are replaced by the permanent teeth. At puberty,
which begins at from the fourteenth to the seventeenth year — a little earlier in the
female — the development of the generative organs is attended with important physical
and moral changes.

The different ages recognized by the older writers were as follows : Infancy, from
birth to the age of five years; adolescence, or youth, to the twenty -fifth year; adult
age, to the thirty-fifth year ; middle life, to the fiftieth year ; old age, to the sixtieth
year ; and then, extreme old age. A man may be regarded at his maximum of intellect-
ual and physical development at about the age of thirty-five, and he begins to decline
after the sixtieth year, although such a rule, as regards intellectual vigor, would cer-
tainly meet with many exceptions.
60

946 GENERATION.

"We do not propose to consider, in this connection, the psychological variations which
occur at different ages, but, as regards the general process of nutrition, it may be stated,
in general terms, that the appropriation of new matter is a little superior to disassimila-
tion up to about the age of twenty-five years ; between twenty -five and forty -five, these
two processes are nearly equal ; and, at a later period, the nutrition does not completely
supply the physiological waste of the tissues, the proportion of organic to inorganic
matter gradually diminishes, and death follows, as an inevitable consequence of life. In
old age, the muscular movements gradually become feeble ; the bones contain an excess
of inorganic matter ; the ligaments become stiff ; the special senses are usually obtuse ;
and there is a diminished capacity for mental labor, with more or less loss of the memory
and of intellectual vigor. It is a curious fact that remote events are more clearly and
easily recalled to the mind in old age, than those of recent occurrence ; and, indeed,
early impressions and prejudices then appear to be unusually strong.

It frequently happens, in old age, that some organ essential to life gives way, and that
this is the immediate cause of death ; or that an old person is stricken down by some
disease to which his age renders him peculiarly liable. It is so infrequent to observe a
perfectly physiological life, continuing throughout the successive ages of man, that it is
almost impossible to present a picture of physiological death ; but we sometimes observe
a gradual fading away of vitality in old persons, who die without being affected with any
special disease. It is also difficult to fix the natural period of human life. Some per-
sons die, apparently of old age, at seventy, and it is rare that life is preserved beyond
one hundred years. In treating of the so-called vital point, we have stated that there
does not seem to be any such occurrence, except under conditions of most extraordinary
external violence, as instantaneous death of all parts of the organism. If we confine
ourselves to physiological facts, we cannot admit the existence of a single vital principle
which animates the entire organism. Each tissue appears to have its peculiar property,
dependent upon its exact physiological constitution, which we call vitality ; a term
which really explains nothing. The tissues usually die successively, and not simulta-
neously, nearly all of them being dependent upon the circulating, oxygen-carrying blood
for the maintenance of their physiological properties. It has been demonstrated, in-
deed, that the so-called vital properties of tissues may be restored, after apparent death,
by the injection of blood into their vessels.

After death, there is often a discharge of the contents of the rectum and bladder,
and parturition, even, has been known to take place. The appearance which indicates
growth of the beard after death is probably due to shrinking of the skin and, perhaps,
contraction of the smooth muscular fibres attached to the hair-follicles. The most
important phenomenon, however, which is observed before 'putrefaction begins, is a gen-
eral rigidity of the muscular system.

Cadaveric Rigidity. — At a variable period after death, ranging usually from five to
seven hours, all of the muscles of the body, involuntary as well as voluntary, become
rigid and can only be stretched by the application of considerable force. Sometimes,
especially after long-continued and exhausting diseases, this rigidity appears as soon as a
quarter of an hour after death. In the case of persons killed suddenly, while in full health,
it may not be developed until twenty or thirty hours after death, and it then continues
for six or seven days. Its average duration is from twenty -four to thirty-six hours ;
and, as a rule, it is more marked and lasts longer, the later it appears. In warm weather,
cadaveric rigidity appears early and continues for a short time. When the contraction
is overcome by force, after the rigidity has been completely established and has continued
for some time, it does not reappear. The rigidity of the muscular system extends to the
muscular coats of the arteries and the lymphatics. It is for this reason that the arterial
system is usually found empty after death. The rigidity first appears in the muscles
which move the lower jaw; then it is noted in the muscles of the trunk and neck, ex-

CADAVERIC RIGIDITY. 947

tends to the arms, and finally, to the legs, disappearing in the same order of succession.
The stiffening of the muscles is due to a sort of coagulation of their substance, analogous
to the coagulation of the blood, and is probably attended with some shortening of the
fibres ; at all events, the fingers and thumbs are generally flexed. That the rigidity is
not due to coagulation of the blood, is shown by the fact that it occurs in animals killed
by haemorrhage.

According to John Hunter, the blood does not coagulate nor do the muscles become
rigid in animals killed by lightning or hunted to death ; but it is a question, in these
instances, whether the rigidity does not begin very soon after death and continue for
a brief period, so that it may escape observation. As a rule, rigidity is less marked in
very old and in very young persons than in the adult. It occurs in paralyzed muscles,
provided they have not undergone extensive fatty degeneration.

Under ordinary conditions of heat and moisture, as the rigidity of the muscular sys-
tem disappears, the processes of putrefaction commence. The various tissues, with the
exception of certain parts, such as the bones and teeth, which contain a large proportion
of inorganic matter, gradually decompose, forming water, carbonic acid, ammonia, etc..
which pass into the earth and the atmosphere. The products of decomposition of the
organism are then in a condition in which they may be appropriated by the vegetable
kingdom.

INDEX.

Abdominal plates 914, 916, 920

Abdominal salivary gland 269

Abducens (see Motor-oculi extern us) 614

Abercrombie, brain of. T08

Absorption 300

by blood-vessels 301

by the mucous membrane of the mouth 301

by the stomach 301

of fats 301

by the intestinal mucous membrane 302

of biliary salts 284, 302

of gases in the intestines 302

by lacteal and lymphatic vessels 302

of albuminoids by the lacteals 313

of glucose and salts by the lacteals 313

of water by the lacteals 314

by parts not connected with the digestive sys-
tem 314

by the skin 314

by the respiratory surface 316

of substances by the lungs, in contagious diseases 316

by closed cavities, reservoirs of glands, etc 817

of fats and insoluble substances 317, 326

variations and modifications of 319

of fluids of greater density than the blood. . . 319, 327

of woorara, venoms, etc 319, 327, 358

of substances which disorganize the tissues 320

influence of the condition of the blood and of the

vessels upon 320

influence of the nervous system upon 320, 327

passage of liquids through membranes (see En-

dosmosis) 821

application of physical laws to the process of 326

Accidental areolse 807

Accommodation, auditory 840

Accommodation of the eye 793

changes of the crystalline lens in 799

action of the ciliary muscle in 773, 800

changes of the iris in 800

Achromatopsia 787

Acid of the gastric juice 238

Acid phosphate of lime in the gastric juice 240

Acoustic spot 843

Addison's disease 481

Additional tones 832

Adipose tissue 183, 503

Adolescence 945

^Esthesiometer 752

Agassiz, brain of 703

Age, influence of, upon the pulse 52

influence of, upon the respiratory movements. . . 132

influence of, upon the consumption of oxygen. . . 143

influence of, upon the exhalation of carbonic acid 147

influence of, upon the power to resist depriva-
tion of food. .. .. 172

Age, influence of, upon digestion 251

influence of, upon the urine 426

variations in the animal heat dependent upon. . . 610

Ages (infancy, childhood, youth, adult age, middle

age, and old age) 945

Agminated glands of the small intestine 263

Air, composition of 14

proper allowance of, in hospitals, prisons, etc.. . . 142

in the veins (see Veins) 103

Air-cells of the lungs 120

Air-swallowing 225

Album Graecum 292

Albumen 177

action of the gastric juice upon 245

comparative action of the gastric juice upon raw

and coagulated 245

not coagulated by the gastric juice 245

Albumen-peptone 245

Albumen, vegetable 178

Albuminoids, action of the intestinal juice upon 267

action of the pancreatic juice upon 277, 286

absorption of, by the lacteals 313

Albuminose 246

Alcohol, action of, in alimentation and nutrition . . 185, 186

elimination of 185

influence of, upon endurance, the power of resist-
ance to cold, etc 187, 509

influence of, upon lactation 370

influence of, upon the elimination of urea 428

Alcoholic beverages, influence of, upon the exhalation

of carbonic acid 149

Aliment (see Food) 176

Alimentation, general considerations 171, 176

Allantois, formation of. 904

first villosities of. 901

vascularity of 905

vascular villosities of 905

Alternate paralysis 618

Amandine 179

Amreboid movements 522

of the vitellus S97

Ammonia, exhalation of, by the lungs 154

Ammonia-theory of the coagulation of the blood 28

Amnesia 706

Amnion, formation of 901

villosities of. 901

enlargement of. 903, 905

Amniotic fluid 903

origin of. 904

antiseptic properties of 904

Amniotic umbilicus 901

Amphioxus lanceolatus, an animal without a brain. . . 696

Amputation, sensation in members after 593

Amyloid corpuscles 468

Ana?mia... 185

INDEX.

949

Anaesthesia ?4(5

Anaesthetics, influence of, upon glycogenesis 471

influence of, upon the sensory nerves 596, 68T

abolition of the reflex excitability of the spinal

cord by 687

Andersch, ganglion of. 762

Anelectrotonus 605

Angular convolution, influence of, upon vision 722

Antihelix of the ear 817

Animal food 177

Animal heat 505

limits of variation in the normal temperature in

man 505

variations of, with external temperature 506

— variations of, in different parts of the body 506

variations of, at different periods of life 503

— — in the newly-born 508

diurnal varieties of 508

relations of defective nutrition to 509

in inanition 509

influence of alcohol upon 187, 509

influence of exercise upon 510

influence of mental exertion upon 510

influence of the nervous system upon 511, 514

influence of the circulation upon 511

sources of 511

seat of the production of 511

relations of, to nutrition. 512

relations of non-nitrogenized and nitrogenized

food to 512, 513

relations of, to respiration 513

relations of, to the consumption of oxygen and

the production of carbonic acid and water 514

effects of division of the sympathetic nerve in the

neck upon 514

intimate nature of processes giving rise to 512

equalization of 521

uses of clothing in the equalization of 521

equalization of, by cutaneous transpiration 521

influence of menstruation upon 876

Antiperistaltic movements of the small intestine 286

Anti-scorbutics 193

Antitragus of the ear 817

Anus, retractors of 290

sphincters of 291, 297, 298

development of 921

imperforate 921

Aorta, development of 932, 983

Aortae, primitive 913, 932, 933

Aortic plexus 733

Aortic valves 89, 48

Aphasia 704

— cases of, in left hemiplegia in left-handed per-
sons 705

Appendices epiploicae 289

Appendix vermiformis 288

development of 920

Appetite for food 172

influence of climate and season upon 172

influence of vegetable bitters upon 172

perversion of, after extirpation of one kidney 404

modifications of, by extirpation of the spleen 478

modifications of. by extirpation of one kidney and

in cases of biliary fistula 479

Aqueous humor of the eye 782

composition of 782

restoration of, after its evacuation 782

refraction by - 793

Arachnoid . . 667

PAGE

Arachnoid, first appearance of. 916

Arantius, corpuscles of 39

Arbor vitee uteri 866

Arctic regions, diet in 509

Area vasculosa of the ovum 93i

Areolar tissue, absorption from 817

Arms, development of. 915, 916

Arnold's ganglion 731

Arrow-root 181

Arseniuretted hydrogen, effects of. 141

Arteries, physiological anatomy of •. . 64

mode of branching of 64

anastomoses of. 65

anatomical divisions of. 65

coats of. 65

muscular fibres of. 66

vasa vasorum of. 67

nerves of 67

lymphatics not found in the walls of. 67

course of the blood in 67

elasticity of. 67

gradual diminution of the intermittency of the

current in 68

contractility of 69

influence of the sympathetic nerves upon 69

irritability of. 69

influence of temperature upon the size of 70

influence of the resiliency of, upon the circulation 70

influence of the contractility of the small vessels

upon the distribution of blood in the tissues 70

locomotion of, and production of the pulse 70

tonicity of 74

variations in the diameter of, at different periods

of the day 74

pressure of blood in 74

pressure in different vessels 77

influence of respiration upon the pressure of

blood in 77

influence of muscular effort upon the pressure of

blood in 73

influence of haemorrhage upon the pressure of

blood in 78

rapidity of the flow of blood in 79

— reason why they are found empty after death.. . 114

Articular cartilage 851

Arytenoid muscle 552, 567

Asphyxia, influence of, upon the circulation, 54, 89, 110, 169

arrest of the action of the heart in 54, 110, 169

power of resistance to, in the newly-born, 143, 169, 510

phenomena of 168

influence of various conditions of the system upon

the power of resistance to 170

Associated movements 592

Astigmatism 794

Atmosphere, composition of 140

Attollens aurem 818

Attrahens aurem 818

Audition, general considerations 615

topographical anatomy of the parts connected

with 817

physics of sound (see Sound) 828

function of the external ear in 885, 849

function of the membrana tympani in 887

accommodation in 840

action of the ossicles of the ear in 841

functions of the semicircular canals in 849

functions of parts contained in the cochlea in ... 849

functions of the organ of Corti in 850

summary of the mechanism of 851

950

INDEX.

PAGE

Audition, development of the organs of 919

Auditory meatus, external 818

external, development of 923

internal 815, 846

Auditory nerves, physiological anatomy of. 815

general properties of 816

galvanization of. 816

distribution of 846

development of 919

Auditory vesicles 919

Auricle of the ear 817

Auricles of the heart 35

Auriculo-ventricular valves, action of 47

Autolaryngoscopy in the study of the mechanism of

deglutition 223

in the study of phonation 554

Axis-cylinder 567

Azygos uvulae 217

Bacillar membrane 776

Bacteria 855

Banting 502

Bartholinus, glands of. 890

Barytone 556

Bass voice 556

Baths, Turkish and Kussian 521

Beard, apparent growth of, after death 946

Beats, a cause of discord 833

Beaumont's table of digestibility of various alimentary

substances in the stomach 250

Beet-root sugar 181

Bellini, tubes of 896

Bertin, columns of. 396, 400

Betoin de respirer 164, 660, 727

Bicarbonate of soda 497

Bicuspid teeth 201

Bile, action of, in digestion 277

color, reaction, and specific gravity of 280

influence of, upon the faeces and upon the peri-
staltic movements of the intestine 283, 286

— influence of, upon the digestion and absorption

of fats .' 283

absorption of the salts of, by the intestinal canal. 284

variations in the flow of 284

resorption of. 317, 327

Pettenkofer's test for 449

coloring matter of. 448

mechanism of the secretion and discharge of 439

secretion of, by the liver-cells 439

secretion of, from venous or arterial blood 440

quantity of 441

variations in the flow of 441

influence of digestion upon the flow of. 441

excretory function of 450

general properties of 442

color, reaction, and specific gravity of 442

composition of 442, 443

excretory and secretory constituents of 443

inorganic salts of. 443

fatty and saponaceous constituents of 443

cholesterine of 446

organic salts of. 280, 444

tests for 449

Biliary acids 444

Biliary fistula 278, 281

nutrition, in a case of 173

— influence of, upon the appetite 479

Biliary salts 280, 444

absorption of, by the intestinal canal 284, 302

PAGE

Biliary salts, origin of 446

test for 449

Biliverdine 448

test for 449

Binocular vision 802

fusion of colors 805

Bitters, influence of, upon the appetite 172

"Black-hole" of Calcutta 170

Bladder, urinary, physiological anatomy of 407

muscular coats of 408

sphincter of. 408

corpus trigonum 408

uvula of 408

blood-vessels of 408

lymphatics of 409

contractions of 409

absorption by 317

mucus of 357

first appearance of 907, 920

Blastoderm, formation of the cells of 899

Blastodermic membranes 900, 913

Blepharoptosis 611, 812

Blind spot of the retina 792

Blood, general considerations 1

extra-vascular tissues 1

effects of abstraction and subsequent return of. . 1

transfusion of 2

quantity of 2

relative quantity of, in animals during digestion

and fasting 4

influence of abstinence from food upon the quan-
tity of 4

opacity of 4

odor of, and development of odor of, by sul-
phuric acid 4

taste of 4

reaction of , 4

specific gravity of 4

temperature of. 5

color of 5, 155

variations in the color of, in the vascular system 5, 155

color of, in veins coming from glands 6, 344, 347

anatomical elements (corpuscles) of 6

plasma of, or liquor sanguinis 6

specific gravity of the plasma of 7

red corpuscles of 6

specific gravity of the red corpuscles of 7

discovery of the red corpuscles of 8

size of the red corpuscles of 8

relations of the size of the red corpuscles of, to

muscular activity in different animals 9

table of measurements of the red corpuscles of,

in different animals 9

enumeration of the red corpuscles of 10

post-mortem changes in the red corpuscles of.. . 11

method for restoring the form of the red cor-
puscles of, after their desiccation 11

structure of the red corpuscles of. 12

development of the red corpuscles of 12. 981

— red corpuscles of, in the foetus 12, 931

nucleated corpuscles of 12, 931

relations of leucocytes to the development of the

red corpuscles of 12

theory of destruction of the red corpuscles of;

for the production of pigment 12

relations of the spleen to the blood-corpuscles. . . 13

function of the red corpuscles of 13, 156, 160

capacity of the red corpuscles of, for the absorp-
tion of oxygen, as compared with the plasma, 13, 156, 160

INDEX.

951

PAGE

Blood, action of the red corpuscles of, as respiratory

organs , 13

leucocytes, or white corpuscles of 13

situations in which leucocytes are found 14

appearance and characters of leucocytes 14

— quantity of leucocytes as compared with that of
the red corpuscles 14

— variations in the proportions of leucocytes 14

proportion of leucocytes in the blood of the

splenic veins 15

— specific gravity of the leucocytes of 15

— development of leucocytes 15

elementary corpuscles of 15

composition of the red corpuscles of 16

analysis of 19

table of composition of the blood-plasma 19

proximate principles of. 20

inorganic principles of 21

functions of water in . 21

•1-1

functions of chloride of sodium in

functions of other inorganic salts in

organic saline principles in

• organic non-nitrogenized principles in

excrementitious matters in

fats and sugars in ,

— organic nitrogenized principles in

plasmine, fibrin, metalbumen, and serine in. . .

peptones in 23

coloring matter of the plasma of 23

— coagulation of. 24

clot and serum of 24

formation of the clot in 24

proportions of clot and serum 24

characters of the clot of 25

characters of the serum of. 25

— coagulating principle of 25

circumstances which modify coagulation of, out

of the body 26

influence of temperature, chemicals, etc., upon

the coagulation of 26

coagulation of, in the organism 26

coagulation of, in animals killed by lightning or

hunted to death 26

coagulation of, in the heart and vessels 27

coagulation of, in the serous cavities and in the

Graafian follicles 27

office of the coagulation of, in the arrest of

haemorrhage 27

cause of the coagulation of 28

theory that coagulation of, is due to the evapora-
tion of ammonia 28

other theories of the coagulation of 28

— decomposition of plasmine into fibrin and metal-
bumen 29

non-coagulation of, when drawn by the leech.. . 80

fibrillation of fibrin in coagulation of 80

— non-coagulation of, in the renal and hepatic veins
and in the capillaries 80

circulation of (see Circulation) 31

function of, in respiration 115

changes in, in respiration (see Respiration) 155

difference in color between arterial and venous.. 155

absorption of oxygen by the red corpuscles of. . 156

gases of. 156

nitrogen in 1 60

condition of the gases in 160

general differences in the composition of arterial

and venous 161

influence of the condition of, upon absorption . . . 820

PAGE

Blood, influence of the composition and pressure of,

upon secretion 346

changes of, in passing through the kidneys 406

supposed changes in the albuminoid and corpus-
cular constituents of, in passing through the liver. 472

changes in, in passing through the spleen 477

relations of, to muscular irritabilit/ 537

Blood-corpuscles, development of, in the ovum 931

Blood-vessels, absorption by 301

first formation of, in the blastodermic layers 980

Bones, action of the gastric juice upon 249

anatomy of 543

fundamental substance of 544

Haversian rods of 544

Haversian canals of 544

lacunae of 545

osteoplasts and canaliculi of 545

marrow of 546

blood-vessels of 547

periosteum 547

regeneration of, by transplantation of periosteum 547

Bone-corpuscles 545

Bntal, foramen of 934

Boys, voice of 556

Brain, circulation in 106

contraction and expansion of, with the acts of

respiration 107, 668

peculiarity of the small vessels of 107, 583, 668

lymphatics of 806

variations in the quantity of blood in 667

' ganglia of 688, 690

— weight of different parts of 6S9

difference in the weight of, in the sexes 689

differences in the weight of, at different ages. . . . 689

specific gravity of. 690

directions of the fibres in 691

• fissures and convolutions of. 6DI

table of weights of, in white and black races. ... 702

table of weights of, in various individuals 702

state' of knowledge concerning the functions of

the pineal gland, pituitary body, corpus callosum,

septum lucidum, ventricles, and hippocampi of 728

rolling and turning movements following injury

of certain parts of 728

Branchial arches 983

Bread, made from gluten 179

Bread, digestibility of 251

Breathing capacity, extreme 137

Breschet, perilymph and endolymph of. 846

Bronchial arteries 121

mucus 856

tubes 118

tubes, development of. 922

Bronzed skin 481

Brunner, glands of 260, 267

Buccal glands 209

Buccinator muscle, action of, in mastication 205

Bursae mucosae 851

synovial 851

Butter 1 *:'•

composition of 874

Butyrine 875

Byron, brain of 704

Cadaveric rigidity 946

Caecum 280

— development of 920

Caffeine 189

Calorification (see Animal heat) 505

952

INDEX.

PAGE

Canals of Cuvier 933

Cane-sugar 180

Canine teeth 201

Calcutta, " black-hole" of 170

Capillaries, circulation in 81

physiological anatomy of 82

epithelium of 82

stomata in the walls of 82

size of 82

capacity of the system of. 84

course of blood in 84, 8T

study of the circulation in, with the microscope

(note) 85

" still layer" in 86

circulation in, in the lungs 88

rapidity of the flow of blood in 89

relations of the circulation in, to respiration 89

causes of the circulation in 90

Capillary attraction 323

blood, non-coagulation of. 30

power, so-called 90

influence of temperature upon the circulation in 91

influence of direct irritation upon the circula-
tion in 91

phenomena of inflammation observed in 92

Capriline 375

Caprine 375

Capro'ine 375

Capsicum 190

Caput coli 288

Carbon, quantity of, necessary to nutrition 192

Carbonate of lime 495

table of quantities of 496

origin and discharge of 496

of magnesia, 497

of potassa 497

of soda, function of 496

of soda, origin and discharge of 496

Carbonic acid, small proportion of, in the air 140

relations of the consumption of oxygen to the

production of 143, 152

exhalation of, in respiration (see Respiration) 144

sources of, in the expired air 153

analysis of the blood for 157

— proportion of, in the blood 159

disengagement of, by the action of pneumic

acid 153, 160

condition of, in the blood 160

sources of, in the blood 160

action of the phosphate of soda upon the capacity

of absorption of, by the blood 160

effects of accumulation of, in the atmosphere 169

in milk 875

relations of the production qf, to animal heat 514

Carbonic oxide, effects of. 141, 167, 169

use of, in analysis of the blood for oxygen.

158, 160

Cardiac plexus 7.33

Cardinal veins 933

Cardiometer 46, 76

Carotid plexus 733

Carotids, development of. 983

Cartilage 548

articular 351

cells and cavities 549

— of Meckel 919, 923

Cartilagine 177

Caruncula 812

Caseine 177, 374

PA.GB
Caseine, vegetable ................................. 179

- action of the gastric juice upon ................. 246

- action of reagents upon ........................ 874

- coagulation of, by the mucous membrane of the
stomach ........................................ 874

Caseine-peptone ................................... 246

Casper Hauser, case of ............................ 803

Castration, effects of, upon the voice ................ 556

Catelectrotonus .................................... 605

Cavernous plexus .................................. 733

Cellulose .......................................... 182

Cement of the teeth ........................... 199, 925

Cephalo-rachidian fluid ..................... 107, 667, 668

- situation of ............................... .... 107

-- quantity, properties, composition, and functions

of. ............................................. 668

- effects of removal of. .......................... 668

Cereals ................................... 179, 181, 183

— proportion of fat in ............................ 183

Cerebellum, weight of ......................... 690, 706

- physiological anatomy of ...................... 706

- comparative weight of, in the sexes ............. 706

- course of the fibres in ......................... 707

- general properties of. ......................... 708

- functions of. ................................. 708

-- extirpation of, in animals ...................... 709

- influence of, upon muscular coordination ........ 709

- recovery of coordinating power after removal of

a portion of. ..................................... 710

- pathological facts bearing upon the function of. . 712

- analysis of Andral's ninety-three cases of disease

of. ............................................. 712

- additional cases of disease of ................... 715

- connection of, with the generative function ..... 719

- comparative size of, in stallions, mares, and geld-

ings

719

- movements of the uterus, testicles, etc., follow-
ing irritation of .................................. 719

- comparative development of, in the lower ani-
mals ............................................ 719

- development of ............................... 917

Cerebral vesicles, formation of. ..................... 917

Cerebrate of soda .................................. 584

Cerebric acid ..................................... 584

Cerebrine .......................................... 584

Cerebro-spinal axis, general arrangement of ......... 666

Cerebro-spinal fluid (see Cephalo-rachidian fluid). 667, 663
Cerebrum, case of supposed regeneration of ......... 5S5

- weight of. .................................... 690

- fissures and convolutions of .................... 691

- motor and sensory cells of ..................... 693

- general properties of .......................... 693

- motor centres in ............................. 694

- functions of. .................................. 694

- extirpation of, in animals ...................... 695

- absence of, in the amphioxus lanceolatus ........ 696

- absence of intellectual faculties in animals after
removal of ...................................... 697

- pathological facts bearing upon the functions of 699

- in idiots .................................... 700

- comparative development of, in the lower ani-
mals ........................................... 701

- comparative development of, in different races of
men and in different individuals. .. ............ 701

- location of the faculty of articulate language in.. 704

- development of .............................. 917

- development of the convolutions of ............. 918

- development of the ventricles of .............. 919

Cervix uteri, mucous membrane of ................. 865

INDEX.

953

PAGE

Cervix uteri, erectile tissue of. 867

action of, in coitus 890

production of mucus by, in coitus 891

Cerumen 363

Ceruminous glands 360

Cheeks, action of, in mastication 204, 205

Cheese 177

from peas 179

Chest-register 559

Chick, development of. 912

Childhood 945

Chloride of potassium 494

Chloride of sodium, function of, in alimentation.. 184, 191

table of quantities of. 492

general functions of 492

effects upon animals of deprivation of 498

origin and discharge of 493

Chlorides, diminution of, in the urine 422

Chocolate 190

Choleic acid 230, 444

Cholesteriue 280

transformation of, into stercorine 295

in the faeces of animals in starvation, in hibernat-
ing animals, and in the meconium 295

in the bile 446

extraction of 447

origin of, by disassimilation of the nervous tissue 451

comparative quantity of, in the bood going to

and coming from the brain 451

comparative quantity of, in the blood upon the

two sides of the body, in cases of hemiplegia 458

elimination of, by the liver 454

comparative quantity of, in the blood going to

and coming from the liver 455

proportion of, in the blood in cases of grave and

of simple icterus 457

proportion of, in the blood in cases of cirrhosis . 457

poisoning by injection of, into the blood 458

Cholesterasmia 458

Cholic acid 280, 414

Chondrine ... 177, 548 |

PAGE

Ciliated epithelium 354

Cilio-spinal centre 798

Circulation of the blood 31

discovery of 31

Chorda dorsalis 913, 914

Chorda tympani 622, 760

influence of, upon gustation 622, 761

influence of, upon the submaxillary gland 623

general properties of 760

Chords in music 832

Chorion of the ovum, formation of 901, 904

— disappearance of villi from a portion of 905

Choroid 771

vasa vorticosa of 772

Chromatic aberration 790

Chyle 334

r specific gravity of 335

coagulation of. 335

table of composition of 336

urea in 836

comparison of constituents of, with those of

lymph 837

microscopical characters of 887

movements of (see Lymph) 887

Chyle-corpuscles 13

Cilia 528

Cilia (eyelashes) 811

Ciliary 'ganglion 731

Ciliary movements 523

Ciliary muscle 773

Ciliary nerves 731

Ciliary processes 773

action of the heart in (see Heart) 40

in the arteries (see Arteries) 64

depressor-nerve of 78, 655

in the capillaries (see Capillaries) 81

in the veins (see Veins) 92

in the cranial cavity 106

derivative 108

pulmonary 109

in the walls of the heart 110

general rapidity of 110

relations of the frequency of the heart's action

to the rapidity of 112

phenomena of, after death 113

influence of, upon the movements of the small

intestine 287

influence of, upon absorption 320

influence of, upon animal heat 511

effects of section of the pneumogastrics upon . . 653

effects of galvanizing the pneumogastrics or their

branches upon 654

reflex influence upon, through the pneumogas-
trics 655

influence of the sympathetic system upon 738

first appearance of, in the embryon 982

fcetal (see Foetal circulation) 935

Circulation of the lymph and chyle (see Lymph) 338

Circulatory system, development of 980

Circumflexus, or tensor-palati muscle 821

Cirrhosis, proportion of cholesterine in the blood in

cases of 457

Cleft palate 562, 924

Climate, influence of, upon the diet 172, 193, 503

Clitoris 869

development of 980

Cloaca 920, 930

Clot of blood (see Blood) 24

non-organization of 27, 30

Clothing, uses of 527

Coagulation of the blood (see Blood) 24

Coccyx, consolidation of 914

Cochlea, bony 823

bony, modiolus of 828, 844

bony, hamulus of S'23, 844

membranous 844

membrana basilaris of. £44

scala tympani and scala vestibuli of 844

lirnbus laminae spiralis of 844

membrana tectoria (membrane of Corti) of 844

membrane of Reissner of 844

the true membranous 845

quadrilateral canal of 846

cupola of 846

distribution of the nerves in 846

functions of, in audition 849

Cocoa 190

Cocoa-shells 190

Coffee, influence of, upon the exhalation of carbonic

acid 149

composition of 187

influence of, upon nutrition 1SS

influence of. upon the elimination of urea.. . 188, 429

Coitus, influence of, upon the rupture of Graafian fol-
licles 572

action of the male in 888

physiological frequency of 883

954

INDEX.

PAGE

Coitus, action of the female in 889

— — action of the cervix and os uteri in 890

production of mucus in the cervix uteri in 891

. establishment of a " continuous canal ''in 891

Colon 288

development of 920

Colors 786

— complementary 78T

theory of the appreciation of. 787

inability to distinguish 7S7

binocular fusion of 805

fusion of, in vision 806

duration of impressions of. 806

Colostrum 376

cream from 377

relations of the subsequent secretion of milk to

the quantity of 378

Colostrum-corpuscles 377

Columnar epithelium 854

Combustion (oxidation) in relation to animal heat ... 514

Combustion-theory of respiration 1G3

Complemental air 137

Concha of the ear 817

Condiments 190

Cone-fibre plexus 777

Cones of the retina 776,791

Conjunctiva - 812

mucus of 357

Connective tissue 531

relations of the lymphatics to 310

Conoidal epithelium 354

Consonance 834, 837

Consonants 562

Contagious diseases, absorption of agents producing,

from the respiratory surface 316

Continuous canal, establishment of, in coitus 891

Contractility 535

Contralto 556

Cooking, development of savors in 177

Coordination of muscular action, connection of the

posterior white columns of the spinal cord with 679, 711
connection of the cerebellum with (see Cerebel-
lum) 709, 718

Copulation (see Coitus) 887

influence of, upon the rupture of Graaflan folli-
cles 871, 872

Corium (see Skin) 381

Cornea 771

anterior elastic lamella of 771

membrane of Descemet or of Dernours 771

blood-vessels of. 771

lymph-spaces of 771

wandering cells of. 771

terminations of the nerves in 771

refraction by 793

development of. 919

Corneal corpuscles 771

Coronary arteries, arrest of the action of the heart by

ligation of. 57

Corpora amylacea 535

Corpora striata, physiological anatomy of. 720

functions of 721

development of 918

Corpulence, effect of diet upon 502

Corpus dentatum of the cerebellum 706

- — of the medulla oblongata 724

Corpus Highmorianum 880

Corpus innominatum (organ of Giraldes) 882

Corpus luteuin, first appearance of. 870

PAGE

Corpus luteum, general characters of 877

in pregnancy 878

measurements of, in menstruation and in preg-
nancy 879

Corpus trigonum 408

Corpuscles of Arantius 39

Corpuscles of the blood (see Blood) 6

Corresponding points in vision 802, 803, 610

Corti, membrane of 844

ganglion of 847

organ of 847

rods, or pillars of 847

function of the organ of 850

Cotugno, humor of 846

Cotyledons of the placenta 910

Coughing 134

Cowper, glands of 888

Cranial nerves 608

anatomical classification of 608

physiological classification of. 609

Cranium, circulation in 106

development of. 915

Cream 871

from colostrum 877

Creatine 418

change of, into urea and sarcosine 419

Creatinine 419

Cremaster muscle 880, 928

Crico-arytenoid muscles 551, 557

- — lateral 551, 553, 557

posterior 552

Crico-thyroid muscles 552, 557

Cromwell, brain of. 704

Crusta petrosa of the teeth 199

Crying 125

Crystalline (organic substance of the lens) 781

Crystalline lens 780

suspensory ligament of 773, 780, 781

capsule of 780

liquid of Morgagni of. 780

stars of. 780

refraction by 793

changes of, in accommodation 799

development of 919

Cumulus proligerus 863

Cupola of the cochlea 846

Curare (see Woorara) 595

Curling arteries of the placenta 911

Cuticle (see Skin^ 381

Cutis vera (see Skin) 881

Cuvier, brain of 702

canals of 933

Cyanosis 938

Cystine 421

in the faeces 293

Dacryoline 814

Daltonism 787

Dartoic fibres 525

Dartos 880

Death, definition of, etc 946

discharge of contents of the bladder and rectum

after.

946

apparent growth of the beard after 946

after breaking up the medulla oblongata 727

parturition after 946

Decidua vera 907

reflexa 907

serotina... .. 911

INDEX.

955

PAGE

Decidute, formation of 907

Defalcation 296

conditions which precede the desire for 297

muscular action in 297, 298

Deglutition, uses of the epiglottis in 117

action of the tongue in 204, 219

influence of the saliva upon 214

physiological anatomy of the parts concerned in . 215

mechanism of 218

— first period of 218

effects of section of the sublingual nerves upon. . 219

— in cases of absence of the tongue 219

— second period of 219

action of the constrictors of the pharynx in the

second period of 220

protection of the posterior nares during 220

protection of the opening of the larynx dur-
ing 220, 224

relations of, to respiration 220

action of the epiglottis in 221

influence of the sensibility of the top of the

larynx in protecting the opening during 221

study of, by autolaryngoscopy 223

third period of 224

action of the oesophagus in 224

length of time occupied in 224

character of the movements of 225

in the inverted posture 225

of air 225

influence of the pneumogastric nerves upon 252

influence of the spinal accessory nerves upon . . . 631

influence of the sublingual nerves upon 634

influence of the superior laryngcal branches of

the pneumogastrics v, pon 651

influence of the inferior laryngeal branches of the

pneumogastrics upon 653

Demours, membrane of 771

Dental bulb 925

follicle 925

Dentine 199, 925

Depressor-nerve of the circulation 78, 655

Derivative circulation 108

Derma (see Skin) 881

Descemet, membrane of 771

Development of the embryon (see Embryon) 911

afterbirth 945

Dextral preeminence 944

Dextrine 182

Diabetes, artificial 405, 470, 663

Diaphragm 121, 123

action of, in inspiration 124

— influence of contraction of, upon the size of the

opening for the oesophagus 125

development of 921

Diaphragmatic hernia, congenital 921

Diastase 182

animal, action of, upon starch 214

Dicrotism of the pulse 73, 74

Diet (see Food) 191

regulation of, in hospitals, etc 192

influence of, upon the development of power

and endurance 493

variations in. in different climates 512

in arctic regions 512, 518

Diffusion of liquids , 324, 826

Digestion, influence of, upon the proportion of leuco-
cytes in the blood 15

influence of, upon the pulse 52

influence of, upon the exhalation of carbonic acid. 148

PAGE

Digestion, general considerations 195

duration of 195

general view of the organs of 195

successive action of the various digestive fluids

in 242

action of the saliva in (see Saliva) 206

action of the gastric juice in (see Gastric juice). . 242

of nitrogenized alimentary principles. . . 243, 267, 277

duration of, in the stomach 249

circumstances which influence 251

— influence of exercise upon 251

influence of sleep upon 251

influence of haemorrhage upon 251

influence of inanition upon 251

influence of age upon 251

in the small intestine 257, 267, 273

action of the intestinal juice in (see Intestinal

juice)

267

action of the pancreatic juice in (see Pancreatic

juice) 273

action of the bile in (see Bile) 277

influence of, upon the quantity of lymph 329

influence of, upon the flow of bile 441

influence of, upon the glycogenic function of the

liver 469

influence of, upon the volume of the spleen 477

influence of, upon animal heat 508

Digestive fluids in the foetus 921, 944

Digitalis, want of action of. upon the heart, after sec-
tion of the pneumogastrics C54, 665

Dilator tubse muscle 821

Disassimilation (see Urine, Faces, Sweat, and Mech-
anism of Excretion) 846

Discords 833

Discus proligerus 863

Dissepiments of the placenta 910

Diurnal variations in the urine 427

Dorsal plates 913, 915

Double vision 802

Dreams... 744

Drinking, mechanism of 197

Drinks ... 184

influence of, upon the urine 427

Duct of Miiller, development of, into the Fallopian

tube 927

Ductless glands 472

enumeration of 478

Ductus arteriosus 932, 933

closure of 988

venosus, closure of 938

Duodenum 257

glands of 260

Dupuytren, brain of 703

Dura mater 667

first appearance of 916

Ear, glands of 860

— uses of the hairs at the opening of. 390

disease of the semicircular canals of 71S

lobule of. 817

Ear, external 817

uses of. 885,849

muscles of. 813

Ear, middle, general arrangement of the parts in .... 818

arrangement of the ossicles of 819

fenestra ovalis and fenestra rotunda of. 819

muscles of 820

arrangement of the tympanic membrane in (see

Tympanic membrane) 835

956

INDEX.

PAGE

Ear, middle, development of 919, 923

Ear, internal 822

physiological anatomy of. 842

distribution of the nerves in 846

liquids of. 846

hair-cells of. 848

Ear, functions of different parts of 849

Ear, internal, development of 919

Effort, muscular 542

Eggs, digestibility of 251

Eighth cranial nerve, third division of (see Spinal ac-
cessory nerve) 627

second division of (see Pneumogastric) 644

first division of (826 Glosso-pharyngeal) 761

Ejaculatory ducts 883

Elastic tissue 525

Electric current in muscles 542

Electricity, action of, upon the nerves 599

action of descending and ascending currents of,

upon the nerves 600

action of a constant current of, upon the

nerves 600,603

Electrotonus 603

Embryon, primitive trace of. 899, 900

development of. 911

time when it becomes the foetus 911, 940

general view of the development of 912

size, weight, and development of, at different

stages of utero-gestation 940

Embryonic spot 900

Embryo-plastic elements 532

Enamel of the teeth 199

Enamel-organ 925

Encephalic circulation 106

Encephalon (see Brain) 688

development of 917

Endocardium 35

Endolymph of the labyrinth 846

Endosmometer 823

Endosmosis 321

influence of membranes upon 323, 325

through porous septa 828

influence of different liquids upon 825

Epidermis (see Skin) 332

first appearance of 916

Epididymis 880, 881

development of, from a portion of the Wolffian

body 928

Epiglottis, uses of, in deglutition 117

cases of loss of 118

action of, in deglutition 221

removal of, from the lower animals 222

cases of loss of, in the human subject 222

action of, in phonation 558

development of 923

Epithelium, action of, in the absorption of fats 818

glandular 343

pavement, mucous membranes covered with. ... 353

columnar, or conoidal, mucous membranes cov-
ered with 354

ciliated, mucous membranes covered with. . 354, 523

mixed, mucous membranes covered with 354

influence of, upon the absorption of venoms 357

Erect impressions of images inverted on the retina. . . 801

Erectile organs, structure of 108

tissues, circulation in 107

tissue of the uterus and ovaries 866

of the external female organs of generation 869

Erection, mechanism of . . iQS

PAGE

Erection, of the penis 889

mechanism of. 889

nerve of 889

of the cervix uteri in coitus 890

Eructation . . 256

I Eunuchs, voice of 5o6

j Eustachian tube 821

j muscular action in dilatation of 821

! Eustachian valve 36, 934

disappearance of 938

Excito-motor action 6S3

Excrementitious matters in the blood 29

Excrementitious principles, mechanism of the pro-
duction of (see Excretion) 846

Excretine , 293

Excretion, distinction of, from secretion 342, 346

mechanism of. 346

general considerations 879

Excretoleic acid 298

Excretory function of the liver 450

Exercise, influence of, upon the pulse 53

influence of, upon the exhalation of carbonic

acid 150

influence of, upon digestion 251

influence of, upon the urine 428

development of power and endurance by 498

— influence of, upon animal heat 510

Exosmosis 322

Expiration 128

— action of the elasticity of the parenchyma of the
lungs in 129

action of the elasticity of the thoracic walls in.. . 129

table of muscles of 130

action of the abdominal muscles in 131

relations of, to inspiration 133

duration of 133

Expression, nerve of (see Facial nerve) 618

Eye, physiological anatomy of. 770

form and dimensions of the globe of. 770

sclerotic coat of 770

cornea of 771

anterior elastic lamella of 771

membrane of Descemet or of Demours 771

choroid coat of. 771

tunica Euschiana of 772

vasa vorticosa of 772

ciliary processes of 773

zone of Zinn 781

iris of 774

ligamentum iridis pectinatum of 774

pupil of 774

pupillary membrane of 775

canal of Schlemm , 775

retina of (see Retina) 775

macula lutea of 776

fovea centralis of. 776

crystalline lens of 780

liquid of Morgagni 780

aqueous humor of. 782

chambers of 782

vitreous humor of (see Vitreous humor) 782

hyaloid membrane of. 782

summary of the anatomy of the globe of 7?3

refraction in (see Vision) 784

considered as an optical instrument 784

axis of 785, 792

angle alpha of. 785

punctum caecum, or blind spot of 792

mechanism of refraction in ... . . 793

INDEX.

957

PAGE

Eye, simple schematic 794

astigmatic 794

. movements of the iris 796

accommodation of, to vision at different distances 798

corresponding points in the retinae of. . .802, 803, 810

movements of 807

muscles of. 807

protrusion and retraction of, by muscular action 808

action of the recti muscles of 808

— action of the oblique muscles of 809

axes of rotation of 808, 809

movements of torsion of. 809

associated action of the muscles of 810

parts for the protection of 811

tarsal cartilages of. 811

development of 918

Eyebrows 390, 811

Eyelashes 390, 811

Eyelids 811

glands of 361

muscles of. 811

development of 919

time of separation of, in the foetus 941

Face, development of 922

Facial angle 702

Facial nerve 618

physiological anatomy of 618

decussation of the roots of. 618

— branches of, within the aquaeductus Fallopii 620

external branches of. 621

summary of the anastomoses and distribution of 621

properties and functions of 621

influence of, upon taste and upon the submaxil-

lary gland (see Chorda tympani) 622, 623

influence of, upon the movements of the palate,

uvula, and tongue 628, 624

functions of the external branches of 625

effects of stimulation of branches of 6^6

influence of, upon mastication, through the buc-
cinator muscle 626

Facial palsy, symptoms of 625

Faeces, influence of the bile upon 288

— quantity of 292

analysis of 293

cholesterine in, in starvation, in hibernating ani-
mals, and in meconium 295

" figured " 296, 297

stercorine in 456

Fallopian tubes 868

fimbrise of 668

mucous membrane of 86S

— opening of, into the peritoneal cavity 868

supposed influence of, upon the rupture of Graa-

fian follicles 872

passage of the semen through 892

— development of, from the ducts of Muller 927

Fallopian pregnancy 892, 942

Falsetto-register 559

Falx cerebe'lli 667

Falx cerebri 667

Fats in the blood 22

Fats, composition of 188

saponiflcation of. 1S4

emulsiflcation of 184

as a single article of diet 184

action of the gastric juice upon 248

— — not acted upon by the intestinal juice 268

action of the pancreatic juice upon . . '. 273

Fats, influence of the bile upon the digestion and ab-
sorption of 2S3

absorption of (see Absorption) 801

absorption of, by the lacteals 802, 817, 326

alleged production of, by the liver 472

relations of, to nutrition 601

formation and deposition of 501

disappearance of, in inanition 502

condition and amount of, in the organism.. 503, 504

anatomy of adipose tissue 508

Fatty acids and salts in the blood 21

Fatty degeneration or substitution 501

Fatty diarrhoea, cases of. 275

Fatty matters of the nervous system 584

Fatty and saponaceous constituents of the bile 443

Fauces, pillars of 216

isthmus of 216

Fecundation, situation of. 892, 896

time when it is most likely to occur 893

mechanism of. 893

Fecundity, limits of, as regards age 874

Fehling's test for sugar 461

Female organs of generation, internal 857

Female organs of generation, external 868

Female, action of, in coitus 889

Female, orgasm in 890

Fenestra ovalis 819, 822

Fenestra rotunda 819, 822, 842

Fenestrated membranes 526

Ferrein, pyramids of. 396, 400

Fibrin 177

concrete and dissolved 23

of the clot 25

non-organization of 27, 80

formation of, by decomposition of plasm ine 29

fibrillation of, in coagulation 30

vegetable 179

action of the gastric j uice upon 245

action of dilute acids upon 246

Fibrin- factors 29

Fibrinogen 29

Fibrinoplastic matter 29

Fibrin-peptone 246

Fibro-cartilage 549

Fibro-plastic elements 532

Fibrous tissue, white, or inelastic 58>

Fifth crania} nerve, small root of (see Mastication,

nerve of) 615

Fifth cranial nerve, large root of 684

physiological anatomy of. (585

ganglion of Gasser 635

branches of 686

properties and functions of 688

operation for the division of, within the cranial

cavity 689

immediate effects of division of. 640

influence of, upon deglutition 641

remote effects of division of. 641

different remote effects of division of, before and

behind the ganglion of Gasser 642

effects of division of, upon the nutrition of the

organs of special sense 642

relations of, to the sympathetic system 643

cases of paralysis of, in the human subject 643

Fila acustica 846

Fish, digestibility of 251

Fisk, James, Jr., brain of. 708

Flax-seed 1 *•-'

Foetal circulation 935

958

INDEX.

PAGE

Foetal circulation, change of, into the adult circu-
lation 936

Foetus blood-corpuscles of. 12

respiratory efforts by 167

urine of 426

glycogenesis in . 469

influence of the maternal mind upon the develop-
ment of 8»8,895

determination of the sex of b9o

at the fifth month 905

time when this name is applied to the product of

fecundation 9H.940

functions of the nervous system in 919

reflex movements in 91

respiratory efforts by 919

digestive fluids in 921, 944

size, weight, and development of, at different

stages of utero-gestation 940

when viable 941

' weight of, at term 941

position of, in the uterus 941

Food, influence of climate and season upon the quan-
tity of. 1T2, 193

definition of 176

nitrogenized principles of 176

animal 177

vegetable 178

non-nitrogenized principles of 180

inorganic principles of 184

quantity and variety of, necessary to nutrition . . 191

regulation of, in hospitals, etc 192

influence of, upon the capacity for labor 192

necessity of a varied diet 193

influence upon nutrition of single articles of,

when taken alone 194

— influence of, upon lactation 369

influence of, upon the urine 427

— influence of different kinds of, upon the glyco-
genic function of the liver 470

Foramen ovale 361 934

closure of... '937

Fossa ovalis in the heart 933

Fourth cranial nerve (see Patheticus) 613

Fourth ventricle 706

Fovea cardiaca. ,

931

- centralis 776

hemispherica g2g

Free-martin 375^ 895

Frontal process, in the development of the face 923

Gall-bladder 433

mucus of 057

development of 921

Galactophorous ducts 366, 367

Galvanic current in muscles 542

Ganglia in the substance of the heart 56 (note), 59

Ganjlionic nervous system (see Sympathetic) 729

Gargling 223

Gases of the blood 156

in the blood in different parts of the system. . . . 159

mechanism of the interchange of, between the

blood and the air in the lungs 161

of the small intestine, uses of. 286, 299

of the stomach

of the large intestine

origin of, in the intestines

absorption of, in the intestines

of the milk . .

298

299

299

302

375

of the urine 425

PAGE

Gases in the body 499

Gasser, ganglion of. 63d

Gasterase 237

Gastric fistula in the lower animals 231

in the human subject 232

Gastric glands 229

Gastric juice 230

mode of collecting 232

secretion of 2b4

modifications of the secretion of zbo

artificial, made by infusion of the mucous mem-
brane of the stomach 235

quantity of 23^

composition of 236

reaction of 2ot>

— specific gravity of 2£6

does not decompose by keeping 286

— antiseptic properties of 237, 247

table of composition of 237

— organic principle of 237

source of the acidity of 238, 241

substitution of other acids for the normal acid

of - 241, 242

ordinary saline constituents of 241

action of, in digestion 242

action of, upon meats, or muscular tissue 243

action of, upon albumen 245

— action of, upon fibrin 245

action of, upon caseine 246

— action of, upon vegetable nitrogenized principles,
such as gluten 246

action of, upon non-nitrogenized alimentary prin-
ciples 248

action of, upon fats 248

action of, upon sugars 248

action of, upon carbonate and phosphate of lime

and upon bones 249

influence of the pneumogastric nerves upon the

secretion of 252

Gastric plexus 7.33

Gelatine 177

French committee on 178, 179, 194

Gelatine of Wharton QQ6

Generation, general considerations 852

spontaneous 854

sexual 854

female organs of, internal 857

female organs of, external 868

male organs of 879

development of the internal organs of 927

development of the external organs of. 930

Genito-spinal centre 410, 882

Genito-urinary system, development of 927

Germinal spot 870

Germinal vesicle 870

disappearance of 897

Giraldes, organ of 8S2

Glands, color of the blood in the veins of 6, 344, 347

comparative quantity of blood in, during activ-
ity and repose 69

lymphatics of . 306

absorption from the reservoirs and ducts of. 817

variations in the circulation in 344

irritability of 345, 535

• elimination of foreign substances by 346

influence of nerves upon 347

general structure of 348

anatomical classification of 349

sebaceous . . 358

INDEX.

959

PAGE

Glands, of Tyson 3ot>

of the ear (ceruminous) 800

Meibouiian 861

ductless, or blood-glands 472

terminations of nerves in 572

Glandular epithelium 343

Glisson, capsule of 431, 432

Globuline 17, 17T

Globulins of the lymph and chyle 333, 337

Glosso-pharyngeal nerves 761

physiological anatomy of 761

general properties of 703

relations of, to gustation 764

Glottis, movements of, in respiration 116, 553

influence of the inferior laryngeal nerves upon

the movements of 116, 553

appearance of, as seen with the laryngoscope. . . 554

development of 922

Glucose (see Sugars) 22, 180, 182

Gluten i 79

bread made from 179

action of the gastric juice upon 246

Glutine 179

Glyciue 2SO

Glycocholate of soda 280, 444, 446

Glycocholic acid 280, 444, 446

Glycocolle 178

Glycogenic function of the liver (see Liver) 458

Glycogenic matter 467

— mode of extraction of 467

Goose-flesh 381

Graafian follicles 859, 860

number of 860

mode of formation of 860

size of 862

coats of 862

membrana granulosa of 863

discus, or cumulus proligerus in 863

situation of the ovum in 863

rupture of 870, 871

macula of 870

influence of copulation upon the rupture of. .871, 872

relations of rupture of, to menstruation 872

— changes in, after their rupture (see Corpus lu-
teum) 877

Grape-sugar 180

Gubernaculum testis 928

Gums 182

Gustation, relations of, to olfaction 758

general considerations of 759

nerves of 760

functions of the chorda tympani in 761

functions of the glosso-pharyngeal nerve in 764

mechanism of 764

physiological anatomy of the organ of 764

influence of the chorda tyinpani upon 622

Gutturals - 562

Haemadrometer 79

Ha?madynamometer 7.~>

Haemagl'oblne .' 17, K>

— absorption of oxygen by 160

Haemaglobuline 17

ITii'inatine 17, 18

Iliomatocrystallinc 17

Haematoidine IS

Haematosis 155

Haemorrhage, difference in the effects of, during diges-
tion and fasting 4

PACE

Haemorrhage, influence of, upon the arterial pressure . 78

— effects of, upon the sense of thirst 174

influence of, upon digestion 251

Haamorrhagic diathesis 27

Hair-cells of the internal ear 343

Hair-follicles . . " ! 887

terminations of nerves in 570

Hairs, varieties of ggg

size of, in different parts ! 385

number of ggg

— hygrometricity of " 886

roots of 886

structure of. . . 888

color of 389

growth of 389

development of 889

shedding of, in the infant 389

sudden blanching of 889

uses of 390

first appearance of 916

shedding and replacing of 945

Haller, vas aberrans of 881

Hamulus of the cochlea 828, 844

Hare-lip 562, 924

Harmonics, or overtones 829

Harmony 832

Hauser, Caspar, case of 803

Haversian canals 544

Haversian rods 544

Head-fold of the neural canal 900

Head-register 559

Hearing (see Audition) 815

Heart, description of the action of, by Harvey 32

general description of the action of 84

physiological anatomy of 35

pericardium of 85

weight of 35

auricles of 35

foramen ovale of 36

Eustachian valve of 86

ventricles of 86

comparative capacity of the right and the left

ventricle of. 36

muscular tissue of 85, 87

comparative thickness of the ventricles of 38

valves of 38, 39, 47, 48

demonstration of the action of the valves

of 39,46

movements of. 40

complete revolution of 40

demonstration of the action of 40

action of the auricles of 40

action of the ventricles of 41

locomotion of 41

twisting of 42

hardening of 42

shortening and elongation of 42

impulse of 43

succession of the movements of 43

relative time occupied by the auricular and the

ventricular contractions of 44

force of 46

sounds of 48, 49

frequency of the action of (see Pulse) 51

influence of respiration upon the action of 54

arrest of the action of. in asphyxia 54

arrest of the action of, by voluntary arrest of

respiration 55

cause of the rhythmical contractions of 55, 58

960

INDEX.

PAGE

Heart, pulsation of, when removed from the body. . . 56
pulsation of, in animals poisoned with woora-

ra 56, 59, 61

ganglia in the substance of 56 (note) 59

arrest of the action of, by ligation of the coronary

arteries 57

contractions of, produced by irritation during its

repose 57

influence of the blood in its cavities upon the

contractions of. 57, 58

influence of the density of its contents upon the

contractions of 58

• irritability of the muscular tissue of 58

irritability of the lining membrane of. 58

• influence of the nervous system upon 58

insensibility of 58

arrest of the action of, by sudden destruction of

the spinal cord 59

influence of the pneumogastrics upon 59, 60, 631

influence of the sympathetic nerves upon 60

influence of the spinal accessory nerves upon 61, 631,

655, 658

palpitation of 59, 61

influence of mental emotions upon 62

summary of causes of arrest of the action of. . . 62

death from distention of 63

death from a blow upon the epigastrium 63

relations of the force of, to the frequency of its

pulsations 78, 112

circulation in the walls of 110

time required for the passage of the entire mass

of blood through 112

— quantity of blood discharged by each ventricular
systole of 112

relation of the frequency of the action of, to the

rapidity of the circulation 112

respiratory efforts after excision of 1G6

temperature of the blood in the two sides of. . 5, 507

want of action of digitalis upon, after section of

the pneumogastrics 654, 665

effects of galvanization of the pneumogastrics

upon 654, 658

development of 932, 934

relative size of, in the foetus and at different peri-
ods of life 934

enlargement of, in pregnancy 939

Heart-clots 26, 27

Heat, animal (see Animal heat) 505

Heat, power of resistance of the body to 521

Helix of the ear 817

Hemiopsia 769

Hemiplegia, comparative quantity of cholesterine in
the blood upon the two sides of the body in cases

of 453

Hemp-seed 183

Henle, tubes of 899

Hepatic artery, influence of ligation of, upon the secre-
tion of bile 440

Hepatic cells 435

Hepatic ducts 435

Hepatic plexus 733

Hepatic veins, non -coagulation of the blood of 80

arrangement of (see Liver) 434

— temperature of the blood in 5, 509

Hereditary transmission 894

Hermaphroditism 930

Hernia at the umbilicus, in the foetus 904, 920

diaphragmatic 921

Hibernation, consumption of oxygen in 143

PAGK

Hibernation, cholesterine in the faeces in 295

Hiccough 125, 135

Hippuric acid and its compounds 417

amount of daily excretion of 417

Homer, muscle of. 811

Horopter 803

Hunger 172

seat of the sense of 173

in diabetes 1 73

after section of both pneumogastric nerves. . 174, 664

after section of the hypoglossal and lingual

nerves 174

Hunted animals, coagulation of the blood in 26

Hyaloid membrane of the vitreous humor 7S2

Hydatids of Morgagni 880

Hydro-carbons ISO

relations of, to nutrition 500

Hydrochlorate of ammonia 497

Hydrochloric acid, action of, upon cane-sugar 243

Hydrogen, effects of confining an animal in a mixture

of with oxygen 143

Hygrometricity 824

Hyoid bone, development of 922, 923

Hypermetropia 789

Ilypnagogic hallucinations 744

Hypodermic administration of remedies 317

Hypogastric arteries 933

closure of 938

Hypogastric plexus 733, 734

Hypoglossal nerve (see Sublingual nerve) 632

Hypospadias 980

Hypoxanthine 421

Icterus, cholesterine in the blood in grave and in sim-
ple cases of.

Idiots, cerebrum of

Ileo-caecal valve

development of

Ileum

Iliac veins, development of

Imbibition 321,

Imperforate anus

Impotence, apparent

Inanition, influence of, upon the exhalation of carbonic
acid

— influence of age upon the power of resistance to.

— phenomena attending

duration of life in

influence of, upon digestion

quantity of lymph in

influence of, upon the glycogenic function of the

liver ".

disappearance of fat in

animal heat in

Incisor process, in the development of the face

Incisor teeth

Incus

development of

Induced muscular contraction

Inelastic fibrous tissue

Infancy

secretion of milk in

Inferior laryngeal nerves (see Pneumogastric)

Inflammation, phenomena of, studied in the capilla-
ries

after section of the fifth nerve

Infracostalis, action of, in expiration

Infundibuliform fascia

Infusoria

457

700

259
934
324
921

148
172
175
175
251
329

470
502
511

819
922
602
531
965
378
652

130

880

855

INDEX.

961

PAGE

Innominate vein, development of 934

Inorganic principles, in the blood 21

— alimentary, union of, with organic principles 184

absorption of, by the lacteals 314

in the urine 421

action of, in nutrition 488

— table of 4s

Inosates in the urine 41

Insalivation 205

entanglement of bubbles of air in the alimentary

mass during 214

Inspiration 122

table of muscles of 123

auxiliary muscles of 127

— relations of, to expiration 133

duration of 133

Insula 705

Intelligence, absence of, in animals deprived of the

cerebrum 697

Intercolumnar fascia 880

Intercostal muscles 122, 125, 130

action of, in inspiration 125

action of, in expiration 130

Intermaxillary process, in the development of the

face 923

Intervertebral discs, formation of 914

Intestinal canal, first appearance of 914

Intestinal digestion 257

Intestinal fistula, hunger in a case of 178

case of, in the human subject 266

Intestinal gases, origin of 299

Intestinal juice 265, 267

action of, upon starch and albuminoids 267

Intestinal villi, development of 920

Intestine, small, physiological anatomy of 257

length of 257

divisions of 257

peritoneal coat of 258

muscular coat of 258

valvulse conniventes of 259, 802

mucous membrane of 259

villi of 261, 263, 302

lacteals in the villi of 268

patches of Peyer of 263, 265, 267

solitary glands of. 264, 265, 267

movements of 285, 286

uses of the gases in 2S6, 299

influence of the circulation upon the movements

of , 287

influence of the nervous system upon the move-
ments of 287, G65

action of the epithelium of, in the absorption of

fats 818

distribution of the pneumogastric to 665

influence of the pneumogastric upon 665

development of 920

Intestine, large, physiological anatomy of 287

— peritoneal coat of 289

muscular coat of 289

mucous coat of , 290

follicles of 290

solitary glands of 291

digestion and absorption in 291

contents of (see Fa?ces) 292

movements of 296

gases of 299

development of 920

Intestines, influence of the bile upon the peristaltic

movements of -.

61

PAGH

Intestines, influence of the sympathetic system up-
on 739, 797

Intoxication, alcoholic 186

Inuline 182

Involuntary muscular tissue and movements. .. 527, 528

Involution of the uterus 948

Iodine, test for starch 181

Iris, influence of the motor oculi coinmunis

upon 611, 796

reflex action of the tubercula quadrigemina

upon 722, 797

influence of the sympathetic nerves upon 741

anatomy of 774

ligamentum iridis pectinatum 774

layers of 774

arrangement of the muscular fibres of 775

blood-vessels and nerves of 775

movements of 796

direct action of light upon 796

action of the nervous system upon 796

consensual contraction of 797

influence of the cilio-spinal centre upon 798

variations in the vascularity of 7!'8

action of, in accommodation 800

movements of, in converging the axes of vision. . 801

voluntary contraction of 801

development of. 919

Iron, function of, in the organism 185

in milk 875

Irradiation 806

Irritability, muscular 56, 59

of the muscular tissue of the heart 58, 59

action of sulpho- cyanide of potassium upon - 59

distinction between muscular and nervous. ... 59, 536

of the arteries 69

of the veins 96

of muscles 585

of glands 535

distinction between muscular and nervous 586

of nerves (see Nervous irritability) 594

Island of Eeil. . .

Jacobson, nerve of. 672

Jacob's membrane 776

Jaundice (see Icterus) 457

Jaws, physiological anatomy of 201

- articulations of 202

Jejunum 259

Jugular veins, development of 934

Kidnoys, effects of destruction of the nerves of.. 848, 405
physiological anatomy of 895

- hilum and pelvis of 895

- calices of 395

— infuridibula of 895

divisions of the substance of 896

cortical substance of 896, 898

columns of Bertin 896, 400

pyramids of Malpighi 396

pyramids of Ferrein 896, 400

pyramidal substance of 896

tubes of Bellini 896

— Malpighian bodies 898, 899

capsule of Miiller 899

- varieties of cells in the Malpighian bodies 899

- convoluted tubes of 899

tubes of Henle 399

- intermediate, or communicating tubes 899

- distribution of blood-vessels in 400

962

INDEX.

PAGE

Kidneys, arterial arcade of. 400

arteriolae rectse of 400

plexus of vessels around the convoluted tubes of 400

portal system of 401

stars of Verheyn 401

venous arcade of 401

lymphatics of 401

nerves of 401

extirpation of 403

extirpation of, upon one side 404

alternate action of, upon the two sides 406

changes in the blood in passing through 406

influence of extirpation of one, upon the ap-
petite 479

development of 928

Krause, corpuscles of 575

Labia majora, development of 930

Labia minora, smegma of. 363

Labial glands 209

Labials 562

Labyrinth, bony 822

membranous 842

ligaments of 842

utricle and saccule of 843

liquids of 846

distribution of the nerves in 846

development of 919

Lachrymal apparatus 813

Lachrymal fluid 814

Lachrymal glands 813

Lachrymal points 813

Lachrymal sac and ducts 813

Lachrymine 814

Lactates in the blood 21

in the urine 418

Lactation, duration of 369

modifications of (see Milk) 369

influence of, upon menstruation 875

Lacteals, in the intestinal villi 2(33

situation of 802

discovery of 302

absorption by 302

course of 306, 311

structure of 808

absorption of albuminoids by 313

absorption of glucose and salts by 313

absorption of water by 314

Lactiferous ducts 366, 3C7

Lactine 375

Lactometers 371

Lacto-proteine 874

Lactose 375

Lamellar elastic tissue £26

Lancet-fish, an animal without a brain 696

Language 550, 560

centre presiding over 704

Laryngoscope 554, 553

Larynx, physiological anatomy of 116, 550

muscles of (see names of the muscles) 551

action of, in respiration 553

action of, in phonation 558

influence of the inferior laryngeal branches of

the pneumogastrics upon the movements of 652

development of 922, 923

Laughing 125,135

Laxator tympani muscle 820

Lecithene 21, 584, 585

in the bile... .. 443

PAGB

Leech-drawn blood, non-coagulation of 30

Left-handedness (see Dextral preeminence) 944

Legs, development of 915, 916

Legumine 1 79

Lenses, refraction by 787

spherical aberration of. 789

chromatic aberration of. 790

correction of 790

Lenticular ganglion. 781

Leucine 421

Leucocytes (see Blood) 6, 13

relations of, to the development of the blood-cor-
puscles 12

development of 15

in the lymph 332, 337

development and function of, in the lymph 333

in colostrum 877

development of, in the ovum 981

Levator anguli scapulae, action of, in respiration 128

Levator palati 217

Levator palpebrae superioris 812

Levatores costarum, action of, in respiration 126, 127

Lichenine 182

Lichens, edible 182

Lieberkiihn, follicles of 260, 267

Life, definition of. 4S7, 504, 853

duration of, in man 946

Ligamentum denticulatum 667

Ligamentum iridis pectinatum 774

Light, theory of the propagation of 785

velocity of 786

decomposition of 7S6

refraction of, by lenses 787

Lightning, coagulation of the blood in animals killed

by 26

Limbus lamina? spiralis of the cochlea 844

Limitary membrane of the retina 777

Lingual glands 209

Linseed-oil 183

Lips, action of, in speech 5G2

development of 928

Liquids, influence of the ingestion of, upon lactation. . 870

Liquids (division of consonants) 562

Liquor sanguinis (see Blood; 6

Littre, glands of 888

Liver, circulation in the veins of 102

question of the formation of urea in 415

physiological anatomy of 431

weight of 431

capsule of Glisson 431, 432

blood-vessels of. 432

attachment of the walls of the hepatic vein to the

substance of 482

vaginal plexus of 482

interlobular vessels of 433

lobular vessels of. 433

intralobular veins of. 434

sublobular veins of 484

anatomy of a lobule of. 435

accessory portal veins of. 435

arrangement of the bile-ducts in the lobules of. . 435

anatomy of the excretory biliary passages of 436

racemose glands attached to the ducts of. 437

vasa aberrantia of 437

gall-bladder, hepatic, cystic, and common ducts

of. 437

nerves and lymphatics of 439

excretory function of 450

extirpation of 457

INDEX.

963

PAGE

Liver, production of sugar by 453

evidences of the glycogenic function of 459

— examination of the blood of the portal system for
sugar 461

— examination of the blood of the hepatic veins for
sugar 462

examination of the blood from the right side of

the heart for sugar 462, 468

does the liver normally contain sugar during life ? 464

formation of sugar in the liver during life, which

is washed out by the current of blood 466

characters of the sugar produced by 406

mechanism of the production of sugar in 467

glycogenic matter of. 467

ferment produced by, which is capable of chang-
ing glycogenic matter into sugar 468

variations in the glycogenic function of. 46y

glycogenesis in the foetus 469

— influence of digestion upon the glycogenic func-
tion of 469

influence of different kinds of food upon the gly-
cogenic function of. 469

— influence of the nervous system upon the pro-
duction of sugar by 470. 662

influence of the inhalation of anaesthetics and ir-
ritating vapors upon the production of sugar by . . . 471

— alleged production of fat by 472

supposed changes in the albuminoid and corpus-
cular constituents of the blood in 472

— influence of the pneumogastrics upon 662

development of 921

proportionate weight of, at different periods of

life 921

first circulation in 933

Lochia 948

Locomotion, passive organs of 543

Locomotor ataxia 679, 750

Lungs, capillary circulation in 88, 110

circulation through 109

parenchyma of 119

air-cells of 120

action of the elasticity of the parenchyma of, in

expiration 129

capacity of. 135

vital capacity of. 138

diffusion of air in 188

lymphatics of 806

absorption by the respiratory surface 316

development of 922

Lunula of the nail 884

Lymph 328

mode of collecting 828

quantity of. 829

— influence of digestion upon the quantity of. 329

properties and composition of 829

color of 829

specific gravity of 830

coagulation of. 830

tables of composition of 831

presence of glucose and urea in 832

corpuscular elements of 832, 337

globulins of 833, 837

origin and function of. 334

comparison of constituents of, with those of

chyle 837

circulation of. 888

causes of the movements of. 888

influence of the force of endosmosis upon the

movements of . . 839

PAGE

Lymph, influence of the contractile walls of the vessels

upon the movements of 889

influence of pressure from surrounding parts

upon the movements of 889

influence of respiration upon the movements of 840

Lymphatic glands 306

function of. 813

Lymphatic trunk, right 806

Lymphatics, not found in the coats of the blood-ves-
sels 67

discovery of 302

anatomy of 808

injection of. 808

mode of origin of 803

valves of 303, 309, 840

course and anastomoses of 304

— parts provided with 305

structure of. 808

question of orifices in the walls of. 309, 818

relations of, to connective tissue 310

of the liver 439

of the muscular tissue 583

Lymph-corpuscles 13

Macula acustica. . 848

Macula folliculi 870

Macula lutea 776

Male organs of generation 879

Male, action of, in coitus 888

erection in 889

orgasm in 889

Malleus 819

development of 922

Malpighi, pyramids of 896

Malpighian bodies of the kidney 398, 399

arrangement of blood-vessels in 400

bodies of the spleen 474

Mammary secretion (see Milk) 864

Mammary glands 865

condition of, during the intervals of lactation 365

structure of, during lactation 866

acini of 866

Manege, movements of. 729

Manna 182

Mannite 162

Maranta arundinacea 181

Margaric acid 183

Margarine 183, 504

Mariotte, experiment of 792

Marrow 546

Mastication 197

table of muscles of 202

action of the muscles which depress the lower

jaw 203

action of the muscles which elevate the lower

jaw and move it laterally and antero-posteriorly . . . 208

action of the tongue, lips, and cheeks in 204

action of the orbicularis oris and buccinator in . . 205

function of the sensibility of the teeth to hard

and soft substances in 205

influence of, upon the flow of the parotid saliva. . 207

nerve of 615

physiological anatomy of the nerve of 615

properties and functions of the nerve of. 617

— — influence of division of the nerve of, upon the

teeth, in the rabbit 617

Mastoid cells 821

Maternal mind, influence of, upon the development of

the foetus...

964

INDEX.

Maxilla, superior, development of 923

Maxilla, inferior, development of 923

Maxillary bones, physiological anatomy of 201

articulations of 202

Meats ^6

action of the gastric juice upon 243

digestibility of 251

action of the intestinal juice upon 267

action of the pancreatic juice upon 277

Meckel, cartilage of 919, 923

Meckel's ganglion f31

Meconium - 295,921,943

Medulla oblongata, decussation of motor conductors

in 677

physiological anatomy of 724

general properties of 726

functions of. 726

connection of, with respiration 726

— vital point in 727

action of, in the reflex acts of yawning, coughing,

crying, sneezing, vomiting, etc 728

influence of, upon glycogeuesis 728

influence of, upon the heart 728

development of 917

Medulla oblongata and pons Varolii, weight of. 690

Medullary plates 913,915

Medullocells 546

Meibomian glands and secretion 361, 364

Melanine 882

Membrana basilaris of the cochlea 844

Membrana granulosa of the Graafian follicle 863

Membrana media of the ovum 903

Membrana tectoria (membrane of Corti) of the cochlea 844

Membranae deciduae (see Deciduae) 907

Membranes of the foetus, formation of 900

Meniere's disease 718, 849

Mental emotions, influence of, upon lactation 370, 376

Mental exertion, influence of, upon the urine 430

influence of, upon animal heat 510

Menstruation, influence of, upon the exhalation of

carbonic acid 148

influence of, upon lactation 370, 376

enlargement of the thyroid gland in 483

variations in the thickness of the mucous mem-
brane of the uterus in 866, 877

identity of, with rut 871, 875

relations of, to the discharge of ova 872, 875

phenomena of. 874

supposed appearance of, after extirpation of the

ovaries 875

influence of pregnancy, lactation, and diseases

upon 875

stages of. 875

stage of invasion of. 875

duration of 876

characters of the flow in 876

cessation of 876

diminution in the excretion of urea in 876

influence of, upon the pulse 876

influence of, upon the temperature 876

Mercury, absorption of minute particles of. 818

Mery, glands of. 883

Mesenteric plexus 733

Mesenteric vein, development of. 984

Mesentery 257

development of. 921

Mesocsecum 289

Mesocephalon (see Tuber annulare) 722

Mesocolon... .. 289

PAGE

Metalbumen 23

— formation of, by decomposition of plasmine 29

Mezzo-soprano 556

Micropile 870, 896

Micturition 409

Milk 177, 364

digestibility of 251

mechanism of the secretion of 368

modifications of. 869

influence of diet upon 369

influence of liquids upon 369

influence of alcohol upon 370

influence of mental emotions upon 370, 376

influence of the nervous system upon 370, 376

quantity of 870

influence of pregnancy upon 370, 376

influence of menstruation upon 370, 376

general properties of 371

specific gravity and reaction of. 371

coagulation of 371, 374

formation of cream upon 371

microscopical characters of 371

table of composition of 373

nitrogenized constituents of 374

albumen in 374

comparison of, from the cow and from the human

subject 374

fatty matters of. 374

sugar of 875

fermentation of 375

inorganic constituents of 375

iron in . . 875

gases in 375

a typical food 375

variations in the composition of. 375

variations in, at different periods of lactation 375

relations of the quantity of, to the previous se-
cretion of colostrum 378

of the infant 378

Milk-fever 378

Milk-globules 372

action of reagents upon 372

structure of 373

Milk-sugar 180

Mitral valve 39, 47

Modiolus of the cochlea 823, 844

Modulation 839

Moisture and temperature, influence of, upon the ex-
halation of carbonic acid 151

Molar glands 209

Molar teeth 201

Monocular vision 804

Morgagni, liquid of 780

hydatids of 8SO

Mosses, edible 182

Motor nerves, action of 591

disappearance of irritability of 596

Motor-oculi communis 609

physiological anatomy of 610

properties and functions of 610

influence of, upon the iris 611, 796

Motor-oculi externus 614

physiological anatomy of 614

properties and functions of 614

Mouth, absorption by the mucous membrane of 301

action of, in phonation 558

action of, in speech 5C2

first appearance of 923

Movements.... 522

INDEX.

965

PAGE

Movements, of amorphous contractile substance

(amoeboid) 522

ciliary 523

due to elasticity 524

muscular 526

associated 592

Mucilages 182

Mucosine 356

Mucous membranes, lymphatics of 306

varieties of 353

Mucus 354

varieties of 355

nasal 356

bronchial and pulmonary 356

of the alimentary canal 85T

of the gall-bladder 357

of the urinary passages 857

of the generative passages 357

conjunctival 357

virulent 857

general function of 857

influence of, upon the absorption of venoms 358

Mailer, capsule of 899

Miiller, duct of (see Duct of Miiller) 927

Muscles, connection of, with the tendons 533

voluntary, terminations of nerves in 570

involuntary, terminations of nerves in 571

lymphatics of. 306

Muscular atrophy, progressive 742

Muscular coat of the arteries 66

Muscular contraction, influence of, upon the venous

circulation 101

influence of, upon the circulation of lymph 840 J

Muscular current 542 j

Muscular effort 542 j

influence of, upon the arterial pressure 78 j

Muscular exercise (see Exercise) 53, 150, 251, 428, 498, 510 |

Muscular fibres, involuntary 227, 527

characteristic mode of contraction of 253, 528

Muscular movements (see Movements) 526

Muscular sense 750

Muscular system, development of 916

Muscular tissue of the heart 35, 37

Muscular tissue, involuntary 527

contraction of. 528

voluntary, amount of 528

development of, by exercise 529

anatomical elements of 530

sarcolemma, or myolemma of 530

reactions of. 533

physiological properties of. 533

elasticity of. 534

tonicity of. 534

sensibility of. 534

contractility, or irritability of 535

irritability of, distinguished from nervous irrita-
bility 59, 536

influence of the blood upon the irritability of. ... 537

restoration of irritability of, by injection of blood 537

contraction of. 538

no change in the volume of, in contraction 533

changes in the form of, during contraction 588

duration of contraction of, under artificial excita-

tion.

artificial spasm of 539

prolonged contraction of (tetanus) 540

sound produced by contraction of. 541

fatigue of. 541

electric phenomena in 541

Muscular tissue, action of the gastric juice upon 248

blood-vessels of 632

lymphatics of 583

chemical composition of 538

Muscular wave 540

Musculine 176, 538

Mushrooms 1 91

Musical sounds (see Sound) 826

Melody 827

Mustache, uses of 390

Mustard 190

Mutes 562

Myeline 566

Myelocytes 583

Myeloplaxes 547

Myolemma 530

Myopia 788

Myosine 538

Naboth, ovules of 866

Nails, physiological anatomy of 888

connections of, with the skin 885

growth of 385

development of 385

first appearance of 916

Nares, posterior, development of 924

Nasal duct 813

Nasal fosste 754

action of, in phonation 553

Nasal mucus 856

Nasals 562

Negative variation 606

Negro, brain of 702

Nerve-cells 576

varieties of 576

striation of, by the action of nitrate of silver 578

connections of, with the fibres and with each

other 579

Nerve-centres, structure of 576

accessory anatomical elements of 583

connective tissue of 583

blood-vessels of 583

lymphatics of (perivascular canals) 588

Nerve-fibres 565

classification of 566

medullated 566

tubular membrane of 566

medullary substance of, or white substance of

Schwann 566

axis-cylinder of 567

simple, or non-medullated 567

gelatinous, or fibres of Remak 568, 735

— striation of, by the action of nitrate of silver 567

Nerve-force 597

non-identity of, with electricity 597

rapidity of conduction of 597

Nerves, of the arteries 67

vaso-motor 67

of the liver 439

structure of 505

accessory anatomical elements of. 568

perinevre of. 569

blood-vessels of 569

branching and course of 569

terminations of, in the voluntary muscles 570

terminations of, in the involuntary muscles 571

terminations of, in glands 572

sensory, terminations of 572, 575

terminations of, in the hair-follicles 576

reunion of 5*5

966

INDEX.

592
594
594
590
5[>9

PAGE

Nerves, motor and sensory ......................... 5S6

- motor, action of ............................... 591

-- sensory, action of

-- general properties of

- irritability of (see Nervous irritability)
_ disappearance of the sensory properties of

- action of electricity upon (see Electricity)

- process of dying of ............................ 601

- galvanic current from the exterior to the cut sur-
face of ....................................... . . 603

- cranial (see Cranial nerves) ..................... 608

- sympathetic (see Sympathetic) ................ 729

- vaso-motor (see Vaso-motor nerves) ............ 739

- development of ............................... 916

Nervous conduction, rapidity of ............ . ....... 597

Nervous irritability distinct from muscular irritability

59, 536

- description of.. . . ............................. 594

-- distinct in motor and sensory nerves ........... 595

- influence of woorara upon ..................... 595

- process of disappearance of, in motor nerves ... 536
-- momentary destruction of, by severe shock ..... 596

- destruction of, by a powerful galvanic shock ---- 597

Nervous system, influence of, upon the heart ........ 53

-- influence of, upon absorption .............. 320, 327

- influence of, upon secretion ................... 317

- influence of, upon lactation ................ 370, 376

- influence of, upon the secretion of sweat ....... 393

--- influence of, upon the secretion of urine ........ 405

-- origin of cholesterine in ....................... 451

- influence of, upon the glycogenic function of the
liver ............................................ 470

- influence of, upon animal heat ............. 511, 514

- general considerations ......................... 563

- divisions of. .................................. 564

- physiological anatomy of the tissue of .......... 565

- anatomical divisions of ........................ 565

- development of .............................. 916

-- functions of, in the foetus ...................... 919

Nervous tissue, composition of ..................... 583

- fatty constituents of. .......................... 584

Nervus intercostalis ............................... 730

Neural canal ................................... 900, 913

- head-fold of. .................................. 900

Neurilemma of the spinal cord ..................... 667

Neurine ........................................... 584

Neutral point ..................................... 605

Ninth cranial nerve (see Sublingual nerve) ........... 632

Nipple, sebaceous glands of ..................... 362, 366

- structure of .................................. 366

Nitrogen, proportion of, in the air ................... 140

- exhalation of, in respiration .................... 154

- in the blood .................................. 160

- quantity of, necessary to nutrition . ............ 192

- in milk ....................................... 375

Nitrogenized alimentary principles ................. 176

- digestion of ........................... 243, 267, 277

Nitrogenized food, influence of, upon the elimination

of urea .......................................... 428

-- relations of, to animal heat .................... 512

Nitrogenized principles, action of the gastric juice

upon ........................................... 245

- action of the intestinal juice upon ....... . ...... 267

- action of the pancreatic juice upon ............. 277

- action of, in nutrition ......................... 493

Nitrous oxide, effects of, when respired ............. 141

Nodes in vibrating strings ......................... 830

Non-nitrogenized alimentary principles ............. 180

- action of the gastric juice upon ---- ............ 248

PAGE

Non-nitrogenized alimentary principles, action of the

intestinal juice upon 267

relations of, to animal heat 513

— action of the pancreatic juice upon 274, 275

Non-nitrogenized principles in the blood 21

action of, in nutrition 500

Non-striated muscular fibres 527

Nose, uses of the hairs hi the nostrils 390

• development of 923

Notocorde 914

Nutrition, relations of respiration to 161

quantity and variety of food necessary to 191

general considerations 486

action of inorganic principles in 488

principles consumed by the organism 497

action of nitrogenized principles in 498

development oi power and endurance by exercise

and diet 498

action of non -nitrogenized principles in 500

modifications of, by various conditions 504

relations of, to animal heat 512

(VBeirne, sphincter of 297

Obliquus externus, action of, in expiration 131

internus, action of, in expiration 131

(Esophagus, influence of contraction of the diaphragm

upon 1 25

structure of. 218

glands of 218

action of, in deglutition 224

alternate contraction and relaxation of 224

effects of division of the pneumogastrics upon . . 662

development of 921

Oils (see Fats) 183

Oken, bodies of 927

Oleine 183, 504

Oleo-phosphoric acid 5S5

Olfaction, mechanism of 758

relations of, to gustation 758

Olfactory ganglia, or bulbs 756

Olfactory commissures and nerves, development of. . 919

Olfactory nerves 754

physiological anatomy of 755

general properties of 756

functions of 757

Olivary bodies 724

Olive-oil 183

Omentum 289

development of 921

Omphalo-mesenteric vessels 904, 931, 932

Ophthalmic ganglion 731

Ophthalmoscope 779, 791

Opium, exaggeration of the reflex excitability of the

spinal cord by 686

Optic commissure 763

Optic lobes (see Tubercula quadrigemina) 722

Optic nerves, physiological anatomy of 767

decussation of 722, 768

general properties of 769

effects of stimulation of 770

expansion of, in the retina 777

919
721
721
917
776

Orbicularis oris, action of, in mastication 205

Orbicularis palpebrarum 812

Organic matter, exhalation of, by the lungs 154

development of.

Optic thalami, physiological anatomy of

functions of

development of ':

Ora serrata of the retina

INDEX.

967

PAGE PAGE

Organic nervous system (see Sympathetic) 729 Pacini, corpuscles of 573

Organic non-nitrogenized principles in the blood 21 Palatals 562

Organic saline principles in the blood 21 Palate 216

Organic nitrogenized principles in the blood 22 muscles of 217

Orgasm, in the male 8S9 action of, in protecting the posterior nares dur-

— in the female 890 ing deglutition 220

Osmazome 178 action of the velum of, in phonation 553

Osmosis 321 action of, in speech. 562

Ossicles of the ear 819, 841 influence of the facial nerves upon the move-

mechanism of the action of 841 ments of 623

Ossification of the skeleton 915 development of 924

time of, for various bones 916 Palato-glossus 217

Osteine 177, 544 ! Palato-pharyngeus 217, 821

Osteoplasts 545 Palpitation of the heart 59, 61

Os uteri 864 Pancreas, physiological anatomy of 268 .

action of, in coitus 890 extirpation of 274

Otic ganglion 731 development of 921

Otoconia, or otoliths... 843, 846 Pancreatic fistula 269

Ovarian tubes 860 Pancreatic juice 268

Ovaries, situation of 858 mode of secretion of 271

ligament of 858, 859 j general properties of. .• 271

structure of 859 j reaction and specific gravity of 272

— cortical and medullary substance of 859 composition of 212

Graafian follicles of 859 quantity of 272

blood-vessels, nerves, and lymphatics of 860 - — alterations of 278

development of 860 action of, in digestion 273

passage of spermatozoids to 892 action of, upon fats 273

first appearance of 927 action of, upon starchy and saccharine prin-

development of the ligament of 928 ciples 273

Overtones 829 action of, upon albuminoids 277

Ovules of Naboth 866 j Pancreatine 272

Ovum, primordial 860, 809 Panniculus adiposus 881

Ovum, situation of, in the Graafian follicle 863 ! Paraglobuline 29

structure of 869 , Parotid saliva (see Saliva) 206

zona pellucida of 869 j Parovarium 863, 928

vitelline membrane of 870 Parturition, separation of the placenta in 911, 942

— micropile of 870, 896 cause of the first contractions of the uterus in. . . 942

vitellus of 870 arrest of haemorrhage after 943

discharge of, from the Graafian follicle 870 \ after death. > 946

influence of copulation upon the discharge of | Par vagum nerve (see Pneumogastric) 644

671, 872 Patheticus 613

— relations of the discharge of, to menstruation 872, 875 physiological anatomy of 613

passage of, into the Fallopian tube 872 . properties and functions of 613

passage of, into the Fallopian tube upon the op- Pavement-epithelium 850, 858

posite side 873 ' Pectine 182

duration of vitality of. 892 . Pectoralis major, action of the inferior portion of, in

coating of, with albumen, in the Fallopian tube respiration 128

892, 899 ! Pectoralis minor, action of, in respiration 128

— union of spermatozoids with 896 Pectose 182

membrana media of 903 i Penis, erection of 889

Oxalate of lime 420 j development of 980

formation of, from urate of ammonia 421 ' Pepper 190

Oxaluria 420 Pepsin 287

Oxygen, absorption of, by the blood-corpuscles Peptic glands 229

13, 156, 160 j Peptone, albumen 245

proportion of, in the air 140 fibrin 246

minimum proportion of, in the air, capable of — caseine 246

supporting life 140 Peptones 23, 246

effects of respiration of pure 141 Pericardial secretion 852

consumption of (see Respiration) 141 Pericardium 85

relations of the consumption of, to the exhalation development of 9£

of carbonic acid 143, 152 Perilymph of the labyrinth 846

analysis of the blood for 158 Perimysium 631

proportion of, in the blood 158 Ferine vre 569

in milk 875 Peristaltic movements of the small intestine 2S5

relations of the consumption of, to animal heat. . 514 influence of the bile upon 258, 286

Oxyha?maglobine 17, 160 influence of the nervous system upon 287

Oysters, digestibility of 251 Peritoneal cavity, first appearance of 914

Ozone. . . . . 140 ! Peritoneal secretion 852

968

INDEX.

PAGR

Perivascular canals 107, 5S3, 668

Perspiration (see Sweat) 391

Petit, canal of 782

Pettenkofer's chamber 142

test for bile 449

Peyer, patches of 263, 267

Pharyngeal glands 209

Pharyngeal plexus 733, 7G3

Pharynx, physiological anatomy of 215

muscles of 217

mucous membrane of 217

action of the muscles of, in deglutition 220

action of, in phonation 558

development of 921

Phonation (see Voice) 554

Phonograph 562

Phosphate of lime, function of, in alimentation 185

table of quantities of 495

general function, origin, and discharge of 495

Phosphate of magnesia 497

Phosphate of potassa 497

Phosphate of soda 497

influence of, upon the capacity of the blood for

absorbing carbonic acid 160

Phosphates, elimination of, in the urine (see Urine).. 423
proportion of, in the blood of herbivora and car-

nivora 423

Phosphorized fats 534, 535

Phrenic nerve 125

Phrenic plexus 733

Pia mater cerebri 667

first appearance of 916

Pia mater testis 880

Picromel 444

Pineal gland 485

Pinna of the ear 817

Pitch of musical sounds 826

Pituitary body 485

Pituitary membrane 755

Placenta, glycogenic function of 469

first appearance of 905, 908

development and structure of 908

maternal portion of 909

injection of, from the sinuses of the uterus 909

connection of the maternal and foetal portions

of 910

structure of, fully developed 910

cotyledons, or lobes of 910

dissepiments of , 910

blood-vessels of 911

curling arteries of 911

villi of 911

separation of, in parturition 911, 942

Placental circulation 933

Plasma of the blood (see Blood) 6

coloring matter of 23

Plasmine 22

decomposition of, into fibrin and metalbumen in

coagulation of the blood 29

Platysma of the uterus 864

Pleural secretion 352

Pleuro-peritoneal cavity, first appearance of 914

Plica semilunaris 812

Pneumate of soda in the blood 21

Pneumic acid 21

action of, upon the alkaline carbonates and bi-

carbonates in the blood 153, 160

Pneumogastric nerves, influence of, upon the action

of the heart 59, 60

PAGE

Pneumogastric nerves, hunger after section of. . .174, 664

— influence of, upon the movements of the small
intestine 287

physiological anatomy of 644

deep origin of 644

ganglia of 645

anastomoses of 645

distribution of 646

difference in the distribution of the nerves of

the two sides, to the abdominal organs 648

— properties and functions of 648

— general properties of the roots of. 649

— properties and functions of the auricular branch

of. 650

properties and functions of the superior laryngeal

branch of 651

influence of the superior laryngeal branch of,

upon the voice 651

influence of the superior laryngeal branch of,

upon deglutition 651

— influence of the superior laryngeal branch of,
upon respiration 652

properties and functions of the inferior, or recur-
rent laryngeal branch of. 652

influence of the inferior laryngeal branch of, upon

the movements of the larynx 116, 652

influence of the inferior laryngeal branch of, upon

respiration 653

influence of the inferior laryngeal branch of, upon

deglutition 653

effects of section of, upon the circulation 653

effects of section of, upon the respiratory move-
ments 653, 659

want of action of digitalis upon the heart after

section of 654, 665

effects of galvanization of, upon the circula-
tion 654, 658

direct influence of, upon the heart 654, 658

condition of the lungs after death following sec-
tion of 659

effects of galvanization of, upon respiration 661

properties and functions of the cesophageal

branches of 662

effects of division of, upon the oesophagus . . 252, 662

properties and functions of the abdominal

branches of. 662

influence of, upon the liver 471, 662

influence of, upon the stomach 252, 663

effects of galvanization of, upon the stomach 663

effects of section of, upon the movements of the

stomach and the secretion of gastric juice 252, 664

distribution of, to the intestinal canal 665

want of action of purgatives, after section of 665

Polar globule of the vitellus 897

Pons Varolii and medulla oblongata, weight of. 690

Pons Varolii (see Tuber annulare) 722

development of. 91 7, 01 ^

Portal system of the kidney 401

Portal vein, distribution of (see Liver) 432

influence of obliteration of, upon the secretion

of bile 440

temperature of the blood in 5

Portio dura of the seventh cranial nerve (see Facial

nerve) 618

Pregnancy, influence of, upon lactation 370, 876

influence of, upon menstruation 875

influence of, upon the corpus luteum 878

Fallopian 892,942

abdominal 892, 942

INDEX.

969

PAGE

Pregnancy, influence of, upon subsequent offspring.. . 894

enlargement of the uterus in 988

enlargement of the heart in 939

duration of 939

multiple 941

extra-uterine 942

Prehension of solids and liquids 197

Prepuce, smegma of 362

Presbyopia 789

Primitive trace of the embryon 899, 900

Prisms, action of, upon light 786

Progressive muscular atrophy 742

Prostate 883

Prostatic fluid, uses of 883

Protagon 29, 584, 585

Protoplasm 522

Proximate principles 20

Ptosis (see Blepharoptosis) 611, 812

Ptyaline 211

action of, upon starch 214

Puberty, influence of, upon the exhalation of carbonic
acid in the female 148

— period of 8T4, 945

Pulmonary artery, pressure of blood in 109

development of 932, 933

Pulmonary circulation 109

Pulmonary mucus 356

Pulmonic semilunar valves 38, 48

— safety-valve function of. 48, 109

Pulp-cavity of the teeth 199

Pulse, frequency of, at different ages 52

in the sexes 52

influence of digestion upon the frequency of 52

influence of muscular exertion upon the fre-
quency of. 52, 53

comparative frequency of, in sitting and standing 52

influence of temperature upon the frequency of. 53

influence of sleep upon the frequency of 53

production of, and locomotion of the arteries 70

investigation of, by the finger 71

gradual delay of, receding from the heart 71

pathological varieties of 71, 74

form of. 71

movements of, in the foot when the legs are

crossed 71

traces of 72, 73

influence of temperature upon the form of.. . . 73, 74

dicrotism of 73, 74

in the veins 99, 106

relation of the frequency of, to the respiratory acts 132

influence of menstruation upon 876

Punctum cajcum of the retina 792

Pupil 774,919

Pupillary membrane 775. 919

Purgatives, want of action of, after section of the

pneumogastrics 66

Pui-kinje, vesicle of. 870

Pus-corpuscles 13

Putrefaction of the body after death 947

Pyloric muscle 227

Quickening 911

Quince-seeds 182

Rape-seed oil 183

Receptaculum chyli 302, 307

Rectum, muscular coat of. 290

physiological anatomy of 291

development of 920

PAGE

Recurrent laryngeal nerves (see Pneumogastric) 652

Recurrent sensibility 590

Reflex action in respiration, question of 167

Reflex action, time occupied by 599

definition of 688

of the spinal cord 684

conditions necessary to the manifestations of. . . 686

exaggeration of, by poisoning with opium or

strychnine 6S6

abolition of, by anaesthetics 687

examples of. 687

operating through the sympathetic system 740

in the foetus 919

Refraction (see Light and Eye) 787, 798

Reil, island of. 693, 705

Reis*sner, membrane of 844

Remak, fibres of. 568, 785

Renal veins, color of the blood in 5

non-coagulation of the blood of. 80

Reproduction (see Generation) 852

Reserve air 136

Residual air 136

Resonators of Helmholtz 881

Respiration, relations of the blood-corpuscles to 13

influence of, upon the action of the heart 54, 110

voluntary arrest of, with arrest of the action of

the heart 55

influence of, upon the arterial pressure 78

relations of, to the capillary circulation 89

relations of, to the venous circulation 105

general considerations and definition of 114

function of the blood in 115

essential conditions in 115

physiological anatomy of the organs of. 116

movements of. 121

ribs, arrangement of. 122

table of muscles of, used in inspiration 123

auxiliary muscles of, used in inspiration 12T

table of muscles of, used in expiration 180

action of the abdominal muscles in 181

types of 131

differences in types of, in the sexes and at differ-
ent ages 132

frequency of the movements of 182

relations of the frequency of the movements of, to

the pulse 182

influence of age upon the frequency of the move-
ments of 132

relations of inspiration and expiration to each

other : 183

arrest of, in straining, etc 188

stethoscopic sounds of. 183

extreme breathing capacity 187

relations in the volume of the expired to the

inspired air 188

diffusion of gases in 189

of pure oxygen 141

consumption of oxygen 141

variations in the consumption of oxygen with

muscular activity, external temperature, and diges-
tion 142

- — variations in the consumption of oxygen, sleeping
and waking 143

variations in the consumption of oxygen with

age.

143

variations in the consumption of oxygen in lean

and fat animals 148

relations of the consumption of oxygen to the

production of carbonic acid 148, 152

970

INDEX.

PAGE

Respiration, effects upon the consumption of oxygen
of increasing its proportion in the air 143

effects upon the consumption of oxygen of con-
fining an animal in a mixture of oxygen and hy-
drogen 143

— quantity of oxygen consumed per hour in 144

changes in the air in passing through the lungs 144

elevation in temperature in the air in passing

through the lungs 144

exhalation of carbonic acid in 144

variations in the exhalation of carbonic acid with

the frequency and extent of the acts of 145

quantity of carbonic acid exhaled per hour in. . . 146

influence of sleep upon the exhalation of car-
bonic acid in 146, 150

influence of age upon the exhalation of carbonic*

acid in 14T

influence of sex upon the exhalation of carbonic

acid in 14T

influence of digestion upon the exhalation of car-
bonic acid in 148

influence of inanition upon the exhalation of car-
bonic acid in 148

influence of diet upon the exhalation of carbonic

acid in 148

influence of alcoholic beverages, tea, and coffee

upon the exhalation of carbonic acid in 149

influence of tea, coffee, and tobacco upon the ex-
halation of carbonic acid in 149

influence of mental depression upon the exhala-
tion of carbonic acid in 150

influence of exercise upon the exhalation of car-
bonic acid in 150

influence of moisture and temperature upon the

exhalation of carbonic acid in 151

— influence of season upon the exhalation of car-
bonic acid in 151

relations between the quantity of oxygen con-
sumed and the quantity of carbonic acid exhaled . . . 152

sources of the carbonic acid exhaled in 153

exhalation of watery vapor in 153

exhalation of ammonia, organic matter, etc., in. . 154

exhalation of nitrogen in 154

changes in the blood in 155

mechanism of the interchange of gases between

the blood and the air in 161

relations of, to nutrition 161

essential processes of 162

combustion-theory of. 163

cutaneous 168

in a confined space 170

relations of, to deglutition 220

connection of the medulla oblongata with 726

influence of, upon the circulation of lymph 840

relations of, to animal heat 518

influence of the superior laryngeal branches of

the pneumogastrics upon 652

influence of the inferior laryngeal branches of

the pneumogastrics upon 653

effects of section of the pneumogastrics upon 653, 659

effects of galvanization of the pneumogastrics

upon 661

movements of the brain with 668

Eespiratory efforts before birth 167, 919

Eespiratory excitants 149

Eespiratory movements, character of, and cause of

these movements 1G6, 167, 660, 727

Respiratory movements of the glottis 553

Eespiratory non-exciters 149

PAGH

Respiratory sense 164, 660, 727

Restiform bodies 725

Resultant tones 831

Rete testis 881

Retina 775

ora serrata of 776

macula lutea and fovea contrails of 776, 779, 791

layers of 776

— — layers of rods and cones of 776, 791

external granule layer of 777

inter-granule layer of (cone-fibre plexus) of 777

internal granule layer of. T77

granular (molecular) lay er of. 777

layer of ganglion-cells of 777

expansion of the optic nerve in 777

limitary membrane of. 77T

connective tissue of 778

connection between the rods and cones and the

ganglion-cells of 778

blood-vessels of 778, 779

sensibility of the layer of rods and cones of. 791

shadows of the vessels of 791

relative sensibility of different parts of. 792

corresponding points in 802, 803, 810

Retinal red, or retinal purple 793

Retractors of the anus 290

Retrahens aurem 818

Right-handedness (see Dextral preeminence) 944

Rigor mortis (see Cadaveric rigidity) 946

Rima glottidis 116

Rods of the retina 776, 791

Rolling movements following injury of certain parts

of the encephalon, etc 728

Rosenmiiller, organ of 863, 928

Ruloff. brain of 703

Rumination 255

Russian baths 521

Rut, identity of, with menstruation 871, 875

Ruysch, tunic of 772

Saccule of the internal ear 843

distribution of the nerves in 846

Sacro-lurnbalis, action of, in expiration 131

Sacrum, consolidation of 914

Sago 181

Saliva 205

Saliva, parotid 206

secretion of 206

action of, upon starch 206

relations of the flow of, to mastication 207, 214

alternation in the secretion of, upon the two

sides 207

Saliva, submaxillary 208

influence of sapid substances upon the secre-
tion of 208

Saliva, sublingual 208

influence of sapid substances upon the secretion

of

209

Saliva, fluids from the smaller glands of the mouth,
tongue, and pharynx ............................. 209

Saliva, mixed ...................................... 210

- influence of matters introduced into the stomach
through a gastric fistula upon the secretion of ..... 210

- influence of the sight, odor, or thought of food
upon the secretion of ............................ 210

- quantity of ................................... 210

- reaction of .................................... 210

- quantity of, secreted during the intervals of mas-
tication... .. 210

INDEX.

971

PAGE

Saliva, mixed, general properties and composition of 210
specific gravity of. 210

sulpho-cyanide in 211

table of the composition of 211

— organic principle of. 211

functions of 212

action of, upon starch 212

• influence of, upon deglutition 214

mechanical functions of. 214

Salivary fistula 206

Salivary glands 205

Saponification 184

Sarcode 522

Sarcolactates 418

Sarcolemma 530

Savors 759

Scala tympani of the cochlea 844

Scala vestibuli of the cochlea 844

Scalene muscles, action of, in respiration 125

Scarf-skin (see Skin) 881

Scarpa, humor of 846

Schlemrn, canal of 775

Schneiderian mucous membrane 755

Schwann, sheath of 566

white substance of 566

Sclerotic coat of the eye 770

development of 919

Scrotum 880

development of 980

Scurvy 193

Season, influence of, upon the exhalation of carbonic
acid 151

— influence of, upon the diet 172, 198

influence of, upon the urine 427

Sebaceous glands 858

first appearance of 916

Sebaceous matter 358, 361

of the nipple 802

Secreted fluids, tabular view of 350

Secreting organs, general structure of. 848

Secretion, general considerations 841

mechanism of 342

— classification of the products of 842

distinction of, from excretion 342

mechanism of, as distinguished from excretion.. 848

— action of glandular epithelium in 843

interrnittency of, as distinguished from excretion 844

— influence of the composition and pressure of the
blood upon 846

influence of the nervous system upon 847, 738

centres presiding over 847

influence of the sympathetic system upon 738

Segmentation of the vitellus 896

Semen 8S8

quantity of 884

general characters of 884

chemical constitution of 884

mucous secretions mixed with 884

in advanci-d age 8S6

ejaculation of 889

penetration of, into the uterus 891

passage of, through the Fallopian tubes 892

time occupied by passage of, to the ovaries 892

Semicircular canals, bony ^_'

Semicircular canals, membranous 843

ampulla; of 848

distribution of the nerves in 846

septum transversum of. 846

functions of . . 849

PAGE

Semicircular canals, influence of, upon equilibration. . 849

disease of (Meniere's disease) 718, 849

development of 919

Semilunar ganglia 783

Semilunar valves, pulmonic 88, 48

pulmonic, safety-valve function of 48, 109

aortic 39, 48

Seminal vesicles 882

Seminiferous tubes 880, 885

Semivowels 562

Sensation in amputated members, etc 593

Sensory nerves, action of 592

disappearance of the physiological properties of 596

effects of anaesthetics upon 596

Septum lucidum, development of. 918

Serine 23

Seroline 295

Serotina, cells of 91 1

Serous cavities, absorption from 817

Serous fluids 851

Serous membranes 850

Serratus magnus, action of, in respiration 128

Serratus posticus superior, action of, in respiration. . . 127

Serum of the blood (see Blood) 24

Seventh cranial nerve, portio dura of (see Facial nerve) 618

portio mollis of (see Auditory nerves) 815

Sex, influence of, upon the pulse 52

influence of, upon the exhalation of carbonic

acid 147, 150

influence of, upon the urine 426

determination of, in the foetus 898

Sexual intercourse (see Coitus) 887

Shells of cocoa 190

Sighing 134, 167

Sinus terminalis of the area vasculosa 981

Sinuses of Valsalva 39, 64

Sixth cranial nerve (see Motor oculi externus) 614

Skeleton, ossification of. 915

Skin, respiration by 168

effects of an impermeable coating applied to 168, 891

distribution of lymphatics in 805

absorption by 814

physiological anatomy of. 380

extent and thickness of 880

layers of. 881

layer of corium 881

reticulated layer of 881

papillary layer of. 881

epidermis 382

rete mucosum, or Malpighian layer of 882

— of the negro 882

horny layer of. 882

general uses of 891

amount of exhalation from 393

development of 916

action of, in the equalization of the animal heat. . 521

Skull, development of 915

Sleep, influence of, upon the pulse 58

influence of, upon the consumption of oxygen . . . 143

influence of, upon the exhalation of carbonic acid 146

influence of, upon digestion 'J.M

phenomena of. • 748

condition of the brain and nervous system in.. . . 74(>

produced by pressure on the carotids 747

theories of. 747. 741)

conditions of various functions in 7 1!>

Smegma of the prepuce and of the labia minora 802

Smell (see Olfaction) 758

Sneezing 184

972

INDEX.

Snoring 133

Sobbing 125, 135

Solar plexus 733

Solitary glands of the intestine 264, 267, 291

Sominering, yellow spot of 776

Soprano 556

Sound, physics of 823

laws of vibrations of. 824

propagation of &25

reflection of. 825

refraction of 825

shadows of 8£5

rapidity of transmission of. 825

noisy and musical 826

pitch of. 826

range of, in music 826

musical scale of 827

quality of. 828

harmonics, or overtones 829

resultant tones 831

summation tones 832

harmony 832

chords 832

discords 833

beats 833

tones by influence (consonance) 834, 837

Sounds of the heart 48

Soups, digestibility of. 251

Spasm, artificial 539

Speech, mechanism of 560

action of the mouth, teeth, lips, tongue, and pal-
ate in 562

modifications of, in cases of cleft palate or hare-
lip 562

Spermatic cells 886

Spermatic cord 880

Spermatiue 884

Spermatozoids 884

discovery of 884

movements of. 885

intermediate segment of 885

action of water, reagents, cold, heat, etc., upon . . 885

development of 885

in advanced age 886

duration of the vitality of, in the female genera-
tive passages 893

penetration of, through the vitelline membrane.. 896

Spheno-palatine ganglion 731

Spherical aberration 789

Sphygmograph 72

Sphincter of the bladder 408

Sphincters of the anus 296-298

Spices 190

Spina bifida .* 915

Spinal accessory nerve 627

physiological anatomy of. 627

small, internal, or communicating branch of, to

the pneumogastric 628

properties and functions of. 628

functions of the internal branch of 629

extirpation of, in living animals 629

influence of, upon phonation 629

influence of, upon deglutition 681

influence of, upon the heart 631, 655, 658

functions of the external, or muscular branch

of, going to the sterno-cleido mastoid and trapezius

muscles 631

Spinal column, development of. 915

twisting of, in the embryon 915

PAGE
Spinal column, temporary caudal appendage of ...... 915

Spinal cord, arrest of the action of the heart by sud-
den destruction of ............................... 59

— lymphatics of ................................. 306

- regeneration of. ............................... 58(>

- neurilemma of ................................ 667

— physiological anatomy of. ..................... 66S

- filum terminale of. ............... ............. 669

— proportion of white to gray substance in differ-
ent portions of. ................................. 669

- direction of the fibres in ....................... 671

- connections of, with the roots of the nerves ..... 672

- general properties of .......................... 673

- excitable and sensible portions of. ............. 674

- transmission of motor stimulus in .............. 676

- direction of motor conductors in ................ 676

-- decussation of the motor conductors of ......... 676

- transmission of sensory impressions in ......... 677

— the posterior white columns of, do not serve as
conductors of sensory impressions ................ 678

— conduction of sensory impressions by the gray
Bubstance of ..................................... 678

- function of, in connection with muscular coordi-
nation ...................................... 679, 711

- decussation of the sensory conductors of. ....... 680

— hyperoesthesia due to injury of portions of. ...... 680

- summary of the action of, as a conductor ....... 682

- action of, as a nerve-centre ..................... 683

- reflex action of (see Eeflex action) ............... 684

— dispersion, or diffusion of impressions in ........ 685

-- development of. ............................... 917

Spinal nerves, distinction between motor and sensory

roots of ........................................ 587

- properties of the posterior roots of ............. 589

- properties of the anterior roots of ............. 590

- distribution of ................................ 606

- connections of, with the spinal cord ............ 672

Splanchnic nerves .................................. 733

Spleen, relations of, to the blood -corpuscles .......... 13

- proportion of leucocytes in the blood of the veins

of. .............................................. 15

-- physiological anatomy of ....................... 473

- fibrous structure of (trabeculae) ................ 474

- Malpighian bodies of .......................... 474

- spleen-pulp ................................... 475

- blood-corpuscle-containing cells of. ............. 475

- blood-vessels and nerves of .................... 475

- contractility of .......... ...................... 476

- chemical constitution of ....................... 476

- functions of. .................................. 477

- changes in the constitution of the blood by ..... 477

- variations in the volume of. .................... 477

-- extirpation of. ................................ 478

- influence of extirpation of, upon the appetite and
disposition ...................................... 478

- development of ............................... 921

Splenic plexus ..................................... 733

Spores

Spurzheim, brain of
Stapedius muscle
Stapes

856

821
819
Starch ............................................ 181

- iodine-test for ................................. 181

- proportion of, in different vegetables ............ 181

- action of the parotid saliva upon ................ 206

- general action of the saliva upon ................ 212

-- action of the gastric juice upon, by hydration. . . 248

- action of the intestinal juice upon .............. 267

- action of the pancreatic juice upon ............. 275

INDEX.

973

PAGE

Starvation (see Inanition) 148, 175

Stearic acid 183

SU'arine 183, 504

iSteno, duct of '206

btercorine 294

formation of, from cholesterine 295

in the fitces 456

Stereoscope 805

riterno-mastoideus, action of, in respiration 127

St. Martin, case of 232

Stomach, physiological anatomy of 226

capacity of. 226

peritoneal coat of. 226

muscular coat of 226

blood-vessels of 228

mucous coat of. 228

pits of 228

glandular apparatus of. 229

— gastric, or peptic glands 229

mucous glands of 2^9

closed follicles of 229

secretion of (see Gastric juice) 230

changes in the appearance of the mucous

membrane of, during the secretion of gastric

juice 234

secretion in different parts of. 235

infusions of the mucous membrane of 235

duration of digestion in 249

digestibility of different aliments in 249

influence of the pneumogastrics upon 252, 663

influence of the nervous system upon 252

movements of. 253

division of, into two compartments, by contrac-
tions of circular fibres during digestion 254

regurgitation of food from 255

gases of. 298

absorption by 801

development of 920

Stomata in the walls of the capillaries 82

Strabismus, external 611

internal 615

Striated muscular fibres 529

Strychnine, exaggeration of the reflex excitability of

the spinal cord by 686

Styloid ligament, development of 922

Subareolar muscle 366

Subclavian arteries, development of 938

Subclavian veins, development of 934

Sublingual nerves, effects of section of, upon deglu-
tition 219

effects of section of, upon mastication 204

physiological anatomy of 632

properties and functions of 633

influence of, upon the tongue and upon degluti-
tion 684

Sublingual saliva (see Saliva) 208

Submaxillary ganglion 731

Submaxillary glands, variations in the color of the

blood in 5, 844, 347

influence of the chorda tympani upon 623

Submaxillary saliva (see Saliva) 208

Sucking, mechanism of 197

action of the tongue in 204

Sudoric acid and sudoratea 895

Sudoriparous glands (see Sweat) 391

first appearance of 916

Suffocation, sense of 166

Sugar in the blood 22

Sugar, characters of 180

PAGE

Sugar, action of the gastric juice upon 24s

not acted upon by the intestinal juice 267

action of the pancreatic juice upon 276

absorption of, by the lacteals 818

— presence of, in the lymph 832

presence of, in the chyle 88T

of milk 875

production of, by the liver (see Liver) 468

process for the determination of 460

Trominer's test for 461

Fehling's test for 461

— character of, produced by the liver. 460

rapidity with which the different varieties of,

(cane-sugar, milk-sugar, glucose, and liver-sugar)

are destroyed in the system 467

destination of, in the economy 471

relations of, to nutrition 500

Sulphate of lime 497

Sulphate of potassa 497

Sulphate of soda 497

Sulphates, elimination of, in the urine 423

Sulpho-cyanide in the saliva 207, 208, 211, 212

Suipho-cyanide of potassium, action of, upon mus-
cular irritability 59

Sulphuretted hydrogen, exhalation of, by the lungs,

when injected into the venous system 154

Summation tones 832

Superfecundation 894

Superfoetation 894

Superior laryngeal nerves (see Pneumogastric) 651

Suprarenal capsules, development of 928

weight of, compared with the kidneys, in the

fetus and adult 928

structure of 479, 480

chemical reactions of 481

functions of. 481

extirpation of 482

Suspensory ligament of the crystalline lens 779

Sweat S91

Sweat-glands 391

number of, in different parts of the surface... 392

Sweat, mechanism of the secretion of 3(J?

influence of the nervous system upon the secre-
tion of 893

quantity of 893

influence of exercise upon 894

influence of temperature upon 394

properties and composition of 894

urea in 894

peculiarities of, in certain parts 395

odor of, in certain parts 895

equalization of animal heat by 521

Sympathetic nerves, influence of, upon the color of

the blood in the veins 6

action of, upon the heart 59, 60

influence of, upon the arteries 69

influence of, upon the movements of the small

intestine 287

influence of, upon animal heat 514, 737

Sympathetic system 72i)

general arrangement of 780

distribution of 730

cranial ganglia of 731

cervical ganglia of 781

thoracic ganglia of 733

abdominal and pelvic ganglia of 783

parts in which the terminal nerves of, are con-
nected vvith ganglionic cells 735

structure of the nerves and ganglia of 735

974

INDEX.

PAGE

Sympathetic system, general properties of 736

connection of, with the cerebro-spiual system.. 736

functions of 737

influence of division of nerves of, upon animal

heat 737

influence of, upon the circulation 738

influence of, upon secretion 733

influence of, upon the urine 738

influence of, upon the intestines 739

reflex phenomena in 740

influence of, upon the iris 741, 797

Sympexions 884

Syncope 62

Synovial bursae 351

Synovial fluid 352

composition of 353

variations of, with use of the joints 353

Synovial fringes 351, 353

Synovial membranes 351

absorption by 317

Synovial sheaths 351

Synovine 352

Tactile corpuscles 574

Tao-foo 179

Tapioca 181

Taste (see Gustation) 759

— action of the glosso-pharyngeal nerve in 764

influence of the chorda tympani upon 622

Taste-buds, or taste-beakers 765

Taste-cells 766

Taste-pores 7G6

Tastes and flavors 759

Taurine 280, 421

Taurocholic acid and taurocholate of soda 280, 444

Tea 189

influence of, upon the exhalation of carbonic

acid 149

— influence of, upon the elimination of urea 428

Tears...

Teeth, physiological anatomy of.

enamel of

dentine of

cement of. ...

814

198

199

199

199

pulp-cavity of 199

varieties of 200

function of the sensibility of, to hard substances,

in mastication 205

action of, in speech 562

Teeth, temporary, development of. 924

primitive band for the development of. 924

epithelial band for the development of. 924

enamel-organ of. 925

bulb of . . 905

follicle :>f . .

925

dentine, or ivory of 925

cement of . . 925

order of eruption of 926

Teeth, permanent, development of. 926

order of eruption of 927

Temperament, in musical instruments 828

Temperature of the blood 5

Temperature, influence of, upon the pulse 58, 73, 74

influence of, upon the size of the arteries 70

influence of, upon the capillary circulation 91

influence of, upon the exhalation of carbonic

acid 151

— appreciation of 754

Temporo-maxillary articulation 202

PAGB

Tendons, sheaths of 351

connection of, with the muscles 533

Tenesmus 297

Tenor-voice 55$

Tensor palati 217, 821

Tensor tympani 820, 837

Tentorium 667, 706

Tesselated epithelium 350, 353

Testicles 879

tunica vaginalis of 880, 928

tunica albuginea of 880

corpus Highmorianum of, or mediastinum tes-

tis 880

lobules of 880

tunica vasculosa of, or pia mater testis 880

seminiferous tubes of 880

vasa recta of 881

rete of 881

vasa efferentia of 881

vas aberrans of Haller 881

first appearance of 927

descent of 928

gubernaculum of 928

Tetanic contraction 540

Tetanus 6s>7

Theine 189

Theobromine 190

Third cranial nerve (see Motor oculi communis) 609

Thirst 174

effects of haemorrhage upon 174

seat of sense of 175

— relief of, by absorption of water by the skin 316

Thoracic duct 302, 306, 307

fistula into ,.. 328,335

Thorax, form of 121

action of the elasticity of the walls of, in expira-
tion 129

Thraenine 814

Thymus gland 483

Thyroid gland 482

structure of 483

functions of 488

enlargement of, during menstruation 483

Thyro-arytenoid muscles 553, 557

Tidal air 136

Titillation 753

Tobacco, influence of, upon the exhalation of carbonic

acid 149

Tones (see Sound) 826

Tongue, action of, in mastication 204

action of the muscles of 204

action of. in sucking 204

action of, in deglutition 204, 219

mechanism of the protrusion of 204

— action of, in phonation 558

action of, in speech 662

influence of the facial nerve upon 624

influence of the sublingual nerve upon 634

papillse of 765, 766

development of 923

Tonicity of muscles 584

Tonsils 209,216

Touch, sense of 751

variations in the sense of, in different parts 751

— extraordinary development of the sense of 751

table of variations in the sense of, in different

parts 753

Townshend, Colonel, voluntary arrest of respiration
and the action of the heart by 55

INDEX.

975

PAGE

Trachea 113, 119

action of, in phonation 557

development of. <J22

Trachealis muscle 119

Tractus spiralis foraminulentus 847

Tragus of the ear 817

Training 493

Transfusion of blood 2

Transudations 343

Transversalis, action of, in expiration lol

Trapezius, action of the superior portion of, in respi-
ration 128

Triangularis sterni, action of, in expiration 180

Tricuspid valve 38, 47

safety-valve function of. 47, 109

TrifaciaL, or trigeminal nerve (see Fifth cranial nerve,

large root of) 634

Trigoiie 408

Triphthongs 5G1

Triplets 941

Trochlearis nerve (see Patheticus) 613

Trommer's test for sugar 461

Trophic centres and nerves 741

Trypsine 272, 277

Tuber annulare, physiological anatomy of 722

function of. 723

development of 917, 918

Tubercula quadrigemina, physiological anatomy of. . . 722

functions of. 722

reflex action of, upon the iris 722, 797

— development of 917, 918

Turkish baths 521

Turning movements following injury of certain parts

of the encephalon *. 728

Twins, one white and the other black 894

one male and the other female 895

question of development of, from a single ovum

or from two ova 941

Siamese 942

Tympanic membrane, physiological anatomy of 835

pockets in 835

connection of, with the ossicles 835

color of 88«

cone of light in S87

uses of 837

vibration of, by influence S37

tension of, by muscular action 820, 837, 838

theory of the action of, in the appreciation of

musical sounds 838

protection of, from concussion 840

Tympanum 818

development of 923

Tyroslne 421

Tyson, glands of 359

Umbilical arteries and vein , 905, 9*3

Umbilical cord 906

valves in the vessels of 906

Umbilical hernia in the fetus 904, 920

Umbilical vein, closure of. 933

Umbilical vesicle 904

Umbilicus, amniotic 901

decidual 90S

intestinal 904

Unconscious cerebration 744

Unison 826

Urachus 907, 920

Uraemic poisoning 403

Urea, influence of coffee upon the elimination of 1S8, 428 j

PAGE

Urea, presence of, in the lymph 882

presence of, in the chyle 836

accumulation of, in the blood, after extirpation

of the kidneys 408

effects of injection of, into the blood-vessels, after

extirpation of the kidneys 403

vicarious elimination of, after extirpation of the

kidneys 403

characters of. 413

where found in the economy 414

artificial formation of 414

decomposition of 414

crystals of 414

origin of. 414

detection of, in the blood 415

question of the formation of, in the liver 415

theory of production of, from uric acid, crea-

tine, etc 415

amount of daily excretion of 416

influence of nitrogenized food upon the elimina-
tion of 428

influence of alcohol, tea, and coffee upon the

elimination of. 168, 423

influence of muscular exercise upon the elimina-
tion of 428

influence of the sympathetic system upon the

elimination of 788

diminished excretion of, during menstruation. . . 876

Ureters, physiological anatomy of 407

contractions of, produced by stimulation of the

eleventh dorsal nerves 409

development of 928

Urethra, physiological anatomy of 409

glands of 883

development of 920

Uric acid and its compounds 416

amount of daily excretion of 417

influence of muscular exercise upon the elimina-
tion of 429

Urinary organs, development of 923

Urine, absorption of the watery portion of, by the

bladder 81T

mechanism of the production of 401

influence of the nervous system upon the secre-
tion of 405

influence of blood-pressure upon the secretion of 405

effects of destruction of the nerves of the kid-
neys upon the secretion of. 405

alternate action of the kidneys in the secre-
tion of 406

mechanism of the discharge of. 4l9

properties and composition of. 410

color and odor of 410

temperature of 410

quantity and variations of 411

specific gravity and reaction of 411

cause of the acidity of 412

composition of 412

table of constituents of 413

fatty matters in 421

inorganic constituents of 421

chlorides of. 422

sulphates of 423

phosphates of. 4-3

derivation of the phosphates of, from food and

from the tissues 423

relation of the proportion of phosphates in, to

the condition of the brain 424

variations in the phosphates of. 424

976

INDEX.

PAGE

Urine, coloring matter and mucus of. 424

gases of 425

variations in the composition of 426

-, — variations of, with age and sex 426

of the foetus 426

variations of, at different seasons and at different

periods of the day 427

variations of, produced by food 42T

influence of nitrogenized food upon 428

— influence of muscular exercise upon the quantity

of. 428

influence of muscular exercise upon the inorganic

constituents of 429

influence of mental exertion upon 430

— influence of the sympathetic system upon 738

Urrosacine 424

Uterine plug of mucus 908, 938

Uterus, mucus of 357

situation and position of. 857

ligaments of 858, 864

— parts and structures contained in the broad liga-
ment of. 858

— physiological anatomy of 863

muscular fibres of. 864

— arrangement of the muscular layers of. 864

— platysma of. 864

mucous membrane of the body of 864

— mucous membrane of the cervix of 865, 866

tubules of the mucous membrane of. 866

variations in the thickness of the mucous mem-
brane of, with menstruation 866

ovules of Naboth of 866

arbor vitse of. 866

blood-vessels of 866

— erectile tissue of 866

erectile tissue of the cervix of 867

— nerves of 867

changes in the mucous membrane of, during

menstruation 866, 876

action of the cervix and os of, in coitus 890

— penetration of the semen into 891

production of mucus in the neck of, in coitus. . . 891

— formation of the membranae deciduae from the
mucous membrane of 907

secretion of mucus by the cervix of, in preg-
nancy 908, 938

— first appearance of the new mucous membrane

of, in pregnancy 90S

development of 928

double 928

development of the round ligament of 928

enlargement of, in pregnancy 938

— cause of the first contraction of, in normal par-
turition 942

— involution of. 94.3

restoration of the mucous membrane of, after

parturition 943

Utricle of the internal ear 843

distribution of the nerves in 846

Uvea 775

Uvula 216

— influence of the facial nerve upon 623

Uvula vesicae 408

Vagina 857,868

— sphincter of 869

structure of 869

double 928

Vaginal mucus . . 357

PAGE

Valentin, limiting membrane of. 5(5t>

Valsalva, sinuses of 39, 64

— humor of. 846

Valsalva's method for protection of the membrana

tympani from concussion 840

Valve, tricuspid 38, 47

— pulmonic 38, 48

mitral 39, 47

— aortic 39, 48

"Valves of the veins, discovery of. 32

uses of, described by Harvey 33, 96

Valves of the heart, action of 46

Valves of the lymphatics 303, 309, 840

Valvulae conniventes 259, 802

— development of <J20

Vas deferens 880, 881

— movements of, produced by galvanization of the
lumbar portion of the spinal cord 882

— development of, from the Wolffian duct 928

Vasa vasorum 67, 94

Vasa vorticosa 772

Vascular arches, in the embryon 933

Vascular blastodermic layer 931

Vaso-motor nerves and centres 67, 739

Vater, corpuscles of 573

Vegetable albumen 178

Vegetable caseine 179

Vegetable fibrin 179

Vegetable food 178

Vegetables, digestibility of 251

Veins, variations in the color of the blood in 5

renal, color of the blood in 5

discovery of valves of 82

uses of the valves of, described by Harvey . 33, 96

circulation in 92, 98

capacity of, as compared with that of the arte-
ries 93

anastomoses of 94

— structure and properties of 94

coats of 94

vasa vasornm of 94

strength of the walls of 95

elasticity and contractility of. 96

— valves of 96,104

those in which there are no valves 98

course of the blood in ' 98

pulse in 99, 106

pressure of blood in 99

— rapidity of the flow of blood in 100

causes of the circulation in 100

obstacles to the flow of blood in 101, 105

influence of muscular contraction upon the flow

of blood in 101

influence of the force of aspiration from the

thorax upon the circulation in 102

of the liver, circulation in 102

entrance of air into 103

— influence of gravity upon the circulation in . 103, 106
influence of a suction force exerted by larger

upon smaller vessels upon the circulation in ., 104

relations of respiration to the circulation in 105

— regurgitant pulse in 106

— development of 983

Velum pendulum palati 216

action of, in phonation 558

influence of the facial nerve upon the movements

of 624

Vena innominata, development of 934

Venae cavse, development of 934

INDEX.

977

PAGE

Venereal orgasm, in the male fe&'J

in the female 891

Venereal sense 754

Venoms, absorption of 319, 32T, 353

Venous sinuses 95

Ventilation of hospitals, prisons, etc 142

Ventricles of the heart 36

comparative capacity of right and left 36

comparative thickness of right and left 83

shortening and elongation of 42

Venules, or venous radicles 93

Verheyn, stars of 401

V ermiform appendix 2S8

Vernix caseosa 363, 916

Vertebrae, first appearance of. 914, 915

Vertebral arteries, development of 932

Vertebral column (see Spinal column) 915

Vertebral plates 913, 915

Vertigo 718

Vesiculse seiuinales 8S2

— development of 923

Vessels, coagulation of the blood in 27

Vestibule of the ear 822, 842

Vibriones 855

Villi of the small intestine 261, 302

— development of 920

Villi of the vitelline membrane 901

Villi of the amnion 901

Villi of the allantois 901, 905

Villi of the chorion 905

Villi of the placenta 911

Vinegar 190

Visceral arches 922

Visceral clefts 922

Visceral plates 914, 916, 920

Vision, influence of the angular convolution of the

cerebrum on 722

physiological anatomy of the organs of 767

area of. 785, 791

laws of refraction, dispersion, etc 785

refraction by lenses 787

myopic 788

hypermetropic 739

— presbyopic 789

formation of images in 791

demonstration of the fact that the layer of rods

and cones is the seat of visual impressions 791

— area of distinct 792

— blind spot in the retina 792

mechanism of refraction in 793

astigmatic 794

movements of the iris in 796

accommodation in — 798

— through a small orifice, like a pinhole 801

erect, although the images on the retina are in-
verted 801

binocular 802

— double 802

— corresponding points on the retina in. . 802, 803, 810

— horopter of 808

monocular 804

— estimation of distance, the form and solidity of
objects, etc 804

— with the stereoscope 805

binocular fusion of colors 805

— duration of luminous impressions in 806

fusion of colors in 806

— irradiation in 806

— accidental areolje in , 807

62

PAGE

Vision, development of the organs of 918

Vital capacity of the lungs 188

variations in, with stature 188

Vital point 727

Vitelline 177

Vitelline circulation S81

Vitelline membrane of the ovum 870

— disappearance of, after fecundation 901

villosities of. 901

Vitellus 870

deformation and gyration of 697

— bright appearance of, after fecundation &97

formation of the polar globule of. 897

formation of the nucleus of 897

— segmentation of 896, £97

Vitreous humor 782

hyaloid membrane of 782

in the embryon 782

— blood-vessels of 782

- — refraction by 793

Vocal chords 116, KO

— action of, in phonation 555

Vocal registers £53

Voice and speech 549

Voice, mechanism of the production of 558

action of the vocal chords in 555

variations in the quality of 555

varieties of 550

in boys 556

range of 556

action of the accessory organs of. 557

action of the trachea in 557

action of the larynx and epiglottis in 558

action of the pharynx in 558

action of the mouth in 558

action of the nasal fossae in , 558

action of the tongue in 558

action of the velum palati in 558

different registers of 558

influence of the spinal accessory nerve upon 629

influence of the superior laryngeal branches of

the pneumogastrics upon 651

Voluntary muscular tissue (see Muscular tissue) 528

Vomiting, mechanism of 2£6

Vowels 560

Vowel-sounds, mechanism of £01

Wagner, spot of S70

Wandering cells of the cornea 771

Water, functions of, in the blood 21

functions of, in alimentation, etc 184. 191, 490

quantity of, necessary to nutrition 191

quantity of, eliminated by the organism 191

absorption of, by the lacteals 814

absorption of, by the skin 815

condition of, in the economy 41'0

table of quantities of, in different tissues 491

origin and discharge of. 492

actual production of, in the economy 516

Watery vapor, exhalation of, by the lungs 158

Webster, brain of 7C3

Weight, appreciation of 751

Wharton, duct of 208

gelatine of 906

Whey 8TI

Wisdom-teeth 201

Wolfflan bodies 913

structure of 927

time of disappearance of, in the female 928

978

INDEX.

PAGE

Wolffian bodies, development of the epididymis from 928

Wolffian ducts 914, 927

development of the vasa deferentia from 928

Woorara, pulsation of the heart in animals poisoned

by 56, 59, 61

absorption of 319, 327

influence of, upon nervous irritability 595

Xanthine..

PAGE
.. 420

Yawning

Yolk, principal, or formative .
Youth...

Zona pellucida.

134

870
945

781

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